Up one level (MaxTrac index) Up two levels (Moto index) Back to Home

Introductory Information on the MaxTrac, Radius and GM300 series radios, the DeskTrac station, and the GR300, GR400 and GR500 series prepackaged repeaters Formerly Maintained by Robert Meister WA1MIK Currently Maintained by Mike Morris WA6ILQ. Compiled By Mike Morris WA6ILQ from information provided by Neil Johnson WBØEMU, Scott Lichtsinn KBØNLY, Bob DeMattia K1IW, Eric Lemmon WB6FLY (SK), Robert Meister WA1MIK (SK), Jeff Kincaid W6JK, Will Martin KA6LSD (SK), Neil McKie WA6KLA (SK), and Don Best N6ALD. Photos by WA6ILQ unless noted. Corrections and additional contributions are invited.

This page is oriented towards the USA marketed radios, simply because it was compiled by USA residents; we described the radios we are familiar with. If anyone would care to share information on the non-USA radios we'd be happy to add them on this page, or even create a region-specific page.

Note: Any prices mentioned on this page (or on any page at this web site) should be taken only as a rough guideline.   This particualr article was written in early 2006.   Motorola adjusts prices quarterly, and offers one set of prices to their dealers / service shops (the so called "NSO" ("National Service Organization") Pricing), another on their telephone order desk (i.e. retail sales), and a third to "self-maintaining" fleet customers (i.e. those that have their own radio shops... cities, counties, police departments, fire departments, etc).   Prices are changed quarterly, so use the mentioned prices only as a rough indication.   If you encounter a large price change on anything where we've mentioned a price we'd appreciate an emailed update.

Note that Motorola numbers their manuals with a part number starting with 68P, then 68-, and currently 68. The first version is identified with a trailing "-O" (meaning "original"), and the first revision is a -A, then the second is a -B, etc., skipping over "-O" if / when they get to it.

The MaxTrac, Radius and GM300 series fathered additional radio designs that are / were sold all over the world, and the products were customized for the local marketplace with region-specific model numbers like GM320, GM340 and GM900. As one example the UK / European region has models that are never seen in the USA. If anyone knows the differences / equivalences we'd appreciate the information.

As one specific example of non-local radios, Moto Australia makes 64 channel Radius mobiles and 16 channel GP300 handhelds that cover 220-240 MHz for the Asian market (specifically the Philippines). Those radios would be very popular in the USA Amateur market for the 219-220 and 222-225 MHz amateur bands.

Next, an eBay warning:

Attention EBay buyers: 1) No matter WHAT the model tag says, no MaxTrac, Radius, M-series or GM300 mobile will ever operate over the entire frequency range listed on its model tag / label.   Each unit will do only a portion of that model tag frequency spread, called a "split", a "bandsplit" or a "range". This is due to the design, and the design follows the laws of physics. In short, if you buy the wrong range radio for your application (one example is a GM300 built for 490-520 MHz and you want to use it on a 462 MHz GMRS frequency) you will have a nice doorstop. It is not practical to range-change a MaxTrac, Radius, or GM300 series radio. On the MaxTrac (which includes the MaxTrac 50 and MaxTrac 300 models), the Radius "LRA" (which includes the M100, M120, M204, M208, M214 and M216 models) and GM300 series (which includes the M10, m120, M130 and GM300 models) radios the third character in the model number indicates the frequency band where a 1 indicates 30-50 MHz (low band), a 3 indicates 136-174 MHz (high band), and a 4 indicates 406-520 MHz (UHF). A 5 indicates either 800 or 900 MHz, later on 5 was reserved for 800 MHz and a 7 indicated 900 MHz. MaxTrac "MGA", "MJA", "MQA", "MWA" series: Unfortunately, there are only two ways to determine the split of your radio. You have to either open the radio up and look at the part number of the RF board, or you have to read the radio (with the appropriate Motorola Radio Service Software, commonly called RSS). If radio programming, the RIB and the RSS are new to you then I suggest you read the "RSS and RIB" page on the Motorola page at this web site, and scroll down on this page to the heading below titled "Programming and the Radio Service Software (RSS)". UHF MaxTracs were made for 406-430 MHz and for 449-470 MHz. Operation below 449 MHz (the range used in the USA for amateur radio repeaters) requires patching the RSS, retuning the VCO, and occasionally may require modifying the radio for manual power and deviation control. In general, unmodified UHF MaxTracs are not happy operating much below 449 MHz. Note that the RF board is not the only part that changes between splits, it's simply the easiest one to check. Just take the top cover off your radio then lift the shield on the RF board and look at the number stamped in black ink. This link jumps into the middle of the article page: MaxTrac, MaxTrac 50, 100, 300, 820, 840, LS, Radius M100, M120, M206, M208, M214, M216, and VR100. On the Radius "LRA" and GM300 series radios the split is encoded in the model number. Only the underlined characters in the examples below are used to decode the split information. The Radius product line is very broad and includes several mobiles and even more handhelds, and to specify just which Radius radio you are talking about you need to use more than just the word "Radius". The Radius "LRA" series of mobiles is derived from the MaxTrac (more details below) mobile. Since the LRA Radius is essentially a MaxTrac inside the note above in the MaxTrac section regarding operation below 449 MHz applies here as well. The Radius LRA model numbers are in the format of: DnnLRA7nnnaa As mentioned above, the n is the band, and the nn is the split: Third character Ninth and Tenth characters Frequency range MHz Notes 1 32 23-36 These low range, low band radios are VERY rare. There are broadcast remote pickup channels in the 26 MHz range, and 30-50 MHz is a commercial 2-way band in the USA. If you can find one this range is ideal for the 10 meter amateur band (28-30 MHz). 1 33 36-42 I have seen some fire departments in this range. This range is a doorstop radio to hams (except as an intermediate frequency, or for parts). 1 34 42-50 The Red Cross has frequencies in the 47 MHz range, National Guard has some at 49 MHz, and these can be "pushed" to the 6 meter amateur radio band (50-54 MHz). 3 A5 136-174 This is the VHF High Band (sometimes 132-174 MHz depending on the product line). Useful to CAP, Amateur and commercial. 4 29 403-420 This is the low split UHF, sometimes called "government range". This range WILL NOT work for 440-450 MHz amateur radio, or for GMRS (462-467 MHz). For most amateurs and ALL of the GMRS users this split is a doorstop radio. Some hams prize them and will gladly trade a radio in another split for them. 4 A5 449-470 This is the UHF band. Useful to commercial, and some amateur as it covers the top of the amateur band. As noted elsewhere on this page unmodified UHF MaxTracs and LRA Radius are not happy operating much below 447-448 MHz. Radius LRA radios were not made in the higher UHF ranges (like 470-490 MHz or 490-512 MHz). If you need one of those two ranges then you need to look in the MaxTrac or GM300 series. 5 A5 806-871 800 MHz band. Useful as parts. The "A5" range radios would not do "T/A". What's T/A ? The hams call it "simplex", the commercial two-way radio world calls it "talk-around", where you talk around the repeater instead of going through it. The A5 radios have a single range VCO and operate in repeat only, the A6 radios have a dual range VCO that talks on both the repeater input and the repeater output (simplex on the output). 5 A6 806-871 800 MHz band. Useful as a doorstop or as parts. The A6 radios have a dual range VCO that provides a simplex/repeat function, the A5 radios have a single range VCO and operate in repeat only. The A6s can be modified to serve as a 900 MHz repeater receiver (but have the wideband filters where 900 MHz has always been narrowband). If necessary the proper filters can be acquired and changed. I've converted several 2 channel radios into 32 channel radios using front panels and logic boards cannibalized from range 33 and from 800 MHz A5 and A6 radios. The GM300 radios had two different front panel labels - some say "Radius", some do not. Either way, this series is very different from the Radius LRA radios. This series includes the M10, M130 and GM300 models and uses a different format model number from the MaxTrac or Radius LRA series: MnnXXXnnanaa, where "n" is a number and "a" is a letter and XXX is three letters, for example in M33XVC00F2AA or M44GMC20C1AA. The third and tenth characters of a GM300 family model number are translated as follows: Third character Tenth character Frequency range MHz Notes 3 1 136-162 This is low split high band, sometimes called a "range 1" radio. It's ideal for amateur radio 2M, VHF commercial and public safety, for Civil Air Patrol and weather. Note that CAP is going to nationwide narrowband in the 2009-2011 time frame, and some geographic areas are fully narrowband as I type this, so wideband-only radios are a VERY poor investment for CAP frequencies. 3 2 146-174 This is high split high band, sometimes called a "range 2" radio and is the most common in VHF. Yes, they will work down at 144-145 MHz just fine, but not a whole lot lower (i.e. I wouldn't try anything below 144 MHz). 4 1 403-430 This is low split UHF, sometimes called "range 1", or "government range". The notes in the Radius LRA section above on this range apply here as well. 4 2 Invalid combination of numbers. 4 3 438-470 This is sometimes called a "range 3" radio and is the most common in UHF. Ideal for amateur radio UHF, commercial, public safety and GMRS. 4 4 465-490 This is sometimes called a "range 4" radio. It will do 470-476 MHz and 482-488 MHz commercial and public safety, might be pushed to GMRS (depends on the individual radio, most receivers will make it to 462 MHz), otherwise it's only good for parts. 4 5 490-520 This is sometimes called a "range 5" radio. Unless you have a need for a radio in this range it's a doorstop, or only useful for parts. In the area where your author lives the only thing in this range is a few police departments... I've converted several 2 channel radios into 32 channel radios using front panels and logic boards cannibalized from range 4 and range 5 radios. 2) Another eBay warning: The D03, D04, M03 and M04 models (where the second character is a zero) are low power (1-10 watt) radios that were designed and marketed for the Low Power Industrial (LPI) radio service (think "in-plant forklifts", golf courses and similar low power usage). The early RF power amplifier boards have the standard driver transistor and a jumper in place of the final. Later RF boards have a different driver transistor and no jumper - the area where the PA transistor used to be was redesigned. You will find "03" and "04" LPI radios advertised occasionally on eBay as 2, 8, 10 or even 15 watt radios. All are rated at 1 to 10 watts adjustable with the power control, however I think the ebay seller advertising a M04GMC as a 25 watt radio was drugged, dreaming or had read too many CB antenna advertisements. They will do 2 to 5 watts all day long (for example, as a point-to-point link radio), and will do 8 to 10 watts intermittently (note the emphasis on the intermittently). Personally I never set them higher than 6 watts on VHF or 5 watts on UHF. One of the LPI radios makes a great garage repeater transmitter at 5 watts, and if you need more power it can drive an external RF amplifier to whatever power level you can afford. And that external amp can be continuous duty...   I have a number of M04GMC pairs in service as commercial repeaters (with a fan on the PA) running 4-5 watts driving Henry Electronics continuous duty 100w UHF amplifiers backed down to 60, 90 or 100 watts depending on the licensed power level. As I write this sentence in 2021 they have been in continuous service since the mid 1980s with very few problems. 3) If you are going to use one of these radios as a repeater, point-to-point link, IRLP node or remote base transmitter you do NOT want to use a high power MaxTrac or Radius LRA mobile. Find yourself a low power M10, M120, M130 or GM300. Why? If you read further down, you will discover that the MaxTrac and the Radius LRA use a microprocessor firmware routine to reduce the power to protect the PA deck from overheating. The M10-M120-M130-GM300 family uses a thermistor to sense the PA temperature and hence "knows" if you put a fan on the PA deck (and you should). Repeater, point-to-point link, IRLP node and remote base transmitters tend to have long transmit times - and it has been my experience that a high power mobile radio is not a good choice. If you ARE going to use one then as a repeater or point-to-point link it only has to talk on one channel so you can use a cheap ebay M10, M120 or M130 - but pick a 03 or 04 (the low power ones) as it is a better choice than a 43 or 44 series as the 03/04 use the same heat sink casting as a 33 or 34 model. See the paragraph below titled "Limitations".

