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The 424 Airfield Control Radar was designed in 1952 to meet an RAF requirement for an Approach Radar. It was designated by the RAF as the ACR7D (note that Cossor also produced a radar to meet the requirement and their equipment was designated the ACR7C. It is thought that only 6 systems of this type went into service). Operating at 3cms wavelength (X-band) the first version used a 14ft. single curvature antenna fed by a hoghorn. Later versions (including the Circular Polarisation variant) used an antenna curved in both planes, but each plane following the same mathematical law, which in the profession is known as an orange peel reflector (as against a double curvature reflector which follows differing mathematical laws in the vertical and horizontal) and was fed by a horn. The antenna was mounted on a transmitter box (housing 2 transmitters), which in turn was mounted on a turning gear (shades of the Type 159 marine radar from which it was derived). The 20Kw transmitter operated with a pulse length of either 0.1 or 0.5 microseconds at a prf of 1000pps. The PPI displays were of the 12inch rotating coil type similar to those used in the Type 45 Marine Radar. Both mobile and transportable versions were produced.
The mobile version was mounted on a Karrier (Rootes Group) Gamecock chassis, which had quite small road wheels to minimise the overall height. Two models only were produced. One painted in red and white stripes as a demonstrator for the UK market, it became a general trials vehicle. The other, painted yellow for export demonstrations, was eventually sold to Argentina.
The transportable version used an aluminium cast pedestal, with outriggers giving stability to the antenna and turning gear. The Displays, the Control Panel and the two Receiver Units were mounted on a folding table in the operations room/cabin.
In the mid 1950s a 424, of the Airfield Control type, was sold to the Vickers Aircraft Company and was installed at their test airfield at Wisley in Surrey.
Type 424 Airfield Control Radars were supplied to over 45 Civil and Military Authorities, a quantity of 22 in the UK and others to countries such as India, New Zealand, Ceylon and Brazil. Total sales were approximately 125.
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