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A Beginners Guide to Repeaters, Questions and Answers... By Kevin K. Custer W3KKC   (AKA "the repeater-builder guy") Maintained by Mike Morris WA6ILQ

For the sake of the complete beginner I'm going to cover all the parts, even those which may seem obvious.

Why a Repeater?
Radio signals - from any source, be it a handheld, a mobile or a base station, have limitations due to distance and terrain. If two radios are far apart, or there is a mountain in the way, they will not be able to talk to each other. To alleviate this, in the early days of radio a relay station was put in the middle - someone at station #2 recieved an incoming message from station #1 and wrote it down. He then flipped a switch from "receive" to "transmit" and transmitted the message to station #3. Eventually this function was automated and the first automatic radio relay station was created by Bell Telephone Labs in 1922. Yes, in the early years repeater stations were called "relays" stations where the station would "relay" a signal rather than "repeat" a signal. Art Gentry W6MEP (SK) didn't know about the 1920s Bell System repeater and he reinvented the first automatic amateur radio repeater in the mid-1950s as K6MYK. Art passed on May 10, 1996. As of the last time this paragraph was updated (November 2023) his repeater is still on the air.

What is a Repeater?
A repeater is an automatically controlled transmitter and receiver that simply transmits what the receiver hears simultaneously. Imagine having a receiver on one frequency, and a high power transmitter on a second frequency with both at a good high altitude (wide coverage) site. Now have someone there who is holding the the transmitter microphone in front of the speaker of the receiver speaker and pressing the PTT button when a valid signal is heard and releasing it when the signal is no longer there.
Now make the operation fully automatic and 24 hours / 7 days. Any user that can be heard by the repeater receiver has the use and effectiveness of the high power transmiter at a optimum location at his control.

Since the major limitation to a repeated systems coverage are is the terrain and the radio horizon you will find most repeaters placed inside a protective structure on the highest point of the service area - be it on a mountaintop, in a building at the foot of a tall tower (with the antenna high on the tower), on top of a tall building, or at the top of a water tower or...

In the midwest there are some towers that are over 1000 feet (300m) and to minimize the loss in the feedlines (mentioned later) the repeaters are installed in cabinets on a platform near the top. In any case, repeater systems are built to be as immune as possible to weather, interference, equipped with large, efficient and very durable antennas, extremely low loss feedlines (with lightning arresters), and with high performance receiving and transmitting equipment that is rated for continuous duty.

And there is more: In order to share the single antenna between the receiver and transmitter a device called a duplexer is used. And then there is a controller that connects the the receivier to the transmtter and handles all the audio processing.

Overall a repeater is not a really complicated device... You start with a location with a radio horizon that covers the desired service area, and you add an antenna, a receiver, a transmitter and all the other equipment needed to connect everything together.

The end result? People using a repeater get much greater range from their personal radio equipment than would be possible talking from radio to radio. This is how an individual with a portable walkie-talkie (handheld) transceiver can communicate with people many, many miles away with good clarity.

Repeaters are also used in police, fire and ambulance service communications (commonly called "Public Safety" or "First Responder"), Commercial (Business) Communications, Federal, State and Local Government agencies, Emergency Communications, businesses (like tow trucks, delivery services, landscapers, etc.) and by Amateur Radio Operators.

Repeaters can be powered by the regular commercial power lines, or they can be connected to multiple sources of power, including batteries and / or generators for when commercial power is lost. Repeaters can be built that are extremely power efficient and may run exclusively from batteries; recharged by solar, wind, water power or any combination.

Here's a link to a solar-powered amateur repeater: https://voiceofidaho.org/war-eagle-site   (off-site pointer, opens in a new browser tab).

What is "Simplex"? (other common terms are "Direct" or "Talk Around")
Simplex is point to point communications without the use of a repeater. Simplex operation utilizes the same frequency for receive and transmit, like a CB radio (i.e. directly portable to portable or mobile to mobile). A lot of the people in the commercial 2-way radio world call Simplex operation "Talk Around" because you are talking around the repeater, not through it.

