GB490281A - Improvements in or relating to two-way communication methods, systems and apparatus - Google Patents

Abstract

490,281. Telephony over power circuits ; distributing music &c. INTERNATIONAL CARRIER - CALL & TELEVISION CORPORATION. Nov. 9, 1936, No. 30509. Convention date, May 23. [Class 40 (iv)] [Also in Group XL] A combined carrier-frequency transmitter and receiver for loud-speaking telephonic communication over power or other lines comprises an instrument acting as a microphone or loud-speaker, a valve circuit operating alternatively as a modulated carrierfrequency transmitter or as a demodulator, and an amplifier, the circuit changes for transmitting and receiving being effected by switches. Transmitting. The rotary switch S is turned one step clockwise from the position shown thereby connecting loud-speaker LS, acting as a microphone, to the input of an amplifying valve VI the output of which is fed to modulating grid 4 of carrier-frequency generator V2 which is coupled by tuned transformer IC to amplifier V3 the output of which is connected over tuned transformer OT to the power line L. Condensers C1, C2, C19 are used to match the output impedance to the line impedance. The switch also short-circuits a portion of the bias resistance R8 of valve V2. Receiving. With switch S in the position shown, transformer OT is connected to the line and operates as an input transformer for valve V2 now functioning as a detector, the audio-frequency output of which is amplified in succession by valves V1 and V3 and fed to loud-speaker LS. General features of the system. Communication may be restricted to apparatus in the same building by the blocking effect of the supply meter M or of chokes inserted in the line, but transmission external to the meter may be permitted if the meter windings are shunted by suitable condensers MC. A jack J is provided for the use of head-phones when receiving. The operating voltages for the valves are provided by rectifier V4. The Specification as open to inspection under Sect. 91 comprises also (1) a modified arrangement, Fig. 2 (Cancelled) (not shown), using a separate microphone and loud-speaker and no change-over switches, reception being on the homodyne principle, (2) arrangements in an operator's set for selecting a carrier frequency for transmission to certain or all sets in the same building, (3) using jack J for plugging in a cathode-ray tube (for television) or recording apparatus, when the apparatus is receiving, or an ordinary telephone, wireless receiver or writing telegraph when the apparatus is transmitting, (4) selectively connecting up wireless receivers for transmission of different programmes, (5) applications of the apparatus to communication over the power lines between traffic control points and police booths, and communication to or on trains. This subjectmatter does not appear in the Specification as accepted.