The Secrets of GBR by Jim Harris G4DRV

In the list of Contents for the November Vital Spark, the first item was ‘Tributes to GBR’. How many people would have guessed that it was a real callsign and GBR has some interesting statistics? For a long time it was one of the few, if not the only, transmitters running at 1,000kW. It was probably built just before the WWII. It operates on a frequency of 16kHz, no its not a misprint, it really is kHz not Mhz.

The power is developed by several banks of water cooled valves connected in parallel with a correspondingly low output impedance. This was nice and convenient for matching because the aerial system (although it was probably some 5 km long) was electrically very short and very very low and hence the impedance was also very low.

So who requires a transmitter of that power at that frequency. It won’t be giving away any state secrets to reveal that it is capable of being received by a submarine just below the surface in the China Sea at almost any time of the day at any time during the sunspot cycle. The trouble is that with such a low rf it is only capable of slow speed morse or digital data but as CW operators will tell you, morse can convey a lot in a very short space of time with the right choice of abbreviations or code.

For its first few years it was powered from the normal electricity supply which meant that people in the nearby town could easily read the morse on dips in the household lighting. By the 1950’s it was powered from a 2MW diesel generator, that way the public would have more difficulty in reading the transmissions but that didn’t fool us, they could still hear it on the normal radios.

Where is this transmitter? It’s just South of Rugby in Warwickshire on the West side of the motorway. It is on the same site as the MSF standard frequency transmitters. The masts can hardly be missed, there are 12 and they are no less than 820 feet high and that makes them more than half as tall again as Beachy Head!  One afternoon, the author’s heavily pregnant wife went missing, she had been taken up to the top of a mast by the line gang so she could see the view of 5 shire counties of Leicester, Warwick, Northampton, Derby and Nottingham.

This discovery was bad enough but then the father-to-be was told that the first AND the last 20 feet had to be climbed without the aid of the open sided lift that conveyed her for the middle bit! Guess which of the partners felt airsick and aged twenty years in as many seconds? You’ve guessed, it wasn’t the wife. When working in the vicinity of GBR it wasn’t necessary to have an inspection lamp connected to the mains because a fluorescent light would operate at full brilliance when the carrier was being transmitted, even though the tube was not connected to anything.

However the flashing light during the morse was inclined to make the eyes go funny!

This phenomenon may have given the inspiration to one person in nearby Daventry who had the idea that he could light his house from the local BBC transmitter. He connected up the wire of the chestnut paling fence into a loop and adjusted it to give suitable coupling to his household lighting, it was switched to the right level by series capacitors. Unfortunately the authorities decided he was cheating and he was duly convicted of stealing the electricity belonging to the Post Office. With the passage of time it is possible that the ‘owner’ has not been correctly remembered BUT one thing for certain was that the ownership was not deemed to be the BBC. Now this begs some interesting questions;

1. When does it cease to belong to the BBC?

2. When or where can we be allowed to pinch a little bit in order to receive the programmes?

P.S. Would you please give my apologies for the missing the AGM.  Unfortunately my duties as RSGB Liaison Officer keep me away. .cp255 ‘GBR’ – A not so well known callsign.

Jim Harris – G4DRV. May 1995.

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