GB640021A - Improvements in transmitting and receiving equipment - Google Patents

Abstract

640,021. Radio ,receiving systems. BRITISH THOMSON-HOUSTON CO., Ltd. July 8, 1947, No. 18055. Convention date, Aug. 17, 1942. [Class 40 (viii)] [Also in Groups XL (a) and XL (c)] In a radar system wherein the transmitter 1 and the receiver 2 are connected to a line 5 leading to a common antenna, the receiver is protected from transmitted pulses by a stub line 8 which is short-circuited at 12 and provided with a spark-gap or other non-linear impedance at 13. The point of connection of the receiver to line 5 is connected to a point in line 8 a short distance away from 12, via a condenser 14 which is resonant at the operating frequency with the inductance presented by line 8 when 13 is short-circuited. The line 8 is also arranged by the provision of condensers 15, 16 to compensate for the effect of reflections from the transmitter 1 on the incoming signals received from the antenna. The junctions of the transmitter and receiver with the line 5 are spaced apart by an odd multiple of a quarter of a wave-length of the transmitter and the stub line 8 is also one quarter of a wave-length between the shortcircuit point 12 and the impedance 13. During reception, the tuned line 8 presents relatively high impedance to the line 5 and therefore has little effect on received signals. During transmission, however, the impedance 13 breaks down and the line 8 presents low impedance across the line 5 so as to protect the receiver 2. The stub circuit has little effect on the transmitter in view of the high impedance produced at the junction 6 due to the short-circuit at 7. During reception when the impedance 13 has a high value, reflection at the junction 6 may be compensated by variable condensers 15, 16 which respectively produce inductive and capacity effects at the junction 6, so as to match the conductance of the receiver with that of the line 5. A constructional arrangement of the junctions 6. 7, lines 5, 8, condensers 14, 15, 16 and spark-gap 13 is described with reference to Fig. 2 (not shown). In this arrangement the spark-gap 13 is placed in an enclosure containing for example, hydrogen or helium, and is provided with spring contacts which engage the line 11 so as to allow for expansion and contraction of the line. The condenser 16 is of the cylindrical type having an inner plug electrode manually adjustable through a rack-and-pinion mechanism. The condenser 15 comprises two plates, one of which is adjustable towards and away from the other longitudinally of a channel 4 by a screw-threaded spindle.