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System Engineering, and a few commments… Compiled from discussions with several knowledgeable people and written, HTML'd and maintained by Mike Morris WA6ILQ.

Comments / critiques / suggestions on this page (actually any page at this web site) are welcome.
Even a email pointing out a typo.

My grandmother was a schoolteacher in the Redwood City area of California in the 1920s through 1970. After grandpa passed in 1972 she lived with us in Los Angeles until 1976 when she passed at age 89. We had a lot of very interesting conversations but one of the things that she said stayed with me was "The universe runs on Biology and Math.  Physics is applied Math.  Engineering is applied Physics".   RIP Elizabeth Margaret Rolofson Morris (1887-1976)

Nowhere is that final phrase – "Engineering is applied Physics" – more true than in antenna systems… cavities, duplexers, isolators and the antenna itself.

There are some standard rules with repeaters.

0.   (zero): Don't be the lightning rod!
   This was pointed out to me after I had written this page so rather than rewrite it and renumber the rules I cheated and added Rule Zero.
   See this excellent article Lightning Protection for Your Repeater System from Advanced Computer Controls. Yes, it is somewhat dated (1984) however the physics hasn't changed.
   See this GE LBI-39067A. The name Ericsson is on it because they purchased the LMR division from GE. It's also a little dated (June 1994) but, again, the physics hasn't changed.
   
   The big names in lightning and EMP protection equipment are " Polyphaser" and " Huber & Suhner". These calculators from Huber & Suhner will be useful.
   
   You will find that Huber & Suhner brand is more common at cellular sites since the early Polyphasers had an issue with iceproofing and waterproofing. Google those names and read their white papers. You will find that at many tower sites that the lightning arrestor is frequently mounted in or on a grounded metal panel mounted in the outside wall of the building.
   The Motorola R56 manual will also be interesting reading.
   Each of the above links opens in a new browser tab.
   
   
1. The antenna system can make or break your repeater all by itself.   A $5,000 repeater with a $50 antenna system performs like a $50 repeater system.   If you are building a system on a budget, do the initial scrimping on the stuff inside the building. It's a lot easier and cheaper to update / upgrade later on. You need a properly performing antenna system before you power the repeater on for the first time.
   
   Simply put, a system that is built with a quality land mobile grade base station gain antenna and quality feedline will hear and talk better than a poor antenna and do so for a much longer time. If you go with quality hardware and proper installation the first time you won't have to do it over and over (like my late father used to say about both hand and power tools: "Buying quality only hurts once", and one of my high school teachers said about both clothes and tools "Buy the best quality you can afford").
   
   A proper repeater receiving system will include the antenna, appropriate feedline, lightning arrestor, duplexer then the receiver. The lightning arrestor is frequently mounted in a grounded metal panel mounted in the outside wall of the building. Everything is connected with quality shielded cables like RG-214, RG-400 or Superflex™. Depending on the individual circumstances and the band (6m, VHF, 220, 440, 1200) there may be some combination of a preselector, a window filter, a pass cavity, a shorted stub filter, a preamp and a multicoupler. In rare cases you might even find an attenuator between the receiver and the next upstream device.
   
   A good Phelps‑Dodge, DB Products or Sinclair antenna connected to quality Andrew 7/8 inch Heliax™ feedline will last 20 to 30 years of seriously hostile winters (you can get by with 1/2 inch on 6 meters and most of the time on 2 meters). How many Comets, Diamonds, Hustlers, homebrew antennas or replacement lengths of LMR‑series or RG‑type feedline will you buy and install in the same 20-30 years?
   
   And "antenna gain" can be deceptive. Basically the gain of an antenna is based on directivity.   To steal an abbreviation from Robert Heinlein*, TANSTAAFL ("There Ain't No Such Thing As a Free Lunch").   Every deciBel of gain is a deciBel that now is going where it is useful instead of going where it it's not useful.   Some people actually think that by picking a higher gain antenna they can overcome "the loss caused by the feedline".
   Go read the "Cheating with Antenna Gain" writeup by Marc Dekenah ZS6MGD at http://www.marcspages.co.uk/tech/antcheat.htm.   ( Here's local copy in case his web site goes away)
   (* in his 1966 SF book "The Moon Is A Harsh Mistress" that is set in the year 2075 and is really worth reading...)
   