Overview and History:

On this web page we are going to attempt to provide an overview of several series of radios. The MaxTrac series of radios is a synthesized dash mount mobile radio that was originally designed to be a "second tier" or commercial / business radio (a "first tier" radio is a public safety grade radio).

As it was related to me, the MaxTrac history can be traced back to the Motorola GmbH (also known as Motorola of Germany) product line called the MC‑Micro (anybody have some details on the MC‑Micro, or a few external and internal photos of a mobile ?).

By the way, the Motorola GmbH MC-Micro radio was also the first repeater-in-a-box (also called the MC-Micro), which interestingly enough, was available as a factory 220 MHz unit. The exciter was an MC-Micro RF board with the receiver components missing, and the receiver was another RF board with the exciter components missing. The MC-Micro Repeater was later marketed in the USA as the R100, but the RSS was very poor and would fail if run on anything faster than a 12 MHz 286-based machine. Despite that it remains a popular unit and many are still in service. They do have a few problems but field fixes (either by Moto themselves or by individual 2-way shops) are available for all of them. Courtesy of Mike Morris WA6ILQ we have the manuals for the German R100 and the American R100 on the R100 page here at repeater-builder.

When Moto USA marketing needed a simple-to-install dash mount radio (think "as easy as a CB radio") the USA engineering staff "americanized" the German MC‑Micro design (sometimes referred to as the German MaxTrac).

Later on, when they decided to sell through retail and mail-order channels they created the "Radius" product line just for that retail sales channel. They took the MaxTrac 50, 100, and 300 models and did both a front panel cosmetic update and a firmware update and rewrite and came up with the "Radius LRA" units (these are the models with "LRA" in the center of the model number). Over 70% of the boards and parts in LRA series are identical to the MaxTrac product line and many can be mixed, matched, and swapped between the two radio series. See the Radius M100, M206, M208, M214, M216 radio models and board info article by WA1MIK in this section for a breakdown of model numbers, board numbers, etc. Note that while a few of the Moto manuals state "M100 and M200", there is no M200 model, the valid names are M100, M206, M208, M214 and M216.   The M100, M206 and M214 models were introduced in the first wave, the M208 and M216 replaced the M206 and M214 in the second wave. There were no "official" 32 channel Radius mobiles, they topped out at 16. If you needed 17 or more channels they wanted you to buy a MaxTrac (or a Spectra).

At the time these radios were on the current sales sheets, the MaxTrac was a "Motorola direct sales channel" product. At that time, trunking products were more or less reserved for direct sales (system engineering was involved), so initially the Radius LRA line did not have any trunked models. The Radius LRA series was marketed by Moto for many years as a retail and mail-order product with no system engineering other than a salesperson on the far end of a phone call.

When the 800 MHz band was taken from TV and allocated to business Moto took the existing MaxTrac chassis and designed an 800 MHz RF board to plug into it and a final amp to drop into the afterburner position... and then had to live with the problems that were created in using a logic / audio board that couldn't handle some problems that trunking created (note that while Moto calls it the "Logic" board in all the documentation, it's really a logic and audio board).

When 900 MHz came along the designers came up with a 900 MHz PA and RF board, and the 2.5 kHz deviation required the designers to redesign the audio / logic board to work with it. They didn't have enough circuit board real estate for the audio compander circuitry so they were forced to redesign one of the two front panel boards as well. As such the 900 MHz MaxTrac and LRA Radius have very few parts in common with any other radio.

The GM300 series was designed after the MaxTrac and Radius LRA models and based on them. As mentioned above the GM300 was labeled both as a GM300 and as a "Radius GM300". For the purposes of this article we are going to divide the product lines into MaxTrac, Radius (the LRA radios) and GM300 (the M10, M120, M130 and GM300 radios).

The GM300 was a hardware redesign to both update the electronics and to fix some of the ongoing problems that were the result of initial design oversights (like adding a temperature sensing thermistor to the PA deck, and an attenuator (switchable on a per-channel basis) to the receiver to reduce the intermod).

The result of the redesign is the single channel M10, the two channel M120 and M130 and the 8 and 16-channel GM300 radios.   The RF side of those four models is the same, the differences are in the logic board and the front panel.

The GM300 family of radios was only made in high band and UHF, Moto never made GM300s on low band, 800 or 900 MHz (but I have seen MaxTrac and Radius LRA radios on those bands with GM300 front plastic).   Usually model numbers superceed model names, as labels on the front plastic are (or the front plastic itself is) easy to swap.   However a common mod / upgrade is to place a 32 channel front panel and logic board in a 2 channel chassis... and that chassis keeps the original 2 channel model number (which is actually located on the RF power amplifier heat sink... and the PAs are the same... I've seen a PA with a 2-channel M130 model number on a 16 channel GM300 radio).

Since at the hardware level the GM300 is so very different from the MaxTrac and the Radius LRA mobile we will consider it a completely separate family in this article.

Because MaxTrac was the first series marketed in the US, and the later Radius and GM300 series radios are so similar to them some people have used the term "MaxTrac" (or "MaxTrac family") to refer to just the MaxTrac series while others use the term to apply to all three series of radios collectively. So don't be surprised if someone points to an Radius LRA or a GM300 radio and refers to it as a MaxTrac.

The antenna connector used on the Maxtrac, Radius LRA, and GM300 family radios is a Mini‑UHF female and very easy to break if you use an adapter and use stiff coax like LMR400, RG213 or RG214. Motorola offered a Mini‑UHF male to BNC female adapter for test bench usage. They still offer an adapter as the HLN8027 Mini‑UHF male to BNC female adapter for about $11. Your author considers a pigtail (mini‑UHF male to N female) with silver plated connectors and quality RG-400 cable to be a requirement for radio sites. The pigtail relieves the stress on the radio antenna connector. The broken connector problem got so bad that Motorola came up with the the 8 inch long HKN9557A Mini‑UHF male to UHF SO‑239 female Antenna Adapter Cable for about $19, and an 8 foot version as the HKN9088A Mini‑UHF male to UHF PL‑259 male Adapter Cable for about $40. You can make your own adapter cables for a lot less money... and you will have the option of better coax (RG‑400) and the connector of your choice (you will want to use silver plated connectors). I made up a few mini‑UHF‑male to N‑female cables for my test bench back when I got started with Maxtracs. A friend prefers mini‑UHF‑male to BNC‑female pigtails for his bench test cables. When you assemble your own then it is your choice.

The table below is in technical groupings, not marketing grouping. Technically, there was a lot of crossover, for example, the M10, M120 and M130 were derived from the GM300 and over 70% of the MaxTrac and Radius LRA hardware is identical. On this web page we are only concerned with the technical similarities so we can intelligently work on and program the radios.

Note that the hyphenated model names (i.e. "M-10", "M-100" or "GM-300") are improper, it's "M10" "M100" or "GM300". Very few Moto model names have an embedded dash / hyphen.

If anyone has the information to replace the "?"s below please send an email to the page maintainer above.

Series Name	Model Names	Model Number Strings (See note 1 and 2)	RSS (See note 3)	Most Recent RSS Version (See note 4)
MaxTrac	MaxTrac, MaxTrac 50, 100, 300, any 8xx	"MGA", "MJA", "MQA", "MWA"	RVN4019 or 4020	R07.02.00a, dated 25-Jun-97
Trunked MaxTrac	MaxTrac, MaxTrac 50, 100, 300, any 8xx	"MGA", "MJA", "MQA", "MWA"	RVN4043	?
MaxTrac LS	MaxTrac LS (150, 450, 800 and 900 MHz trunking)	"UGQ", "UJQ", a very few "LRA"	RVN4152	?
Radius (See note 5)	Radius M100, M206, M208, M214, M216, and VR100	Almost all "LRA", and a very few "MJA"	HVN9173	R08.00.00 dated 05-May-93
GM300 (See note 6)	Radius M10 (single channel) and M130 (two channel) radios	"XVC" (M10), "XQC" (M130)	HVN8177	R05.00.00 dated 01-Oct-94
	Radius M120 (two channel) and GM300 (6, 8 or 16 channel) radios, plus the GR300, GR400 and GR500 repeaters (see note 7)	"GMC", "GMK", "GMR"
There were also some data radios that were based on various MaxTrac, Radius and GM300 models (including the M10). We have no information on these or on the VR100... Contributions are welcome.
Table notes: 1) The strings referred to are the ones in the center of the model number. "MGA" was a typo of MJA" - see the "MaxTrac VHF, UHF, and 800 MHz radio models" article. A typical model number is M33GMC09C3AC which is part of the GMC series. If a model name conflicts with a model number then you have to check the boards inside and the PA deck... and the model tag is on the PA deck... and PA decks can get swappeed instead of repaired, and sometimes someone swapped a front plastic, but sometimes someone swapped a 16 or 32 channel logic board and front panel into a 2-channel radio. 2) The MJA, GMC, and GMR series are conventional, the MQA was trunking-only, the MWA series was dual mode (trunking and conventional for talk-around). I'm not sure if the UGQ and UJQ were trunking only or dual mode. 3) The RVN4018 came on 5.25 inch floppies, all the rest came on 3.5 inch disks. For additional information on RSS please see the "Programming and the Radio Service Software (RSS)" section below. 4) The column is headed as "Most Recent", but since all of these radios are discontinued I might as well have headed it as "Last". Some documentation refers to it as "Version", some as a "Revision". By the way, the "Version Numbers" or "Revision Number" by itself means nothing without the model number / part number of the RSS itself since when referring to the version or revision number one must be careful to specify which RSS part number is being considered. For example, "R05.00.00" by itself means nothing, since HVN8177, RVN4023, RVN4043, RVN4175, RVN4077, HVN9007, and RVN4001 (to name just a few) have all been issued in version "R05.00.00", and all are for different radios and are completely incompatible. 5) The Radius name was originally intended for the radios that Moto sold through retail outlets, like sporting good stores, or via telephone sales organizations. Almost anyone could get a Radius dealer agreement. Once the sales channel was in place Moto started selling all kinds of stuff as "Radius" products. Since we are limiting ourselves to one particular mobile radio here we are specifically saying "Radius LRA". And we are pretending that the GM300 was never marketed as the "Radius GM300" or the GRnnn repeaters (where nnn was 300,400 or 500) were never marketed as the "Radius GRnnn" repeaters. 6) The two channel M120 and M130 are the same radio except for the cosmetics and the fact that the M120 has the low end control and audio board (with the 5-pin accessory connector) and the M130 has the high end control and audio board (with the 16-pin accessory connector). 7) The GR series repeaters were normally shipped with two GM300 family radios, but these repeater cabinets have been seen with every possible combination of radios that have 16-pin accessory connectors - and you can build an adapter cable to use a radio with a 5-pin acessory connector as the transmit radio. And a 5 pin radio can be used as the receiver in a carrier squelch situation.

