Fitted to the Vickers Varsity
A VHF (Secondary) Radar
Rebecca & Eureka formed a system of portable ground-based
beacons and airborne direction finding equipment initially
to assist the air-drop delivery of supplies to the Allied Armies
groups in occupied Europe.
Rebecca was the airborne station,
and Eureka was the ground
The ground based beacon consisted of a super-regenerative
and transmitter, originally operating in the frequency range 214 - 234
from a battery via a vibrator power supply unit. A portable
aerial was erected when communications was required.
Rebecca & Eureka was a system initially designed to assist in the
of supplies to the British Army or Resistance Groups in occupied
during WWII, and which later expanded into a blind homing and
aid for most of the aircraft in Allied service. Much of the
credit for the development of this system must go to
and J.W.S.Pringle of T.R.E. (UK Telecommunications Research
Rebecca I was created by bolting a transmitter on to an A.S.V.
Vessel) Mark I receiver. An experimental version of Rebecca I and
Eureka I built at T.R.E. was demonstrated at the C-in-C, Army
Command in the summer of 1941. The Rebecca system
the Special Operations Executive (S.O.E.) and a number were built
the use of Partisans in the underground movement in Europe.
Encouraged by trials of Rebecca I the Airborne Forces Equipment
authorised in the summer of 1942 the development at low priority of a
II system suitable for tug and paratroops aircraft. The
principle of multi-channel operation in the air with up to 40
per beacon was established and remained the aim throughout the
It was also decided (wisely as it turned out) that Rebecca II
be built as replaceable sub-units within a common frame to allow
future changes in requirement.
Both Rebecca II and Eureka II were developed by Murphy Radio with
pre-production of Rebecca II by Dynatron Radio. Frequency
by remote control was achieved by a rotating turret with pre-set
capacitors in the Transmitter and Receiver radio frequency
Due to the limited availability of components and design effort
Radio was obliged to use available G.P.O. (General Post Office)
exchange selector mechanisms so that although the cockpit control
had 5x5 channels the equipment had only four positions.
but five position manually controlled turrets were available on
II. The latter and most early marks of Eureka operated
transmit/receive with duration determined by battery capacity, six
with Eureka I and II, three hours with Eureka III. Variants
Rebecca II were manufactured later with modified radio frequency
to also operate with Coastal Command Beacons on 173-176
Many Bomber, Fighter and Coastal Command aircraft fitted with
radar had adapted Rebecca II sub-units boxed in smaller frames to
Rebecca facilities via the I.F. and video units of the main radar.
Historical Development cont.
In the meantime, preliminary trials with Eureka II had shown that it
rather too heavy to be handled by the path-finders and a
Eureka III, was designed and developed in conjunction with
using American 9000 series miniature valves. Early models
Rebecca II installed in Dakota aircraft were flown to America
with Dr.R.Hanbury-Brown who was largely responsible for
American interest. The Americans produced their own version
Rebecca but largely copied the Eureka III design. AN/PPN-1, AN/PPN-2
Eureka - AN/TPN-1 (Transportable) Eureka. AN/APN-2 (Rebecca)
from the SCR 729 Airborne Interrogator of which a 1,000 sets were
delivered before mid 1944 for use in 'D-Day operations.
portable beacon supplementing Rebecca-Eureka sending a continuous
wave coded signal every 30 sec. for two hours over a 30 mile
The British Eureka III, including 6 Volt
batteries was carried in a
harness around the waist of the paratrooper who had only to unclasp the
remove and erect the telescopic aerial, to operate the equipment.
of many of the gliders to reach their target even in visual
over Sicily led to a rushed development of Rebecca III, a
low power super-regenerative set. Five transmitter and
frequencies could be manually selected in the air.
times were limited to about thirty minutes to avoid drain of the
battery. A Rebecca IIIN was developed for strike aircraft
Fleet Air Arm in support of the Army and Marines in the Pacific
Early in 1944 there was a plan to develop a range of miniature B7G
miniature components, plugs, relays, etc. within the U.K. Rebecca
was chosen to be the guinea pig for this exercise and development
the set placed with E.M.I. in view of the large scale production
The technical design and performance of the equipment was fully
in T.R.E. report T2701, Part I dealing with design, and Part 2
data on the vast range miniature components incorporated.
but a small control box and the c.r.t. indicator unit was
and sealed within a pressurised cylinder. Six pre-set
and receiver frequencies were selected on the control box located
the cockpit and continuously tuneable using an ingenious motor driven
balance resistor network without having to open up the pressure
Ericsson developed a lightweight aerial/display switch unit based
on a T.R.E. design to switch both radio frequency and video on
same contact so as to obviate the "Christmas Tree" effect on
Marks. The production plan was for 8,500 sets over two
with installation in future and current aircraft and as a
for Rebecca II, (7 types in the F.A.A. and 14 in the R.A.F.),
of the sets light weight 40lbs (18kg), small cockpit units and
tropicalisation. A meter display system developed by A.C.Cossor
later added to some of the aircraft. The end of the war
some of Rebecca IV activities but the system remained in service
many years with Transport Command out in the Far East.
Murphy Radio developed lighter non-pressurised versions of
in various formats using some of the Rebecca IV techniques for
aircraft as well as the higher power Eureka IV and V beacons.
Regrettably Rebecca/Eureka in the field did not always live up to the
high promise of the trials, mainly due to poor operational
and damage to ground equipment. Throughout the war the use
Eureka I and Eureka II with the resistance movements was fairly
Of special merit was the use of Eureka I in Norway from October
to April 1944. Despite having been buried during the whole
one summer and part of one winter the operator deployed the
successfully in seven glider/supply operations.
Principles of Operation
The airborne Rebecca equipment radiates 5µSec duration
pulses on a VHF spot frequency. On receipt of the
pulses the Eureka ground based beacon triggers its associated
causing responses to be radiated on a different frequency, but at
the same p.r.f. (pulse repetition frequency) of the interrogating
transmitter. The returned signals received in the aircraft
both the right-and-left Rebecca receiver aerials are displayed on
a cathode ray tube indicator unit,
time-base of which is synchronised with the original pulse from
Rebecca transmitter, and applied to the Y-plates of the
The received signals are switched into the receiver in
with the switching of the video-frequency output signals to the
X-plates of the c.r.t. In this way, if the beacon is to the
right of the aircraft,
the signal to the
right of the timebase will have the greater amplitude, in which
a right turn will be necessary to make the signals on either side
the timebase equal in amplitude. This would indicate that
aircraft was then flying directly towards the beacon.
The ground based Eureka beacon complete with its aerial is air-dropped
and assembled on the dropping zone. The Eureka transponder
based on a super-regenerative receiver with a separate
valve and powered by a battery operated vibrator. A coding
which is part of the Eureka beacon periodically causes the width
the beacon response pulses to vary at Morse Code intervals for
purposes. This function may also be manually controlled for
of simple messages.