   And don't get fooled by dB gain values. The marketing people at the manufacturers prefer dBi because it produces a more impressive number. Look at the dBd numbers (if you can find them). dBd is dB (dipole), where the reference dipole is a resonant half-wave dipole antenna. The antenna advertisements and ham radio oriented catalogs show the dBi numbers, or just might show db. dBi gain numbers are based on a ball-shaped waveform around a point source - and that is only valid at microwave frequencies - dBI=dB (isotropic). To convert them just subtract 2.15 from dBi to make dBd. If an advertisement or a catalog has gain value with just "dB" or "DB" it is likely dBi.
   
   
2. This goes hand in hand with Rule number 1: Everything depends on how well you hear. Always favor your system receiver and the receiving antenna system. A system's coverage area is primarily determined by how well it receives stations in the field, not by how much transmitter power it has. You can always swap transmitters (or amplifiers) for more power, but if you can't hear the users the repeater is useless.

   In an email Dan Woodie KC8ZUM for pointed out:
   For every doubling of output power it only gives you 3 dB of OUTBOUND gain while likely effectively decreasing your INBOUND gain by raising the noise floor due to desense or wideband noise caused by PIM or other sources. The more power you run the harder it is on everything in your signal chain and you have to make sure everything is rated for the increased power. A much more effective way to increase your coverage is to use antenna gain or better Heliax to decrease feedline losses (which can help inbound and outbound signals by changing one run of coax or one antenna if running duplex on a single antenna).

   And users love hand‑helds. And handhelds usually have a 1/4 wave antenna and use the users hand or body as a pseudo ground plane. In other words, a rubber duck or a rubber rat tail is an instant ‑3 to ‑4 dB loss. And if the user is in a car he probably has the metalized coating on the glass that most car makers are using to reduce the solar heating inside the vehicle. That metalized glass acts like a Faraday cage and does a good job of RF shielding… That's another ‑10db… And then there is the mobile flutter…
   
   
3. This goes hand in hand with Rule number 2: Concentrate on minimizing the insertion loss on the receive side of the system. Test for Effective Sensitivity at least twice a year – this includes tests with the transmitter on (but keep in mind the effective sensitivity can be a dynamic value as different transmtters at the shared site key and unkey).
   
   
4. This goes hand in hand with Rule number 3: Maximize your received signal by maximizing the isolation from receiver to all the on-site RF emitters. Which might include the switching power supplies used by the other tenants (this includes the POE switchers used by the WISP tenant and their 2 GHz / 5 GHz radios mounted on the back of their panel antennas). Or the adjacent building that has the 5kw FM broadcast station that just filed for an increase to 35kw. Or the brand new electric fence charger around the antenna tower base.
   
   
5. Keep good records - a site logbook is important, ESPECIALLY if you can get the other site tenants to add entries to it. If something changes between visits you need to find out what changed and why. It may have been something that someone else did!
   Example: At one multi-tenant commercial site the landlord (American Tower Corp) replaced the old, tired and dead ceiling flourescent tubes with LED tubes. The bean counter that selected the new lighting hadn't a clue on RF. As a result the noise floor on 220 MHz and UHF went up - but only when the lights were on! And the lights were on only when there was a tech at the site! So there was an intermittent problem, but none of the radio techs had made any changes to any of the systems there! One of the techs finally figured it out and notified the landlord. The immediate fix was switching back to flourescent tubes.
   
   
6. With repeaters, the best you can afford may be barely good enough.
   
   
7. You can't "balance" a system unless you can define your user demographics - i.e. who you are balancing it for. Are you catering to the base stations, to the mobiles, or to the handhelds?
   A repeater system that has the transmitter power to reach out to the outlying base stations and mobiles that have 60‑100 watts ERP could be accused of being an alligator system (all mouth and minimal ears) by a user with a 2‑watt handheld that has a ‑3 dB rubber duck antenna.
   See Rule 2 above on vehicles…
   On the other hand, a system that is designed and engineered from the outset to support hand‑helds and has multiple voting receiver sites and a single centralized transmitter (or a multi-site simulcast transmit system) could be accused of being an elephant system (all ears and a small mouth).
   
