I quickly learned that long range short wave reception was dependent upon the state of the ionosphere, the region of the Earth's upper atmosphere ionised by radiation from the Sun. When short wave radio signals are beamed upwards from the transmitting site at a shallow angle (typically between 15 and 20 degrees above the horizon) the ionosphere is able to reflect them back to the ground rather like a mirror reflects light falling on it. The highest radio frequency signals pass right through the ionosphere and away into space; the lowest frequencies are completely absorbed.
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. The up and down sequence, known colloquially as a 'hop', may then be repeated enabling the signals to be received by listeners potentially many thousands of miles beyond the Earth's horizon. Part of the radio energy is absorbed by the ionosphere at each hop and, eventually, the reflected signals become too small to be of any practical use. The trick was to find the right frequency for usable signals to be reflected back to the receivers on the ground and it was the day-to-day task of the controller at Gangodawila to demand transmitter frequency changes as he deemed fit to achieve that.
The behaviour of the ionosphere depends, amongst many other things, on how much radiation from the sun there is and that in turn is determined by sun spots. Sun spots come and go in a regular and largely predictable 11-year cycle. When there are few sun spots, the 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 is partly or entirely in darkness, the ionisation is reduced.
Throughout most of my time at Gangodawila conditions over the UK-Sri Lanka radio circuit were very poor because 1954 had been a ‘sun spot minimum’ year in the 11-year cycle and throughout 1955 there was very little solar activity. The signals from UK had to make two hops through the ionosphere by day, and three by night, to reach Sri Lanka. 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 radio stations operating on adjacent frequencies to break through and cause considerable interference. From Spring 1955, as the sun spots very gradually increased from what had been the lowest levels ever recorded since records began, we at Gangodawila were able to maintain reliable reception from the UK for only two to three hours out of every 24. That was a source of great worry to the Air Force chiefs.
To optimise the signal strength of each of the main CAF circuits, we tuned three different receivers to the same frequency and connected each receiver to a rhombic aerial beamed in a slightly different direction and in a slightly different location in our antennae farm. This was known as triple-diversity reception. The theory was that signals being received from slightly different directions and locations would not all fade or be distorted by interference at the same moment or to the same extent. Clever circuity (multiplexes) combined the three incoming signals and then fed the resultant signal to the equipment which operated the teleprinters.
The BBC's short wave audiences in South Asia and the Far East also, of course, suffered from bad reception caused by the low sun spot numbers. Accurate and timely 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 broadcast stations.
The BBC received lots of gratuitous reception reports from ordinary listeners around the world who were using ordinary short-wave domestic radios, but 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 state-of-the-art highly directional aerials, they came back to me immediately, asking me to monitor particular frequencies at specific times. I told Flight Lieutenant Gibbs, my Boss at the SCC at Negombo, what I was doing and he gave me his blessing - and encouragement.
The two Tony's meet up again for the first time since we were about 4 years old. Of course, we wouldn't pose in that friendly fashion these days in case it was misconstrued!!
On 3 March 1955 I wrote in my diary: "One of the greatest coincidences in my life occurred today. Two chaps were posted here from Negombo - a Junior Technician and an SAC, both telegraphists. While they were having dinner I noticed on his kitbag that the Junior Technician's name was Cullen. I didn't think much about it at the time but later, when I heard him say that his father was a Prison Officer, I realised then that he was 'Little Tony' Cullen." He had joined the RAF as a Boy Entrant when he was 15 years old. We had been playmates in 1938-39 when our Dads were Prison Officers at Strangeways Prison and we hadn't met or heard of each other since then. (That story is here. Tony knew about the breaking of windows of some empty married quarters but his version of the story was that I had done the tapping and he had merely watched!)
Reception conditions worsened as the sunspot count remained at historic low levels throughout Summer 1955. The BBC requests became more urgent and more specific and involved me in monitoring frequencies which were not currently in use to see if they were free of jamming and not in use by other genuine broadcasters. I was soon one of the first 'amateurs' to start reporting directly to Bush House, at the BBC's request, on reception from the BBC's new Far East Relay station in Singapore which was designed to provide more reliable reception over the whole of the Far East. In addition to plain language comments, my messages routinely contained internationally recognised five-figure groups which represented nothing more sinister than frequencies and reception conditions - and one day that caused me a minor problem.
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 requests always came 'reply-paid'. My first cable 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 message and that was strictly forbidden. Eventually a senior official was called. When I explained 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 the BBC's incoming cables were delivered to me personally at Gangodawila by Cable & Wireless messengers and I was able to hand to the messenger my latest report. Such power and influence the BBC had.