Does anyone have an original MaxTrac, GM300, M10, M120 or M130 brochure?

Here is the original Radius LRA mobile brochure.

One of the major differences between the MaxTrac / Radius product line and the GM300 product line is that the MaxTrac and Radius radios control the RF power output with a timer that watches the PTT key-down time, where the GM300 series actually measures the PA deck temperature with a thermistor.

Another difference is that the front end has a local / distant attenuator that can be enabled or disabled on a per channel basis to minimize the received intermod.

A third difference is that many MaxTrac and Radius UHF products covered the USA UHF band at 406-420 MHz and 449-470 MHz. The commercial band in many places in the world is 440-470 MHz. The GM300 family was designed from the outset to include a 438-470 MHz range.

A fourth difference is in the data sheets and RSS only... Moto Marketing reduced the maximum channel count from 32 in the MaxTrac to 16 in the GM300 in an effort to force the folks who needed more than 16 channels into a "first tier" radio like the Spectra. But they didn't tell the radio itself that! The 8-channel GM300 will do 12 channels, I've seen a 16-channel GM300 do 24, 32 or even 40 channels just fine (but you need the high-end logic board in it, and have to patch the RSS, and there is an article on this web site on doing just that).

The designers used the fact that the Radius LRA mobile was a born-again MaxTrac to do a update on the firmware and resolve a few bugs.   They took advantage of the fact that the Radius line would be all conventional and removed the trunking functionality from the Maxtrac logic board microprocessor firmware, freeing up some program space.   This let them fix a few bugs and add a few features - one of which is remote frequency select from the digital input control lines in the 16-pin accessory port - called "channel steering" by the marketing folks.   The "channel steering" feature makes it possible to use a Radius (or a GM300) as a frequency agile (or PL agile) remote base or link transciever controlled by the digital output lines from your repeater controller.

The channel steering feature in the Radius LRA mobile requires a 16-pin logic board and Version 21.01 firmware or later. The Radius RSS and firmware only offers three channel select input lines, not five like the GM300 (one line gives you 2 channels, two lines gives you 4 channels, three gives you 8, four gives you 16 and 5 gives you 32). The three channel select lines on a Radius limits you to 8 channels (channels 1 through 7 plus whatever the front panel has selected - and while it usually stays where you leave it, I don't count on the front panel selection staying put during a power cycle... especially on a mountaintop remote base).

If you have a MaxTrac and can locate a copy of the Radius version 21.01 firmware, the matching RSS and the matching Lab RSS you can brain-wipe your MaxTrac and make it a Radius.

The GM300 offers a much more flexible channel steering system - but the capability is dependent on the logic board inside the radio. If you have the HLN8074 series logic board you are limited to 3 bits / 8 channels. If you have the HLN8070 series board you can do 4 bits / 16 channels or 5bits / 32 channels. Fortunately you can tell from the model number which board is installed. The MnnGMC20xxxxx radios are 8 channels, the MnnGMC29xxxxx is 16 / 32 channels. If you are going to use a GM300 as a remote base you really want the 16 / 32 channel version. Look for the "9" in the model number (there can only be one).

If you patch the RSS to allow 32 you can channel steer with five input lines allowing 32 channels... If you can get by with 15 channels you can have one additional input function - transmit PL inhibit, for example). Personally, I only channel steer with 7 or 15 channels, the 8th or the 16th is whatever the front panel was left in, and I don't trust that to stay put after DC power has been removed and restored. I only program one channel on repeaters, link or APRS tracker radios.

This document describes the I/O connector settings and shows one way of handling channel steering. You can also use multiple logic lines from a repeater controller to do the binary selection. The Scom 7K controller has six output lines (originally intended for CTCSS tone selection) that is ideal for this.

One last comment on channel steering: Many folks use the feature to implement a frequency agile remote base on their repeater, for example a VHF GM300 programmed with 2m channels on a UHF repeater. Repeater sites usually do not need high power on their remote bases as the range is usually limited by geography and topography. The low power and high power MaxTracs, Radius LRAs and GM300s use the same heat sink casting. Hams tend to have long transmit times - and it has been my experience that the extra power is not worth the extra heat, and the trip back to the site to replace a fried RF power amplifier! Despite this warning if you are going to use a MaxTrac, Radius or GM300 as a remote then please consider running your remote base radios at around 2/3 to 3/4 rated power and when possible use the low power (1 to 10 watts, D03 / D04 / M03 / M04) plus a small amplifier, or a mid-power (10-25 watts, D33 / D34 / M33 / M34) radios.

There are some frequencies that the MaxTrac, Radius and GM300 just don't work on due to internal birdies. Robert Meister WA1MIK did a very nice writeup on this phenomenon. And don't forget the 3rd harmonic... 145-148 MHz triples into 435-444 MHz. Some areas have repeater inputs and link frequencies between 435-445 MHz.

As an aside, all three product lines are based on a single-synthesizer design, which uses a single VCO. Due to this fact none of these radios will operate full duplex (this is why the DeskTrac tabletop base station and the GR300, GR400 and GR500 series repeaters used two separate radio chassis inside the box). There is a GM300 variant called the R1225 that is full duplex (two synthesizers) unit and can operate as a repeater, a full duplex base or a full duplex link. It can do wide or narrow on a per channel basis. The R1225 full duplex radio / repeater module is the heart of the GR1225 tabletop repeater and the RKR1225 rack mount repeater. You can click here for that overview article.

The low band, high band and UHF MaxTrac and Radius logic / audio boards are pretty much identical and interchangeable within their own product lines, but all of the boards and firmware used in the 900 MHz radios are unique to that radio with the exception of the display board. In other words, the 900 MHz radio design is very unique and except for the display board you can't mix parts between it and any other band.

From an email to repeater-builder:

Another unique MaxTrac that doesn't mix control boards well is the famous (or infamous, take your pick) Ontario Hydro low band MaxTrac. (Ontario Hydroelectric is the electrical power utility for portions of Canada). The model number is ACD51MJA9HA5AK, where the AC signifies Canadian manufacture, the rest is a regular model number. Really, it should have been either an "-SP", an "S" or an "X" model (see the "Figuring out what you have" page at this web site on how to break down a radio model number).

The Ontario Hydro MaxTrac is / was a special 42-50 MHz radio with a standard 42-50 MHz RF board and power amplifier mated with a very interesting logic board derived from the standard HLN9313A unit.

The stock MaxTrac/Radius/GM300 logic board uses a 2 kilobyte 24-pin EEPROM in a 24-pin socket, soldered into a 28-pin PC board layout (leaving the top four pins of the 28-pin circuitry unused). Obviously the designer of the HLN9313 planned on someday needing expanded EEPROM space so he or she included it from the beginning. The Ontario Hydro radios use an 8-kilobyte 28-pin EEPROM in a 28-pin socket, soldered into the same 28-pin PC board layout location in the PC board and then two jumpers (implemented with zero-ohm surface-mounted resistors) are moved around. The firmware is a special chip labeled VLN5443A. All of this is described in the manual revision 6802950A44-A, part of the 68P80102W84 MaxTrac manual, described below.

A standard HLN9313A logic board The 24-pin EEPROM chip socket is soldered into the bottom 24 pins of a 28-pin EEPROM layout.

The special 99-channel logic board A 28-pin EEPROM chip fills all the pins

The 99-channel RSS is also special - VVN4167A for 5.25 inch floppies or VVN4168A for 3.5 inch floppies. Several people have tried swapping an Ontario Hydro logic board into a high band or UHF radio and they claim that it does not work. Apparently when the RSS was modified for 99 channels it was stripped down to the 42-50 MHz range only. I've been told that someone could just add additional entries to the MDF file for 99 channel VHF and UHF radios, but I think it would take someone with an advanced debugging package that could "look" into the 68HC11 CPU chip and the RSS and see where the problems/limitations are before you could have a 99 channel high band or UHF MaxTrac.

Many stock 42-50 MHz MaxTracs and Radius LRA radios have been upgraded to the Ontario Hydro configuration - all it takes is a 42-50 MHz radio with the standard HLN9313A logic board (the only one with the 16-pin accessory connector), the special firmware, the special RSS, a 28-pin socket, the larger EEPROM chip, and some time to swap the sockets, chips and move two chip resistors on the bottom of the board (used as jumpers). The biggest problem is locating the special firmware and the special RSS - everything else is simple.

And if anyone has modified a HLN9313 logic board and then patched the RSS to support a 99 channel configuration on high band or UHF (it should be possible) and would like to do an article then let us know - even anonymously. WA6ILQ has received more than one CD in the snail-mail with a note saying "for repeater-builder" and no return address on the envelope.

Narrowband:

The GM300 radio was offered in factory wideband and narrowband models. Occasionally it was necessary for a service shop to convert an RF board. Due to this situation Moto parts made up narrowband conversion kits for the GM300 / M10 / M120 / M130 mobiles. The parts kit numbers are HLN9575 for VHF and HLN9576 for UHF. The price list note says "UHF 12.5K CONVERS/MOBILE" and "VHF 12.5K CONVERS/MOBILE". Both of the kits are about $80 (2007 price).

From an email to repeater-builder:
These conversion kits can be used on limited versions of the Radius M100 / M200 and the MaxTrac mobile radios. Kit HLN9575 is for VHF RF boards and they must be HLD4321C or later (136-162 MHz) and HLD4322C (146-174 MHz) or later. Kit HLE9576 is for UHF RF boards and must be HLE9310B (449-470 MHz) or later.

The kit contains all surface mount components and this is why the kit is limited to the later (surface mount) RF boards. The kit contains the narrow IF filters as well as some caps and resistors and some instructions. The instructions that comes with the kit was scanned and is here.

The UHF kit documentation errors in that it mentions a limited number of frequency ranges - it would lead you to believe that the GM300 series radios do not operate in the 403-433 MHz range and the GM300 465-495 MHz and 490-520 MHz models do not exist, despite the fact that lots and lots of radios were built in those ranges.

Note that if you convert a radio to narrowband it is not switchable - it's either wide (with the original parts) or narrow (with the new parts).

