GB7BK is co-located with GB3RD at Aldworth in Berkshire, on the Downs to the west of Reading. The picture shows the joint equipment cabinet – GB7BK is the unit labelled Motorola.

Transmit Frequency439.7375MHz
Receive Frequency430.7375MHz
AntennaStacked dipoles
ERP14dBW (25W)
Access methodColour code 3
Base StationMotorola DR3000
CoverageClick here to view predicted coverage (60km). Plot provided by the ETCC.

On the 12th September 2015, the first DMR (Digital Mobile Radio) repeater operated by the TVRG became operational. This is a UHF repeater with the callsign GB7BK and is co-sited with the VHF analogue repeater GB3RD on a site about 11 miles WNW of Reading town centre.

The philosophy with DMR repeaters is that they are part of a network linked by the internet, in this case the DV Scotland Phoenix network. The Phoenix network was connected to the world-wide MMR MARC network. MARC stands for Motorola Amateur Radio Club,who originated the concept. The subject of DMR is quite involved and information can be gleaned from anumber of sources.

A basic overview:-

A DMR transmission occupies a 12.5kHz bandwidth channel but can carry two simultaneous separate transmissions, thus being spectrum efficient. The transmissions uses two timeslots to achieve this. The DV Scotland Phoenix repeaters are all connected to the internet and this allows connection to the various talkgroups. Talkgroups are effectively virtual places where users can go to and talk to other users on the same talkgroup.

GB7BK offers access to following talkgroups on the two timeslots. These are the same for most Phoenix repeaters but a few have additional local geographical talkgroups. For a complete list and latest updates please see DV Scotland Phoenix

The following table shows the talkgroups that can be accessed from GB7BK. Those which are shown in red are User Activated (UA) talkgroups. Those shown in black are not UA and are sometimes referred to as “Always On”. This means that if there is a signal on one of these talkgroups, the audio will be relayed through GB7BK., bearing in mind you can only hear one talkgroup on a timeslot at any one time.

In contrast you will not hear audio from any of the UA talkgroups unless the particular talkgroup has been activated. To activate a UA talkgroup, you simply need to transmit on that talkgroup. Then, as soon as there is a break in the transmission of the UA talkgroup any subsequent audio will then be heard. The concept of UA talkgroups can be confusing and I hope the description above has been of some help.

Please always bear in mind that when you use the “calling channel” talkgroups such as TG1, TG2, TG13 and TG235, you will be activating a large number of repeaters when you probably only need to use two in most cases. That is why you should move to a UA talkgroup once you have established contact.

If you want to see what is happening in real time, then go to the DV Scotland Phoenix dashboard here

How GB7BK came about:-

IIn late 2013 the first DMR repeater in the south of the U.K. became operational, which was GB7NS at Caterham in Surrey. This could be worked from parts of Reading and the surrounding area. Some amateurs obtained DMR radios and the usage of DMR increased considerably throughout 2014. The number of DMR repeaters increased dramatically especially in the Kent, Essex and London area.

TVRG considered the possibility of putting on air a DMR repeater but decided to wait and see how the system evolved. At a meeting in January 2015 it was decided to put an application to OFCOM for a DMR repeater (GB7RU) located at a new site in Tilehurst, west Reading. This was to be co-sited with a new analogue 70cm repeater, GB3RU. In April we received the go ahead for GB3RU but learnt that GB7RU had be rejected because of the frequency requested. We then suggested other frequencies but these had to all be in the same DVU frequency band. Eventually we were told that the Primary User (MOD) would not permit any local frequencies to be used in the allocation used for U.K. DMR repeaters. This meant we had to look for a new site.

By far the most difficult part of putting any repeater on air is to find a suitable site at an affordable price. We also had to consider that the proposed site should be sufficiently far away from MOD sites otherwise the frequency would be rejected again. This ruled out all of the town of Reading and its suburbs. Any site to the East of Reading would overlap too much with GB7WL and GB7NS. We therefore considered the existing GB3RD site on the Berkshire Downs. This wasn’t ideal as it wouldn’t cover Reading that well and we wouldn’t be able to have a high antenna because the GB3RD antenna is mounted on a pole not a mast. There could be also problems with internet access from such a remote site, as proved to be the case.

However, we decided to go-ahead and put in the application to OFCOM. We changed the callsign from GB7RU (Reading UHF) to GB7BK (Berkshire) as this was more sensible for the site which is 11 miles away from Reading.

Approval was received and the repeater became operational in September 2015. Coverage was OK and more or less in line with predicted coverage map . We obtained internet access using a 3G wireless router but this proved to be erratic and unsatisfactory. Subsequently, we have been given permission to use the site owner’s broadband which has improved matters considerably. However, it must be remembered that the site is fairly remote and outages occur from time to time.