AI Mark VII (Slot 233) and Mark X (slot 234) AI Radars

[el cid again]

Suspicious of stock ranges due to the Mark IV issue,
I found that Mark VII and X should be 18 instead of 40 or 90 respectively.
The X should have a higher accuracy at the same range as the VII.

AI MK X AIRCRAFT INTERCEPTION RADAR
The AI MK X is a modified version of the American SCR 720 Radar. It required a two man crew, the operator giving instructions to the pilot over the intercom. It was used in aircraft like the Mosquito for nightfighter operations. The system radiates 0.75 microsecond pulses in the centimetric band at 9.1 cms. The peak power being approximately 70 KW. The aerial system, housed in a Perspex dome on the nose of the aircraft, consists of a small vertical dipole at the centre of a parabolic dish, the dipole being used for both transmission and reception.

The first British designed centimetric AI radar was the AI MK VII /MK VIII, this had a similar performance to the MK X although the scanning and display methods differ considerably. A British MK IX system was also developed that was more sophisticated, as it had ‘lock and follow’ capabilities, but problems in meeting production quantities and timescales required, prevented it from being adopted and the American MK X was used instead.

The MK VIII scanning system was what is termed a 'spiral scan'. In this system the dish is rotated about it axis and gradually deflected sideways, tracing out a spiral in the sky, out to an angle of about 45 degrees, The deflection then returns slowly to the zero position when the process is repeated.

In the MK X, the parabolic dish is rotated continually about its vertical axis. It is also slowly tilted up and down which effectively traces out a helix in the sky, much like looking out from the centre of a coil spring. The rear half of the scan, some 210 degrees, is blanked off, as its field of view is interrupted by the structure of the aircraft. The presentation of the information displayed to the operator is also different. In the MK VIII, a single tube with a circular display was used. The target range is measured from the centre of the tube with the target appearing as a segment of a circle, its angular position defining the azimuth and elevation and the length of the segment showing how much the target is off axis. As the target approached the axis of the aircraft, the segment gradually extended to a full circle.

The MK X has two tubes, the left one or the ‘C’ scope displaying the target as a spot on an azimuth/ elevation grid. The right one or the‘B’ tube has again an azimuth calibration on the horizontal axis but the vertical axis shows the range of the target. A range marker line, adjustable by the operator, can be moved up and down the trace to select a particular target. The control used to adjust the marker is calibrated in range, giving a more accurate reading from that obtained from the graticule markings. Only when this marker line overlays the target does the target appear on the left hand ‘C’ tube. The amount of vertical scanning or tilt can be selected by the operator and has 5 switched ranges. The maximum scan is +40 degrees to -20 degrees down to -5 degrees to +10 degrees. A fixed -5 degrees is used when homing onto a beacon. The range can also be selected from 2 miles, 5 miles, 10 miles up to 100 miles for use with a homing beacon.

The beam width is some 10 degrees with a vertical rotation speed of 360 RPM. (100 rpm for the beacon range). There are 12 scan lines up and 12 down for the +40/-20 degree range, giving a full scan time of 4 seconds