Patent GB-583743-A (GB)
Title: Improvements in or relating to radio transmitting and receiving systems
IPC: G01S7/03
Filed: 1944-11-24
Abstract: 583,743. Wireless transmitting and receiving apparatus; radiolocation. BANWELL, C. J., WESTCOTT, C. H., and LEES, R. J. Nov. 24, 1944, No. 23499. [Classes 40 (iii) and 40 (v)] In a combined transmitter and receiver, the aerial, the transmitter and the receiver are connected by feeders to a common point, and switching means controlled by the transmitter output prevent that output from passing to the receiver, whilst permitting energy received during intervals between transmissions to pass unimpeded to the receiver. The switching means comprise discharge devices associated with quarter-wave or other tuned branch lines. The system has particular application to radiolocation systems employing pulses. In Fig. 2, the three feeders are marked A, T, R, and a discharge gap G1 is placed at a quarter-wavelength, or an odd and multiple thereof from the junction B. The gap breaks down and shorts the line R during transmission, and causes the branch R to present high impedance to the energy passing from the transmitter T to the aerial A. To prevent received energy from passing to the transmitter, a line comprising a second discharge gap G2 is connected at C distant a quarter-wavelength from the junction B. The gap G2 is a quarter-wavelength from each end of the line, the outer end of which is shorted. During transmission, the gap G2 breaks down, and the line including it presents high impedance at the point C. When not transmitting, the feeder T is. in effect shorted at C, so that it presents high impedance at B to the received energy which therefore passes unimpeded to the receiver R. Coaxial instead of open-wire lines may be employed as feeders (Fig. 3, not shown) ; and the gap G1 may be placed at the outer end of a half-wave line branched at the point G1, Fig. 2. The quarterwave line extended beyond G2 may be omitted. Either gap may be replaced by two gaps a quarter-wavelength apart. At high frequencies, the inductance of the gaps Gl, G2 is neutralized by series condensers, HI, Fig. 6, so as to give a short-circuit at D, E when the gaps are conducting. Stubs terminating in condensers F, G are about one-third of a wave-length long, giving inductive reactance at D, E which at the mean frequency neutralizes the open-circuit capacity of the gaps G1, G2. During reception, the stub G presents zero impedance at C and high impedance at B, so that received signals pass along the path BDJ to the receiver R. In a modification (Fig. 7, not shown), the condensers HI are replaced by sliding telescopic elements. The distance of G2 from C is telescopically adjustable, and the condenser F is omitted. The distances BD, DJ, Fig. 6, are made variable by telescopic line elements. At lower frequencies, networks of lumped reactance, Fig. 8, are used. When receiving, energy passes from the aerial feeder A to the receiver feeder R through a network comprising condensers C1, C2 and inductances L1 ... L4, the gaps G1, G2 being non-conducting; and the network C3 ... C5, L5 ... L8 offers high impedance against energy passing into the transmitter feeder T. During transmission, the receiver is shorted by the gap G1, whilst the shorting of the condenser C5 by the gap G2 enables energy to pass unimpeded from the feeder T to the aerial A. The Specification also describes modifications. (Figs. 4 and 5, not shown), in which the transmitter feeder and the aerial feeder are balanced with respect to earth.