One major thing to remember is that the radio won't program on the new "in between" narrowband frequencies since the kit only narrows up the receiver IF amplifier, compensates for the lower level of receiver audio recovery and reshapes the exciter modulation. The synthesizer step does not change, so the newly narrowbanded radios will not do the "in between" channels. The modified radio is useful only on the channels it would program on before and the lack of the smaller synthesizer step will be an issue if you expect to be able to progran the new "in between" frequencies into your radio.

Remember to readjust the transmitter modulation level and receiver squelch settings after you install the kit!

There is some disagreement as to if the radio will be type accepted for narrowband service after the mod is done. No type acceptance sticker is provided with the kit. Note that the MaxTrac and Radius model numbers do not have a narrowband option, only the GM300 series model numbers do (the seventh character is a "2" for factory wideband, a "0" for factory narrowband). For example, the M44GMC20D3AA is a wideband radio, the M44GMC00D3AA is the same radio in narrowband.

Please do the next guy that works on the radio a big favor - put a note inside the radio chassis that says that the radio has been narrowbanded with the (part number) kit, and the date. And put the note inside the radio, NOT scotch taped on the inside of the lid / shell / cover... I've seen them end up on the wrong radio.

Note that the GR1225 is the wide/narrow replacement for the GR300, and there is an upgrade kit for the GR400 rack-mount and GR500 wall mount packaged repeaters that replaces the two GM300s with one R1225 full duplex radio module that is programmable wide or narow on a per channel basis. For more info on the R1225 (including PDF'd manuals)see the web page here.

Personal opinions:
I've not looked at the schematics in detail, but I suspect that you could take the parts list from the narrowband kit information above and acquire the similar through-hole parts and with them you could narrowband the older RF boards.   Such a kit would work on the MaxTrac as well as the Radius LRA M100 / M2xx series since once you get past the through hole vs. surface mount issue from the wideband / narrowband aspect the RF boards are esentially the same between the GM300, MaxTrac and the Radius LRA. I also think the kits will work on the Maratrac since the receiver / exciter is basically the guts of a 5-pin MaxTrac mounted in the Maratrac chassis.

Programming and the Radio Service Software (RSS):

No matter if you have a MaxTrac, Radius or GM300 family radio, or which band radio you have, the synthesizer is controlled by the radio's internal microprocessor whose operation is controlled by the codeplug (a block of binary data) which is generated with the Radio Service Software (RSS) and loaded into the radio through the Radio Interface Box (RIB). To do any reprogramming of the radios you need the correct RSS, a RIB, the appropriate cables, and a slow PC with a real serial port.

The MaxTrac was designed in the days when the average user had a 16 or 20 MHz 386 and the bleeding edge software development computers were 25, 33, 50 or 66 MHz 486-based machines. The MaxTrac and Radius RSS requires a real serial port as it bypasses the operating system and talks to the serial port hardware directly. The earlier version of RSS run only on slow computers as it uses software timing loops to create critical delays (the last revisions of the RSS are less sensitive to this than the earlier ones). You must have an appropriate older computer booted into pure MS-DOS or PC-DOS (version 5 or later) and this does NOT mean a DOS window in any version of Windows!!! If RSS, the RIB or DOS is a new topic to you I suggest that you see the Motorola RSS and RIB page at this web site. There are more details including some "old computer" notes there.
Update 2022: There is a freely downloadable software package called "DOSbox-X" that will run GM300 RSS and do it sucessfully. Just configure it to emulate a 233 MHz Pentium II. It's unknown if it will run Maxtrac RSS. If anyone has please contact WA6ILQ with the DOSbox-X configuration parameters you used and he'll update this paragraph.

The MaxTrac, Radius and GM300 series are programmable radios as opposed to crystal based. Their internal processor runs a program that is contained in either the CPU chip or in a Programmable Read-Only Memory (PROM) chip (referred to as firmware). If you are going to be doing any upgrading, or you are converting a trunking radio to conventional, you will need a PROM-based radio (which leaves out the HLN9123 low-end 5-pin logic board) and a 27C256 PROM chip programmed with the correct firmware image.   you will need to look at the model number table to determine which radios have the expanded logic board. And if you take a logic board from a cheap 800 MHz eBay radio it is most likely going to have trunking firmware, so you will need a replacement conventional firmware chip anyway (or a firmware chip image file if you plan on erasing and reburning the existing chip).

Speaking of trunking, if you find a firmware chip in a radio that has the name "Scholer-Johnson", "SJI", "CVT-2-400", "ver. 2.14", or any combination thereof then you have one of the radios that was converted to LTR trunking (usually 800 MHz, but occasionally seen on UHF or high band). To convert it back to a regular radio you need the stock conventional firmware, and then you get to blank and reinitialize the logic board. Occasionally you find the stock firmware in an antistatic wrapper stuck inside the radio but that is extremely rare. If you want to do anything with a SJ trunked radio (even just to reprogram the frequencies) then you need the Scholer-Johnson-authored RSS to talk to it. If you don't have it then all you can do is to swap firmware and do a full realignment from scratch (since without it you can't read and save the tuning data before you blank the board).

If anyone is familiar with the SJ-equipped trunking radios and would like to write a SJ-to-regular conversion article, we'd love to have it. Just contact WA6ILQ. And he'd love to acquire a 465-490 Scholer-Johnson GM300 (and the RSS).

The last MaxTrac conventional firmware (version 5.34) is available from Motorola at the time of this writing as part number HLN5569A and it supports the max channel count in a low band, high band or UHF radio. The 900 MHz conventional radio uses a different logic board, and uses different firmware - it's FVN4019A version 30.03 (or later). The last pricing on either part number had was about $25. There have been reports that Moto is no longer selling firmware chips and people have had to acquire them elsewhere. More notes on firmware, including a list of 10 different part numbers, is in the "Introduction to..." article in this section.
If you need a PROM / EPROM programmer I've used the Pocket Programmer and never had a problem. The original ones used the parallel port, the newer ones are USB.
Disclaimer: I'm not related to that company in any way, I'm just a very satisfied customer.

The MaxTrac-specific RSS is part number RVN4019 (on 5.25 inch floppy disks), or RVN4020 (on 3.5 inch floppies). Neither will work on the MaxTrac LS (trunking) models. Later versions were offered on 3.5 inch disks only. The most recent (and last) version was used in preparation of the articles in this section. It is Moto part number RVN4019K which identifies itslef on the startup screen as Revision R07.02.00a, and dated 25-Jun-97. This version is known to work on Pentium processors as fast as 800 MHz. The Maxtrac RSS Manual is 68P80900Z03-J and we'd love to have a PDF of it. The author uses a Panasonic CF-27 laptop for MS-DOS radio programming and a CF-30 for Windows 7 (32-bit). The Panasonic CF-series have a hardware serial port. That is important as soem of the USB based serial adapters hasve problems.

The Radius M100, M206, M208, M214, M216, and VR100 radios use a different RSS, model HVN9173H, version R08.00.00 dated 05-May-1993, commonly called RADMBL (short for Radius Mobile). It was available on 3.5 inch media only.

The GM300 series, which include the M10, M120, M130 and GM300 mobiles (which are the radios in the GR300 desktop and GR400 and GR500 packaged repeaters) use RSS HVN8177. As of this writing the current version is R05.00.00, dated 01-OCT-94. This RSS is only available on 3.5 inch diskettes.

A DeskTrac is a tabletop station that was shipped containing either one (a base) or two (an intermittent duty repeater) MaxTrac mobile radio chassis and uses RVN4079, which also has the MaxTrac software as part of it (either RVN4019 or RVN4020). Yes, the DeskTrac RSS package contains two separate RSS packages, one for the radios and the other for the control board.
But look inside the case before you go looking for RSS - I've seen surplus DeskTrac cases with Radius LRA and GM300 radios in them!
Note that the white plastic case that was designed for the DeskTrac was also used for the Spectra series radios under a different marketing name. The Spectra Consolette (desktop station) is covered on the Spectra page at this web site.

Since the stock DeskTrac uses MaxTrac radio(s) the MaxTrac section of the ebay warning notes above regarding operation below 449 MHz applies to the DeskTrac as well (unless you put a 438-470 MHz GM300 in it... but the channel display goes nuts as the data format is different).

More DeskTrac notes are in the text below.

To do any logic board swapping in a MaxTrac you will need the MaxTrac Lab RSS, a totally different package. And there are at least two different versions of the Lab software "out there".

The RSS reads the radio and looks up the model number in an internal table that "knows" what the band limits are. Programming any frequencies outside the preprogrammed limits requires using the "Shift" trick or patching the limits in the RSS (i.e. hex editing the RSS file). Operation outside the firmware-imposed band limits will result in the power control and deviation control functions in the radios going totally berserk - one of the most common results is that the transmitter goes to full uncontrolled power output - I have seen a 60 watt low band MaxTrac put out 109 watts... and you couldn't turn it down. The frequency range was 42-50 MHz and the owner was trying to program Red Cross frequencies in the range of 47.40 MHz to 47.550 MHz as well as 6 meter amateur frequencies near 52 MHz and 53 MHz. Below 50.00 MHz the power control functions worked just as they should, above that the radio was uncontrollable. There is an article by Bob Meister WA1MIK on the MaxTrac page describing the fix to this problem - and the fix applies to all bands.

The transmitter deviation level is also controlled by the RSS and the radios microprocessor. The total deviation level can also go a little crazy when the radio is programmed outside the limits. Bob has another article on getting the 900 MHz MaxTrac to fully cover 902-928 MHz and the deviation fix is in that article. While the article is written for the 900 MHz radio the circuitry used in the deviation fix applies to all bands.

It's interesting but Moto's RSS software can do things the radio can't - so make sure you don't have the same function (i.e. PL decode out, COS out, etc.) programmed for more than one pin on the accessory connector at the same time. While the RSS will let you do it (the programmer forgot to check for that), the radio doesn't work right if you do... And the symptoms are not what you would expect... So in your programming procedure add a step right before you write to the radio: if you've changed any of the I/O pins go through them one by one, and make sure that no function is duplicated. The radio will do strange things if any are.

People missed this when I had it in standard sized font, so...

On any radio that is new to you you need to download the existing codeplug (the existing frequency, tone and radio-wide data) and archive it.   It's better to have a backup and never need it than to need it and not have it.

Before you reprogram your new radio you need to TEST the radio on it's original frequencies BEFORE you do anything to it. Make sure the receiver receives properly, and the transmitter makes proper power and modulates correctly. You don't want to reprogram it or modify it and discover it has problems and only then realize you don't know if the radio was good to start with.

On any radio that is new to you do NOT assume that any accessory connector pin programming is present, or if it is there, is correct for your radio environment.

Always plan on reprogramming any newly acquired radio to meet your own requirements.