Then there are such things as Simplex Repeaters. A slang term for these is a "parrot repeater". These devices use one frequency and listen on the frequency for activity, when it detects a valid signal it will begin to audio record that activity for a pre-determined time; common values are 30 seconds to 1 minute. After the activity ceases or the time has expired, the unit will stop listening, key the transmitter and play back what it has recorded. This method of communications is somewhat cumbersome over a conventional repeater; because you are forced to listen to what you said earlier in time and the channel usage is problematic as you never know when someone else is recording; however it should not be discounted as these types of systems can be very beneficial in some circumstances.

What is "Duplex"?
The simple explanation of duplex is simultaneous bidirectional communication. In radio this utilizes two channels, with one channel in each direction. If the signals flow in both directions simultaneously the communication is "full-duplex" else it is "half-duplex". Repeaters operate full duplex and the operation is like your telephone, where the incoming signal and the outgoing signal operate at the same time. In contrast, a handheld or mobile radio operates in half duplex mode because only one person can talk at a time. Since the "repeater" listens and talks at the same time in relaying your message, it operates in full duplex mode. Some amateur communications can be full duplex, many older mobile radios like the Motorola GGV, GKT (all tubes), Motrac, Motran, Mocom-70, Micor and GE Mastr II could be modified (and were) to operate full duplex with two separate antennas.

Nearly all communications circuits used by computers are two-way, so the distinction between simplex and duplex is seldom made in that universe.

How does a Repeater work?

At first glance, a repeater might appear complicated, but if we take it apart, piece by piece, it's really not really so difficult to understand. A basic repeater consists of several individual pieces that, when connected, form a functional system. Here's a simple block diagram of a repeater:

The above diagram is simplified; some items (including
the power supply and lightning arrester) are not shown.

The collection of the antenna, the feedline, the duplexer, and the interconnecting cables is frequently called the "antenna system".

Antenna -
A repeater antenna is usually a high performance, durable, and very efficient antenna located as high on a tower or structure as possible. Antennas of this type can easily cost from $500 to $2000 or more, and that's not including the feedline and other supporting equipment (like a lightning arrester), or the tower. On the other hand, when properly installed and maintaned the high quality antenna and feedline can last from 10 to 35 years or more. The author helps maintain several commercial and amateur systems and some of them are using antennas and feedlines that were installed in the mid-1960s and properly maintained.

Most repeaters use only one antenna, some use two, and some of those share the receive antenna among serveral repeaters. When a single antenna is used it simultaneously serves both the transmit and receive RF (Radio Frequency) signals that are going in to and out of the repeater.

Feedline -
The feedline on most repeaters isn't just a long piece of common coaxial cable, it's usually what's called Heliax (note that Heliax is a trademark, but like Kleenex it's become a general term). Some people call it "hardline" but that's a totally different product. For the differences between "heliax" and "hardline" please see the first part of this page. Both are more like a pipe with a hollow center conductor than a cable. Heliax is hard to work with, has a minimum bend radius and is very expensive. So why do we use it?   Performance!   The signal loss is much, much lower in hardline or Heliax than in standard coaxial cable, so weaker signals can be received and more power gets from the antenna to the receiver. A hard rule is that once any percentage of a received signal is lost that you can't get it back. Remember, the signal at a repeater site doesn't just travel a few feet to an antenna like in a mobile radio. It may go several hundreds of feet up the tower to the antenna, and the loss goes up rapidly with distance. Just for fun check out the specs on a roll of coax some time and see how many dB of loss you'll get from 200 feet of cable, and remember 3 dB is 1/2 of your power, and 10 dB is 90% of your power. Heliax also tends to be much more durable and long life than standard cable, which increases reliability and helps minimize the financial expense, and the tower climbs to replace it.

