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Motorola SpectraTAC
and Auxiliary Receiver
Information Page
Compiled by Mike Morris WA6ILQ
(see the notes at the bottom of the page)
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What's the connection between the Motorola Micor and the SpectraTAC?

The name "Spectra" is used in two very different Moto product lines: there is the Spectra mobile radio, which has its own page here at Repeater-Builder.com, and there is the SpectraTAC receiver voting product ("TAC" = "Total Area Coverage" in the Moto catalog).

What does this have to do with the Micor product line, you ask?

The original design of the Micor station had separate chassis for the receiver, exciter and control shelf, all linked by 50-pin ribbon cables. At that time multconductor ribbon cable and the insulation displacement connectors were a fairly new product and Moto had nothing but trouble with them. It wasn't long until Moto came up with a Unified Chassis design that eliminated the riibbon cables entirely. Moto needed a second receiver for the unified Micor chassis and the engineers took the early Micor receiver chassis and did some redesign. They came up with one that could function as a second or even more (I've seen six in a system), as a stand-alone auxiliary receiver, and with a different set of cards, as a voting receiver in the SpectraTAC product line. And after the the 50-pin ribbon cables and the connector products matured they lived on as the PC and mainframe SCSI-II disk drive intercabling.

The Aux Receiver / SpectraTAC Receiver is a separate rack mount chassis that holds a standard Micor receiver board (low band, mid band, high band, UHF, 800 MHz or 900 MHz), supporting PC boards in card slots, an optional metering card and an optional power supply. The card complement varied with the particular application. These cards resemble those in a Micor or MSR2000 repeater control shelf, however the cards are NOT compatible with a Micor or MSR shelf, and neither the Micor nor the MSR cards are compatible with the Aux Receiver / SpectraTAC shelf.

People unfamiliar with the product look at the chassis and see a model number TLN1991A or TLN1991B and think that they have a valid model number. They do, but what they have is for the rack-mounted bare sheet metal box. The TLN1991x is not a receiver. It is, according to Motorola, a "Receiver Housing Assembly" that is used for all models of auxiliary, satellite and SpectraTAC voting receivers.

As you can see from the above, an eBay listing that identifies a chassis as a "TLN1991 Receiver", a "TLN1991A Receiver" or a "TLN1991B Receiver" IS TOTALLY BOGUS - the TLN1991x is the sheet metal, and just the sheet metal!   To have useful identification of what you are bidding on you need:

  1. The factory model number, which is in the format of (letter)(digit)(digit)RT(letter)(dash)(4 digits)(one, two or three letters).
  2. The part number of the receiver board (they are in a three-letter-and-four number-and-a-letter-suffix pattern).
  3. The model numbers off ALL of the plug-in cards (they are in a three-letter-and-four number-and-a-revision-letter pattern (like TRN6080A)
  4. If there is or is not a power supply module in the chassis (just look to see if there is a transformer visible in the hole in the back).
  5. If there is a metering card (it will be in the right-most slot), take the cover off the receiver board and see if there is a cable plugged into the metering connector on the receiver. If not, the metering card is useless.
If you have an exisiting chassis that does not have a metering card and buy one in surplus make sure that it comes with the metering cable, as it will be useless without it. If there is no cable then don't pay a lot for it (or plan on making up your own cable, and the special metering plug is no longer available).

No matter what the configuration, these chassis are useful as point-to-point link receivers, control receivers, or when you need to add a receiver to an ex-paging base station when you convert it into a repeater.

To go into more detail, the basic Aux Receiver is a chassis with a receiver, the common audio card (the left-most slot), an optional PL or DPL card (in the second slot), and an optional power supply. The only difference between an Auxiliary receiver and the SpectraTAC receiver is that the SpectraTAC version added the voting encoder card into the third slot, which is necessary for the chassis to handshake with the SpectraTAC voting shelf at the other end of the wireline or microwave link. In other words, the "Encoder Module" is useful only if you have a SpectraTAC voting shelf at the other end.

The receiver board used in any version of the chassis is a plain-jane Micor receiver board, and all the other articles at this web site that cover modifications to the receiver board (i.e. mods for 2m or 220 MHz) are applicable. This also means that you can move a chassis to any band (as long as the receiver antenna coax connector matches - the low band, mid band, high band and UHF units used a chassis-mounted SO-239 antenna connector attached to an internal cable that terminates in an RCA plug that feeds the receiver card. The 800 and 900 MHz units use a type "N" connector, high grade teflon cable for the internal cable and an SMA connector for the receiver.

A receiver whose part number starts with TLB followed with 4 digits and from 1 to three letters is a "low band" receiver, and was made in 3 splits that covered the 30-50 MHz range. A TLC series receiver is the "mid band" model and covered 66-88 MHz range in 2 splits, a TLD is the "high band" board and covered 136-174 MHz in 3 or 4 splits, a TLE is a UHF receiver somewhere between 406 and 520 MHz (in as many as 7 splits), a TLF is either 800 or 900 MHz.

