A Basic Guide to Analog Repeaters
What is a repeater?
A repeater is a receiver/transmitter combination that is usually placed on a high location listening and simultaneously retransmitting the received signals. By doing this two stations can communicate that might not be able to do so via a direct path.
In order to listen and transmit at the same time, repeaters use two frequencies and the difference in frequency is known as the offset. Without having an offset the repeater would simply hear itself and nothing else.
Even with the offset, the two frequencies are close enough that some additional isolation is required to prevent overloading the repeater receiver. Isolation is achieved by placing a device called a duplexer, or sometimes cavities in both the receiver path and the transmitter path.
On the 2-meter ham band the offset is 600 kilohertz. On the 70cm band the frequency offset is generally 5Mhz because the band is wider than 2m and can accommodate the larger split. The duplexer or cavities can also provide better isolation.
For this exercise we will concentrate on the 2m band. As a general rule repeaters with an output frequency (what you listen to) below 147 Mhz have an offset of minus 600 Khz. Repeaters with an output frequency above 147 MHz have a positive 600Khz frequency.
- You listen on 146.700Mhz
- You transmit on 146.100Mhz
- This repeater therefore has a minus offset of 600Khz
- You listen on 147.250Mhz
- You transmit on 147.750Mhz
- This repeater therefore has a plus offset of 600Khz
Modern amateur radios usually have the off set programmed into them and all you need to do is set the + or - shift and the radio will do the rest.
How do you call someone on a repeater?
Always listen first to make sure someone else isn't using the repeater. If there is no traffic you can put out a general call by saying VK3XXX listening on VK3RMM. If someone is listening they may reply to your call and you can begin a conversation.
To call a particular person just say VK3AAA this is VK3XXX are you about John? If John VK3AAA is available he will answer you and you can begin the conversation.
As previously stated ALWAYS LISTEN first before you transmit. It's fine to join a conversation just wait for a break in transmission and then announce your callsign. The next person to transmit will acknowledge you and invite you to join in.
If you are on a particularly busy repeater its a good idea to move to a simplex frequency if you are in range of the other station. This allows other stations without a direct path to use the repeater.
Remember to wait until the repeater has reset its timer (see REPEATER TIMERS below) , otherwise your turn short will be cut short, then leave a couple of seconds before commencing your transmission. This delay allows other amateurs to put out a quick call or announce emergency traffic.
There is no need to use your callsign on each over as the regulations only require you to identify with your call sign every 10 minutes. It is good practice to identify with your callsign when you have finished your conversation.
If you are in a round table discussion using a repeater to avoid 'doubling' (two or more stations talking at the same time) make sure at the end of your over to hand it to the next operator.
Example: VK3AAA to take it this is VK3XXX. If you don't do this it will end up in total confusion as to whose turn it is.
Most repeaters have an inbuilt 3 minute timer and will shut down after this time. This is so that everyone gets a fair go using the repeater.
Make sure that the repeater resets the timer at the end of an over. This is done by letting the repeater transmitter to drop out before you start talking. On some repeaters you may hear a courtesy tone that indicates the repeater timer has reset and there is no need to wait for the repeater transmitter to drop out.
If you jump in without letting the repeater reset your over is limited to three minutes minus the duration of the previous over. If the repeater times out it will not reset until all traffic using it has stopped. You will also occasionally hear the repeater identify itself using morse code.
Some repeaters in high noise areas have tones access enabled on them to prevent false triggering of the repeater. The tones are sub audible and you must have the tone enabled on your transmitter to access these repeaters.
Most repeaters in Victoria that have tone enabled use the standard 91.5 Hz tone. Check the callbook or enquire with your local club to see if you need to program a tone on your radio for the local repeater.
Some dual mode repeaters (Analogue and Digital) have tone access on both the transmit and receiver. This is done so that your analogue radio needs the receive tone to open the squelch and you don't hear the repeater when it is operating in digital mode.
Most modern amateur radios have the CTCSS option installed in them.
These tones are the same as used on your telephone. These are generally used to access certain functions on a repeater. This could be getting the repeater to respond with local temperature, time of day or perhaps battery condition. Not all repeaters have this function.
The more common application is for accessing IRLP (Internet Repeater Linking Project) enabled repeaters. Using DTMF tones you can link to another IRLP enabled repeater either here in Australia or around the world. A list of IRLP nodes and current status can be found at http://status.irlp.net/index.php?PSTART=3
The only valid signal report that can be given on a repeater is to indicate that incoming signal you are listening to is fully quietened. This means that there is no back ground noise on the persons signal can be heard. Remember that the signal strength on your radio is not an indication of the other persons signal but is an reading of how well you can hear the repeaters output.
Some Common Q Codes Heard on Repeaters
- QTH - What is your location? Or my location is
- QSL - I understand or can you acknowledge receipt
- QSY - I am changing frequency to, or can you change frequency to
- QRZ - Who is calling me?
- QRT - I am finished transmitting or please stop transmitting
- QSO - Can you communicate Or I can communicate
- QRM - I am experiencing interference (man made)
- QRN - I am experiencing interference (natural)