BBRC visit to RSGB NRC and Bletchley Park

On Saturday 22 April 2023 five club members, Dave Lomas G4XOW, Gabor Harmath M0LPZ, Chris Rowlands G5CTH, Greg Head G4EBY and Charlie Mitchell G0SKA met at Bletchley Park for an arranged visit to the RSGB National Radio Centre, which is accessed via the Bletchley Park Museum (free entry for RSGB members).

First stop, to beat the crowds, was the NRC, where we were welcomed by the station manager Martyn Baker G0GMB, who had come in especially. Martyn took this photo of our party and said he would submit it to Radcom.

Pictured, left to right, Chris, NRC volunteer Ed G3ZLX, Charlie, Dave, Gabor and Greg

We were then shown round the impressive station and shown how the various rigs worked. The main station comprised a Flex 6600 driving a Gemini linear to 400 watts and the antenna is a 3 element Steppir at about 12 metres.

An HF contest was on so we were easily able to make a few QSOs into Eastern Europe. The contest exchange was RS report and operator’s age. G0SKA was quite staggered when the ages of the other contest stations were 38, 25, 17, 16 and almost unbelievably 9.   All were very competent contest operators.

Greg was especially impressed with the satellite station working on 10 Ghz through the QO100 geostationary satellite on all modes using just two small Sky satellite dishes. The equipment was modest with an FT817 on 2m to drive a transverter and could easily be set up by the club for operation from Farnham Common Village Hall. This would give members and visitors a good experience of operating real radio without the problems of HF noise or VHF low activity.

We all then enjoyed some excellent fish and chips in the Hut cafe before moving on to the museum and enjoying a fairly quick look round some of the other huts.

Next to come was a visit to the fascinating National Computer Museum next door.

After looking round exhibits of many historic computers and calculators we moved on to the codebreaking section.

In the first room, which contained  a huge bank of AR88 receivers and a copy of  the original  “Tunny” computer the volunteer gave an excellent (and as clear as is possible with such a complex subject)  explanation of how coded messages were received as RTTY and transposed into letters/numbers.

Decoding the text was highly difficult as the analysts at Bletchley Park had never even seen the kind of encoding machine used by the Germans. Enter Bill Tutte a Cambridge mathematician who after some months managed to decode two messages. He was aided by the fact that the operator who had sent both messages had broken the cardinal rule of using a fresh 12 character key code for each message. He used the same code for encoding both messages. (For those interested there is a summary of his methods on his Wikipedia biography. ) He then explained the development of the Tunny computer and the “Heath Robinson” punched tape comparator. This whole process even after its development still took around a day or two to decode each message, so many messages were decoded too late to be of major use. Clearly an increase in speed of decoding was essential. The answer came in the next room.

In this  room  was a working copy of  Colossus, the replacement for Tunny – this was a more advanced electronic computer which cut down the decoding time to hours and enabled much critical real time information to be communicated to military commanders within minutes. This had a decisive effect on the outcome of the war.

All in all we agreed it was almost enjoyable day and the only problem was there was not enough time to see everything.

Charlie, G0SKA

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