|The CH system was able
to display range and bearing. Furthermore, by alternately switching
the transmission to aerials of different heights and by knowing
the patterns (i.e. zones that would be flooded by that transmission
from the different aerials) it was possible to collect ground
reflection echoes from the aircraft as well as direct echoes.
By comparing the strength of the returned signals from the different
aerials, it was possible to calculate the elevation of the aircraft.
This method is often referred to as the
'split beam' method
The fourth parameter is equally important:
is it a friendly aircraft or an enemy
The first approach was to fit the aircraft with variable tuning
aerial so that when its scanning frequency matched the CH
station's output frequency, resonance would occur and extra-large
'blip' would appear on the oscilloscope screen. There were
a number of discrepancies with this arrangement and so Vivien
Bowden developed a new system
A small airborne transmitter gave out a specific pulsed (beacon)
signal. All CH systems had a separate receiver tuned to the
same frequency band. Upon receiving the coded signal, it was
fed directly to the main radar display and synchronized with
it. Thus the operatorwould recognize the 'friendly' aircraft.