Duplexer -
This device serves a critical role in a repeater. To make a long story short, the duplexer separates and isolates the incoming signal from the outgoing and vice versa. Even though the repeaters input and output frequencies are different, the isolation is still needed. Why? Have you ever been in a place where there's lots of RF activity, and noticed the receive performance of your handheld radio degrades to some degree? This is called desensitization, or desense, and it's a very bad thing on a repeater. The receiver gets noisy or gets desensitized to the point of total deafness from the strong RF signals being radiated in its vicinity and confused about which signal it should receive. The result is poor receive quality, or in extreme cases, complete lack of receive capability. Keep in mind that in this example, the radios are picking up radiated power from one another and that's enough to cause trouble. Now imagine how much trouble there will be if you not only have the transmitter and receiver close together, but connect them to the same antenna! Transmitting only a few hundred KHz away in frequency would blow away the input to the receiver if the equipment was simply connected together with a Tee. That's where the duplexer (mentioned later) comes in; it provides the isolation that prevents the receiver and transmitter from "hearing" one another. And the more isolation the better.

Some repeaters use two antennas to provide the nedded isolation, however the most common method is is a device called a duplexer. It has the shape of multiple tall canisters and is designed to pass a very, very narrow range of frequencies and to reject all others. Other slang names for a duplexer is cavities, cans, bottles or jugs. There is some loss to the system because of the duplexer (called the "insertion loss"), however, the advantage of being able to use a single antenna and a single feedline usually outweighs the drawbacks.

Receiver -
This unit receives the incoming signal. This receiver is generally a very sensitive and selective high performance one which helps weaker stations to be heard better by the repeater. It's also usually where the CTCSS (Continuous Tone Coded Squelch System), "CG" or "PL" decoding takes place. More on this later. The receiver is a VERY important item bucause if you can't hear the users the repeater is worthless.

Transmitter -
Most repeaters have a transmitter composed of two parts: an "exciter" and a power amplifier. Depending on the manufacturer(s) it may be in one chassis or two. The exciter creates low level RF energy on the proper frequency and then modulates it with the audio. The power amplifier stages simply boosts the level so the signal will travel further. Transmitters come in two types: intermittent duty and continuous duty. One that is rated for continuous duty is preferred.

The transmtter power is generally balanced to the recevier and antenna system performance. The goal is that if you can hear the repeater, you can talk to it.

The "Station" -
The term "Station" is used in the 2-way radio industry to describe a stationary two way radio set; which includes the transmitter, receiver and sometimes the control circuitry. One example is the Dispatch Station for a fire department. A "Repeater Station" is a station designed to be used as a duplex repeater.

Controller -
This is the brain of the repeater. It handles station identification (through either morse code ("MCW") or voice), activates the transmitter at the appropriate times, controls the autopatch (if so equipped), and sometimes does many other things. Some repeaters also have a DVR (Digital Voice Recorder) for announcements and messages. The controller is a little computer that's programmed and optimized to control a repeater. The various manufacturers and models of controllers have different useful features like speed-dial for phone patches, a voice clock, facilities to control a remote base or linking to other systems, etc. The controller gives the repeater its "personality". Whenever you're using a repeater, you're interacting with its controller. In the early days of repeaters the controller was a large chassis full of relays and timers. These days a controller is most often a microcomputer based unit. Most are purchased, some are designed and built by the system owner.

What is a Phone Patch or Autopatch? AKA "The Patch"
Many repeaters have a feature that allows you to place a telephone call from your hand-held or mobile radio. Phone calls are generally restricted to the local calling area of the repeater to avoid long distance charges to the repeater's sponsors. If in doubt, ask if the repeater has an open patch and how to access it. When using the patch it is common courtesy to announce your intentions, e.g. "This is N3XZY on the patch". This may help to prevent anyone from keying up while you are trying to use the function. In most areas when you are finished with the patch the accepted protocol is to announce it, e.g. "This is N3XZY clear the patch". Some systems record all telephone calls, and their protocol might include announcing the time and date... e.g. "This is N3XZY clear the patch at one-thirty-p-m on Tuesday June sixth".

