BID 700 (Vendor)

    This was the synchronizer for BID610. The 610 had 2 modes of operation -  Mode A , self sync for landlines and quality radio links i.e. microwave. The disadvantage of this mode was one error would propagate through the registers, produce an unacceptable garble, and require a further "N" characters to clear.

    Mode B used the BID700 to produce timing pulses and keep the receive in step with distant transmitter. It also enabled traffic flow security. This was the usual mode for HF links.

    BID700 with cover off. To its right is one with cover on. Blank panels are installed in the top most position of the the other racks.  It is believed that the racks without BID700 are the local circuits working "Mode A" using landline/microwave links. This was a standard layout for full duplex HF link - two 610's (Tx and Rx), two control units (under the 700), and 2 power supplies at the bottom of the rack. (Photo  submitted by Ray Fortin)

    Some comments from a person who worked on the BID700 production line. "In 1967, I worked for Plessey Automation, Cheapside, Liverpool and my job was to test BID 700’s – a hundred of them. As I remember, there were three units: the main unit, a power supply and (I think) a control unit. We would test in two phases:  plain to Crypto and Crypto to Plain. The final test test comprised of linking two sets together and going from Clear-->Clear. A government contract stipulated the procedures to be used and including the message we had to type on an 33ASR  teletype. – “the time has come for all good men to come to the aid of the party”

    Although assembly was undertaken in an open factory, testing was undertaken in a special MOD compound with security guards all over the place – it would have been very difficult to take any photographs"

The BID700 cover had an oval window to observe indicator lamps. This rack was set up for a full duplex HF link. (Photo via RP)

    Credits and References:

    1) Ray Fortin <raymondfortin(at)>

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June 3/12