When you acquire your MaxTrac or Radius radio remember to download and save the original (i.e. commercial frequencies) code plug (for one thing, it contains the tuning information). If you screw something up you will want to be able to backstep to something that is known to be good. If you have access to Lab software make a second backup using that as the Lab backup copies a lot more data to the saved file. And remember, a floppy disk is NOT a good long term archival medium. Hard drive space is CHEAP. Personally I copy any code plug that I want to archive to an archive directory on my hard drive, using both regular and Lab software (each to a different disk file), and that archive set gets copied to a USB backup hard drive and two different CD-RWs. More details are on the RSS / RIB pages at this web site.

Final note: If you have problems programming a radio, and nothing seems to work, open it up and look at the part number of the logic board and the RF board, then compare that to the radio model charts. You may find that the model number tag on the PA heat sink is wrong!
From a posting a while back on the repeater-builder mailing list:

I have found out that my radio is NOT a MaxTrac M100 as the model number tag on it says. It is actually a Radius M216 with a MaxTrac M100 PA and tag on the back. Apparently someone along the line had swapped the original PA with one from an M100.

Limitations:

Above all, remember that the MaxTrac, M-series, Radius LRA series and GM300 are MOBILE radios, made with minimal heat sinks, and while they can be used quite readily as a low-to-medium performance repeater receiver, or as a link receiver, you can NOT use it as a repeater transmitter, as a link transmitter or as an IRLP node radio without due consideration to the normal mobile radio limitations on RF power and duty cycle.

Remember that the beauty of a repeater is that it is a device that allows one-to-many communications rather than a cellphone, which is limited to one-to-one. As such, while any individual user may only transmit for 10 to 30 or even 60 seconds the repeater is transmitting for the duration of the transmissions of all of the users continuously one after the other. And if it's an IRLP-linked repeater then the user count - and transmit time - just increased to add all the users on the other end of the link or reflector.

As a 10% to 15% duty cycle radio the MaxTrac, Radius and GM300 (and the GR series repeaters that were made from them) are designed to transmit for no more than 10 to 15 seconds out of each 100 seconds. This is not to say that you can't transmit for three minutes, but the transmitter is going to get hot, and the longer it talks the hotter the mobile radio gets. These radios were designed for a 10% to 15% transmit duty cycle, and the internal power control circuitry is the only thing preventing the radio from burning itself up.

The MaxTrac and Radius radios have power control circuitry that turns the transmitter power down if you talk too long (all it does is measure PTT time), where the GM300 series radios actually measure the PA deck temperature with a thermistor (hence they "know" if there is a fan present or not). Due to the timer design the MaxTrac and Radius radios assume that there is no fan.

The MaxTrac and Radius power control timer can create a situation where the transmitter goes into power shutdown on its own, which can happen in the middle of a conversation. This WILL happen in a long transmit situation. The radio might not be hot (due to a strategically placed fan), but the microprocessor "knows" it has to be, and steps the transmitter power down to zero. It'll recover for a few minutes after it's unkeyed, then do it all over again until it has adequate time to rest. You really don't want your repeater fading out during something important like a search and rescue operation, or even a 911 autopatch call. The article on Manual Power Control (in this section) shows how to address this problem by bypassing the shutdown control. Just make sure you have a suitable external temperature control system in place (fans, etc). And it would still be a good idea to put a thermal snap-action switch on the heat sink and use it to trigger a backup fan - and maybe a repeater controller announcement.

Despite these comments, if you ARE going to use one then pick a 03 / 04 (the 1-10 watt radios) or 33 / 34 series (the 10-25 watt radios) radios as it is a better choice than a 43 or 44 series (the 25-45 watt radios).

In short, with very, very few exceptions, any mobile radio (Motorola or otherwise) used as a link or repeater transmitter is a recipe for failure, especially if the system includes EchoLink or IRLP... as I said above, the repeater is transmitting for the entire conversation of all the users, one after the other, however with a linked system the user pool now includes everybody on the local system plus everybody on the far end node, or if connected to a reflector then every person on every node that is connected to the reflector.

I've seen a photo of a 110w Spectra trunk mount mobile where the power control failed and let the transmiter run at full blast for as long as PTT was held down. Then one day the driver sat on the microphone for an hour during a road trip. The transmitter PA burned itself up and the radio was not economically repairable (which is why you enable the idiot timer into any mobile radio that has one and set it for 30 seconds or 1 minute).

The "Executive Summary": If you are going to put up a repeater (or a point-to-point link that will have a similar duty cycle), don't use a low-end low duty cycle mobile radio (from any manufacturer) as the transmitter. It's one thing to use a mobile radio based repeater like a GR300 (or similar) in a shopping mall environment to talk to the rent‑a‑cops or to tell housekeeping to clean up little Johnny's spilled ice cream cone, but you want something with a higher duty cycle as your primary area repeater.

These radios were designed for a range of RF power - for example, the D04 (or M04) series is a 1-10 watt radio, a D34/M34 is a 10-25 watt radio, and a D44/M44 series is a 25-45 watt radio. 25 to 45 means not more than 45, but also not less than 25. If you run outside that range, it will be inefficient and run hot.   Yes, strange as it may sound, a D44 run at 15 watts runs hotter than when run at 30 watts.

Even this DeskTrac tabletop base (which has a MaxTrac inside and
also came in a repeater version with two MaxTrac radios inside)
has the MOBILE limitations.

Using an external power amplifier: If you want to use one of these radios to drive an external power amplifier, look for a D03 or M03 (VHF) or a D04 or M04 (UHF) radio. Those are specifically designed as 1-10 watt radios and can be adjusted to anything in that range. 5 watts is plenty to drive an external amplifier to whatever power level you can afford. The author maintains a number of commercial repeaters made from M04GMCs (with a fan on the PA) running 4-5 watts driving continuous duty 100 watt Henry Electronics amplifiers backed down to 60, 90 or 100 watts (depending on the license). They have been in service since the mid 1980s with very few problems.

If you have a MaxTrac, Radius LRA or GM300 series radio with a dead PA deck then you can use the exciter output directly into an amplifier that is designed for that power level. The exciter output (from the RF board) on MaxTracs, Radiuses, and GM300s is anywhere from 20 to 50 milliWatts, depending on the operating band (220 mw on 900 MHz).

The schematic diagrams show signal levels of +13dBm to +17dBm for various VHF/UHF/800 MHz radios (that's 20-50mW), but +23.5dBm for the 900 MHz models (there's where you get 220mW). These power levels have been confirmed by actual measurement. The exciter output connector on the RF board is a female Taiko-Denki connector. The male connector require a unique crimping tool to be installed properly, and they are designed to fit only a few types of coaxial cable. https://rfconnection.com/ will make custom cables with T-D connectors for very reasonable prices. So get a jumper with a T-D on one end, and a single-hole female BNC on the other and you are good to go.

Initial Checkout, Repair, Tools, and Hardware Oddities:

(This section covers the mobile radios - see the DeskTrac Overview article in this section for additional information on the tabletop station.)

CAUTION:     DON'T LET THE SMOKE OUT !
The Motorola mobile radio products made prior to the Maxtrac mostly used push-pull audio power amplifiers and audio output transformers, and drove the speakers as a hot wire to ground. The MaxTrac, Radus, GM300 and many later radios eliminated the audio transformer and they run the the speaker as the push-pull load directly... this means both sides of the speaker are floating above ground. This quirk is significant on your workbench: any audio test equipment that would normally connect to the speaker (such as you would use to make a quieting measurement) must be on the far side of a audio isolation transformer. Motorola has a low-power one as part number SLN6435 in their test equipment catalog (being "test equipment", it's high priced - at about $80 in 2006), and they also include a cheaper but higher audio power one in every tabletop base station (part number 2580188B01, about $35 in 2006) since common wireline remote controls expect ground-referenced audio to drive the remote sepakers.
In a pinch you can connect a 2 watt resistor of any value from 8 to 22 ohms to the radio as a speaker load, and use a 600 ohm to 600 ohm line transformer between the radio and the test equipment. I've had good luck with 600 Ohm-to-600 Ohm transformer (like a Triad TY145 - available from Mouser Electronics (p/n:553-TY145P) under $4 as I write this). Note that the audio bandpass characteristics of whatever isolation transformer you use will have to be wider than the audio frequencies you hope to pass through the radio. The Triad TY145 is a broadband audio transformer and if you use that one you won't have to worry about that.

In short, if you ground one of the speaker leads the odds are better than 75-25 that you will let some of the magic smoke out of your radio. So use an audio isolation transformer to prevent this - just put the transformer between the radio and any load that isn't a floating (an ungrounded) stand-alone speaker.

Some radios have this sticker, some don't.   Believe it and heed it.
Run all MaxTrac, Radius LRA and GM300 radios with ungrounded (floating) speakers.

The radios that have a 16-pin accessory connector DO NOT have the internal speaker connected by default - it takes a jumper plug to enable it. More details (including a photo) will be found in other articles.

You will need T8, T10 and T15 Torx™ screwdrivers to open and work on the radios. Torx head fasteners are getting more and more common in the automotive world and most tool stores, even Home Depot, Wal-Mart and Harbor Freight now carry the screwdrivers and bits. Note that the T8 is less common in the prepackaged kits... I've seen a number of bubble-packed kits that started at T10 and went up in size so you may need to hunt a little for a set that includes the T8 size. Personally I avoid the sets with a single handle and changeable bits as my primary bench tools - it seems that you spend as much time changing bits as working on the radio. And after a while the bits get loose in the handle and won't stay put, so you spend more time looking for the dropped bits on the floor (or wedging a piece of paper or foil into the handle to keep the bit in place).

To open the radios you will need to remove the two screws from the control panel (T15) and the four flat-head screws from the sides (T10). Pull the control panel outwards from the front of the radio just a little to free up the top and bottom covers, then pry the covers off. They are identical and split in the middle of each side. Sometimes they're hard to get apart, but nothing else holds them together. Usually you can get them going by using a flat blade screwdriver and starting in the front where the edge is exposed over the metal chassis. If you need to remove the logic board you will need a T8 screwdriver to remove the small flat-head screws that hold the logic board's heatsink to the side of the chassis.

If you acquire a radio and don't know it's history, as you do the initial bench check you will want to check it for frequency accuracy - and test both the receiver and the transmitter separately. First check to make sure all the screws that hold the boards in place are tight. If they are at all loose you will have an unstable and / or microphonic radio. If you find a stripped hole then you will have to use a larger diameter screw. Personally I install a HeliCoil™ to salvage the threaded hole. Or you can relegate that radio to the "to be cannibalized" shelf (i.e. use it for spare parts). I've a number of "frankenstein" radios in service (built up from spare parts).

If your new-to-you GM300 family radio is off-frequency AND it is shock / vibration sensitive you will find that in many cases if you clean the pins and jack between the boards very well the problem goes away. Once the pins are clean a microdrop of a product called "Stabilant-22" (also known as "Tweek") on each pin helps a lot. The 15 mL bottle size is carried by Motorola Parts as part number 1180369E78.

