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.

BandModeLocationOutputStatusLast Updated
GB3PE2mVoiceThorney Toll, Peterborough145.675 MHzOperational
GB3PI2mVoiceBarkway145.750 MHzOperational with temporary repeater HW
PA fail in normal HW
GB3PY70cmVoiceMadingley433.200 MHzOperational
GB3PX6mVoiceBarkway50.780 MHzReduced Power08/06/14
GB3PV23cmD/ATVMadingley1316.000 MHzOperational
GB3PS23cmVoice / BeaconBarkway1297.075 MHzOffline10/11/14
GB7PI70cmD-STARBarkway439.9125 MHzGateway offline due to PC PSU issue, local use only25/08/15
GB7PT70cmFSK 9K6 DigitalBarkway439.7125 MHzOffline16/04/15
MB7UM2m2m APRS DigiMadingley144.800 MHzOperational
MB7UPI2m2m APRS Digi + iGateBarkway144.800 MHzOffline (PC PSU issue)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

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.

GB3PE Update – 27th October 2012

Last week I visited site at Thorney Toll to change out the repeater controller for one that improved the audio quality through the repeater, and to give an inter-over indication.

It is still planned to change to a G1YFF logic in the future, though Jake has other projects to complete first, and this one will be his first FX5000 integration – not just plug in the back of the box, a proper connection into the repeater control module.

For now, I have swapped out the recalcitrant Zetron 37 for a far far better Zetron 38Max that I have purchased and loaned to the CRG for the job.

The first thing you noticed is the quality of the through audio – it’s much much better (couldn’t be any worse!), being fuller and far louder. If anything, it’s a little more “punchy” than it is when the FX5000 is placed in it’s own talk-through mode without the controller plugged in. It’s certainly easy on the ear when mobile.

And then there’s the “K”. I had considered using trailing pips, but that may cause issues with the Echolink that Andy G6OHM kindly provides for GB3PE.

When you drop carrier, you’ll notice a little squech tail. I have set the Zetron to do this so weak signals chopping in/out don’t send K K K K K K as they’re falling out (one of the reasons why the old box didn’t have a pip was it sending the pip the moment that CTCSS decode was lost!). People who have radios that provide a “reverse tone burst” when they de-key will have no squelch tail. (A “reverse tone burst” is a period of around 300mS where the transmitter remains keyed after the PTT is released, with NO CTCSS on the signal – it allows the repeater to close it’s input before the signal is lost, so there’s no squelch crash. It’s a feature on just about every PMR radio, yet only a few ham rigs do it).

Echolink is working correctly via GB3PE (when Andy has it switched on – see the CRG homepage for the status indicator). There were a few issues initially, but Andy has resolved those now. We still hope that at some point in the future we’ll be able to have Echolink, and other facilities like IRLP or AllStarLink on GB3PE 24/7.

MB7IPE – our new APRS iGate, built up by Gavin M1BXF, went on site too. At first there was a problem where PE’s TX was getting back into the RX and keeping the repeater open, but appearing like a very weak signal. Turning MB7IPE off made it go away. After some searching and testing, it was found that the power cable for the APRS unit was pretty well a 1/2wave at 2m, and causing some kind of parasitic re-radiation into the RX. Chopping it to “just long enough” cured the issue, as well as winding the aerial feeder into a choke, just in case.

The other issue I found was MB7IPE causing de-sense to PE’s input, even with a filter inline. Something that didn’t appear on any bench tests. So it was removed back to my workshop for tests & mods where necessary. With PE’s input only 275KHz away, it was going to be a problem! However, following a little head scratching, and a good suggestion by Rob M0VFC, I have added a relay into the PTT line, which is energised by the “COR” signal from the repeater (Carrier Operated Relay). This means that MB7IPE’s TX will be disabled when there is a valid signal on the input of GB3PE. I had hoped to use COR to control the DCD in the TNC, which would allow it to buffer packets until the coast was clear to transmit. Sadly the TNC-X that is used for the APRS digi does its DCD in software, and there are no hardware means of providing this.

I hope to get MB7IPE back on site early next week (w/c 29th Oct).

Again, at some stage in the future, we hope to have internet connectivity for our systems on site, which will enable the iGate for MB7IPE.

What we did find, during its short tenure on site last week, is that it can hear MB7PI, and MB7PI can hear it, which puts it in direct contact with our main iGate at Barkway.

Coming up next is the CRG AGM on November 28th at The Sun, Waterbeach, Cambs. All welcome (only paid up CRG members can vote) – I look forward to seeing you there!

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