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GB3EX The 70 cm repeater at Silverton north of Exeter
||Output: 430.950 MHz
||Input: 438.550 MHz
||CTCSS: 77 Hz
The original GB3EX located on Haldon Hill was closed down in January 2011 after over 20 years service, due to the site rent becoming unaffordable.
A suitable new site was identified, and although it potentially had excellent coverage, there was no infrastructure there, except for an agricultural building. The Exeter Repeater Group was faced with a number of technical challenges, such as providing power sources.
Note that as at 10th October, GB3EX is temporarily suffering from reduced sensitivity & output power.
Access to the site is limited at present, but remedial work will start ASAP>
It was anticipated that there would be a long delay in getting Notice of Variation (NOV) approval from OFCOM but to our great surprise we received the licence 3 weeks after submitting the application; grateful thanks to the ETCC and OFCOM for excellent work.
This repeater came on air on 31 March 2014 after being built by Exeter Amateur Radio Society members John G8XQQ, Pete G3ZVI, Keith G7NBU and Skip 2E0TGT
The original GB3EX used 1.6MHz split, for the new GB3EX we have opted for 7.6MHz split. This is technically much less complicated in terms of filtering and also avoids the use of 433/434MHz causing interference to LPD’s.
Pete G3ZVI wrote a fascinating article for the April 2015 edition of RSGB's RadCom magazine, in which he says that the construction was a great example of teamwork.
The repeater is mounted in a plastic box and has been elegantly and expertly designed and built by John G8XQQ.
GB3EX is co-sited with a RAYNET repeater. There are three transceivers (2 x UHF & 1 x VHF). RAYNET operation is in-band UHF repeat and crossband to 2 metres. Remote DTMF management is used to switch off GB3EX and switch on the RAYNET system.
Since there was no mains electricity on site, battery power and solar panels are used. We found that Tait 8000 series mobiles with the control head removed had the lowest standby current, being commercial equipment they are also very reliable.
In June 2015 a telemetry encoder designed and built by Nick M0NRJ was added to the repeater in order to monitor the battery state.
GB3EW the VHF repeater in Exeter
||Output: 145.6125 MHz
||Input: 145.0125 MHz
||CTCSS: 77 Hz
GB3EW first went on the air on 25/07/08 using an FT7800 as the transmitter and an Icom 24G as the receiver. Filtering comprised two “ Beer Barrel” cavities that later went to GB3SW.
Initial operation was with two antennas .
A Vertex 5000 was fitted 15/08/08.
A Circulator was fitted 15/05/09 which allowed single antenna working.
The loan cavities were replaced 10/06/09.
Tait 800 Series II was installed 20/11/10 (rehomed from South West Ambulance Trust).
While G8XQQ’s QTH allowed good coverage of the city of Exeter, wider area was not brilliant. On the top of Stoke Hill was a Roman signal station on the highest point around the city. Located there is a riding stable; on the top of one of the stable blocks is an abandoned ROC cabin. We used one of the fields owned by the stable for a HF field weekend. Discussions with the site owner lead to an investigation of the ROC cabin; while it was an excellent prospect, it was clear that a lot of work was required to make it habitable.
Furthermore the roof of the stable was leaking. We agreed with the owner that we would make the roof good while refurbishing the cabin. We had to call in a professional contractor to fix the main roof, which did not come cheap. Work on the actual cabin was carried out by our own team. A 20 foot mast was clamped to the cabin wall and topped by a professional grade 3dBd gain collinear manufactured by Communication Aerials.
GB3EW was moved into place on 30th October 2016, no mean feat since the repeater (Tait T800) and the cavities were really heavy, everything having to be hauled up a single ladder.
GB7EW The UHF DMR repeater in Exeter
||Output: 439.525 MHz
||Input: 430.525 MHz
||Colour Code: 3
||QTHR: Co-sited with GB3EW
Operational 5th October 2020. Motorola DR3000.
Currently operational for local use (no internet connection). When connectivity is achieved, the repeater will initially be part of the South West Cluster
Some Thoughts on Repeater Performance and the Isolation Between Receiver and Transmitter
Vertical versus horizontal antenna separation