Gee Receiver R1355
& Indicator Unit No. 62A
with RF Unit No. 27
GEE was a navigation system for aircraft
that was evolved by British scientists to meet the needs of the Royal Air
Force during World War II, at a time when both Bomber and Coastal Commands
faced serious navigational problems.
The system subequently remained in service until 1970.
Accurate navigation by day and night
under conditions of radio and radar silence in indifferent weather, by unlimited
numbers of aircraft flying under conditions where tactical considerations
prevented straight and level flying, called for a position fixing aid which
could be operated quickly and simply.
GEE became operational about the time that the thousand bomber raids
commenced in 1942, and when the battle of the Bay of Biscay was reaching its
maximum. It was the first serious attempt to provide the navigator with
a rapid means of determination of position, and seldom has any one invention
so faithfully and quickly satisfied the requirements for which it was developed.
The principle of operation was the measurement of the time difference
between the reception of pulses from ground transmitters (working in pairs),
measured on a cathode ray tube display in the aircraft. Two or more Slave
ground stations, working with a common Master station, constituted a complete
Gee Chain. The time difference between signals from two pairs of stations
were measured simultaneously. When the readings were referred to precomputed
lines on a special chart, the two simultaneous position lines obtained combined
to give a position fix for the navigator.
To secure a position line, an aircraft had to be within range of two transmitters,
and to secure a position fix, within range of three stations, ie., a common
Master and two Slaves.
|The Gee airborne receiver R1355, ref 10D/13032,
serial number G060635 is illustrated above with the matching Indicator Unit
Type 62A ref, 10Q/13000, serial number G23681.
The RF section of the R1355 is provided by a plug-in
RF unit, type RF24, RF25, RF26 or RF27, each covering a different frequency
range to avoid interference from enemy radio countermeasures.
The R1355 receiver also contains the EHT power supply for the indicator
unit CRT. Indicator Unit Type 62 (fitted with SP61 valves) and Indicator
Unit type 62A (fitted with EF50 valves) are both suitable for use with the
A Gee Test Set Type 210, ref 10S/16002, serial number 488 is used for test
and alignment of the Gee airborne navigation system.
A later tropicalised version of the R1355 receiver was
given the designation R3645, and may be distinguished by the 2 position rotary
selector switch. The R3645 operates with Indicator Unit Type 299 only, as
in this case the CRT EHT supply is located in the Indicator Unit. An
example of the R3645 is illustrated in the third row of photographs below
on the right.
|The above R1355 receiver and Indicator Unit Type
62A were donated by the DRS Restoration Adviser George Rawlings, after completion
of a restoration program and the construction of a Gee system simulator.
The equipment is currently in full working condition,
and can be displayed "working on the bench" in Building
The system runs on an 80 Volt 1500Hz supply at 8 Amps which is obtained from
a 24Volt dc to ac motor-generator set (mounted under the bench).
In an aircraft installation, the 80 Volt 1500Hz supply was obtained from
an engine mounted generator and fed to the Gee equipment via a voltage control
In this bench test configuration, a solid state pulsed generator modulating
an RF oscillator provides simulated Gee A (Master), B and C (Slave) pulses
for the receiver.
In the original aircraft installation the received signal was fed from a
rod aerial mounted on the outer body to the R1355 RF Unit via a separate
aerial tuning unit Aerial Loading Unit Type 51, Ref 10B/16025.