In my first few days in the Operations Room I learned that long-range, short-wave radio reception was dependent upon the state of the ionosphere, that region of the Earth's upper atmosphere, anywhere between 100kms and 1,000kms above the earth’s surface, ionised by radiation from the Sun. This was a subject that had not been covered during my training at RAF Locking. When radio signals are beamed upwards from a transmitting site at a shallow angle (typically between 15 and 20 degrees above the horizon) the ionosphere is able to reflect some of them back to the ground, rather like a mirror reflects light falling on it. The highest radio frequency signals, above about 25 MHz, pass right through the ionosphere and away into space; the lowest frequencies, below about 3Mhz, are completely absorbed. The trick was knowing, at any given time, which was the highest and which the lowest usable frequency.
The behaviour of the ionosphere depends, amongst other things, on how much radiation from the sun reaches the earth and that is determined by sun spots. Sunspots are temporary phenomena on the Sun's surface caused by natural fluctuation in the sun’s magnetic fields; they appear as spots darker than the surrounding areas and they come and go in a regular and largely predictable 11-year cycle. (Don’t go looking for them, or at them, without wearing suitable eye protection.) When there are few sun spots, the earth’s ionosphere is relatively inactive and short-wave reception becomes more difficult – certainly much less predictable. The ability of the ionosphere to reflect radio waves also varies according to the time of day, because when the line of transmission from transmitter to receiver is partly or entirely in darkness, the ionisation is naturally reduced.
Under the right conditions, the ionosphere reflects radio signals back to the ground at the same angle as they arrive. Having a GCE ‘O’ Level in trigonometry and knowing that radio waves are essentially the same as light waves, I could readily understand that. One up-and-down iteration, known colloquially as a 'hop', may then be repeated enabling the signals to be received by listeners potentially many thousands of miles beyond the transmitter. Part of the radio energy is absorbed in each hop and, eventually, the reflected signal becomes too small to be of any practical use. It was one of the tasks of the shift controller at Gangodawila to demand transmitter frequency changes as he deemed fit to achieve the best reception.
To optimise the incoming signal strength of each of the main CAF circuits, we tuned three different receivers to exactly the same frequency but connected each receiver to a different rhombic aerial beamed in a slightly different direction and in a slightly different location in our extensive antennae farm. This was known as triple-diversity reception. The theory was that signals being received at slightly different locations and from slightly different directions would not all fade, or be distorted by interference, at the same moment or to the same extent. Clever circuity, called multiplexes, combined those three incoming signals and then fed the resultant combined signal to the equipment which operated the teleprinters.
Conditions over CAF2, the UK-Sri Lanka radio circuit, were very poor throughout most of my time at Gangodawila because 1954 had been a ‘sun spot minimum’ year in the 11-year cycle but even during 1955 there was still very little solar activity. (In fact, years later it became clear that the 1954/55 sun spot minimum had been the lowest and longest lasting ever recorded.) To reach Sri Lanka, signals from UK had to make two hops through the ionosphere by day, and three by night. Each hop through the ionosphere not only degrades the strength but also the quality of the received radio signals – and that, in turn, makes it easier for other radio stations operating on adjacent frequencies to break through and cause considerable interference. From Spring 1955, we at Gangodawila were able to maintain reliable reception from the UK for only three to four hours out of every 24. That was a source of great worry to the RAF chiefs.
The BBC's short-wave audiences in South Asia and the Far East also, of course, suffered from poor reception caused by the low sun spot numbers. Accurate and daily reception reports were vital to the BBC engineers, not least because the Soviet and Chinese Governments, amongst others, deployed literally thousands of transmitters across the length and breadth of those vast countries to deliberately jam BBC and Voice of America programmes.
The BBC routinely received lots of gratuitous reception reports from ordinary listeners around the world who were using simple short-wave domestic radios. However, finding a particular station on a particular waveband at a specific time was always a bit hit and miss for those listeners. When I wrote off a letter to the BBC offering to send regular reception reports using our professional radios connected to our state-of-the-art highly directional aerials, they came back to me immediately, inviting me to monitor particular frequencies at specific times. I told Flight Lieutenant Gibbs, my Boss at the SCC at Negombo, what I was proposing to do and he gave me his blessing – and encouragement.
Reception conditions worsened as the sunspot count remained at historic low levels throughout Spring and Summer 1955. The BBC requests became more urgent and more specific and involved me in monitoring frequencies which were not currently in use but not reserved for other genuine broadcasters, to see if they were free of jamming. I was soon one of the first 'amateurs' to start reporting directly to BBC Headquarters in Bush House, at the BBC's request, on reception from their new Far East Relay station in Singapore which had been designed to provide more reliable reception over the whole of the Far East.
After a few weeks, the BBC asked me to start sending my messages by international cable from the local Cable & Wireless office in Colombo because air mail letters were no longer fast enough. Fortunately, I didn't have to pay for the cables because the BBC’s specific requests always came 'reply-paid'. In addition to plain language comments, my messages routinely contained internationally recognised groups of numbers which represented nothing more sinister than frequencies and reception conditions. My first cable included several dozen five-figure groups and caused quite a flutter when I handed it in at the Cable & Wireless office in Colombo. I think the counter clerk must have thought that I was sending a secret coded message and that was strictly forbidden. Eventually a senior official was called. When I explained to him what the text meant and pointed out that the BBC was the sole addressee, he approved my message for transmission. Thereafter my cables were accepted without question and not only were the BBC's incoming cables delivered to me personally at Gangodawila by Cable & Wireless motor-cycling messengers, but I was able to hand to the messenger my latest outgoing report. Such power and influence the BBC had.