BridgeCom Systems Guide to Repeater Systems, With An Emphasis On Duplexers.

BridgeCom Systems Guide to Repeater Systems, With An Emphasis On Duplexers.

Have you ever wondered what makes a repeater system? Or interested in setting up your own system? This article will explain all the components of a repeater system. With an emphasis on duplexers and why a person would get one.

Parts of a repeater system

A repeater systems contains 5 core parts. They are the power supply, Repeater, duplexer(optional), feed line, and a antenna(s). We will breakdown all of the parts in the next few paragraphs

Power Supply.

Most electronic devices require DC(Direct current) Power. The electricity that comes out of your wall socket is in fact AC (alternating current). Your power supply is responsible for converting the AC into DC. It is also responsible for getting the correct power to the device. Your power supply will regulate the current and prevent surges from destroying your equipment. Duracomm Power supplies work fantastically for any radio application.

You can find them at the bottom of the article.


The purpose of a repeater is to extend the range of other radios. Think of it as a signal amplifier. For example; A handheld or mobile radio in a vehicle will transmit to the the repeater. The repeater will then receive that signal and then immediately transmit it over a much larger area. Repeaters are generally mounted on high altitude locations relative to the surrounding area.


A duplexer is a tunable pass, pass/notch, or notch filter. It separates the transmit and receive signals. A repeater With a duplexer can transmit and receive simultaneously.  Using a duplexer allows you to use only one antenna instead of two. And thus half the feed line. The advantage of using only one antenna saves money but also is quite helpful on congested tower sites. Where it may not be possible to get two antenna locations.

Feed Line

Feed line is simply a specialized wire that transmits signal from the repeater to the antenna and back.


The antenna is where the signals go in and out. If you have a duplexer, only one antenna is required. If not, two are required. One for transmit, and one for recieve.

Why A Duplexer:

Cost Savings - Use only 1 antenna and feed line.

Using a duplexers enables the use of only one antenna and feed line. Eliminating the second antenna and feedline set. This can save hundreds if not thousands of dollars in equipment!

Convenience - Do half the work.

By only having to mount 1 antenna. You are cutting the amount of work in half. This gets the system up faster and leaves more time to talk on the system.

Now you only need one antenna location. If you have a tower you can now use the top instead of having to use the top and a lower location on the tower. Using the top enables maximum coverage.

Accessibility - Only secure one tower spot.

In a lot of areas tower space is in high demand, very limited, and expensive. It can be hard to get a spot to mount 1 antenna, let alone 2. Having a duplexer makes getting a tower slot much easier and a lot cheaper. Leasing a slot for one antenna on a commercial site could cost $5000 a month! Double that or more for 2 antenas. If that isn't enough to convince you I don’t know what will.

Good news. -BridgeCom Systems has everything you need.

BridgeCom Systems Supplies all of those components, and will help find what you need.  Not only is having a duplexer convenient. Getting an all included repeater system package from BridgeCom Systems is even more convenient! Please call us at 816-532-8451, send us an email at or visit our product selection.

Our Repeaters and Duplexers have been tried and tested all over the world.

Check out our testimonials page for proof






Power Supplies


Rack Mount:

Feed line:





If you don’t find what you looking for. Call us at 816-532-8451 or send us an email at

If you have any input on the article, please leave a coment below. 

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Bob Norris - August 14, 2018

Wantabee repeater owners/hosts:

All you need to do is promote the advantages of having a repeater for emergency communication services for your local community. You would be surprised at what the city fathers might do to assist the in the setup of an amateur repeater. Most cities have their own water systems with water towers and they make great repeater locations and most likely “rent free” including the electricity to run the system.

Brian Dolan - May 3, 2018

Send any and all info possible. Thank You. Brian Dolan

Daniel Kochanowicz - April 27, 2018

@charles McCormick.
Hello Charles, This is Daniel From BridgeCom Systems. Don’t get discouraged. There are many other much less expensive options for your repeater system antenna. You could put up your own tower for instance. If you want to put up a system. You can do it. We’d love to help you.
-Thank you, Daniel

