Ship-and-shore terminal equipment
01 July 1930
Ship-and-shore communication denotes a system whereby a telephone set on board a ship may be connected by means of 2-way radio-link, normally operated on different wave-lengths, to telephone systems on shore. The circuit is quasi-duplex as on other radio links and long 4-wire circuits, in that a speaker is only heard when listened to at the far end. The terminal equipment, provided by Standard Telephones and Cables for this service, comprises a receiver and transmitter with suitable feeders to non-directional aerials on board the ship, receivers at Baldock and transmitters at Rugby, all of which are provided with feeders and directional aerials similar to the transatlantic and other services. The shore aerials are not so directive as those for working with fixed stations, because the bearing of the ship varies considerably in the course of its voyage, and a compromise between direction and wave-length must be accepted for the different locations of the ship, three wave-lengths being at present allocated. The directive aerials provide a transmission gain of about 13 db on the equivalent half-wave radiator. At the London trunk exchange the operation of the service is similar to other radio links with special technical-operator positions. The standard Post Office, voice-operated, anti-singing valve-switching is employed. On the ship carrier noise in the local receiver is minimised by suppressing the radiated carrier when it is not modulated.