If the entire radio is waaaay off frequency (both transmitter and receiver) and cleaning the pins doesn't help AND it is NOT vibration sensitive... well, this is very rare these days, but does show up once in a while...
The RSS contains a "warp" adjustment to bring the reference oscillator (the main frequency determining circuit in the radio) back on channel, but Motorola had a bad batch of the 14.4 MHz reference oscillator crystals that drifted beyond the ability of the warp adjustment. The story that I heard from two independent sources is that the offshore crystal manufacturer tried to cut one too many corners and didn't fill the crystal cases with dry nitrogen during manufacture, but nobody knows for sure (or if they do, they aren't talking). The crystals passed receiving inspection, were assembled into radios and shipped to customers. Within a year or two they had drifted to the point of being almost unusable. Any surplus MaxTrac is old enough now that any bad crystal has probably already been changed out by the time it is in an amateur radio operators hands, but you occasionally find one that has been a shelf spare all its life. While a crystal house like International, Bomar or JAN is one source for a replacement, Motorola Parts is cheaper in this case (and since it's a stock item you won't have to wait for it). The part number for the 14.4 MHz crystal is 4880174D05 (when you get it don't be surprised if it's labeled "14400.00", "14400", or "14.4"). The part number is the same in the MaxTrac, Radius and GM300 series and it will set you back around US$14. In the GM300 manual Moto says this crystal is not field replaceable but it obviously was in the days of the mass swapout under warranty (supposedly Moto was shipping out thousands of replacement crystals per month for several months). There is a paper tag glued to the side of the factory crystal with an 8-digit number that contains the temperature coefficient information that needs to be typed into the RSS (see this photo), and naturally a new crystal will be different than the old one, but the data on the label on your old crystal should be a good starting point. See the paragraph titled "Reference Oscillator Coarse Adjustment Procedure" on the GM300 info page in this section.

If the transmitter is on frequency then the main crystal is fine. If just the receiver is off frequency (or seems dead) then you will need to check the frequency of the second oscillator crystal. The VHF high band, UHF, and 800 MHz MaxTracs and Radiuses use a 44.645 MHz, crystal, part number 4880008K02, which has been replaced with 4880606B02 for about $20US as of August 2008. If you have a M10, M120, M130 or GM300s look carefully at the old crystal before you order the replacement as some used the 44.645 MHz crystal and some used a 44.845 MHz crystal (part number 4880908W04). The VHF low band radio uses the same 14.4 MHz master oscillator but it uses a 10.245 MHz crystal (part number 4880908W01). The 900 MHz MaxTrac uses the same 14.4 MHz master oscillator but it uses a 38.695 MHz crystal (part number 4808005K21) that no other model uses. Again, in each case the "real" Moto part is probably the cheapest (and since it's a stock item you won't have to wait for it).

There is one exception to the "off frequency" info above. If you have a trunking 900 MHz MaxTrac that has been converted to conventional, and it is about 12.5 kHz off frequency, check the firmware chip part number !   For example, if it's programmed to 927.5000 and you find it transmitting on or near 927.4875 or 927.5125 (and it's consistently off the same amount across the band) that's the second thing you check (the first, as mentioned above, is the pins that connect the two boards). The 900 MHz radios use unique firmware and having a VHF / UHF / 800 MHz chip in a 900 MHz radio will cause multiple problems, but the most visible and easiest to check is that its off frequency !   DO NOT just "make do" and program the radio 12.5 KHz off so that it lands on your target frequency, use the correct firmware !   The off-frequency problem is just the most visible of the problems you will have with using VHF / UHF / 800 MHz firmware in a 900 MHz radio.

If you are not going to be using the accessory connector in the radio (i.e. you will be using it as a mobile) then you can ignore the next paragraph. On the other hand, if you are going to be using it as a link receiver, as a control receiver, or as an IRLP or Allstar radio, then you need to pay attention.

There is a 3-pin jumper on the logic / audio board of all the MaxTrac, Radius and GM300 radios that selects the mode of pin 11 in the accessory connector of all the non-900 MHz radios. A shorting jumper selects the "A" position or the "B" position. Note that this jumper does not affect the speaker audio, it only affects this one pin in the accessory connector. In the "A" position the pin is fed a constant level of un-muted flat audio (i.e. not de-emphasized). In the "B" position (the factory default) the pin is fed a constant level of squelch-muted normal audio (i.e. de-emphasized) which makes it ideal as a source of receiver audio for feeding to a port on a repeater controller, or to an IRLP or Allstar interface. Needless to say, unless you specifically want flat un-muted audio you want this jumper in position "B". So the first time you have any new-to-you radio open for the first time you will want to verify the setting of this jumper (and in reality, all of the jumpers).

Some other notes on 900 MHz MaxTrac and Radius LRA radios...

Courtesy of Greg Stahlman KJ6KO:

The 900 MHz MaxTrac logic board is unique and has several differences from the low band, high band and UHF ones, two of which are important to those of us that use them in repeaters:

First, unlike the low band, high band and UHF radios the JU551 jumper on the logic board HAS NO EFFECT on the de-emphasis of the audio that feeds pin 11 on the accessory jack! This is because the 900 MHz radio has different audio pathing and the de-emphasis is done in the "HEARCLEAR" circuitry on the microphone connector / HEARCLEAR board. JU551 will only select between raw discriminator audio and squelched, high-pass-filtered (PL Filtered) receive audio. The pin 11 audio will NOT be de-emphasized either way! If you want de-emphasized receiver audio, you need to pull it from pin 8 on the microphone jack. If you want de-emphasized receiver audio on the 16 pin accessory connector you need to remove the JU 661 bumper block and add a jumper wire internally from the center pin of JU 551 to pin 8 on the microphone jack.

Second, the microphone input (pin 2) on the 16 pin accessory connector is NOT pre-emphasized! Again, this is done in the HEARCLEAR circuitry on the microphone connector / HEARCLEAR board. If you want normal (pre-emphasized) transmit audio, you must use the microphone jack on the front of the radio, perhaps with a DC-blocking capacitor in line (+ side towards the radio). The rear connector does work, but it delivers non-pre-emphasized (flat) audio to the transmitter.

On 900 MHz and higher the feedline needs a lot more attention than on the UHF and lower frequencies. Personally, I prefer to use the kits designed by Moto for 800 and 900 MHz that use the white Teflon (both dielectric and jacket) low loss coax for any 800, 900 and 1200 MHz mobile antennas. Moto has a nice kit of the NMO mount and 14 feet of coax kit - part #0180351A78 at around $24 each (as of Feb 2011). The coax uses a stranded center conductor (which is A Good Thing when you are mounting the NMO mount on a vehicle trunk lid... in fact there is no excuse to use solid center conductor coax for any mobile installations).

More details on the internal jumpers in these articles:

• MaxTrac and Radius Logic Board Jumpers
• GM300 family Logic Board Jumpers
• Flat Audio, and Pre- and De-Emphasis explained

Cosmetic parts:   (including the speaker)

If the MaxTrac / Radius volume control knob is missing, you need to order out part number 3680144M01 (or 3680106M03 for the GM300 series), the MaxTrac 2-channel conventional escutcheon (faceplate) is 1380276L02, the MaxTrac multiple-channel conventional escutcheon is 1380277L01, the accessory connector gasket is 3280014N03, a replacement plastic case half for any of the MaxTrac, Radius LRA or GM300 series radios (the top and bottom is identical) is 1580127L01.

I've seen MaxTrac, Radius LRA and GM300 family mobiles mounted vertically on truck dashboards (i.e. with the front panel horizontal and facing up). In that situation the the speaker grille area seems to be a magnet for coffee cups and soda cans.   If the internal speaker in your new-to-you radio is buzzy or raspy you might want to check the speaker cone - in fact the entire internals of the radio - for coffee or soft drink residue.   Sometimes you find that the internal speaker is electrically open.   If you decide to replace the speaker, for whatever reason, a new internal speaker was part number 5080085D02 or D03 (depending on which book you read), both of which have been replaced by p/n 5004639J01 that will run you around US$7 (as of early 2009); of course both are NLA in 2017.   An alternate speaker, one with integral mounting flanges, is 5080496Z01 and it too is NLA from Motorola, but you will find some of the J01 and Z01 speakers on a popular auction site.   BTW, the stock internal speaker is a 22 ohm, 5 watt device.   If you are running a MaxTrac, Radius LRA or GM300 as a mobile in a noisy vehicle you will tend to run the volume up loud.   Well, the tiny internal speaker gets real distorted real quick as you crank up the volume.   In those cases you really will want an external speaker - and the one made for the MICOR or Syntor speaker is an excellent choice.   Likewise if you are running a MaxTrac, Radius LRA or GM300 as a base station in a noisy office you will find that an external speaker makes a world of difference.

More speaker notes, including model numbers for the better external speakers are below.

If you need to you can purchase a complete new plastic front panel from Motorola for about US$35 and its part number is HCN3217B. It comes minus the escutcheon, that's the flat plate that surrounds the buttons and labels their functions. Or you can scavenge a front panel from an 800 MHz MaxTrac, which are common and cheap, and install a new escutcheon so the buttons are labeled properly. The six channel radios commonly have the scan button labeled as Exit, so if you want a new full feature escutcheon as I said above it is part number is 1380277L01.

Replacing the Antenna Connector in the radio:   (with some notes on the DC power connector)     (hint: don't do it unless you really have to)

The chassis-mount coax connector on the back of a MaxTrac, Radius LRA mobile, and GM300 is called a "Mini UHF" female connector and in many cases these radios are the first time that some people have seen this connector.   The female connector Motorola part number is 0980131M01. They cost about $6 each and come in bags of 5. This part IS still a currently available part because it's used on so many Motorola products. Even the Quantar uses one. The Motorola part number for the male connector is 2880376E84 and this part number is a crimp-on connector for RG-58 sized cable.   There is a Mini UHF male to full size UHF Female adapter available as part number HKN9557A.   Several antenna manufacturers sell kits that include the mini-UHF male connector already mounted on the antenna cable. There are a wide variety of test adapters available from RF Industries.

Do not use an adapter to connect a RG213 or RG-8 sized cable to the mini-UHF connector on the back of the radio - you cna break the adapter or the connector. Use a pigtail cable with a mini-UHF male to a "N" or SO-239 female.

Sometimes the chassis mount female coax connector on the radio needs replacing...   I've seen several with a damaged center pin that makes intermittent contact with the coax center pin, and I've seen one that was really mangled to where you could not screw the male connector on it.   Often the little "teeth", (that keep the plug from rotating when tight) get worn off.

The problem is that replacing it is a lot more work than you would expect due to the way the radio was designed and put together (the antenna connector is soldered to the bottom of the RF amplifier board, which is a major pain to remove), so don't proceed unless you really have to.   If the only problem you have is worn teeth and the antenna cable connector becomes loose on its own try slipping a tiny O-ring on the center pin of the plug, then tightening the connector enough to compress the O-ring about halfway.   The increased friction will prevent the antenna connector from coming loose. Note that this trick is only a stopgap, you WILL have to replace the connector eventually, but it can buy you several years in a base station environment.   By the way, this same trick (with a larger diameter o-ring) works on full size PL-259s (it's a very common trick used on CB radios installed in the big 18-wheel trucks).