Todd Schutter - April 27, 2018

May I suggest going into a little more detail on the importance of using the correct type of feed line for a repeater install? There are many good reasons for this. First, on many tower installs, if you or your club don’t own the tower, most all commercial sites will require a bonded, professional crew to climb the tower for any work that needs to be done. This gets expensive very quickly. Using a poor quality or incorrect type of feed line WILL cause a failure of your system. Hiring a crew (any professional climb will require at least 2 people) to replace a faulty feed line will wipe out any savings you made with your coax. Add to that, you end up buying the more expensive, correct feed line anyway.
So what is incorrect feed line? The following is from Mike Morris, WA6ILQ and :
“In duplex service you want to avoid any coax that has dissimilar metals rubbing against each other (such as Belden 9913) or any LMR-(any 3-digit or 4-digit number) cable since both use an aluminum foil shield rubbing against a copper braid (and they are not the only ones with that type of construction). In a coax cable any dissimilar metals in contact with each other are bad news. Aluminum oxide is formed when raw aluminum is in contact with oxygen, and the chemical reaction that converts the top few molecules of the exposed surface of aluminum into aluminum oxide is almost instantaneous. Aluminum oxide makes a dandy diode. All those millions of contact points between the copper braid and the aluminum oxide layer on the aluminum foil become millions of little tiny diodes. In the presence of high RF power levels all those little diodes cause RF noise. The amount of noise energy on any one frequency (such as on your repeater input frequency) is a low level, but when you have the noise source inside the same feedline that feeds a sensitive receiver it doesn’t take much level to be audible.
I repeat – any cable that has dissimilar metals pressed together, even inside a jacket, will sooner or later create wideband noise (sometimes called duplex grunge) when hit with RF power. Even something as simple as a 1-foot-long jumper between the feedline and the antenna at the top of the tower can cause major desense problems (and for a long time the major antenna manufacturers were shipping 9913 jumpers with their antennas). 9913 is usable in an indoor simplex environment, but you will find that 9913 or any dissimilar metals cable, especially LMR-(any 3-digit or 4-digit number), is a disaster just waiting to happen on a duplex system.”
In that case, what is the correct type of feed line? Again, from WA6ILQ:
“First of all, despite what you read elsewhere, “hardline” is not Heliax™ and Heliax™ is not “hardline”.
True hardline (sometimes called rigid feedline or rigid line) is most commonly used in broadcast (AM, FM and TV). It does not flex – it’s based on concentric pipe with an insulator between the inner and outer conductor. From the outside it looks like flanged pipe. Common sizes range from 3/4 inch to over 8 inches in diameter. It is much lower loss than coax or even Heliax." “On the other hand, RG-214 has two silver-plated braids and a silver-plated inner conductor. RG-393 is similar but has a Teflon® outer jacket. Both are the larger diameter (i.e. RG-8 / 213) size coax and RG-142 / RG-400 is the smaller diameter (RG-6 / RG-58 / RG-59) size. Please save yourself some grief and use real Mil-Spec RG-214 or RG-393 as the jumper between the feedline and the antenna. And please be a very annoying and nagging perfectionist about the installation and waterproofing of all feedline and jumper connectors outside the building.” "You will minimize your feedline problems if you stick to Superflex, RG-214, RG-393 or RG-400 on the radio side of the duplexer, and Superflex, Heliax and RG-214 or RG-393 on the antenna side of the duplexer. Use RG-214 or RG-393 as the jumper between the duplexer and the Heliax, and between the Heliax and the antenna. Note that RG-400 has more loss than the larger diameter cables – it’s spec’d at 9.6 dB of loss per 100 feet at 400 MHz. It’s short jumper material, not feedline material! You will want to use all silver plated connectors and absolutely minimal adapters (and those need to be silver plated) in your connections from the transmitter or receiver to the duplexer, from the duplexer to the feedline and from the feedline to the antenna. NO nickel plated or chrome plated anything in the RF path anywhere! Nickel and chromium are ferrous metals and as such both are an intermod creator anywhere around RF. It’s detectable at 10 meters and 6 meters and has proven to be a real problem at 2 meters, 220, 440, 900 and 1200 MHz. Mark Abrams WA6DPB said it well when he said “One nickel or chrome plated anything can really ruin your whole day”. Another rule is nothing but Teflon® insulated silver plated connectors and minimal adapters on anything above 30 MHz."
Before you plan out or purchase anything for your system, go to and read everything you can. It will save you a huge amount of frustration!
73, Todd, KY4TS

charles mccormick - April 27, 2018

$5000 per month to maintain an antenna smashes my dreams of hosting a repeater.

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