About the CRG

The Cambridgeshire Repeater Group (CRG) owns and operates amateur radio analogue voice repeaters on 6m (GB3PX), 2m (GB3PI) and 23cm (GB3PS), a D-Star repeater on 70cm (GB7PI) and a high speed packet node on 70cm (GB7PT) from a site at Barkway near Royston plus an analogue voice repeater on 70cm (GB3PY), a 2m APRS digipeater (MB7UM) and an amateur television repeater on 23cm (GB3PV) from a site at Madingley west of Cambridge. Both Barkway and Madingley are former Pye/Philips towers however both are now owned and maintained by Arqiva. These repeaters serve users in the Cambridgeshire, Bedfordshire, North East Hertfordshire, North West Essex, West Suffolk and South West Norfolk areas. To the north of the county we operate the Peterborough 2m FM voice repeater (GB3PE) from a site at Thorney Toll.

The CRG hold the callsigns G3PYE and G6PYE which are used to help promote the group on-air. More information, including the history of the CRG can be found on the About the CRG page.

CRG Subscriptions

CRG Membership subscriptions run annually from the AGM, see the CRG calendar for this year’s date.
Membership rates for 2014/15 are: ordinary membership £10 per annum; family membership £15 per annum.
We also have “Extra” & “Gold” memberships available, for those fortunate enough to be able to spare us a little extra – please contact the Membership Secretary (Neil, G4HUN) for more details.
Please help the group by paying your subscription promptly. As always, your subscription will get you into the CRG Rally for free.
For those who haven’t yet paid (and those who’d like to join), you will find the CRG membership form on the CRG Membership Page. or pay online by going to the Products Page.

Repeater Status

Please email technical if you have any reports regarding any repeater below.

BandModeLocationOutput in MHz
StatusLast Updated
GB3PE2mVoiceThorney Toll, Peterborough145.675
(-600 KHz)
(-600 KHz)
(+500 KHz)
Operational full power - Reports welcome19/10/15
(-67 MHz)
GB3PS23cmVoice / BeaconBarkway1297.075
(-6 MHz)
Offline - Antenna fail10/11/14
(-9 MHz)
Gateway offline due to PC PSU fail
Local use Ok
GB7PT70cmFusion / C4FMBarkway439.7125
(-9 MHz)
MB7UM2m2m APRS DigiMadingley144.800 MHzOperational08/06/14
MB7UPI2m2m APRS Digi + iGateBarkway144.800 MHzOffline (Mk2 being built)25/08/15


2010-02-27 11.25.52

Flossie is the groups Amateur Radio Demonstration Vehicle.  For more info about Flossie please visit the Camb-Hams page on her.

CRG Events

Please see the CRG calendar for more dates.

CRG News

GB7PT Returns to service

At 1300z today, GB7PT returned to service. The CRG’s first digital repeater, originally carrying 9K6 FSK as a “bit regenerative repeater”, now supports C4FM (aka Fusion). The FSK logic will return when issues with the C4FM controller are resolved . Other digital modes may be added too, making GB7PT the a proper multi-mode digital repeater.

Coverage tests using the machine in “Auto” mode (allowing analogue use) are looking good, considering the repeater is sharing the GB3PX tri-bander at only 37m AGL.

Reports via the web forms on the CRG website are welcome.

UPDATE – 17th October 2015 – GB7PT now operating in digital mode only (C4FM/Fusion)

CRG Fusion & DMR Questionnaire


To open this questionnaire in a full screen then go here.

CRG 2014 AGM Change of Venue

Due to reasons beyond the groups control, the Sun at Waterbeach is not available for us on Weds 26th for the AGM.

The 2014 CRG AGM will be held at :

Red Gate
Newnham House
Cambridge Business Park
Lint to map: http://bit.ly/1uI8rPu
Parking is in the car park either side of the building, in any space except those labelled as Mewburn Ellis.
The main doors will have locked by 7pm, so we’ll post someone there to let people in before the meeting starts; after that Rob VFC stick a post-it with his mobile number on it for any late-comers.

We’ll be in a meeting room on the ground floor.

Special thanks to Rob M0VFC for organising this for us at such a late stage

Please pass this on to anyone you know that may be interested and not have access to this website.

vy 73




The Cambridgeshire Repeater Group

Update – GB3PS, GB7PI, GB7PT, and MB7UPI

I have visited site and investigated the issues with GB3PS (23cm voice and beacon), and GB7PI (70cm DStar).

GB7PI has been returned to full service after an issue was found with the 24v to 12v converter (again), causing a considerable volts drop to the supply. That’s all fixed, though a new converter will be required at some point in the near future.

GB3PS is not “audible” at more than a few hundred yards from the site. Checking the equipment showed that the repeater and beacon are working correctly, just that the RF wasn’t making it to the outside world.