The antenna connector itself is rather easy to replace, but you must remove the circuit board from the power amplifier to extract it.   That also means you must unsolder and remove the DC power connector from the circuit board first.   This is much more difficult than it initially seems.   The connector leads are thick and the circuit board holes are just barely big enough for them.   The holes in the PC board also have copper sleeves inside that connect both sides of the circuit board together.   These sleeves often come out when extracting the power connector, requiring further work to fix the newly created damage.

So if you really have to change it, the large mass means that you need to use a larger soldering iron, or even a soldering gun to heat each lead, then remove as much solder as possible from the joint.   I keep my late father's old Weller 8100 soldering gun (purchased in 1958) in the bottom of my tool box just for jobs this.   Once the solder is out of the way you can remove the power connector mounting screws (using a T10 screwdriver), then pull on the connector as you alternately and quickly heat each lead at the circuit board.   Eventually you will be able to wiggle it out and then you can do a better cleaning job on the leads and holes.   Another option is to chop the old power connector apart using a Dremel Moto-Tool equipped with a rotary saw blade, then remove the individual pieces (if you have decided to replace it then who cares if it comes out in one, two or several pieces - minimizing the damage to the circuit board is much more important).

Once the DC power connector has been extracted, you can remove the screws holding the circuit board and RF components to the heat sink.   The mini-UHF antenna connector can now be unsoldered from the board, or you can remove its mounting nut and remove it with the circuit board.   It's probably better to install the new RF connector into the heat-sink first, then clinch the nut down TIGHT, then reinstall the circuit board, then solder the antenna jack.

Since the DC power connector is already loose on your bench, I'd take a good look at it.   If it's worn, damaged or mangled I'd seriously consider replacing it.   A new one is part number 0980255E01 and Moto parts price (at the time of this writing - early 2006) is around $11 each.   Yes, it's a little steep, but the hard work of removing the old one IS already done ...

Accessory Connector Notes:

Depending on the radio model it will have either a 5-pin or 16 pin accessory connector.   Most hams look for the 16-pin radios because they are easier to interface to other equipment.   That's fine as it leaves the 5-pin radios for me, and adding a single resistor and a single NPN transistor gets you a COR signal.   Adding a DE-9 pigtail cable is easy (see the article in this section).   And 9 pins are plenty to do everything I need to do... (including feeding power into a receive-only radio and connecting it to bypass the power switch on the volume control).

The radios with a 5-pin accessory connector have the internal speaker on full-time, where the ones with a 16-pin connector enabled it with a jumper on the accessory connector.   This jumper can be implemented in any one of several different ways:
1) an official MaxTrac jumper plug inserted in the back of the radio,
2) a soldered jumper wire inside the radio bridging the two pins together.
3) a PC style two-pin option jumper inserted in the back of the radio (not recommended in a mobile environment, but just fine as a base radio, as a link radio or as a control receiver in a rack),
4) and I've seen one radio where the previous owner simply bent the two pins together (so they were touching) and then soldered them together. It required replacing the entire accessory connector before you could insert a standard accessory plug into the back of that particular radio.

To enable the internal speaker you will want to tie pins 15 and 16 together or connect an external speaker to pins 1 and 16.   Note that one side of the speaker in the MaxTrac and Radius LRA series radios and both sides of the speaker in the later M10, M120, M130 or GM300 series radios is / are hot, and grounding a hot wire (even momentarily) will let the lifetime supply of magic smoke out.   The MaxTrac and Radius LRA series uses two inexpensive individual transistors as an audio output stage, the GM300 series uses an expensive audio power module.

Above shows where to put the PC jumper - the rightmost two vertical pins. By the way, the exposed power pin is the positive pin.

This is the pinout of the 16-pin accessory connector.   See the interfacing articles for a complete list of pin functions.

YOU CAN NOT USE THE ABOVE JUMPER TECHNIQUE ON MOST FACTORY-PROGRAMMED RADIOS.

You will find that most radios are programmed for the alert / alarm function when they land on the surplus market.   The alert pin is grounded when normal (i.e. not in alert mode) by a jumper from pins 7 and 9 and removing the jumper (i.e. lifting the alert pin off of ground) causes the radio to transmit the alarm signal.   The PC jumper on the speaker pins shown above is only usable on radios that have the alert function disabled in the programming of the radio codeplug (which is one of the first things I do when I program a new-to-me MaxTrac, Radius LRA or GM300 family radio).   Just go into the signaling menu and see if there is an MDC1200 system defined, and if so, set its "Emergency Alarm" field to "None".   More details can be found on the Interfacing pages.

Note that the GTX radio uses the same 16-pin accessory connector, and it also needs a speaker enable jumper plug... but the connector has a very different pinout, which is covered on the GTX pages elsewhere on this web site. DO NOT plug a GTX optioned jumper plug into a MaxTrac, Radius or GM300!! YOU WILL DAMAGE THE RADIO as covered in this warning article - you will kill the audio output capacitor and 9 times out of 10 the shorted cap will kill the MaxTrac speaker amplifier transistors or the GM300 audio output module (which is expensive).

The plastic 16-pin accessory connector shell (the piece that plugs into the radio) is DigiKey's part 104422-1-ND.   At the time of this writing DigiKey's price is about a US$1.50 each, or about US$1.25 each for quantity 25.   AMP makes a wide variety of contacts for this shell with varying wire sizes and plating types.   The one most appropriate for 22 AWG wire is DigiKey part number A3007-ND (AMP 1-87309-3) at about 14 cents each (or about US$12.50 per hundred).   And these pins are gold plated! Mouser part numbers are 571-1044221 for the connector (under US$2.00) and 571-1873093 for the pins (about US$0.20).

The pins snap into the connector body, and once in place are designed to not come out (as you would expect).   To remove one you need the pin extraction tool, Moto part number 6680947W01, which can be purchased by itself for about $2, but it is more economical to buy the HLN9242A 16-pin Accessory Kit, which includes this tool along with nine pre-terminated wires, a connector body, and 16 extra (i.e.. loose) socket contacts.   At the time of this writing the HLN9242A kit costs about US$7.

Or if you have a piece of 0.020 inch steel shim stock around you can make a pin extraction tool.   Look on the "Keys Page" elsewhere at this web site for a photo and the measurements.

Or if you are very careful you can use a tiny pick tool.

There's an instruction sheet that explains how to remove the pins in the GM300 article in this section.   Open that article, scroll down to the Accessory Jack section and click on the image that's there. It shows the extraction tool, and where to insert it.

HINT: If you are just getting started I suggest you buy a HLN9242A kit as you get a connector body, 16 loose pins, 9 pre-ended wires, and a pin removal tool.   Then when you need more plug bodies or pins just order them from DigiKey or Mouser (both companies part numbers are in the interfacing articles in this section).
Or... There is also the HLN9457A Hardware Kit (click here for a photo) that is specified for the GM300 but works just fine on the MaxTrac, Radius LRA and CDM series... it has has 16 connector pins, five wires that are eight inches long, with pins already crimped on them however this kit is missing the tool. The price is in the $5 to $6 range.

The GKN6271 is Moto's official ignition sense cable kit.

Replacing the Accessory Connector in the radio:     (hint: don't do it unless you really, really have to)

Occasionally you run across a radio that needs a new 16-pin accessory connector.   Maybe one pin is bent, soldered to another, or even broken off.   The part number for the 16 pin right angle accessory connector is 2804503J01, at around US$5.25 (early 2007 pricing).   Like the microphone jack, do not try and unsolder and remove all 16 pins of the old jack !!   It's dead anyway, just use a large pair of diagonal cutters and chop apart the old connector.   Once all of the individual pins are free then unsolder each pin one at a time from the bottom and lift each individual pin out of the top of the board with a pair of needle nose pliers.   When all are removed clean out the holes with a solder sucker or a round wooden toothpick. Now mount and solder the new connector.

I've never seen a radio with a 5-pin connector that needed replacing but if you come across one the replacement part number is 0180747T09.

Speakers:

If the internal speaker is not loud enough, the standard Moto mobile speaker with a 5-pin plug is part number HSN4019B, or the same speaker with a 16-pin plug is HSN9326A (photo), or you can take an old Motrac, Motran, MICOR, MASTR Pro or MASTR II vintage swapmeet speaker and change the plug (just make sure that both sides of the speaker are internally floating off of ground).   There are also amplified speakers that are part of Motos "Power-Voice" line such as the HSN1000B (used in fire trucks, and other noisy environments).

From an email from Jeff Kincaid W6JK:

The MaxTrac family radios have a built-in front panel speaker and sometimes you will find a radio that has the jumper wire that connects the physical speaker to the logic board missing (the radio was obviously used only with an external speaker).   A leftover lead from a PC case that has a 2-pin push-on connector on one end will fit the speaker connector on the audio/logic board and substitute temporarily - look in your PC parts box for a leftover front panel red or green LED, or the wiring from a reset button.   Just push the two-pin female plug onto the MaxTrac logic board and cut the wires to length then solder the wires to the speaker. At this point you will find that the case half won't go on because the plastic body of the PC connector is too tall... been there... done that...   The quick and dirty solution is to remove the two female pins from the PC plug body, put heat-shrink on them individually and push each one onto the logic board pins (see this photo). Note that they will vibrate loose in mobile service but this will get you by in a base station environment or until you can locate the proper connector... some PC sound cards use the actual 2-pin connector that Motorola used and you may find one in someones junk box or at a PC repair shop.

Microphones, and Replacing the Microphone Connector in the radio:

Occasionally you will find a radio with a bad microphone jack - perhaps from wear, or perhaps from corrosion problems (green mold).   Sometimes it's not obvious until the RIB programming cable or the microphone does not make contact or is making intermittent contact.   Don't attempt to clean it, you are just wasting your time (been there, done that several times).   The genuine Moto mike jack for all of the MaxTrac / Radius / GM300 series is part number 0980132M01, available for about US$4 from Motorola Parts.   Do not try and unsolder all 8 pins and remove the old jack!!   You don't want to risk lifting the copper traces on the board (been there, done that, wasn't pretty... was salvaging someone else's screwup).   Just use a large pair of diagonal cutters and chop apart the plastic body of the old jack (relax, you are replacing the jack because it's dead anyway), then bend all of the 8 pins straight up away from the board, lifting out the pieces of the plastic body as you go.   Once the eight individual pins are free from the plastic body and standing up in the breeze then unsolder each pin one at a time (from the bottom of the board) and lift it out (with a pair of needle nose pliers) from the top of the board.   When all eight pins are removed clean out the holes with a solder sucker, compressed air or a round wooden toothpick.   Now mount and solder the new jack.