The chassis model number breaks down as per this table - but realize that the receiver boards can be swapped in 5 minutes, and a number on a chassis may not be accurate - really, you have to look at the actual TLB / TLC / TLD / TLE / TLF part number stamped on the receiver board.

Aux Receiver / SpectraTAC Receiver Chassis Model Number Breakdown
Numbers in [ brackets ] are references to the table notes at the bottom
Typical model number: C04RTB-3108C
Cabinet
Type [1]		 Transmitter
Power [2]		 Frequency
Band [3]		 Series Supply
Voltage [4]
B
Base
Station
Cabinet		 Always
zero		 1
30-50 MHz		 RT
Micor		 A
+12vDC
C
Compact
Cabinet		 2
66-88 MHz		 B
120vAC
N
No
Cabinet		 3
132-174 MHz		 K
120/240vAC
4
395-520 MHz		 N
No
power
supply
5
800 or 900 MHz
7
900 MHz

Typical model number: C04RTB-3108C
Squelch
Type [5]		 Deviation [6]
Frequencies [7]
Configuration [8]
Version
1
Carrier
(no card)		 0
15 KHz		 0
One Freq		 0
Satellite
receiver
(no voting
encoder card)		 A
3
PL
(PL card
added)		 1
5 KHz		 3
Two Freq		 8
Voting
receiver
(voting encoder
card added)		 B
6
DPL
(DPL card
added)		 2
2.5 KHz		 9
Four Freq		 C

Table Notes:

  1. The leading "B" indicates a Base station cabinet, a leading "C" indicates a Compact series cabinet, a leading "N" indicates no cabinet was shipped with the unit.

  2. Since there is no transmitter, the transmitter power output indicator digit is always zero.

  3. Do not trust the band indicator in the model number as it takes 5 minutes or less to swap a receiver card in the field. Always look at the part number on the actual receiver board when evaluating any surplus unit. Each of the frequency bands are divided in frequency ranges (called "splits") and any given receiver card was built for a specific split (like 42-50, 132-150.8, or 450-470 MHz). If you are buying a surplus chassis make sure that you purchase one containing a receiver card made for the split you need (or plan on range-changing the card you have, or swapping the receiver card). Also make sure that the receiver comes with the proper channel element included. For more information see the Micor pages at this web site for a list of receiver board part numbers and channel element numbers.

    Another point: These units were manufactured during the time period that band 5 was both 800 and 900, and after the transition that created band 7. So a surplus band 7 unit was definitely shipped with a 900 MHz receiver card, but a band 5 could be either 800 or 900 MHz.

  4. The "A" series chassis do not have a power supply module installed (it can be added in the field) and are dependent on another source of +12vDC and +9.6vDC, be it a Micor station, or an adjacent "B" or "K" unit. Many surplus units have had the power supply removed, so make sure that if you are buying a surplus chassis and need to power it from the AC mains that it has a power supply installed. "K" units are rare in the USA. "N" units were the same as "A" units - they required an external source of +12vDC and +9.6vDC. A common modiufication was to bolt a 7809 three-legged voltage regulator down to the chassis with a silicon diode in the ground lead (raising it to 9.7v) or a 7808 with two diodes (9.4v) so that the chassis could be powered by 12v only.

  5. Changing from carrier squelch to coded squelch requires BOTH changing the audio card and adding the appropriate Coded Squelch card. Changing squelch types involves changing out the squelch card (or adding one into the second slot if you have a carrier squelch station). Do not trust the chassis model number, always look in the second card slot. Make sure the card is a SpectraTAC card, it is unique to this chassis, a Micor station card or a MSR2000 station card will not work. Also the same blank PC card was used for both tone and DPL, one half was stuffed for PL, the other half for DPL (see this photo). You can add the missing parts and have a combination card that will decode both tone and DPL on an OR basis (i.e. either the proper PL tone or the proper DPL code will unsquelch the receiver), or add a SPDT toggle switch and have it be one or the other.

  6. A "0" is a very rare beast as the market for wideband radios is very limited. It was a special order for the broadcast industry as some stations had (still have?) VHF and UHF remote pickup channels. 99.9% of the time you will find a "1" in this position. If you find a "2" it indicates that the original receiver was configured for 2.5 KHz deviation (i.e. 900 MHz).

  7. Finding anything but a zero in this position is rare, but adding additional frequencies is no different and no more difficult than on a regular Micor receiver. All Micor receivers support either 4 or 12 channel elements. Factory single frequency chassis have an internal jumper that connects the F1 line to ground.

  8. There are other configuration options (not listed) that include the presence of an optional double-wide metering card (an audio amplifier and a loudspeaker) which goes in the right-most slot. If anyone has any additional configuration options information please let me know and I'll add them to the table.

Here's a photo of the front of the chassis.


Here's a photo of the rear of the chassis. This particular one has a BNC-to-N adapter on the antenna jack. There is also provision for plugging in a Micor handset to allow communications with another technician at the SpectraTAC voter site. The power cord pig-tail allows daisy-chaining of the AC power cords between units. While you could theoretically daisy chain an entire rack of receivers, the manual says one power cord for three or less receivers.