   

Both the receiver and the transmitter depend on the antenna system - no matter if it is a duplexed single antenna or separate receive and transmit antennas. Both the antenna(s) and the feedline(s) are the most critical components in any radio station (amateur, commercial, public safety, whatever). It doesn't matter if it is a home station, a mobile, a repeater, a remote base or a point‑to‑point link. Perversely the antenna system is usually the most difficult to install, maintain, or troubleshoot… and it seems like all of the troubleshooting usually has to be done during extreme climate conditions like in freezing temperatures and / or high winds while up on a tower. If you are installing a repeater or a point‑to‑point link that will be primary in any type of critical services situations it does not make any sense to go "cheap" on the antenna system. Creative (legal) aquisition of good quality equipment, yes. Low or poor quality equipment, no… that decision will always come back and haunt you.

And don't forget that most of the really good commercial 2-way sites are owned by people that have been burned – and badly – by ham radio groups in the past. Some owners have been burned repeatedly. And the big owners (American Tower, Crown Castle, etc.) have no interest in renting to what they might consider to be a future problem. The profit margin just isn't worth the possible future hassles.

Some sites require a bonded and / or certified tower climber to do the work. If that's the case you can expect to have to pay some big bucks - both an arrive‑on‑site fee plus an hourly rate. Some tower monkeys charge from the time they leave home to the time when they arrive back home. Some charge from when they arrive until when they leave. Some charge by the vertical foot - doing something at 175 feet costs more than at 75 feet. So replacing your $120 Diamond or Comet antenna at 200 feet up the tower may cost upwards of $900, and in some cases upwards of $1500, and that's EACH TIME (2003 prices). For that much money you could have had a NEW Commander Technology, Sinclair, DB Products or a Phelps-Dodge complete with NEW Heliax the first time instead of a Diamond and cheap no-name LMR‑400‑type cable… and no need to touch it or replace it for 20 years or more. At one of the sites where I have equipment there is an about-40 year-old ham antenna (Stationmaster-type fiberglass, with a top support) with 7/8‑inch Heliax of the same age that still works perfectly (yes, the antenna has been re‑gell‑coated at least once, probably twice).

A receiver preamp can help some systems, but realize that good preamps are all about the internal noise figure (NF) of the preamp, the amount of gain it provides and the point where it overloads. The lower the NF, the weaker the signal that will be heard. Regarding gain, most modern preamps have gain on the order of 14‑18 dB in a single stage. That's enough to take a signal that's barely above the noise floor and make it very usable on a decent receiver. But what works on the workbench may not be what works at the site… it's all about effective sensitivity. If you're already hearing down to the noise floor without a preamp then adding one isn't going to make any improvement in sensitivity and in fact may create new problems. But if you do decide to add a preamp, don't attempt to use it to make up for a long, lossy feedline – there's a good reason that the professionals use inch‑and‑five‑eights Heliax for a UHF, 800 or 900 MHz receive antenna: minimal loss. I've also seen three‑and‑one‑eighth and six‑and‑three‑eights Heliax. Likewise don't attempt to use a preamp to make up for a poor receiver - you need to fix or replace the receiver.

And watch those antenna splitters (also known as multicouplers)... At one commercial site we have a UHF antenna that feeds eight receivers. The 8‑port multicoupler has a measured insertion loss of 14.1 dB, and there is nothing wrong with it, that's just the norm for an 8‑port.

Many commercial sites use shared top‑of‑the‑tower "community receive" antennas that feed a preamp / multicoupler panel. These systems are very popular at UHF, and to a lesser extent at VHF or 220 MHz.

Example: The author of this article visits a 5300 ft mountain top communications site on a semi-regular basis. This site is home to a 120 foot (37m) tower. The top of that tower is dedicated to receive‑only antennas ‑ one each for VHF (high band), 220 MHz, UHF, 800 MHz, 900 MHz and 1200 MHz. There are also hot spare antennas already in place for each of the aforementioned bands except for 220 and 1200 MHz. The master receive antennas for the VHF (138-174 MHz), 217-225 MHz and UHF (400-512 MHz) bands are broadband omni 10 dB antennas manufactured by Sinclair Technologies (SD218 and SD318 series). The VHF and 220 MHz antennas are connected to 7/8 inch Heliax, the others feed their own runs of inch‑and‑5/8 inch Heliax. Each of the runs of Heliax terminate into a separate AngleLinear High Level preamplifier panel for that band.

At that site all of the systems I maintain are UHF (6 on 472 and one on amateur 440) so I am most familiar with that antenna system. The output of the high level AngleLinear UHF preamplifier feeds a multicoupler (splitter) and that feeds a bank of "window" filters. Each window is eight Sinclair cavities in series. The lowest frequency window is for the UHF ham band. Southern California is In-low, out-high so that filter is 440-445 MHz. The next window is for the commercial repeaters that receive from 455‑460 MHz. The third window is for the commercial repeaters at 465‑470 MHz. The fourth window is for the 473‑476 MHz commercial repeaters that run a +3 MHz offset (yes, that is "T" band TV channel 14, and in the Los Angeles area it's been allocated to LMR for as long as I can remember). Finally, the fifth window is for the 509‑512 MHz public safety repeaters (yes, that is "T" band and TV channel 20).
The entire UHF window filter system completely fills a 7 foot rack that has't been touched in 20+ years… There has been no need to. A properly configured window filter doesn't need it.

The adjacent rack has the post‑window distribution amplifiers – each window filter feeds an AngleLinear distribution amplifier panel for that range's repeater receivers. Each distribution amplifier panel is typically an amplifier feeding a 4-port multicoupler with each port feeding another amplifier feeding an 8-port multicoupler.
The overall system engineering is such that from the base of the antenna to the system receiver the path has about +2 to +3 db gain.

On the commercial VHF side generally the higher frequency of the pair (and there is no standard offset) is the repeater receiver. As I said above at that site there is a single broadband VHF high band 136-174 MHz 8-pole Sinclair antenna. The Heliax feeds a high level VHF AngleLinear preamplifier and then a distribution amplifier. And each VHF receiver has a series pass cavity between the distribution amplifier and the receiver.

Another site has enough 220 MHz repeaters that it was pracital to set up a master receive antenna system. The configuration is similar: a high gain tower-top amtenna connected to 7/8 inch Heliax, feedline then a level preamp feeding a window filter which feeds a distribution amplifier and that feeds a multicoupler feeding the individual repeater receivers.

Yet another site has a the tower-top +10db gain Commander Technology antenna (the old SuperStationmaster design), 7/8 Heliax, then the high level preamp then the 8 cavity window filter, then a 4-port multicoupler. Each port of that feeds a distribution amplifier which feeds an 8-port multicoupler to the repeater receiver.

In most repeaters the duplexer provides a certain amount of isolation between the receiver and the transmitter (some systems, like those that use two antennas, or even two sites, don't use duplexers). If the amount of isolation, however it is acquired, is greater than what is required (the excess is sometimes referred to as "headroom"), then the system design is adequate for the job (see the article Some thoughts on Repeater Receiver-to-Transmitter Isolation on the previous page). That situation is fine until they decide to add a preamp to help out the handheld users. Then they discover that the amount of isolation isn't enough. They forgot that you need (at least) the same amount of extra isolation ("headroom") as the amount of gain the preamp provides, since it raises the apparent noise floor as well as the signal of interest. In many cases you will have to fight with desense when you add a preamp (a top‑quality preamp like an AngleLinear will help). Always have enough extra headroom in your receiver, transmitter and duplexer to handle either or both of a couple of situations: First, the site owner adds additional transmitters to the site, or second, that you want to add a preamp later on. If the duplexer is your primary provider of receiver‑to‑transmitter isolation then do not scrimp on the duplexer.

Next to a quality antenna and feedline the duplexer provides the primary receiver‑to‑transmitter isolation. Because it is primary it is the most critical part of a good repeater system ‑ but that is worthless if the repeater receiver and transmitter does not have good isolation built into the radio or radios that you are using. The use of double‑shielded coax between the duplexer and both the transmit and receive antenna connections is a must to limit the problem of the transmitter signal leaking into the receiver input and desensing it (the Motorola GR300, GR400, GR500, CDR500 and CDR700 low-end repeaters were (in)famous for using cheap coax on their factory duplexer harnesses. In those units simply swapping the three factory-provided RG58 cables for quality RG-400 (NOT LMR-400) usually gets you from 2 dB to 6 dB reduction in desense).

Good RF bypassing on any wire leaving or going into the repeater and control circuitry is a must. This keeps any RF from causing problems in the audio circuits and control circuits of the radio. Then you need a good sharp front end on the receiver, good intermod rejection, and good clean transmitter signal with no spurs. A large majority of the lower cost repeaters from Bridgecom, Yaesu, Motorola, and others are built from modified mobile radios that have a DC‑to‑daylight front end, and that's asking for trouble at a site with high RF levels. A in‑line pass cavity on the receiver will help, but that adds measurable insertion loss. Your author ran into this on a GR300 tabletop repeater (dual GM300 mobile radios) at a shopping mall… The receiving radio died and the local shop replaced it with a CDM mobile… The GM300 is a mobile and hence has a wide front end, the CDM has a varactor tuned front end. The desense was noticeably lower on the new CDM receiver. Swapping the RG-58 coax in the GR300 for RG-400 lowered the desense.

Back to duplexers… Long ago I gave up on four-cavity duplexers (two cavities on each side) on VHF/2m, 222 MHz and 440‑470 MHz UHF, I use the six cavity pass / reject type exclusively. It's not unusual to see 2 to 3 µvolts of VHF transmitter noise 600 KHz away from your repeater transmitter. Duplexer tuning is very, very critical. A return loss bridge is preferred, a spectrum analyzer with a tracking generator is the second choice. And don't tune the duplexer on the bench, then transport it to the site over a bumpy four‑wheel‑drive road, and expect it to be as precisely tuned when you get there. Likewise don't trust the tuning of ANY duplexer once it's been shipped – always assume that the transportation will shake things up. Always have the test gear with you at the site to verify final tuning after mounting it in the system rack.

On the transmit side, never forget that SWR is not the only measure of antenna performance. A low SWR only means that the transmitter is "seeing" a reasonably non-reactive load. That is, it is neither capacitive or inductive, it looks like a 50 ohm resistor (a dummy load). The SWR tells you nothing about what is really important, the antenna efficiency, the antenna noise level, its pattern (gain) and decoupling of the RF from the feedline. And don't forget that the feedline loss runs both directions and can dramatically affect the SWR reading !! Your transmitter sends power up the feedline (let's say it's 100 watts), and some gets lost going up (let's say that it's 20% and 80w gets there). The lightning-damaged antenna reflects some power back down (let's say it's 10%, or 8 watts). The 8 watts comes back down, and 20% gets lost, and you see 6.4 watts on the Bird wattmeter. So you see 100 watts going up and 6.4 watts coming back, and you think the SWR is a lot better than it really is at the antenna. Look at this web page on the topic: Power Antenna Manufacturing Inc. SWR Calculator (an offsite link). It removes the "masking effect" of the feedline loss.

Before you sign a site agreement, pay your money, and go to the trouble of installing a complete system you will want to measure the noise floor on your target receive frequency at the site. Just borrow an appropriate already-installed antenna for fifteen minutes or so (with permission) and make the measurement (i.e. if you are installing a VHF system use a VHF antenna). If "site A" has a 0.8 µV noise floor (due to the broadcast and paging systems there) and "site B" has a 0.1 µV noise floor take a guess as to which site will hear better (and I have seen sites that have noise floors that are above 3 µv on the frequency of interest… Yes, over three microvolts, not zero‑dot‑three).

If the problem signal is a local on-site or near-site transmitter (or even two) don't give up. A simple 1/2-wave shorted stub filter between the antenna and the receiver can be made from a coax "T" adapter with the perpendicular port (the third port) connected to a length of coax cable (even RG-58) as a stub and a sewing pin as a test short. You move the the sewing pin down the coax to find the sweet spot (to fine tune the length), and then make a fully soldered shorting connection at that point. There is almost zero insertion loss on a shorted stub and the shorted stub does a very good job of filtering out a nearby transmitter better than any bandpass filter will do. And I've seen two shorted stubs in use on one receiver... one was for an FM broadcast frequency, the second was for a VHF paging frequency.

An alternate method is a 1/4-wave stub, in fact back in 1961 GE issued DataFile Bulletin 10002-1 (opens in a new browser tab) on using a 1/4-wave stub to reduce interfering signal strength and showed how to do the fine tuning with a trimmer capacitor. Like the 1/2-wave stub the 1/4 wave stub has less insertion loss than any cavity or bandpass filter. I like the 1/2-wave shorted stub better, it's easier to manufacture and there isn't a fragile trimmer cap that someone could damage or use a golden screwdriver on...

No matter how you do it, notching out the specific offending signal with a tuned stub is far more effective than adding a bandpass filter that has insertion loss.

There are modern spectrum analyzers with digital memory and some can do additive recordings - they can hands-off assemble the worst-case scenario, and I have seen one of those parked at a site for two weeks. But there are workarounds: on a site visit in the 1990s I saw a motor home parked outside the building, and inside there was a tripod with a video camera tight-focused on a spectrum analyzer… the gentleman volunteered that he had borrowed a good but abandoned-in-place antenna for the analyzer, had his motor home (with a refrigerator, a microwave oven, a TV and DVD player) outside, and that he had a enough 6-hour videotapes to get over 96 straight hours… he said he was going to sleep for 5 hours and 45 minutes at a time (he claimed he had two alarm clocks, just to make sure) then change tapes… He volunteered that when he got home he was going to do frame grabs with his computer, superimpose them and build up a worst-case analyzer image.

Once you have a site interference profile mapped, you may chose to install a UHF system at a particular site if the noise floor on VHF is intolerable (or vice versa). And don't overlook 220 MHz, as the 220 noise floor at many sites can be much lower than either 2m or UHF. And the atmospheric noise at 220 is lower than 2m or UHF as well. Remember that with repeaters it all depends on how well you hear (see the article on measuring effective sensitivity). Given the limits of antenna power rating, feedline and the local geography / topography, increasing the talk range is easy - how much amplifier, duplexer and antenna can you afford?

When you go attacking a desense problem, don't assume that any on‑channel receiver noise is a function of energy from the transmitter. That's often not the case. The transmitter can be absolutely clean, the cavities and / or duplexer tuned perfectly, but nevertheless, if there is some corroded metal joint in the antenna induction field, it will generate broadband noise, some of which inevitably will be on channel noise. It may take crawling all over the tower to find it. Or the source could be someone's old LMR-400 cable on their simplex dispatch system. You can play with your transmitter, duplexer and cables forever and it won't mitigate this problem. It may be in the adjacent building, or the one a 1/2 mile away that has a 350 watt transmitter and a 10dB antenna. Basically, you find the biggest culprit, solve that, and try again, and keep doing this until you find the last culprit, or untill you're fed up. Think "whack-a-mole".

There are several publications that you should look at if you are going to be doing any serious antenna systems work at a site. One is the site owner/manager's requirements, others are below on this page in each section. Another is the Motorola "R56" "Standards and Guidelines for Communication Sites" manual. A good overview of that manual is here. And for a long time the BLM web site has had a PDF of an older version for free download. There are three versions "out there" that I know of. There is the March 2000 68P81089E50-A, the September 2005 68P81089E50-B, and the April 2017 68P81089E50-C versions. If there is a later one please let the page maintainer know. The CD-ROM version is 9880384V83. Obviously the ‑C version is the one you want. There were some very significant updates in the later versions. Quite a bit of content was added in addition to some content that was changed. One big difference was a change in naming conventions to clearly define different parts of the Bonding / Grounding infrastructure to better define their purpose (Bonding or Grounding). Every so often someone posts the PDF of the ‑C manual (it usually gets taken down rather quickly) but it's worth Googling for it every so often… Just look for "6881089E50-C" or "68-81089E50-C".
And if anyone discovers that it's been updated to a ‑D or a ‑E please let the page maintaner know.

Another good (but very dated) reference is here (if there is a newer version the page maintainer is not aware of it): GE/MA-Com/Tyco Installation Manual LBI-39185C titled "Specifications, Guidelines, and Practices, Tower Requirements and General Specifications".

