Repeater

Electromagnetic waves attenuate as they pass through a transmission medium. Each transmission medium can only be used for a certain distance. However, you can exceed the physical medium's maximum effective distance by using an amplification device called a repeater. These devices not only amplify the signal, but also amplify the distortion.

What's a repeater?

A repeater is a term for a device used often in Ham Radio as well as police/emergency radio communications. It consists of typically a transceiver (a fancy term for a sometimes-glorified two-way radio, from a shortened transmitter+receiver), a controller (the "brains", which sees if someone's talking and fires up the repeater access, plus often more)and a duplexer (usually an ugly can that keeps the repeater form deafening itself with its own transmissions; see the node for it for more info.)

A repeater receives signals (normally narrow-band voice) and rebroadcasts them on a different frequency (known as the repeater shift). A repeater can be used for long(er)-distance communication on higher frequencies, mostly on 2 meter AKA 135-170 MHz bands and above. However, repeaters are occasionally known to duplex as low as 10 meters.

Why repeaters?

Well, say you want to chat with a friend on another side of a hill. Your transceiver can't see hers and vice-versa. So what to do? Why not put a repeater on top of the hill? Both of you can now talk to each other, and often many other hams still further away (depending on the height of the hill upon which the repeater sits).

A little more on repeater shift

Why not transmit on the same frequency than the frequency you get the signal on? It seems like it would make sense, until you think of a frequency chunk like a wire: you rarely have an amplified signal on a power amp for a stereo coming out of the "in" wire. If you do, you'd get all kinds of nasty problems with feedback, cancellation, standing waves and other unpleasant things. It is, however, possible sometimes to have two FM signals on top of each other with some intelligibility. However, the practice is not recommended as they are never (almost) in phase with each other and sound terrible.

The repeater shift amount varies from band to band, and on some ham bands the sections of the band used for repeaters are paired, or overlaid on top of each other, with some overlap. What does this mean? The output frequency for one repeater with an input frequency that is shifted up sits next to a bunch of positively shifted inputs, and vice-versa.

A repeater is assigned a frequency by a regional committee known as the frequency coordinator.

Below is a sample chart for how repeaters are spaced out on the 2-meter band (a band is just a chunk of radio space). The output is shown in the boxes, and the direction and amount (in KHz) of shift for the input frequency. For example if a repeater sits on 145.435 MHz it should have an input frequency of 144.835MHz.

  ____         ____         _________       ____
 |-600|       |+600|       |-600|+600|     |-600|
-------------------------------------------------------
145.1-145.5  146.0-146.4  146.6-147-147.4  147.6-148

The chart was copied out of a Yaesu HT manual, I should probably improve on it, as it's rather terse

Sources:
ARRL 1994 Handbook, ©1993 the Amateur Radio Relay League
McKibbin, Mark (editor); The WWARA's Pacific Northwest Repeater Directory

In computer networking, a repeater is a device which takes an incoming signal and then repeats it. If it is a digital repeater it will regenerate the signal, which will clean up any distortions. If it is an analog repeater it will amplifly the signal, including any distortion. Repeaters must follow the 5-4-3 rule, which states that you can only have 5 segments of cable connected by 4 repeaters, and only 3 of the segments can have a host. Repeaters have pretty much been made obsolete by hubs, which are basically multiport repeaters. Hubs, in turn, have mostly been replaced by switches. Because a repeater is a transceiver, it can take an electrical signal and convert it to an optical or radio signal.

Note: These observations are just that, no more than a little description on how amateur radio repeaters are used in the New York City metropolitan area. Practices and acceptable behavior may change from region to region and country to country.

Briefly, an amateur radio repeater is a device that retransmits signals so that they may be heard over a wider range than single frequency ("simplex") communications. Repeaters have an input and output frequency. An operator transmits into the input and is heard on the output, which is the frequency monitored to "hear" the repeater. Sometimes a tone system like CTCSS (PL) is used to block interference.

To use a repeater, transmit on the input with the correct CTCSS tone. When releasing the microphone, the operator should hear a few seconds of carrier before the signal drops below the squelch. Many repeaters nowadays have a "bleep" or chime to tell you if the transmission was successful. Bleeps also remove any necessity to say "over" or "go ahead" at the end of a transmission. Use of these words have survived in areas where end of transmission tones are not common.

To announce you're around, just say "W2xxx listening" or "W2xxx monitoring". Some people get creative and say "W2xxx listening and standing by". Usually a simple call works well enough. CQ is generally not used on repeaters since stations are expected to have strong signals through the repeater.

To identify every ten minutes as per FCC law, just say your callsign at the end of your "turn". While you're talking to more than one station in a "roundtable", pass the conversation along by naming the next person to go. When leaving, you can repeat the other station's and your call sign, or just give your call sign with some announcement like "I'm in the driveway now" or "good night" or something, just to let everyone else know if you're staying on or not. If you are left alone as the last person in a conversation, just say you're either "clear" (shutting down the station) or "listening" at the end of the final transmission to tell whether or not you're willing to stay on the repeater.

Some operators make a big to-do about other operators using a sort of new ham radio lingo that's partly CB and partly HF (shortwave) usage. One example is saying "QSL" instead of "yes" or "okay". On CW (morse code), QSL? means "will you confirm this contact with a QSL card?", a verification of the contact having taken place. Another CW term misued is QTH for "where do you live?". QTH? means "your location?" in CW. Another is blatant use of CB lingo, including "handle" and "roger", though in my experience the CB-ese drops out after the newly minted operator has spent a few months on the air. For nearly every case, use common, understandable language when on the repeater. What is necessary for slow data transmission on CW is irrelevant and perhaps a bit silly on voice communications.

As a tight room with 200 regular visitors might be, ham radio repeaters are more than a bit cliquish. Yet many operators prefer higher-frequency communications to HF; given the high number of operators restricted to the upper bands it's crucial that everyone at least be able to understand one another.

1. A specialist in the automobile accident claims racket who has posed as the 'victim' of many accidents and has several suits pending concurrently in courts. 2. A recidivist. 3. A second criminal act committed against the same victim.

- american underworld dictionary - 1950

Re*peat"er (-?r), n.

One who, or that which, repeats.

Specifically: (a)

A watch with a striking apparatus which, upon pressure of a spring, will indicate the time, usually in hours and quarters

. (b)

A repeating firearm.

(c) Teleg.

An instrument for resending a telegraphic message automatically at an intermediate point

.<-- or a telephone signal --> (d)

A person who votes more than once at an election

. [U.S.] (e)

See Circulating decimal, under Decimal.

(f) Naut.

A pennant used to indicate that a certain flag in a hoist of signal is duplicated.

Ham. Nav. Encyc.

 

© Webster 1913.