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WB 900
The WB900 system was known as the 1+1 subscribers carrier system.  The system allowed for two direct exchange lines to be on one pair of wires.  Effectively it was a Party Line, but the two lines were discrete and the two users had no idea they were sharing.

This system was introduced due to the lack of line plant available around the country.  An electronic unit was provided in the premises of one user and a circuit card was fitted in the exchange.

Two different styles of Subscriber Units were produced: the original had a square edged cover, coloured grey/brown, whilst the later models with a compander, were coloured white and larger in size.

Eight different models were produced all with different modifications.  These were marked as /1, /2 up to /8.  The exchange line unit had to match as well e.g. Subscriber Unit WB900/6 must be connected to an Exchange Unit WB900/6.

The earlier systems were problematic, suffering from noise issues, until the /5 or /6 Subscriber Unit was introduced.

The Subscribers Carrier unit used a battery for power, which was charged from the line.  But if the audio user was a high calling rate customer, or they continually left their handset off hook, then the battery would not charge.  In these situations a Power Unit No. 53A would be fitted to the Subscribers Carrier unit.

Works Specification WB685 was the design guide (Dated 1970).

Introduced circa 1976.

Guidance Notes on the WB900

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Click here for a GEC marketing leaflet

WB900 1+2 System
It also appears that the WB900 started life as a field trial in 1967 in the Preston Telephone area.  Documentation is scarce on this but Works Specification WB656 advises that it is a 1+2 systems which refers to a system which provides for one audio and two carrier circuits.  The audio circuit used a Telephone WB900/A, whist the carrier circuits used Telephones WB900/1 and WB900/2.  No other equipment was used at the customers premises and the telephone lines were just teed together.

Works Specification WB653 advises on the equipment required at the exchange end of the 1+2 system.  The equipment consisted of an Equipment, Carrier WB900, Power-Panel WB900, Channel Panels WB900/A,  WB900/1 and WB900/2, and a Ringing Generator and Test Panel WB900.  All the equipment was to be located in the same room as the MDF.

All the above equipment was released on a Loan Requisition, which was renewable at six monthly intervals.

All the exchange equipment was produced by GEC.

 

 
 
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