Some people build their own repeater antennas from scratch, frequently copying a commercial design, sometimes doing their own experimental thing. Others rebuild surplus commercial antennas, others just buy something new. It's worth getting to know someone who knows how to bend and weld aluminum rod and tubing, and someone else that has access to hot‑dip‑galvanizing equipment, and someone that can build a phasing harness… The antenna systems page at this web site has detailed drawings of many good commercial antennas (and their harnesses) - and they are detailed enough to be used for amateur construction / duplication.
And please let the page maintaner know if anyone finds a source of replacement harnesses for the DB‑408, 411, 413 or 420 antennas.

It's also worth getting to know the local two-way techs and building / site owners.
One example: Over a decade ago an acquaintance acquired a very expensive low band antenna (the same model is over $3700 in 2025) after a phone call from a tech employed by another site tenant alerted him that a certain site had a recently abandoned‑in‑place 47 MHz side-mount dipole antenna. The acquaintance contacted the site owner, let him know that he had heard about the antenna, and the owner confirmed that the tenant had moved out and left the antenna on his tower. My acquaintance asked if he could have it if he could arrange to have it removed. The answer was yes. So he rearranged his schedule to follow the site owner to the site (i.e. at the site owners convenience), and after confirming the type of antenna my acquaintance asked if he could pay the site owners preferred tower climber to remove the antenna, but the owner waved that off. The owner said that he was going to have the climber at the site the following week for another reason, he'd have the climber remove the antenna, and the acquaintance was welcome to it. He could be there to haul the low band antenna away or it would be left at the site for his next visit. The acquaintance borrowed a vehicle with a roof rack and hauled the antenna away. That acquaintance rebuilt the antenna to 52 MHz and it is in service at a different site.

The Metric System - learn it!   The U.S. has been slow to adopt the Metric system of measurement, yet in ham radio circles we use metric terminology daily ("80 meters". "2 meters", "23cm" and more). However whenever I'm building an antenna, or a phasing harness, I'm doing conversions back and forth all the time. I often thought that it would be very nice to have a dual-marked metric / fractional shop ruler and tape measure (both Metric and English graduations). After all, there is a good reason that duplexer inter-cavity cables are precisely cut to an eighth of an inch (about 3mm). Well, after some searching I found that Stanley Tools of New Britain, CT has a model 33-726 (8 meter / 26 feet) steel tape, and there's a model 34-827 PVC coated fiberglass 30 meter / 100 foot for doing long runs. And I'm not saying that Stanley is the only one, there are several manufacturers that make metric / fractional tape measures. Most of the big "super home centers" don't seem to carry metric / fractional tape measures with any consistency, but you might try one of the smaller, family-owned hardware stores to see if they can special order one for you. My local Ace store was happy to do that… A metric / fractional tape measure can make your next antenna construction project go much more quickly and with more confidence that everything has been measured correctly.

Update July 2011: Harbor Freight has a 50 meter / 163 foot composition tape for under $12. It's metric on one side and feet on the other. However they caution you, on a sticker on the housing (and the sticker frequently goes missing), that temperature and humidity can cause the tape material itself to stretch and shrink as much as a full inch causing that much inaccuracy in the full length. But getting a 150+ foot measuring tape for under $12 is a darn good deal. Just don't use it for making a duplexer harness or making a dipole array - that's what the steel measuring tapes are for.

Update 2021: Amazon is carrying the Stanley 33-726 metal tape (8 meter / 26 foot) for under $30.

Update July 2023: Amazon has been out of stock of the Stanley for over 6 months however they have the Klein Tools 9375 metal tape (7.5 meter / 24 foot) for under $30.

Credits and Thanks:

Alex KJ7KIN made some very useful comments on some of the wording of the material above.

Contact Information:

The author, Mike Morris WA6ILQ, can be contacted here.

This material is © copyright 2003 and date of last update by WA6ILQ. It was at this web site on another page that was created in 2003, and was moved to this page on 12-Nov-2011.

Layout and hand coded HTML © Copyright 1995 and date of last update by Mike Morris WA6ILQ

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.