How to capture a radio signal


Antennas, used to transmit and receive telecommunications signals, are as varied as the people for whom they are designed to serve. Herewith Modulation presents a selection of photos of some of the antennas used by the Department of Communications.


An HF array at the Ashton, Ont., field site used to study the lowest part of the ionosphere (the D region) by observ­ing HF waves partially reflected from the region. The array consists of a grid of 40 half-wave dipoles suspended some 90 ft. from the ground by 25 wooden poles. The large physical size of this array compared to those at higher frequencies is dictated by wavelength (at 3 MHz a wavelength is 100 meters; at 300 MHz it is one meter). The D region, which strongly influ­ences the propagation of VLF to HF signals, was extensively studied by CRC using this facility from about 1964 to 1974.

This UHF antenna, which transmits and receives signals at 450 MHz, is used for ionospheric studies at the Ashton, Ont., field station.



To the left in the background is an array of cross yagis, which provides a back-up for reception of signals from the Isis satellites at 136 MHz and provides command signals at 148 MHz to the Isis satellites.

A VHF-UHF antenna, 60-feet in' diameter, with a parabolic reflector dish, which operates in the 136 MHz and 400 MHz band and is used for telemetry with the Alouette and Isis satellites, the first Canadian, ionospheric satellites.

Two terminals constructed and operated by the Communications Re­search Centre. The land-mobile terminal on the left has adjustable transmit and receive yagi antennas.

View of the UHF small terminal, with radio equipment in foreground and antenna in background. Ron Yank is shown operating the radio equipment, with Dave Barlow pointing the antenna in the direction of the satellite. The antenna was used in Tacsatcom experiments. The portable earth station was used for voice and data communications with the satel­lite. It was also used in the 1970 royal tour of the North by reporters sending their reports south.

The high frequency direction findings (HFDF) array near Richmond, Ont. This array consists of 94 individual elements in two arms some 243 m and 2134 m long. (The photo shows the elements of the longer arm.) These arms are at right angles to each other in the form of a cross. An individual receiver is provided for each element. These, to­gether with a computer that performs control, calibration and data processing functions, are housed in a lab at the centre of the array. The lab is underground to avoid interference with the array.

The facility is used to research the variations in direction of arrival of HF signals transmitted from known locations. Such knowledge is required to refine and improve existing direction finding techniques.


Log periodic dipole antenna used for HF (6 to 40 MHz) communications at CRC. This antenna is rotatable by means of an electric motor at the base of the tower which is under remote control.

This 10-metre antenna was used in teleconferencing demonstrations be­tween France and Canada with the French-German Symphonie satellite. It transmits audio-video signals at 6 GHz and receives at the 4 GHz level. The antenna is portable and self-contained. The wheels, part of the running gear, can be seen on the back leg of the antenna's tripod.

This 1.2-metre parabolic dish has been used in the Hermes satellite experi­ments. The portable earth terminal re­ceives TV signals only.

These two satellite earth termi­nals, 1.2 metres and 0.6 metres in diameter, were also used with the CTS experiments. The portable TV-receive- - only terminals were designed to be prototypes of a terminal that could be mass produced for about the cost of a color TV set.

A close-up of the outdoor unit for the prime focus terminals, such as the 0.6-metre terminal in photo 10. Signals captured by the dish for the satellite transmitter are focussed into this unit which extends from the centre of the dish and then fed into a cable which carries the signals to the TV.

These two 1.6 metre diameter dishes were on loan from Phillips of the Netherlands and the Mullard Research Centre in England. The dishes were the first attempt by Phillips at development of a TV-receive-only terminal and were used in Hermes demonstrations.


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