Early Radio Research
Partial Reflections Experiments
Early research at the Radio Physics Laboratory (RPL) focused on auroral disturbances, partial reflections experiments and whistlers. The early work on auroral disturbances was important because of its effects on radio propagation. The Aurora Borealis, or Northern Lights, are caused by the emission of electrically charged particles (electrons and protons) from the sun. As these particles pass through the earth's atmosphere they cause the gases to become luminescent, a phenomenon not unlike passing electricity through a neon sign. Auroral disturbances affect radio propagation to a very considerable extent. The problem is acute in Canada, since auroral disturbances occur most frequently along a roughly circular zone which is centred on the geomagnetic pole. The research at the RPL took the form of fundamental investigations into this phenomenon and its causes, together with the assembly of practical data for forecasting radio propagation conditions. In the early days, physicists from the RPL were posted at the University of Saskatchewan where they worked on ionospheric and geomagnetic problems related to the auroral disturbances. Research work and observations were also undertaken at Ottawa, Saskatoon, and at Resolute Bay on Cornwallis Island in Canada's Arctic archipelago.
A set of prediction tables, especially designed for the Polar regions, was computed by Defence Research Board staff as the result of a request from the Royal Canadian Navy. These tables, were used in the Service, for predicting the best frequencies for communications between various points, especially in the auroral zone. In addition, the "oblique programme" was initiated to check the relationship between vertical and oblique frequencies. During the war, this relationship was computed on a purely empirical basis with results which were not entirely satisfactory. The Defence Research Board, by operating communications between Ottawa and Saskatoon, was able to provide a more scientific basis for frequency selection.
Closely connected with the auroral research programme were the ionospheric propagation studies, which began by conducting partial reflections experiments. The chief instrument used in these studies was a vertical sounder which is an electrical apparatus capable of transmitting a radio impulse straight upwards, of receiving and timing the echo of this impulse on the ground, and then of calculating from this the height of the reflecting ionospheric layer and the critical value of the frequency which just penetrates the layer and is not returned to earth. This type of vertical sounder was used extensively in fundamental research at RPL, while at the various observer stations in Canada which were operated by the Department of Transport for the Defence Research Board, observations were taken every fifteen minutes around the clock. In addition to ionospheric height and critical frequency recordings, radio, weather, magnetic, auroral and other special measurements were taken as part of the world-wide participation in the International Geophysical Year between July 1957 and December 1958. To support this programme, Canada arranged for ten small portable sounding equipments to be sited throughout the country to give coverage from Alert to Ottawa and from coast to coast.
More fundamental research was done at RPL on radio astronomy. The emphasis was on ionospheric investigation rather than on astronomical or cosmological studies because it was felt that the ionospheric research had a more direct bearing on radio communications. To assist in this work RPL had a twenty-foot radio telescope for use at five hundred megahertz, installed at the 'Quiet Site' north-west of the Shirleys Bay site.. This radio telescope employed an antenna which focused radio waves so that they could be picked up by a sensitive radio receiver. The main use of the telescope was to study the relationship between the sun and ionospheric disturbances. In addition to the twenty-foot radio telescope, there were several smaller equipments at RPL for use in the fifty megahertz range for interferometric studies of extragalactic sources such as Cassiopeia A and Cygnus A.
The work on radio astronomy may be broken down into three main types. First there was the monitoring of cosmic noise to measure ionospheric absorption. Secondly there was the monitoring from a discreet source in order to measure star scintillations and to obtain data on the fine-scale structure of the ionosphere. Lastly, there was the monitoring of solar noise as a measure of solar activity, and the correlation of this with other ionospheric and geophysical data obtained in the auroral zone.
Another study which was fundamental to work being done at RPL was on "Whistlers". Whistlers are disturbances observed in the VLF band (3-30 kHz) which are caused by lightning flashes. They vary in frequency and last for about one second. Lightning sends out radio waves which can be detected over a very wide band, from frequencies well below audibility to the very high frequency range. Some of these waves enter the ionosphere where they travel relatively slowly and where they are guided along the lines of force of the earth's magnetic field. The waves then follow the force lines up through the outer atmosphere, rising to heights of many thousands of miles, then cross the equator and drop back to earth at the far end of the force lines in the opposite hemisphere. The importance of this discovery was that it was the only method which was available to give information of the magnetic field and electron density in the outer reaches of the ionosphere, 500 to 1,000 miles above the surface of the earth.
Another aspect of research at RPL was the work being done on tropospheric scatter propagation. This study was being conducted in the 45 and 500 megacycles bands and research indicated that those frequencies could be used for radio communications up to ranges of 400 miles. Large transmitters and huge antennae would have been required for communications in these frequencies.
Goodspeed, Captain D.J. A History of The Defence Research Board of Canada. Ottawa; Queen's Printer, 1958.