The BID/150 speech encryption key
generator is a single channel device for use with the C42 and C45 Larkspur
Combat NET Radios. This was the first Combat Net secure speech system whose
key was set through the use of punch cards within the device.
It was first used operationally by the 15th
Signal Regiment during the Aden crisis in the late 1960's and was widely
used from Battalion level up to Corps Headquarters. Used from the mid-1960's
until the early 1980's. This example is held by the UK Royal Signals Museum
in Blandford Forum, UK. (Photo credits withheld on request).
|To set the daily key, three IBM style (80 col x 12 rows) keycards
( marked X, Y and Z) were placed into three readers situated behind the
module covers. Those key cards were used for a 24 hour period then destroyed.
Close-up of 150/1 control panel.
||Close-up of BID/150 keycards. Note the date
sequence on the cards. Click on image to enlarge.
|This is a double terminal setup for BID 150's and two Digital Modulation
(DM) boxes in a FV432 Armoured Personnel Carrier. The DM devices are in
front; the BIDS are in the rear; the radios are on the other side of the
vehicle. (Image source unknown)
The DM box is the interface between the BID/150 and the
radio set - C42 or C45. It lets the operator select clear or secure working.
Clear working means analogue speech from the microphone is fed to
the transmitter, to frequency modulate the VHF carrier; the receiver feeds
analogue speech through the DM box to the headset. These are conventional
military radio harness functions.
|Above and below: Internal views of the Digital Modulation
In secure mode the analogue speech signal is digitized,
then encrypted by combination with the digital key generated by the BID/150;
the digital stream is then fed to the transmitter, to pulse modulate the
carrier. (The No.3 versions of the C42/C45 sets were modified to permit
FM or Pulse Modulated working) On receive, the sequence is reversed.
Two sets could have their DM boxes linked by a 4-way cable to allow
rebroadcast of clear or secure signals. The rebroadcast sets could be up
to 1/2 mile apart. The DM box and radio set also provided an intercom function
over the cabling in these circumstances. The BID/150 was not needed for
simple rebroadcast of secure signals: receive on one set, transmit by the
other on a different frequency. The DM box could also be linked by up to
1/2 mile of 4-way cable to a small red RDDM box, allowing limited control
of the set by a remote operator - select clear or secure, receive or transmit;
only a local operator could tune the set.
Good radio performance was needed for reliable secure working. To
this end, vehicles carrying the C42-DM-BID/150 system were issued with
a 27-foot mast and an elevated antenna. The set carried a 'Goodman Box',
to check signal strengths and antenna performance. The operator had searching
set-up and performance drills to be strictly followed.
Close-up of the Digital Modulation device.
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