Radar Recollections - A Bournemouth University / CHiDE / HLF project






'AI' Air (or airborne) Interception. Special electronic interception
equipment mounted in an aeroplane. Space inside an aeroplane
dictated that much shorter wavelengths than those used for
ground-based equipment had to be developed. Centimetric radar
proved to be the defining breakthrough.

'ASV' Air to surface vessl radar. This was a system particularly used for
detecting 'U'-boats. New and novel scanning aerials were needed.
'ATS' The Auxiliary Territorial Service. Many women wanted to play their
part in the defence of Britain. This force was set up to undertake
a wide variety of jobs that had previously been undertaken by
men. Thus the men were released for active duty.

'Bandits' RAF slang for "enemy aircraft approaching".
Cavity Magnetron A special type of diode valve that has resonant cavities built into
The anode. The valve has to operate within a strong magnetic
field. The type invented by Randle and Boot in 1940, paved the
way for much more precise centimetric radars to be produced.
They were much more powerful generators of microwaves than
anything that had gone before.

'Chain Home' [CH]: The first operational defensive radar system in the world.
The chain of stations was constructed between 1937 and 1939
along the east coast of Britain. The radar operated at a
wavelength of 12 metres.
'Chain Home, Low' A development from the 'CH' system that was designed to detect
low flying aircraft in particular. It worked on 1.5m wavelengths.
A further modification was 'Chain Home, extra low' which worked
on 10 cms wavelengths.

Dipole A simple aerial; usually a folded rod and designed to work at
approximately half the wavelength for the particular frequency
being used.
G.C.I. 'Ground Control Interception' was the term given to the technique
of directing fighter planes from a control centre on the ground. A
combination of observation, radar and radio telephones were used
to direct the pilot to intercept the enemy planes and in the most
strategically advantageous way.

GEE A ground-based radio-navigational system that relied upon pulsed
beams being sent to the aeroplane. The system became
operational in March 1942 and the accuracy of bombing raids
Goniometer A device consisting of 2 pairs of crossed dipoles that can interpret
both the direction and elevation of an incoming radar echoes from
two receiver aerials; at a known distance apart. Physically, the
Goniometer knob was an integral part of the radar operator's
control panel. A pair of coils (controlled by this knob) balance the
signals from the two aerials in a way that indicates the direction
of the source.

'Happidrome' An RAF 'slang' term for the operations control room. Because the
control officer could look down on the plotting table; a
comparison with a theatre was naturally made.

Hertz The unit of frequency (1 Hz = 1 cycle / second); named after
Heinricht Hertz in 1888, an early pioneer of electromagnetic
radiation research.

H2S A self-contained blind bombing system carried entirely in the
aircraft. The system developed from AI but required a downward
and spiral rotating scanner. The system became fully operational
in January 1943. The phrase 'Home Sweet Home' could have a
number of meanings but is generally thought to refer to the
aeroplane's ability to 'home in' on its target.
I.F.F. An early additional feature to the 'CH' system that allowed the
ground controllers to differentiate between 'friendly' aircraft and
enemy ('foe') aircraft. The friendly aircraft were fitted with a small
transmitter that sent a coded signal at the same frequency as the
interrogating radar that, when received, could be incorporated in
the cathode ray tube display. Any aircraft not sending this signal
could be assumed as hostile.

'Jamming' The various techniques that were used to over power, confuse and
distort the radar and radio-location equipment used by the enemy.
Many ingenious methods were employed an both sides to fool the
'METOX' A special receiver that was installed on German 'U'-boats. This
receiver could detect the signals from an ASV equipped aircraft.
This early warning equipment allowed the surfaced 'U'-boats to
escape by crash diving.

Modulator The specific component in a radar transmitter circuit that
generates pulsed waves of electromagnetic energy.
OBOE This was another ingenious bombing guidance system but this
was controlled from the ground. Radio beacons transmitted a
'guide-path' signal which the aircraft crew could receive as a
series of morse codes; dashes if the plane was to the right of the
exact flight path and dots if they were to the left of it. If the plane
on the correct target flight path the navigator would hear a
sound like an oboe.

Parabolic array An advanced type of transmitter aerial employed for centimetric
radars. A dish-like reflector ensures that the transmitted signal
leaves the dish as a narrow pencil-like beam.
'Pipsqueak' The formalized 'language' used between ground control and the
pilot. The terminology evolved using terms that were clearly heard
during battle and less likely to be mistaken over the radio.
Examples include: "bandits", " 12 o'clock high" and "tally ho".
The letters of the alphabet were used to identify individual aircraft
eg. "T for Tango" or "V for Victor". This scheme significantly
improved the accuracy of communication between the ground
staff and the pilot.

P.P.I The 'Plan Position Indicator' was a great advance in the field of
radar display. G.W. Dummer replaced the standard horizontal
'left to right' trace with a rotating radial trace emanating from the
center of the screen. A pre-requisite for this development had
been an effective synchronized rotating aerial. Transparent maps
could be superimposed on the screen to give a readily
understandable picture of the activity in the sky above.
'RDF' Radio Direction Finding…. A misleading term that really meant
'Radio Location' and was the general term used to describe the
the area of science involved. The Americans coined the term
'Radar' and it was rapidly adopted.

Skiatron The Skiatron was a modification of the PPI display that involved
The back-projection of the image underneath a large , circular
glass table. The idea was to improve the visual display so that
controllers and operators alike could see what was happening.
'SLC' Search Light Control. The integrated set of arrangements that
allowed a group of search lights to pick out and hold aircraft

'timebase' The term that refers to the 'no signal' electron trace seen upon
an oscilloscope screen. The length of the trace can be adjusted
and the time taken to make each sweep can be calculated. It is
from this fundamental parameter that the time for a signal to
return (as an echo) can be calculated and then, knowing in the
speed of the wave, target range can be determined.
T.R.E. Telecommunications Research Establishment…. The title given
to the unit set up at Worth Matravers in May 1940. The name
was deliberately misleading as the work carried out had nothing
to do with telecommunications. The staff, somewhat
irreverently said later, that it stood for "travels 'round England"
in reference to their constantly being relocated.

Waveguides Round-section and square-section tubes that were used to take
receiver signals from the aerial to the receiver. The signal loss
was far less than using conventional cables. The wave would
reflect off the inside of the tube. Internal dimensions were
therefore critical.
'Window' Alternatively known as 'chaff'. This was a device that was used
as an effective 'jamming' technique. Thin strips of aluminium,
about 21 cms long were dropped from an aeroplane and would
create 'blips' on the enemy radar with the same dimensional
characteristics as a real plane(s). The system was used to great
effect to mask the true location of the D-day landings; 6th June

'Yagi' array A type of directional aerial consisting of a folded half-wave
dipole and up to 20 'director' rods in front and one reflector
rod behind. Still commonly seen today for domestic television