Many surplus receiver chassis have a self-contained AC mains power supply that has two power connections - the chassis-mount one that is for the power line, and a pigtail lead that is an output that allows up to three chassis to be powered from one AC outlet. The ones that are missing the power supply ran from external sources of +12vDC and +9.6vDC. Yes, any chassis that does not have an internal supply needs a both +12vDC and +9.6vDC. A number have been seen with a field modification that adds a 9.6 regulator inside.

The cards that plug into the unit are dependent on the application. The Voting Receiver or the Auxiliary Receiver systems used the Coded Squelch and Encoder cards, where an IMTS mobile telephone system used the TLN5946A "Receiver Quality Signal (RQS)" cards. The possibilities were:

Manuals:
Spectra TAC Voting and Satellite Receiver Instruction Manual, 6881039E45, about $12 in Feb. 2007.
Spectra TAC Comparator Reference Manual, 6881039E50, also about $12 in Feb. 2007.
Both contain full specs, installation, maintenance, troubleshooting, schematics, board layouts, and parts lists for the receivers, all plug-in modules, the power supply, and the chassis / backplane. There are sections for VHF low-band (25-50), mid-band (72-76), and high-band (132-174), UHF (406-512), and 800 MHz (806-821) receivers. The later revisions contain the information for the 900 MHz receiver board.

Additional Info:

  1. There is no AC power switch. More than one chassis has been modified with a toggle switch mounted next to the fuse post (on the rear).
  2. There is no indicator that power is applied to the chassis. A front panel power indicator can be implemented on the audio control module (which is necessary for a functional receiver - every other module is optional). Simply add a green LED above the word "RCVR" at the top of the card, with a series resistor from the +12v pin to the LED, and ground the other side of the LED.
  3. Likewise, there is no indication of COR / COS / channel busy / a carrier present. Another LED can be added next to the squelch potentiometer.
  4. The LED on the PL or DPL decoder card is not a decode indicate LED. It is switched on by one pole of the disable switch (i.e. it is in carrier squelch when the LED is on, and in PL or DPL when it is off). A common mod is to relocate the red LED to just above the disable switch, and in the newly vacated hole (where the LED used to be) add green LED wired as a decode indicator.
  5. Moto made a special "Extractor Tool" to get the cards out of the Micor chassis or the Aux receiver chassis: part number 66-83574F01.
  6. The tuning tool specified in the aux receiver manual is part number 66-84387C01.
  7. The extender card for servicing the modules is 1-80700B25.
  8. The "Receiver Interconnect Board" (that connects the receiver board to the module motherboard) is TRN8538A.
  9. The "Module Interconnect Board" (the module motherboard) is TRN6090A.
  10. The TRN8625A is the shield kit, and consists of the 1-807796B67 front cover and the 1-80799B72 rear cover.
  11. The TPN1158A is the power supply module (add this to a "RTA" or an "RTN" to make it a "RTB" unit).
    Option C28AB added the TPN1141A "Emergency Power Kit" which consisted of nothing but a 12v 8ah gell-cell and a 2a fuse between the + and - terminals on the module backplane. All of the AC power supplies had the charger circuit (R108, a 20 ohm resistor, set up as a constant voltage charger. If you value your battery life, remove that resistor and use a modern external charger designed for maximum battery life.
  12. The VHF/UHF antenna cable (N to RCA plug) is a TKN6998A, and the 800/900 MHz cable (N to SMA) is a TKN6999A. If you are going to install an 800 or 900MHz receiver in an existing VHF / UHF chassis you will have to locate (or manufacture) a TKN6999A cable (or cheat and make or acquire a female RCA to male SMA adapter cable).
  13. The chassis offers an intercom function between the receiver location and the other end of the wireline circuit. This required a TMN6067 handset to be plugged into the backplane connector labeled "handset". The handset was Option C192AA in the order book.
  14. Option C12AE adds either the TLD8421 preamp (136-150MHz) or the TLD8422 preamp (150-174MHz) and the associated TKN6807 cable kit. This 10db gain preamp bumps the receiver sensitivity from 0.5uv to 0.25uv. Frankly, AngleLinear makes a better preamp. See the Micor page for details.
  15. Option C12AD adds either the TLE8191 preamp (406-450MHz) or the TLE8192 preamp (450-512MHz) and the associated TKN6812 cable kit. This 10db gain preamp bumps the receiver sensitivity from 0.5uv to 0.25uv. Frankly, AngleLinear makes a better preamp. See the Micor page for details.
  16. Option C2466 added a TLE1082 6-port UHF antenna multicoupler to allow one antenna to drive multiple receivers, but at a cost of some considerable insertion loss. You would be much better off if you used a preamp-based multicoupler. You will want to use 50 ohm terminations on any unused ports.

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This page created 05 October 2008

The author would like to acknowledge the contributions from from several submissions to the Repeater-Builder mailing list, and from conversations with several hams that have battled the quirks of the Aux Receiver chassis, including Will Martin KA6LSD, and A. Nony Mous.

Motorola® and SpectraTAC® are registered trademarks of Motorola Inc.

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.