DVR -
A DVR is a Digital Voice Recorder, or in modern terms a "voice mail" system for the repeater. Usually it's an option that is installed into the controller.

Repeater Operation -
Operating using a repeater isn't difficult. A good source of info is the ARRL Repeater Directory. It's an inexpensive book, published annually, with repeater listings from all over the USA. It contains frequency, offset and whether the repeater is + or - in shift (see "offset" below), whether or not it requires a CTCSS tone, and other system features (like an autopatch, emergency power, or repeater-to-repeater linking).
Another source is the RepeaterBook web site. (off-site pointer, opens in a new browser tab)

What is "Offset"? (sometimes referred to as "Repeater Offset")
In order to listen and transmit at the same time, repeaters (no matter what frequency band) must use two different frequencies. On the 2 meter ham band these frequencies are usually 600 kHz apart. As a general rule in the USA, if the output frequency (transmit) of the repeater is below 147.000 MHz then the input frequency (listening) is 600 kHz lower. This is referred to as a negative offset. If the output is above 147 .000 MHz or then the input is usually 600 KHz above. This is referred to as a positive offset. However in any given area the offset rules can be different.

Virtually all of the radios sold today that are manufactured for the amateur market offer a feature that automatically sets the offset once you have chosen the operating frequency. As an example if the repeater output is 145.270 MHz then the input, or the frequency it listens on is 144.670 MHz (i.e. 600 kHz below the output). If you have the automatic offset enabled with your radio tuned to 145.270 MHz the transmitter will automatically switch the transmitter to 144.670 MHz when you push the PTT switch (Push-To-Talk). When you release the PTT to listen, the radio automatically reverts back to 145.270 MHz to listen on the repeater's output frequency.

Standard USA Amateur Radio Repeater Input / Output Offsets
Band	Offset
6 meters (50-54 MHz)	No real nationwide standard, it varies widely. Most common are -500 kHz, -600 kHz or -1.0 MHz
2 meters (144-148 MHz)	Up and down 600 kHz, depends on frequency.
1.25 meters (222-224 MHz, also called "220")	Down 1.6 MHz.
70 cm (440 MHz, also called "UHF")	Up or down 5 MHz, depends on local area usage.
33 cm (900 MHz)	-25 MHz.
23 cm (1200 MHz)	-20 MHz.

Note: There are exceptions to the above so check your local repeater listings.

Why do Repeaters use an Offset ?
Becasue they have to. A repeater must use a different transmit frequency than receive frequency. Otherwise the repeater transmitter would totally block the repeater receiver once it started transmitting. This is a form of duplex, or two frequency operation. It is known as half-duplex as you do not receive and transmit at the same time but normally use the push-to-talk button on your microphone to switch between the two. Don't forget to release to listen.

Most repeater installations use the same antenna for transmit and receive. Without having an offset the repeater would simply hear itself when it was transmitting on the same frequency it was listening on. Even with the offset, the two frequencies are close enough that antenna system isolation is required. Again, in most systems this isolation is afforded by the duplexer.

What is Carrier Access, Tone Squelch, CTCSS or a "PL" Tone?
Carrier Access, or Carrier Squelch means that the repeater is looking for a carrier on the receiver frequency to open the squelch. A circuit called a Carrier Operated Switch (COS) or Carrier Operated Relay (COR) senses the squelch opening, and tells the repeater that there is a carrier on the input. The controller keys the transmitter, thereby repeating the signal.

