Rotor radar system
Type 14 CHEL/GCI
The
Type 14 CHEL/GCI (Chain Home Extra Low/Ground Controlled Intercept) was a 10
centimeter radar, the first Type 14 was working at Sandwich in January 1944.
The development of the Type 14 arose because the Type 7
metric GCI radar had been subject to both electronic and window jamming and
could not detect very low flying aircraft. The simplest way around the problem
was to modify the Type 13 Centimetric Height (CMH)
equipment by mounting its aerial horizontally, instead of vertically, and rotate
it horizontally. Earlier marks used twin "cheese" antennas (note:
after examining the original it appears that the top "cheese" has
been "cropped" in this photo!) and the only differences between Mk's
II, III, IV and V were in the operational facilities. In 1944 a new antenna
was designed for the Mk VI consisting of 1/2 inch steel tubes at a separation
of 1 and 1/4 inches in the shape of a horizontal cylindrical paraboloid. It
was fed by a linear waveguide slotted feed.
The
Mk VI antenna measured 25 feet by 8 feet, giving a much better range performance
over earlier marks. The horizontal beamwidth was 1o and the vertical
beamwidth was 3o. Coverage within the beam was good though somewhat
limited in the vertical plane. To get around this two versions were manufactured,
one for low cover and the other, tilted back, to provide cover at higher angles.
The first models of the Type 14 gave good low cover. Bomber aircraft were detected
at 20 miles when flying at 50 feet above the sea and at 50 miles when flying
at 1000 feet. At 6000 feet the detection range was 90 miles. Bearing and range
accuracy were good. (Watching The Skies).
Some
impression of the size of the Type 14 Mk VI antenna can be gained from the colour
picture that features me on the right hand side. I am 1.8 metres (6 feet) high.
There is also someone standing on the extreme right of the service platform
in the black and white photograph. I took the colour photographs at the aviation
museum at East Fortune airfield in 1989. The radar transmitter/receiver is housed
in the "hut" at the rear of the reflector and which rotated with the
antenna. The linear feed array is housed in a clear plastic tube that is mounted
horizontally across the face of the reflector.
An interesting experimental modification comprised of attaching two Type 14 Mk VI antennae end to end and with many modifications to the electronic equipment became the basis for the development of the Type 80 radar.
The typical characteristics of the Mk VI were:
|
Peak power: |
500 Kw |
|
Pulse length: |
0.6 or 1.9 us |
|
P.R.F.: |
500 pps |
|
Frequency |
3 GHz (10 cm) |
