Patent GB-533453-A (GB)
Title: Improvements in or relating to wireless signalling apparatus or other apparatus employing radio frequency methods
IPC: H04B1/12
Filed: 1939-08-28
Abstract: 533,453. Wireless signalling; impedance networks. HODGES, G. Aug. 28, 1939, No. 24702. [Classes 40 (iii) and 40 (v) ] A circuit, which may be used (1) for eliminating unwanted signals, (2) for reducing fading, or (3) as a tuning circuit, comprises an inductance L, resistance R, and a condenser C, associated with an impedance Z connected as shown in Fig. 1, phase and amplitude matching adjustments being provided such that certain signal potentials developed across the resistance R and impedance Z may be balanced out, so that they do not reach an output circuit, at the same time permitting other signal potentials to reach the output circuit. The inductance L may be the coil of an ordinary wireless receiver or a loop aerial, and the impedance Z may be a resistance, inductance, condenser, tuned circuit or a second loop spaced from the first one. A second condenser may be connected across the elements C, R, Z, Fig. 2 (not shown). The received signal potentials are applied to the loop C, R, L, and to the impedance Z, e.g. as in the combined loop and " vertical" aerial in a direction-finder. Eliminating unwanted signals of different frequency. The unwanted signal potentials developed across R and Z are brought into phase opposition by tuning the circuit CRL approximately to the unwanted signals, and their amplitudes are matched by adjusting the take-off point X or the impedance Z so that they produce no effect on the output circuit. The circuit is not balanced for signals of wanted frequency. Eliminating unwanted signals when using a directive loop. Preventing fading. If the inductance L is constituted by a loop aerial, Figs. 4 and 5 (not shown), unwanted signals may be balanced out as described above by matching the phase and amplitude of the potentials across R and Z. The loop need not be rotated to balance out signals from any particular direction, since the circuit will balance out signals from any direction, and discrimination between wanted and unwanted signals is afforded not only by any difference in their frequencies but to a much greater extent by any difference in the direction from which they come. A loop aerial circuit employed in this way discriminates also between signals of the same frequency reaching the aerial from different directions and may thus be used to reduce some kinds of fading, one wave being suppressed and the other passed. The circuit will also discriminate between waves differently polarized. Tuning or filter circuits with a resonance curve which is flat over a band of frequencies or which may rise on each side of a carrier. If a modulated carrier is applied to the circuit CRL, Fig. 1, and the carrier frequency partly balanced out as above, the side-bands will not balance out to the same extent and an output having the desired frequency response curve may be obtained. Amplitude-matching arrangements. Adjustable valve circuits may be used for matching the potentials across R and Z, Figs. 6 and 8 (not shown), in addition to or in place of the variable tapping X, Fig. 1. Valves arranged as limiters may be used.