GB547677A - Antenna system for modulated-carrier signal receivers - Google Patents

Abstract

547,677. Wireless receiving circuits. HAZELTINE CORPORATION. March 4, 1941, No. 2933. Convention date, March 23, 1940. [Classes 40 (iii) and 40 (v)] Relates to receivers which can be used at will either with a loop antenna or with an antennaground system and in which the antenna-ground system 17, 18 is coupled by switch 19, 20 to the receiver 13 through the loop aerial 22 by means of an impedance 21. According to the invention this impedance tunes the antenna system 17, 18 at a frequency near the lower end of the band covered by the loop aerial. When the antenna 17, 18 is not in use, a condenser 23 tunes the impedance 21 to the intermediate frequency of the receiver 13, thus forming a trap circuit to prevent interference at this frequency. In the modified circuit shown in Fig. 6, the inductance 21 is replaced by a small inductance 30 coupled to the loop antenna and a larger inductance 29 having distributed capacity C 29 which makes the coil 29 resonant at a frequency above the tuning band. A resistance 31 damps the primary circuit whether the switch 19 is open or closed, thereby improving the uniformity of response of the antenna system and reducing the effects on the alignment of the tuned circuits of the receiver due to connecting in the antenna 17. In the circuit shown in Fig. 4, the antenna 17 can be connected to the loop aerial by a band rejector filter having two series inductance arms 24, 25 and a series-tuned shunt arm 26, 27, the circuit 24, 26, 27 including part of the loop being sharply tuned to the intermediate frequency to reduce interference, and the circuit 25, 26, 27 including the capacity of the antenna 17 being broadly tuned to a frequency at the lower end of the frequency band. A series resistance 28 has a similar function to the resistance 31 in Fig. 6. The inductance 21, Figs. 1 or 30, Fig. 6, may be a coil of cross-sectional area small in comparison with that of the loop aerial and arranged near one end or comer of the loop, Figs. 2a, 2b (not shown).