Continuous Tone Coded Squelch System, or CTCSS, is a radio communications industry name for a standard signaling scheme. It provides an electronic means of allowing a repeater to respond only to stations that encode or send a very precise audio tone at a very low level superimosed on the transmitter along with the microphone audio. The CTCSS system is used to prevent the repeater receiver from responding to unwanted signals or interference (it's looking for both the carrier and the tone before the signal is considered as valid). If a repeater is "in tone mode" that means it requires a CTCSS tone to activate the repeater. If it is in "Carrier mode" then it is ignoring the CTCSS decoder, if there is one. Modern repeater controllers offer a way to switch back and forth, even automatically, between the two modes. Originally there were 32 standard tones, now there are 37. Some manufacturers offer more (up to 51), but most repeaters use one of the original 32 so as to allow the older radios to use the system. Aftermarket tone generators from several different manufacturers allow any station to be set up to transmit a CTCSS tone. The tones are in the 63-260 Hz range and are called sub-audible, because they're below the normal voice audio range of 300-3000 Hz. This doesn't mean you can't or won't hear them; they can be quite noticeable depending on the radio you're using (better radios filter the low pitched tone out of the receive audio).

"PL", an acronym for "Private Line", is Motorola's proprietary name for CTCSS. General Electric uses the name "Channel Guard" or "CG" for the same system. Other names, such as Call Guard, Quiet Channel or Quiet Tone are / have been used by other manufacturers.

In days of old, repeaters that used PL were considered to be closed or private. This is no longer the case as tone operation has become more the rule instead of the exception. Uninformed people use CTCSS to "solve" interference problems. It doesn't. It just covers them up, or hides them. The unwanted signal is still on the repeater input, the tone decoder simply prevents the repeater from keying up and making it obvious.

Of course, everything these days is digital. A later system called "Digital Coded Squelch" or DCS uses 85 different sub-audible digital bit streams. Motorola uses the name "Digital Private Line", or "DPL" for this mode. Other manufacturers use different names. DCS is gaining in popularity since more radios now come with it as a standard feature.

How do you call someone on an Amateur Repeater?
First, listen to make sure that the repeater is not already in use. Then listen some more. If you are a new ham that has never used a repater before it might pay to listen for a week or so and see what goes on, who seems to be the "regular users", and if you know any of them.
Your page maintainer did a variation of this in the late 1960s... listening to a local repeater on a tunable receiver and overheard a few hams arranging to meet for lunch at a local restaurant. He bicycled over to that restaurant and located the three gentlemen in a back booth, introduced himself and over lunch got to know them and was invited to the local club meeting.

When you are satisfied that the repeater is not in use, begin with the callsign of the station you are trying to contact followed by your callsign. e.g. "W3ABC this is N3XYZ". If you don't establish contact with the station you are looking for, wait a minute or two and repeat your call.

If you are just announcing your presence on the repeater it is helpful to others that may be listening if you identify the repeater you are using. e.g. "This is N3XYZ listening on six-two-five". This allows people that have multiple radios (or are listening on radios that scan several repeaters) to identify which repeater you are using (and therefore which microphone to pick up to answer you).

If the repeater you are using is a busy repeater and if your contact is nearby you may consider moving to a simplex frequency (transmit and receive on the same frequency), once you have made contact with the station you were calling. Repeaters are designed to facilitate communications between stations that normally wouldn't be able to communicate because of terrain or transmitter power limitations. If you can maintain your conversation without using the repeater, going "simplex" will leave the repeater free for other stations to use.

Repeater Etiquette
The first and most important rule is LISTEN FIRST. Few things are more annoying than someone that "keys up" in the middle of another conversation without first checking to make sure the repeater is free. Saying that your volume control was down too low and you didn't hear any conversation is no excuse - it just says that you were stupid and didn't check your own station before you used it. If the repeater is in use, wait for a pause in the conversation and simply announce your callsign and wait for one of the other stations to acknowledge you.

When you are using the repeater leave a couple of seconds between exchanges to allow other stations to join in or make a quick call. Most repeaters have a "Courtesy Tone" that will help in determining how long to pause. The courtesy tone serves two purposes. Repeaters have a time-out function that will shut down the transmitter if the repeater is held on for a preset length of time (normally three or four minutes). This ensures that if someone's transmitter is stuck on for any reason, it won't hold the repeater's transmitter on indefinitely.

