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WWII UK SOE
UHF duplex ground-to-air radio
- wanted item
S-Phone was a two-way full-duplex UHF radio system, developed in 1942
in the UK, for use by the Special Operations Executive (SOE) during
WWII. It was used by resistance groups and SOE agents operating behind
enemy lines, for communication with intelligence officers in airplanes, flying
close to the occupied territory at high altitue.
The S-Phone consisted of a ground unit and a matching airborne unit.
The ground unit is also known as Type 13, Mk II, Mk III or Mk IV [A].
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The airborne transceiver was developed by Major Hobday of the Royal Signals [1].
The transceiver that was used on the ground was developed by Captain Bert Lane,
also of the Royal Signals. The systems were built, tested, further improved
and installed by Charles Bovill,
who also worked on the Rebecca and Eureka
navigation systems.
The ground unit was carried on the chest of the operator, with a
webbing kit holding it in place. An open dipole antenna,
consisting of two short rods, was plugged into the front of the unit
and aimed in the direction of the airplane.
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The image above shows the ground transceiver that was carried on the chest
of the ground operator, who would aim the antenna towards the plane
simply by looking at it.
This way it was possible to set up a two-way voice
link up to a range of 30 miles, with a maximum height of 10,000 ft,
permitting the ground operator to guide the airplane to the dropping
or landing zone.
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The high directivity of the antenna and the low power of the transmitter,
ensured that the signal could only be picked up by the plane and not by
any distant ground monitoring station. The microphone
was encapsulated in rubber, completely shielding off the mouth,
so that enemy scouts in close proximity of the dropping zone
could not hear the operator speaking.
Apart from guidance during landing or dropping, it was also used
for passing 'coded' messages and instructions between field agents and
staff officers back in London. The image on the right shows a ground
operator with the transmitter on his chest talking into the microphone.
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Sticking out at the front of the transceiver is the vertical open
dipole antenna that should be aimed at the airplane.
The ground set transmitted at 337 MHz, whilst the airborne transmitter
operated at 380 MHz, both with an output power of 0.1 to 0.2 Watt.
Power was supplied by a series of batteries and a vibrator pack,
all of which were carried in the webbing kit.
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The image on the right shows the interior of the ground-based S-Phone.
At the left are some miniature (midget) valves
and at the right is the
audio transformer. Further images below.
At the center of the unit is a rectangular piece of pertinax with
a two-pin socket for the antenna.
The device shown here is probably a Type 13 Mark III.
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- S-Phone Ground
This is the body-worn transceiver that was used on the ground.
It is featured on this page and several versions were released
between 1942 and 1944: the Type 13 Mark II, the Mark III
and finally the Mark IV (1944). The Mark II and Mark III versions
each had 4 valves, whilst the Mark IV was equipped with 5 valves.
- S-Phone Air
This is the airborne counterpart of the above Type 13 ground transceiver.
It consisted of a transmitter with 2 valves and a receiver with no less
than 13 valves in order to pick up the week signals of the ground station
at distances of more than 30 miles.
- S-Phone Ship
The S-Phone could also be used for secure communication between a ship
and a passing airplane in a similar manner to the gound-based S-Phone.
In addition, it could also be used for secure communication between
two ships. For this an extra transmitter/receiver pair was installed
that used the alternate frequencies.
- S-Phone Suitcase
Like the S-Phone Ship, this version was equipped with a double
transmitter/receiver pair to allow switching between standard and
alternate frequencies. It was used for secure point-to-point connections,
such as the secret radio link between Sweden and occupied Denmark,
known as Minestrone.
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S-Phones are very rare these days and Crypto Museum would very much
like to add it to its collection. The device featured on this page
is part of the collection of Museum Jan Corver in The Netherlands.
If you have an S-Phone available, or if you know where we could find
one, please contact us. Your help is much appreciated.
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Website no longer available in january 2015.
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© Crypto Museum. Created: Sunday 11 August 2013. Last changed: Tuesday, 31 May 2022 - 12:36 CET.
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