Linesman/Mediator system
Radar Type 84
The
Marconi Type 84 L-band radar operated on a wavelength of 23 cm. The magnetron
developed a peak power of 2.5 Mw at a PRF of 250 pps and a pulse width of 10
uS. The Type 84 was originally designed for a 6 Mw magnetron, however problems
with the magnetron meant that production had to go ahead with the 2.5 Mw magnetron.
The head was a bit of a novelty, for the design allowed for two separate radar's
working "back to back". In the original design the Type 84 radar was
going use one reflector whilst the other was going to be used for a narrow beamwidth
IFF Mk 10 SIF, this option was never installed though.
The antenna reflector measured 60 ' wide by 21' 8" high and was manufactured using aircraft manufacturing techniques. The same reflector design went on to be used in the Type 85 S-band radar. The eight feed horns were phased in such a way that the antenna radiated a cosecant squared radiation pattern. Doug Robb took this Type 84 photograph, note the man (Dan Henderson, a presenter from BBC television) standing on the boom.
The
rotating cabin below the antenna was connected to the modulator building below
by a tube containing slip rings that carried power and signals up to the rotating
parts. The antenna rotated at 4 rpm and the transmissions broke through on every
television set for miles around! Every 15 seconds there would be a burst of
white "sparkles" on the TV screen and the speaker would emit a "zzziipp"
sound lasting around a second or so as the radar beam passed across the TV aerial!
The antenna could also be sector scanned if required. The small aerial mounted
on top of the Type 84 is a secondary surveillance radar (SSR), a descendant
of the World War II IFF (Identification Friend or Foe) system. In the black
and white photograph the IFF antenna is mounted at the end of the boom below
the radar feed horns.
The transmitter and receiver equipment were located in the brick building below the antenna (the building is not too obvious in these photographs), whilst the signal processing equipment was housed within the R12 building at Linesman sites (thanks to Andy Perkins and Chris Googe for supplying this information).