When a ham is talking and releases the push-to-talk switch on their radio, the controller in the repeater detects the loss of carrier and resets the time-out timer. Many of the modern computerized controllers allow the owner to program a "beep" to indicate that the timer is reset. This beep is called the courtesy beep, or the courtesy tone. If you wait until you hear this beep (normally a couple of seconds) before you respond, you can be sure that you are pausing a suitable length of time. After you hear the beep, the repeater's transmitter will stay on for a few more seconds before turning off. This is referred to as the "carrier delay", or the "hang in timer". The length of the delay will vary from repeater to repeater but the average is about 2 or 3 seconds. You don't have to wait for the transmitter to drop off the air before keying up again, but you should make sure that you hear the courtesy tone before going ahead. Some owners configure the controller to reset the timer without a courtesy beep, so if you don't hear a beep just wait a full second before keying your microphone.

Note: If you don't wait for the beep the time-out timer may not reset. Some repeater clubs have a rule that if you time-out the repeater you get to buy a round of coffee at the next ham club meeting.

What is "Tailgating"?
That is when a user jumps in immediately after another user unkeys and before the reset beep. This is done when you want to jump in and are counting that there is enough time before the timeout timer activates.

What is "Doubling" ?
When two stations try to talk at the same time their signals mix in the repeater's receiver and results in a buzzing sound or squeal. When you are involved in a roundtable discussion with several other stations it is always best to pass off to a specific person rather than leave it up it the air. e.g. "W3ABC to take it, this is N3XYZ" or "Do you have any comments Fred?, this is N3XYZ". Failing to do so is an invitation to chaos and confusion.

It is for this very reason that when groups hold scheduled Nets (network of hams meeting on air at a predetermined time), they assign a Net Control station. The Net Controls job is to make sure there is an orderly exchange and that all stations get a chance to speak. Listen to a local net and you will get an idea of the format and how the Net Control juggles the various stations and traffic. It's a job almost anyone can handle (a written script helps), but as you will discover, some are much better at it than others. And if you try your hand at being Net Control for a night, you will discover just how hard it can be! (and you will gain a lot of respect for those that have the knack to do it and make it sound easy). A well run net is both informative and entertaining! And it is great practice for a disaster communications situation. The twenty ot thirty stations in the net could very easily be deployed at twenty ot thirty different locations and be coordiating the delivery of supplies.

What is a "Control Operator"?
The Part 97 of the FCC Rules requires all stations in the Amateur Service that are capable of operating unattended must be monitored for proper operation while in the unattended mode. This monitoring function is accomplished by a control operator. The Control Op can be the licensee of the station or anyone he or she chooses. In many cases, he or she also ends up being the person that answers questions about the repeater.

What is "White Noise"?
White noise is a term used to describe a spectrum of broad band noise generated in a receiver's detector and is sampled to control the receiver's squelch. When you open the squelch control and hear the rushing noise from the speaker, this is white noise. When the receiver is in carrier squelch mode the squelch circuit uses the presence of that noise to decide that the signal has gone away and it should mute the receiver speaker. When the receiver is in tone squelch mode it uses the absence of the tone AND the presense of the noise to indicate loss of signal. The "squelch tail" is that burst of white noise that you hear that starts when someone unkeys and ends when the squelch circuit actually mutes the receiver audio (some people mistakenly use the term to refer to the carrier delay mentioned above).

I hope this article has explained the Repeater in enough detail that you understand what it is and how to use it. If there is any part of this article that seems vague or confusing, please write me and I'll do my best to explain it better.

Email Kevin: kuggie //at// kuggie //dot// com
 

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Text and HTML Copyright © September 6, 2003 by Kevin K. Custer W3KKC
All Rights Reserved.
A few details added and the HTML cleaned up around 2005 by Mike Morris WA6ILQ
The "Why a Repeater" paragraph added 10/2023

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.