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GB3SS User Guide

RF Bandwidth

The repeater is configured for narrowband operation with 7.5kHz channel bandwidth, 12.5kHz channel spacing and 2.5kHz deviation as per current regulations. Most newer transceivers are designed or can be configured for narrowband operation. If your radio has an "FM-N" (narrow) mode, use this with the repeater. If you only have 25kHz channel spacing, you can still use the repeater, although there may be some distortion on your transmissions through the repeater. The repeater always transmits at narrowband deviation, so the audio level will seem slightly low on 25kHz radios.

CTCSS Access

GB3SS is equipped with CTCSS encode and decode. The CTCSS frequency is 67.0Hz (tone "A" on the RSGB RMC's CTCSS plan. For easy repeater operation, enable CTCSS encode on your transceiver if you have it. You won't have to worry about sending tonebursts and there is no time-out. You can also enable CTCSS decode on your radio to avoid hearing the regular beacons and eliminate the squelch crashes when the repeater stops transmitting. Most radios have CTCSS encode but fewer have decode as well (it's often an optional extra).

When using CTCSS, all you have to do to open the repeater is key up and talk for at least two seconds. The 2-second requirement reduces spurious activation of the repeater. If you don't meet the 2-second carrier requirement, the repeater does not open fully, but silently reverts to standby.

If you enable CTCSS decode on your transceiver, your received audio will be muted after the first "pip" at the end of an over. As soon as another over starts, the audio is unmuted. Thus you don't hear the repeater close down (there's nothing to hear apart from the second "pip" anyway) and you don't hear the regular beacons.

Toneburst Access

In case you don't have CTCSS, you can still open the repeater by transmitting a 1750Hz toneburst of at least 400ms. The repeater opens when the toneburst ends (to preserve listeners' hearing!). You must keep transmitting after the toneburst ends and transmit for at least 2 seconds to open the repeater fully, otherwise the repeater will silently revert to standby. This helps prevent interference signals opening the repeater.

If you have an auto toneburst (i.e. pressing the PTT automatically sends a short toneburst), you should wait until the toneburst ends before speaking, otherwise your first few words will be muted. It's not necessary to send a toneburst at the start of each over, so disable the auto toneburst if possible.

If you do not use CTCSS, you will be subject to a 4-minute talkthrough timeout which helps prevent the repeater becoming stuck in talkthrough if there is a jamming interference signal keeping the receiver squelch open.

Talkthrough Timing

After the repeater is opened for talkthrough, it stays open until either a timeout occurs or no transmissions are received for 10 seconds. The timeout is set at 4 minutes.

Each "over" must be at least 1 second long (the repeater assumes that very short transmissions are interference blips), and there is a 1-second hang time before the "end-of-over" pip is sent. This allows slightly broken signals (e.g. mobile flutter) to be handled properly, and other users can break into a QSO.

At the end of each over (and after the hang time) an acknowledgement "pip" is sent. If the transmission used CTCSS, a "T" is sent, otherwise an "E" is sent. If the transmission ended within 20 seconds of timeout a "5" is sent. This pip indicates that the timeout timer has been reset and another user may transmit. Do not transmit before the pip, or you may be cut off by the (now much closer) timeout.

20 seconds before timeout, listeners will hear a Morse "S" warning, and at timeout, the repeater transmits a "SK" (Morse "end of work") timeout warning and closes down. When the long-winded user (or other interference) stops transmitting, the repeater transmits a Morse "C" to indicate that the repeater input is clear and reverts to standby. The repeater must then be accessed as normal to re-start talkthrough.

If nobody transmits at the end of an over, the repeater sends a second pip 5 seconds after the end-of-over pip, and reverts to standby 5 seconds after that. The repeater must then be accessed as normal to re-start talkthrough.


The RSGB Repeater Management Committee provides estimated coverage maps for UK repeaters based on elevation data and computer simulation. The estimated coverage for GB3SS is shown below. Actual coverage is better than this in some areas. Blue indicates good/excellent mobile coverage, and magenta indicates acceptable mobile coverage