Repeaters

As a newly licensed Technician, you’ll probably be operating in one of the popular VHF or UHF bands, with a handheld or mobile rig (transceiver). One of the problems with VHF/UHF operation is that it is normally restricted to line-of-sight paths. If your antenna does not have an unrestricted view of the other stations antenna, it may be difficult or impossible to maintain communications. Thus the concept of the repeater was developed, where a sensitive base station receives signals on one frequency, and retransmits them on a different frequency, usually within the same band. The cellular base station is basically a repeater as well, it is just linked to a whole network of such repeaters to optimize the coverage to any handset. The earliest amateur repeaters actually worked with AM signals, as FM equipment was not readily available to the amateur community. This changed when many businesses sold their old vacuum tube FM business band radios for newer solid-state versions, and amateurs bought up these radios and modified them for operation in the amateur bands. The relative popularity of 2 meter and 440 MHz repeaters is largely due to the availability of these inexpensive business band radios. FM operations in the VHF and UHF bands expanded and repeaters built by clubs and individuals improved the coverage of these radios. The increased popularity of these frequencies did not go unnoticed by equipment manufacturers who then realized there was a marketplace for radios in these frequency bands. It also explains why there is relatively less activity in the 1.25 meter band since there was no surplus equipment available for that band, and why we lost 220-222 MHz portion of that band to commercial interests in 1998 (use it or lose it – hey did I mention that 11 meters was once a ham band? But that’s another story).

The repeater is typically placed on a local high spot and improves the ability of low-powered mobile or portable stations to communicate with each other over a much wider area by providing improved propagation paths and retransmitting the mobile signals at higher power levels. Some repeaters have multiple receivers located around the coverage area to further improve the possibility of picking up weak or blocked signals. A linear translator is similar to a repeater in function, but instead of receiving a transmission and demodulating it to modulate another transmitter, it shifts the frequency of the signal and amplifies it. As the term implies, this is done as a linear process, so the type of modulation (AM, FM, SSB, CW) does not matter. Linear translators are the basis of many satellite systems. How much coverage is available from a repeater? It is largely dependent on the terrain, and the height and gain of the repeater antennas, but on the East coast there is a repeater along I-95 in North Carolina that provides coverage along that superhighway from the Northern to Southern border of the state. On the west coast, some repeaters are placed atop mountains to provide coverage from the foothills to the sea, and may be linked to repeaters that cover the eastern side of the mountains into Arizona and Nevada.

Repeaters are constructed and financed by individuals or clubs, some of which exist mainly to support the repeater. Most repeaters are “open”, meaning they are available for anyone to use, although some require the use of a subaudible tone to gain access. This is also referred to as CTCSS (continuous tone-coded squelch system) or Private Line (PL), and provides a means to keep noise bursts or other nearby repeaters from triggering the repeater to transmit. Most new radios (including handheld models) have the ability to add these subaudible tones to your transmission, some even have the ability to decode them on receive, so your radio won’t respond unless the proper tone is sent. Repeater directories usually list what the required tone frequency is – see your radio’s manual to find how to select it.

Open repeaters are great for people traveling through an area, looking for directions or a place to eat, and during emergencies. But there are real costs involved in operating a repeater, such as the transmitter, receiver (s), cavity filters, antennas and towers, and controllers. While much of this cost can be amortized, eventually equipment may need to be repaired or replaced, and there may be continuing costs for the lease of phone lines or rental for antenna space on existing towers or buildings. In some areas (mainly on the east and west coasts, or in large metropolitan areas) there are many repeaters available (for example, there are a dozen repeaters in the Baltimore, MD area). If you are a regular user of a repeater, consider joining the sponsoring club, as one of the main uses for dues may be the maintenance of the repeater. Then the next time you are out of area, using a repeater to find some help or just a little companionship on a long drive, you know you have done your part to provide this ability in your neck of the woods.

You usually won’t find people calling “CQ” on a repeater. Instead, if the repeater is not occupied, just announce your callsign, or say something like “KB3XXX monitoring” to let people know you are available and on frequency. Since a repeater is a shared resource, it is not unusual to find a “roundtable” in process, where a number of stations are talking to each other. This is quite common during the morning and evening rush hours when a large number of people may be traveling with their radios on, and you will usually find the same group of people on who share a particular schedule. This gives you the ability to get real-time traffic reports! In the days before cell phones, this is the way many accidents got reported, as there is usually someone at their home monitoring, who can call 911, or your repeater may be connected to an autopatch (a gateway that connects the repeater to a phone line). While most autopatch-equipped repeaters have limited the ability to dial out to club members, many have an open access to dial 911.

Signal strength meters on many FM radios are extremely non-linear, and the more common way of indicating the quality of a signal is to indicate its signal-to-noise ratio. As signal levels increase in an FM receiver, they tend to “capture” the detector, rather than having it driven by the noise. If you lower the squelch setting on your receiver on an unused channel, you will hear a loud rush of noise. The stronger an incoming signal, the lower this noise becomes, and this effect is basis of many squelch circuits. A signal with no perceived background noise is called “Full quieting”. A mobile or portable station may vary from full quieting to somewhat noisy and possibly to so low that the squelch circuit cuts them off at times as they move around. In a simplex conversation, you can lower the squelch to hear the station further down in the noise, but a repeater uses the squelch circuit to key the transmitter off and on, and thus must set a higher threshold.

To join an ongoing conversation on a repeater, just insert your callsign in the breaks between various users talking, and wait to be recognized. Often a repeater will have a “courtesy beep” that will signifying the end of one user’s transmission – time your call to coincide with this “beep”, as other users will be waiting for it. All repeaters have timers to keep from becoming “stuck on” and transmitting non-stop. The length of time you can talk is limited by this timer, which is typically set to 3 minutes (thus making egg timers a great addition to your shack if you tend to be long-winded). If the repeater “times out” because someone has talked too long, it will not reset until after the offending station has stopped transmission. The courtesy beep also indicates that the timer has been reset, which is why users wait to hear it. If you are trying to find a specific person, ask to make a short call, and if your friend is monitoring, you can pass on a simple message, or the two of you can arrange to meet on a different repeater, or a simplex frequency, so as to not interfere with the ongoing conversation. Clubs will often have weekly “on-the-air” meetings, or nets (short for network) scheduled for a certain time and day. These can be huge roundtables, and so usually are “directed” by a master-of ceremonies, called the net control station (NCS), who will ask people to “check in” to the net alphabetically or by member number. When your chance comes, announce your callsign, wait to be recognized, and then the NCS will give each person a chance to talk in rotation.