GB639651A - Improvements in or relating to electrical circuit for transmitting and receiving - Google Patents

Abstract

639,651. Acoustic directional apparatus. STEVENS, A. H. (Submarine Signal Co.). July 6, 1945, No. 17358. [A Specification was laid open to inspection under Sect. 91 of the Acts, May 6, 1946.] [Class 118 (ii)] In a system for transmission and reception of compressional wave energy in which the same unit is used for both transmission and reception and in which high frequency electrical oscillations of the desired frequency are impressed across the unit as a transmitter by means of a transformer, the secondary of the transformer is connected to the unit in series with an independent inductance and capacity and an amplifying unit is shunted across the inductance for reception purposes, the impedance of the shunted inductance being substantially less than the impedance of the transmitting and receiving unit. The arrangement described, which may be employed for distance measurement by measuring the interval between the transmission of a signal and the reception thereof after reflections at an object the distance of which from the position of transmission it is required to determine or, for two-way communication between two similar but remotely located units, has for its object to prevent damage to the receiving amplifying unit when the system is in the transmitting condition. In the described embodiment as applied to distance measurement the output of a highfrequency generator 18 which is switched during transmission periods by cam-operated contacts 16, 17 is coupled to the transmitting and receiving unit 1, which may be a highfrequency oscillator of the magnetostriction or piezo-electric type, by means of the network L1, L2 and C1, L1 and C1, being adjusted to form a series resonant circuit at the operating frequency and L2 having a value which depends on the maximum voltage which may be impressed across the receiving amplifier 5 without causing damage thereto. During transmission periods the full output of the generator 18 is impressed across the series arrangement of the unit 1 and the inductance L2 but, because of the selected value of L2, only a part of this voltage (about 40 per cent) is impressed across the amplifier 5. The efficiency of the circuit is greatest when the impedance of L2 is somewhat below that of the unit 1. During reception periods contacts 16, 17 open and the entire received voltage across 1 is impressed across L2 since the impedance of the series resonant circuit L1, C1 is a minimum. The output of 5 is connected through the commutator ring 12 and brush 13 to an indicating device such as a neon discharge tube 11 which is carried on an indicating disc 10 driven by the continually rotating shaft 9.