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170 AUSTRALIAN RADIO — THE TECHNICAL STORY

equipment manufactured in Australia was exported to overseas
countries.

By 1969, the capacity of the solid state 1.9 to 2.3 GHz equipment
had been increased to 960 channels and the transmitter power raised
to 2.5 watts. Also by 1972, the transmitter power of the solid state 150
MHz 12-channel equipment had been raised to 200 watts. Additional
types of solid-state broad-band bearer equipment were added to the
microwave range during 1974, including 300 channel equipment for
the 4.4 to 4.8 GHz band and 120 channel equipment for the 7.4 to 7.7
GHz band.

By way of emphasising Australian capability with solid-state
equipment, it is interesting to note that members of the engineering
team engaged on the microwave broad-band bearers described above
were also responsible for a number of other important solid-state
equipments designed for operation in the same band. One such
project comprised the design and local manufacture of outside
broadcast links (7.125 to 7.425 GHz) and studio to transmitter links
(7.725 to 8.275 GHz) used by many of the Australian television
broadcasting organisations. These equipments, which incorporated |
watt transmitters, were first made in 1974 and their manufacture has
continued into the 1980s.

Although not in the nature of a broad-band bearer, another
example of special interest includes the design and manufacture
during 1974-75 of a number of 5 GHz transmitters for the prototype
of the Australian-designed “Interscan” microwave instrument
landing system (MLS). In accordance with the overall philosophy of
the new system, solid-state equipment was mandatory. To achieve the
power level of 20 watts required for the azimuth and elevation
transmitters with the devices then available, it was necessary to use a
buffered 1.25 GHz source driving four parallel paths each comprising
a power amplifier followed by two varactor doubler stages, the four
paths then being combined into a common output circuit. In the case
of the flare transmitter similar basic principles were employed; two
separate sources operating at slightly different frequencies and each
followed by two parallel paths were used to give two separate outputs
of 10 watts each.