AI MK8 Airbourne Interception Radar.

The AI Mk7/8 was the first centimetric Airborne Interception Radar, appearing in about 1942/43 and installed in Beaufighters and Mosquitoes. The earlier AI MK4 only worked at a frequency of 200 MHz. Gone are the multiple aerials all to be replaced by a single transmit/receive aerial mounted at the centre of the radar dish. The dish is mounted in the nose of the aircraft behind a transparent cover. At 10cms(3000MHz) the radar beam is much narrower, almost operates like a torch beam and thus the radar beam can be made to sweep around the sky looking for a target. The dish is used to focus the beam and point it in the required direction. The dish is spun on its axis and initially the beam is directed forwards. The dish is then progressively turned 'off axis' thus sweeping a spiral in the sky in front of the aircraft. When it reaches a maximum spiral outwards it returns to the centre on an inwards spiral. The whole process is repeated continuously.

The AI MK8 Receiver contains the Klystron, the unit that protrudes from the front of the receiver and can be removed as an assembly. The Klystron is used as a local oscillator in conjunction with the Magnetron, the main radar pulse generator.

The AI MK8 Indicator Unit has the central single CRT the operation of which can be seen on the animation simulation as follows

Demonstration animation of a Night Fighter AI MK8 (Airborne Interception) radar.

The radar screen is the green circle on the left and the target aircraft simulation appears on the right. The target aircraft at night is invisible to the pilot until the target is within a few hundred yards of the night fighter and the pilot is directed onto the target by information given to him by the radar operator from the information on his radar screen The target echo appears on the radar screen as a yellow arc of a circle. In practice the screen is just one colour (green) but in this animation it has been changed to yellow to make the echo easier to identify. The distance of the arc from the centre of the screen is proportional to the distance that the target is in front of the night fighter. The direction of the echo indicates the direction of the target (up, down, left or right) and the length of the arc tells the operator how far the target is 'off axis', When the target is 'dead on axis' the target echo becomes a complete circle. The band of noise at the bottom of the radar screen is an echo due to reflection from the ground, below and forward of the aircraft. when the beam sweeps downwards.


Return to Home Page