Details of the GB7KR repeater

GB7KR is a multi-mode 70cm voice repeater located near Kidderminster in the West Midlands.

It is licensed for both digital and analogue modes, but is currently on test in analogue mode only, while the digital equipment is sorted out.

Output frequency is 430.8875 MHz, with the input 7.6 MHz above, on 438.4875 MHz. Modulation and filtering are to “narrow” specifications (2.5 KHz deviation, 12.5 KHz spacing).

Access is by CTCSS-only, tone 118.8 Hz. CTCSS is present on the output, except during beacons.

Coverage is limited at present, because the repeater is working on a temporary low-gain antenna at reduced height. The map shows the intended coverage for the normal antenna and mast.

VOIP Linking

The repeater is semi-permanently linked to GB3KC (Stourbridge), to extend KC’s coverage to the south of Iverley Bank, and to provide coverage for portables in Kidderminster.

GB7KR will automatically unlink from ‘KC if an “outgoing” Echolink connection is made using DTMF commands, and will re-link once the connection clears.

To prevent unsolicited connections from interfering with GB3KC’s traffic, GB7KR does NOT allow INCOMING Echolink connections. It is therefore marked BUSY on the Echolink system. Anyone who attempts an incoming connection is diverted onto GB3KD.

Control Logic

Control logic is currently the same as our other two repeaters, GB3KC and GB3KD, and runs on a DOS machine. Audio processing is done digitally by the control software.

There is a Morse Code “courtesy signal” 3 seconds after the last valid transmission. This will be “K” if the repeater is not connected to anywhere, “C” if it is connected, and an “I” if the transmission came in via the Internet. Other signals are “O” meaning “over-deviated”, “Q” meaning the audio is too quiet and “W” meaning the signal strength is weak.

It is good practice to wait for the courtesy signal before commencing transmission, because this gives the repeater chance to reset  for the next “over”, and for other people to break in. You CAN “jump the K”, but if you allow more than 3 minutes to elapse without a courtesy tone, the repeater will “time out” and lock you out.

The repeater’s carrier stays on for 8 seconds after the last valid transmission. It may sometimes give a Morse identification before closing down, if it has been a while since the last one.

Mutual Interference

The RSGB’s Repeater Mismanagement Committee allocated GB7KR to a channel just 12.5 KHz below that of GB3KC, knowing that there would be some mutual interference.

This is deliberate policy on their part, aimed at forcing “wide” (25 KHz) repeaters like GB3KC to upgrade to “narrow” (12.5 KHz) specs. Their logic is that, because both repeaters are run by the same group, we are more likely to fix any problems.

Such changes take time to implement. GB3KC will either need major surgery to change the filters, or the repeater unit must be replaced.

So for the time being, there are places, such as the A449 north of The Whittington pub, where GB7KR’s output signal is made unsable by sidebands from GB3KC.


Callsign: GB7KR
Location: Near Kidderminster, West Midlands
TX frequency: 430.8875 MHz
RX frequency: 438.4875 MHz
Split TX/RX: 7.6 MHz
Channel spec: Narrow (2.5KHz deviation, 12.5KHz channel spacing)
Modulation: Analogue and DMR (currently analogue-only)
Analogue CTCSS: 118.8 Hz (tone J) on RX and TX
1750Hz Access: No
Antenna: White stick collinear
TX Power: 22W ERP omnidirectional
Intended Coverage: Kidderminster town and immediate surroundings as far as Iverley Bank, Chaddesley Corbett, Hartlebury etc.
VOIP Linking: Echolink – Outgoing connections only. Usually linked to GB3KC in Stourbridge.
TX/RX: Pair of Kyodo KM450 mobiles.
Duplexer: ?
Computer: Pentium 333, DOS 7.00 (Raspberry PI + MMDVM to be added)
Control Software: E-Link Software VOIP Repeater for DOS.
Talk Time: 3 minutes maximum per “over”.
Keeper: Richard G0EWH



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