Sun Spots and Other Elevated Topics!

During the UK football season I used to re-transmit the BBC General Overseas Service football results programme over our VHF transmitter. My excuse was that the transmitter needed to be tested at least once a week!

1955 was a year of very low sun spot activity and for most of my time at Gango conditions over the UK - Ceylon circuit were very poor. In the 1950s short wave propagation was still a bit of a mystery to amateurs and professionals alike. I started seriously studying the subject with the help of some very friendly BBC engineers in Bush House, London. In return, I sent regular reception reports to the BBC overseas' HQ in Bush House. When the BBC started using its Far East Relay from Singapore, I was one of the first 'amateurs' to start reporting on reception from those transmitters. Flight Lieutenant Gibbs, the Signals Officer, knew what I was doing and gave me his blessing.

Briefly, low sun spot activity means that the lower and more congested frequencies have to be used for long range circuits instead of the higher and less congested frequencies. Congestion equals interference from other users and that interference, QRM, played havoc with teleprinter reception. For CAF2 from UK we typically used frequencies in the 15MHZ range for all-daylight paths and frequencies as low as 5MHZ for all-night paths. Because the radio paths between UK and Ceylon, great circles, passed through at least 5 time zones, for about half of any 24 hour period the reception paths were day-night. In the first half of 1955 we could maintain reliable reception for only 2 to 3 hours out of every 24. This was a source of great worry to the Air Force chiefs and so CAF40 became very important. It was up to the watch keeper at Gango to decide when the UK transmitters needed to be retuned to a different frequency to get better reception.

Half way through my tour, when I volunteered to become a watch keeper, I discovered that adventurous use of the sun spot prediction tables that were provided for us every month, and regular monitoring of the technical quality of direct BBC General Overseas Service transmissions from UK to South Asia and relays from the BBC Singapore station, enabled us to choose frequencies that kept us 'in traffic' for 8 to 10 hours per day. I found that on good ionospheric days in the northern hemisphere summer months we could use frequencies as high as 21MHZ for a few hours starting at 1100 local time and then reception from UK was perfect. Reception from UK had to be by means of at least 2 hops through the ionosphere and at night on the lowest frequencies three hops were needed. By contrast, conditions on CAF6 from Singapore were always excellent because the distance meant that the signals had to make only a single hop through the ionosphere. The circuit to Melbourne was also extremely reliable in spite of the low sun spot numbers, often over 21 hours per day in traffic. Although it was long range and two hops, there was relatively little other radio traffic on the frequencies we needed to use and so we had little trouble from QRM (QRM = interference from non-natural sources.)

We had to tune our SSB (single side band) receivers by the sound of the single sideband tones alone - experience taught us to recognise when the receiver was exactly in tune. The operators at the distant transmitter stations needed up to 20 minutes to change frequency but we could tune our receivers in a matter of 10 seconds or so. We had crystal-controlled wave-meters to help us tune our receivers to the precise frequency of the distant transmitter but, with practice, we could do it without using the wave-meters. For each circuit we aimed to tune three receivers to each frequency; each receiver was connected to a different directional rhombic aerial; each aerial had a slightly different 'beam', ie it was aimed in a slightly different direction. Initially it surprised me to discover that Colombo was on a Great Circle bearing of approximately 095 degrees from UK and that the radio signal passed over the Soviet Union. Since then I have always found Great Circle maps fascinating for offering a different perspective on the Earth. Connecting three aerials and three receivers in this manner was known as triple diversity reception. The theory was that if the signal from one aerial was fading or distorted due to atmospheric conditions, it was unlikely that it would be fading at exactly the same time from the other aerials. Circuits within the system evened out the signals and discarded distorted signals. It was a very clever technique and for most of the time it worked very well. We fed the data outputs from all our receivers down a vast array of secure landlines to the Centre at Negombo. (NB In those days we called antennae - aerials.)

Each of our three main SSB circuits provided six parallel data channels. Normally five of the channels were encrypted and at Gango we could not read the data. Channel one was always unencrypted and was used for communications between ourselves and the controller in the Signals Control Centre at Negombo, and between him and the UK controller. We at Gango used channel one constantly instead of using the far from reliable telephone system and so I had to learn to use a teleprinter. Fortunately teleprinter keyboards were very similar to typewriter keyboards and so the typing skills I learned, by trial and error, stood me in good stead for the rest of my life.

For those rare occasions when the landlines connecting the output of our receivers to Negombo were out of action, we had a single medium-powered VHF transmitter which fed an aerial at the top of a large tower. We always called this tower Snow White, but no-one seemed to know why. We then fed all the receiver outputs down a single channel on the VHF transmitter - I knew how to connect it up but the technicalities were beyond me. During the UK football season I used to re-transmit the BBC General Overseas Service football results programme over our VHF transmitter. My excuse was that the transmitter needed to be tested at least once a week! All the RAF units in Ceylon, apart from China Bay in the far north, could receive this service. The chaps were all very grateful because few of them, if any, had short wave receivers capable of receiving the BBC in their living accommodation. It was obviously illegal but no-one ever complained!

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