A quick check with my Sitemaster shows what looks like an open circuit feeder. That *could* be a break in the LDF5-50 feeder running up the tower, or it could be the aerial gone O/C. Until I get a chance to carry out a “Distance To Fault” test, I won’t know. The light was fading while I was on site, so I couldn’t carry out any visual inspections (from the ground) of the feeders.

The fault is affecting GB7PT, and MB7UPI as they share the same feeder and aerial (a 2/70/23cm tri-bander).

Until we know what’s at fault, we can’t start the process of getting it fixed.

vy73 Rob M0ZPU


GB3PS and GB7PI issues

Just a quick note to let you all know that GB3PS and GB7PI are both suffering with issues at the moment.

Our 23cm repeater appears to have gone silent, though I have received the weak signals from the 70cm driver, which tells me that some of it is still alive. My assumption is that the power supply to the PA has failed.

Our DStar box – GB7PI – has been warbling away rather than passing recognisable speech. Something has gone awry in the TX, as off-air audio passed through to the network is coming out fine on other DStar nodes.

I have booked a site visit through the Arqiva Gateway system, and hope to get to site in the next day or so to investigate. It is possible that GB7PI may need to be sent off for repair.

I am hoping that the GB3PS fix will be a quick one.

Any queries, please don’t hesitate to contact myself, either via email (chairman@cambridgerepeaters.net) or on air.




MB7UM Mk2 Installed – 29/05/14

With the help of Joe M0ZRN and Rob M0VFC, our MB7UM APRS Digipeater at Madingley has been updated.  The new  MB7UM Mk2 is a new design for the CRG with a Raspberry Pi (thanks to Bob G1SAA for donating it) and a TNC-Pi at its heart, http://tnc-x.com/TNCPi.htm. The radio is a Kenwood TK-759E (752 variant) and it was all installed onsite on Thursday 29/05/2014.

2014-05-28 22.36.35

2014-05-28 22.37.03

Testing MB7UM Mk2 after installation shows very promising results with APRS beacons, both to and from MB7UM, being decoded in places they were not on the old hardware, quite a few stations have reported improvements in decoding and being decoded by MB7UM Mk2 over the original hardware.

2014-05-29 20.44.56

In the short term we have configured MB7UM Mk2’s callsign as ‘MB7UM-2’, this will allow a separate set of stats to be generated in APRS.fi which we can then compare to the original data (callsign) and see the changes within the stats APRS.fi generates http://aprs.fi/info/a/MB7UM-2

The original MB7UM (Mk1) had an add-on developed by Gavin M1BXF which beaconed telemetry data including temperature, 12v & 24v voltages and if the mains has failed.  The new MB7UM Mk2 will do the same but with an extra temperature sensor mounted outside the cabin to give addition temperature data. of the weather outside.  The new sensor suite has been the main development in the Mk2 system and comprises a PICAXE-20X2 chip reading the sensors and then communicating with the Pi over i2c. The hope is to document this and roll it out and make it available to anyone wishing to do something similar, so watch this space…


We also have a 3G modem connected to the Pi, in the short term it can run as an I-Gate but this might not always be configured, MB7PI at Barkway is the CRGs main APRS I-Gate for the moment, the 3G modem is there mainly for remote admin as we commission the setup so don’t worry if you notice MB7UM-2 stops gating APRS data.

2014-05-28 22.37.412014-05-28 22.39.27

Comments about any change in coverage, decode success, or lack of, would be very much welcome.


Gavin Nesbitt, M1BXF.

CRG Technical Coordinator

Chairman’s Note – 20/02/2013

I have some good news for the CRG.

A while ago, we were presented with a bill for business rates for the use of two sites we use by the site owners Arqiva. It was a considerable amount of money into 4 digits, something the CRG, as a voluntary non-profit group could ill afford.

Following discussions with Arqiva, they have graciously agreed to absorb those costs and will not be charging us “our share” of local authority business rates. The CRG is grateful for the kind benevolent offer made by Arqiva, which will enable us to remain on their sites, providing coverage for Cambridgeshire and surrounding areas, for both “pleasure” and “resilience” use.

Arqiva are showing continued support for amateur radio these days, as it is seen as a breeding ground for the next generation of engineers.

The CRG & Camb-Hams, together with the other societies in Cambridgeshire, are keen to promote the hobby among the younger generations. The Camb-Hams have already helped Cambridge105 run a number of “build a radio” sessions with local schools, and will be looking to do more in the future. The Cambridge University Wireless Society continues to promote amateur radio within the world of higher education, and also offers courses for those wishing to obtain all grades of licence.  Everybody on our repeaters no doubt now knows someone newly licensed due to such efforts.

As a group we are keen to support these initiatives as can be seen in the CRG Student Radio Loan Scheme. If you have any suggestions on how you think the CRG, or the Camb-Hams, could do more to encourage new people to the hobby, or you would like to get involved in any aspect mentioned above, then please contact us.

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