This article on our GB7PC DMR Repeater on the South West Cluster is reproduced from the April 2024 edition of the PARC GB2GM Newsletter, by kind permission of the author, Terry G4CDY.
A Digital Repeater for Poldhu
By Terry G4CDY
(April 2024)
Since the beginning of April, we have had a full duplex DMR repeater operating from the clubhouse at Poldhu. The repeater GB7PC is part of the comprehensive South West Cluster which provides linked VHF and UHF coverage as far east as Hampshire, employing 19 repeaters.
The Poldhu repeater was proposed and is now managed by Chris M0TIK, the installation being carried out by Dave Wright G3XOU. The South West Cluster was keen to improve its coverage in West Cornwall, the Lizard and if possible as far west as the Scillies. They and particularly Dave, have kindly loaned us the actual repeater, the cavities and the aerial for a period of 12 months with the possibility of us purchasing it in the future.
Dave came down from Tavistock and spent a long day installing the system. All went smoothly with the exception of linking to the Internet via our router. It would not connect to the South West Cluster’s server! Fortunately, Dave had taken the precaution of bringing a 4G radio modem which cured the problem, but we do need to investigate why it would not work with the club’s Internet connection.
All the details of GB7PC can be found on QRZ.COM but are summarised below:
| Call Sign: | GB7PC |
| DMR ID: | 234119 |
| Repeater Keeper: | G3XOU, to become M0TIK |
| Frequency: | RV48 (TX 145.600 MHz, RX145.00 MHz) |
| Power: | 13.6 dBW (or 22.9 W) ERP |
| Antenna: | Diamond X-50 at 10m AGL (see photo) |
| Duplexer: | 4 off temperature compensated cavities AFL SC-140-2N |
| DMR Colour Code: | 7 |
| Timeslots: | One for local and one for DX South West Cluster, Website: http://thesouthwestcluster.co.uk (new tab) |
| Operational since: | 3 April 2024 |
DMR is a proprietary professional digital radio technology originated by Motorola in the USA. Other technologies such as DSTAR, Fusion and M17 are amateur radio standards encouraged by radio manufacturers. They all allow direct radio contacts via the local repeater but also links to a network of other repeaters and stations by way of the Internet. For example using a hand held radio in Hayle one could talk to a similar individual in Sydney, Australia.
One unique feature of DWR is that it provides two independent voice channels in one 12.5 KHz radio channel. With the SW Cluster repeaters, one is for local use and the other for linking. The speech is not quite BBC quality but it is very acceptable!
There is a bit of a learning gap when one first becomes involved with DMR, such as a great deal of of new terms like colour code, timeslot, zone, contact and code plug. Incidentally, a code plug is simply a small file which contains details of repeaters and simplex setups that can be installed in the radio. One can write one’s own from scratch, obtain one from the South West Cluster website or even have it installed by the seller of the radio when purchased.
The first contact through GB7PC was made by Bob G0FGX and several club members are already using it. These include Jim G8GLL, Richard G4WKW, Chris M0TIK and myself G4CDY.
In the past there has been a 2 metre beacon GB3SSS, beaming towards the west from the Poldhu site but it has been off the air for some time. It is the intention to reinstall this beacon and David has very kindly loaned us an extra cavity to act as a filter on a new beacon to prevent the repeater from being desensitised by its phase noise.
DMR is the cheapest of all the digital radio technology and 5 watt handheld transceivers such are available for less than £90 from most of the ham radio emporium. Don’t forget to ask about a code plug!
Notes by Richard G4WKW
Since this article was written, the repeater has undergone some upgrades, including a good connection to our Internet router in the Maconi Centre (so it no longer uses a 4G mobile data connection).
Following feedback, I have altered the power information for the repeater from the original “13.8dbW EIRP (approx. 25 watts)” in Terry’s article to the correct value of “3.6 dBW (or 22.9 W) ERP”, as provided by Dave G3XOU, the repeater keeper, who set everything up and owns the equipment.
The repeater also has undergone a fair bit of testing and use, with successful contacts being made via the South West Cluster between the Isles of Scilly and Basingstoke (via GB7PC and the recent GB7CW repeater in Winchester) !!!
An update on the cost of a DMR radio. I have personally bought a number of them from different vendors, but my best purchase was for a Boefeng DM-1701 at £33 delivered to my UK address! They are normally about £40 from that Chinese vendor and make excellent 5W dual band (2m & 70cm) DMR and FM radios with the OpenGD77 firmware installed. Unlike the native firmware, with OpenGD77 firmware they can whole the complete Worldwide DMR Contacts database (for everyone active in the last year), which is something over 270,000 contacts at the moment!
If anyone is considering buying a DMR radio, or upgrading and old one, I would be very happy to help and advice you and install an up-to-date codeplug and DMR Contacts Database on your radio for you.
We will be publishing a page with information on the GB7PC Repeater later.
The number of repeaters on the South West Cluster is constantly evolving and has increased since the 19 repeaters that Terry refered to (there are currently 29 of them in the list, although 4 are off-air, with one of those temporarily, due to a site move).
South West Cluster Website: http://thesouthwestcluster.co.uk (new tab)