Note that the base station and mobile microphones for the MaxTrac, Radius, GM300 and several other radios (including the DeskTrac) look absolutely identical, but may or may not be interchangeable because they can be wired differently inside (the differences involve only the first two pins, see the pinout table below).
So yes, any RJ-45 microphone can be plugged into any MaxTrac series radio, but if the first two pins are wired different it may not work.   Before you purchase microphones that have a RJ-style plug on the microphone cord you need to verify that the wiring is compatible.   There is a table of known good microphone part numbers below.   If you have one that works but isn't on the list, please let us know the model number so we can add it.   Addtional parts information is in the parts catalog PDFs available on the main index page.   Note that there are errors in these catalogs, so always check with Motorola's Parts ID group before placing your new microphone orders.   Since pin 1 and pin 2 in the mobile microphone jacks are unused we take advantage of that in the interfacing article.   Both pins ARE wired on the DeskTrac tabletop base / repeater, and one is wired to power, so be careful.

We would welcome any photos or schematic scans for any item in this list:

• HMN1035 hand-held microphone, full size microphone with 10 foot cord (schematic) (uses Hang-Up Clip HLN4606A)
• HMN1035C Palm-size microphone (see the HMN3596A microphone below).
• HMN1037B non-backlit DTMF Microphone   (photo)
• HMN1038 Standard beige base station (desktop) microphone, with PL defeating "Monitor" button (schematic)   (full documentation, extracted from the 900 MHz MaxTrac manual).
  The black version is the HMN3000 (see below). A replacement cord for either one is available as a repair kit, as 3080043N04 or as HKN4291 "Microphone Cable Kit"
• HMN1056D hand-held microphone, compact (palm-size) with 7 foot cord (uses Hang-Up Clip HLN4433 or HLN9073B).
  The "D" series of this microphone (and probably some of the earlier ones) is glued or solvent-welded together during manufacture and you can't open it without serious effort. See the photos of the interior of a 1056D in the "Microphone Hang-up Mechanisms" article in this section for more details. The microphone cord (part number HLN9559A for the 7 foot version) plugs into the bottom of the microphone itself with a telephone style RJ-series plug.
• HMN3000B black base station (desktop) microphone - list price in 2009 was about US$120. (full documentation)
• HMN3013A non-backlit DTMF Microphone, for 820/840 Series
• HMN3031B base station (desktop) microphone similar to HMN3000 listed above but used on carrier squelch radios, does not have a PL defeat button
• HMN3174B Palm-size microphone (Radius, black) with green/red LED (schematic)
• HMN3220 - This is a kit that consists of one HMN1056D microphone and one HLN9073B hang-up clip bundled together
• HMN3413 black plastic microphone
• HMN3596A Palm-size microphone (black)   (photo)   (schematic)   (full documentation, extracted from the GM300 manual).
• HMN4016A Noise Canceling mobile microphone
• RMN5068A black base station (desktop) microphone
• TDN8305A or B (photo)   This is the basic DTMF mike specified for the GM300 radio. It is not backlit.
• TDN8310 Backlit DTMF Microphone
• TDN8306A or B
• TDN8307A, B or BSP
• TDN8309A or B
• TDN8310A or B
• TMN6169A or B   This is the fancy DTMF mike specified for the GM300.   It has memory dial (also called autodial), last number dial, and is back-lit.
• AAREX4617A Telephone style handset   (photo 1   photo 2)     (2008 price is over US$120)

CES made some aftermarket microphones for the MaxTrac/Radius/GM300 series radios. They made both 12-button and 16-button versions. One of the DTMF mics is the model 600LRAD (about US$150).

The Moto built TouchTone / TouchCode / DTMF microphones have a different model number to cover every seemingly different combination of non-backlit or backlit, trunking or conventional, and every mobile radio connector from the 1950s Motrac on up.   All are covered in the Motorola Touch-Code Encoder Microphone instruction manual 6881114E07, which as of this writing (mid 2009) is still available from Motorola Parts for about US$3.   The model tables in the manual mention fifteen different DTMF mikes, including the HMN3013A used on the trunked MaxTrac/Radius/GM300, and the HMN1037A used on the conventional MaxTrac/Radius/GM300. On this particular manual do not get the original or -A version, get the -B or newer version, as they've added a bunch of useful info with the -B version.

Internally the Motorola DTMF microphones are built as a two-board stack, one with the keyboard and electret microphone cartridge, the other with the electronics.   The conventional and trunked microphones are two similar products that share the same outer case and PTT button and internally have a different set of circuit boards.   Several internal parts (JU1, R4, R18, R19 and CR9) and the cord/connector are changed / configured for the different microphone models.   Yes, you can convert one to another by changing cords and the internal parts, but it's much easier if you stick within the conventional or trunked versions (i.e. if you need to do a cord swap on a microphone for a conventional radio then start with a conventional mic).

There is no factory 16 button DTMF microhone for the MaxTrac/Radius/GM300 other than the expensive and hard to find 16-button CES model.   Midland made some 16-button DTMF microhones that were usable on Motorola radios (including the MaxTrac/Radius/GM300 series) with not much more than a connector change.   E. F. Johnson also made some 16 button microphones that can be rewired.   Unfortunately I do not have the CES or Midland model numbers, or the EFJ modification info.
If anyone has done a Midland or EFJ microphone conversion would like to donate the info, even anonymously, we'd love to have it.   Contact the page maintainer above.

If you have an old junker carrier-squelch-only microphone (i.e. no PL hangup function built into the hangup button) that has been dedicated to the test bench / workbench it might be worth mounting a toggle switch in the case... wire it so that flipped one way pin 3 is open (the radio is in carrier squelch), the other way it's in PL mode (pin 3 is shorted to pin 4).

MaxTrac / Radius / GM300 / DeskTrac Microphone Jack Pinout When looking at the front of the MaxTrac radio the microphone jack is vertical, with the locking clip to the right. Motorola numbered the pins with pin 1 at the top, nearest to the volume control.   This is backwards from the common RJ45 Ethernet connector. The DeskTrac has a horizontal microphone jack with the locking clip at the bottom, and the pins numbered from left to right like ethernet.   Six of the pin functions are the same as the MaxTrac. The 900 MHz GTX mobile also has a horizontal microphone jack with the locking clip at the bottom, but it's numbered from right to left to match the MaxTrac. Another way of remembering the pin number is this: Hold the connector with the pins facing up, the locking pin down, and the cable towards you. The pin numbers are 1 through 8, left to right for the DeskTrac, and right to left for the MaxTrac. MaxTrac, Radius, GM300 and GTX Pin Description DeskTrac and Ethernet Pin 1 On the low band, high band, UHF and 800 radios both pin 1 and pin 2 are fed to the logic board but are unused. On 900 MHz radios these pins never leave the front panel board but are unused. See Note 1. On a stock DeskTrac this pin has +5vDC on it. See Note 2. 8 2 Same situation as pin 1. On a DeskTrac schematic this pin is labeled "HD". 7 3 The receiver is in carrier squelch when this pin is floating, and when it is grounded (if the channel has PL or DPL programmed) the receiver must have the proper PL or DPL to unsquelch it. The method of grounding this pin varies with which model of microphone is used. See note 3. 6 4 Ground 5 5 Microphone audio and preamp DC bias voltage. 4 6 PTT (ground to transmit). 3 7 The radio schematic labels this pin as "SCI+" in some books and "SPI+" in others (and the books don't agree - some say Serial Communications Interface, one says Serial Command Interface, some say Serial Programmable Interface, others Serial Peripheral Interface). Either way, it's the bidirectional programming data lead, which is used by the RIB for programming the radio, so leave this pin taped off inside the microphone. Some microphone cords do not even have a conductor in the cable for this pin. The special plug that was used to put a trunking MaxTrac into test mode simply grounded this pin with a pin 7 to pin 4 jumper. 2 8 In palm microphones this pin is unused, as it carries audio out intended for a handset earpiece. In the radios the audio level coming from the radio on this pin is a fixed level (not affected by the volume control) which works very well as a source of repeat audio (i.e. de-emphasized). 1

Table Notes:
Note 1: On the low band, high band, UHF and 800 MHz MaxTrac radios, the microphone jack pins 1 and 2 run through the internal cable to spare pins on the logic board where they sit unused. On the 900 MHz board (with HearClear), these pins are not attached to anything on the board (solder pads only) as the two connections from the logic board are used to provide +9.6V and enable/disable signals for the HearClear hybrid module located on the microphone jack / volume control circuit board. In the 900 MHz radio there is one unused lead in the cable between the logic board and the microphone jack / volume control circuit board and could be wired to pin 1 or pin 2 of the microphone jack and used for other purposes, such as providing a COR signal to the outside world. On low band, high band, UHF or 800 MHz radios this lead was used to provide the headset audio to pin 8 of the microphone jack through a 560 ohm resistor located on the logic board. On 900 MHz radios the headset audio is obtained at the output of the HearClear hybrid module (which is already on the microphone jack / volume control circuit board, so they put the 560 ohm resistor there and freed up a signal pin on the logic board.

Note 2: CAUTION: Some surplus DeskTracs have been found with a modification which replaces the +5vDC on pin 1 with +12vDC.   I've been told of, but not personally seen, similarly modified mobiles. Don't count on this pin being unused in a new-to-you MaxTrac / Radius / GM300 or at +5vDC in a DeskTrac until you verify it. My conjecture is that this mod was done for one of three reasons:

1. To power a low-drain outboard device.   One of the DeskTracs seen with this mod was known to have been used with an external telephone interconnect unit at one time (if you are not familiar with the term "telephone interconnect" just think "commercial 2-way radio autopatch").
2. To allow the use of a MaraTrac programming cable (which is identical to that of a MaxTrac except for one additional wire in it to power the RIB from the +12vDC that is on pin 1 of the MaraTrac programming connector). This makes for easier programming as the tech does not need to crawl around on the floor hunting for a convenient unused AC outlet to plug in the RIBs wall-wart power transformer.
3. To run a packet TNC that was interfaced to a DeskTrac digipeater through the microphone jack.

Mounting Brackets:

The exterior threaded holes in the side of the MaxTrac/Radius LRA amd GM300 radios that are intended for the mobile bracket are metric threaded - 5.0mm by 0.8 thread. This is a common thread.

The standard "trunnion bracket" for the MaxTrac / Radius LRA / GM300 series is the HLN5198A, originally listed for the MaxTrac 820-840 series but will fit any MaxTrac series, Radius M100, M206, M208, M214 or M216 series, or GM300 series radio (click here for a photo - the plastic bag has four sheet metal screws to mount the bracket, and two metric thumbscrews to mount the radio in the bracket).

The locking MaxTrac / Spectra mobile mounting bracket is HLN4426A. Unless the lock has been changed (and that is easily done, and many fleet sales had nonstandard locks) the standard 2135 mobile key will open it. More key info is on the radio keys page.

Due to the oversize (heavy) heatsink on the high power low band MaxTrac they designed a special heavy duty bracket for it, part number 07D80911W01. If you try to use a standard bracket on the high power low band MaxTrac you will soon be buying the special bracket. Click here for photos:   Photo 1       Photo 2

DC power: