GB624662A - Improvements in or relating to high frequency communication systems - Google Patents

Abstract

624,662. Frequency modulation. WESTING- HOUSE ELECTRIC INTERNATIONAL CO. Jan. 28, 1947, No. 2624. Convention date, July 7, 1944. [Class 40 (v)] In a high-frequency communication system of the kind in which the signal is amplitudemodulated on a subcarrier wave which is then used to frequencymodulate the carrier wave, the amplitude-modulated sub-carrier is recovered at the receiver by a discriminator involving balanced rectifiers within a waveguide, and is fed to an ordinary radio receiver. Fig. 3 shows a form of the discriminator, in which the received F.M. carrier is fed to a wave-guide 11 with two opposed rectifiers 16, 17 connected across it. The end of the guide communicates by an opening. in a partition 15 with a cavity 14 resonant with the carrier. A loop 19 picks up wave energy from the cavity and feeds it to the junction of the rectifiers, the lead 18 being of such a length that at the mean frequency the wave is in quadrature with that traversing the rectifiers, and there is no voltage across the load resistors 22, 23. As the frequency deviates, voltages appear across 22, 23 representing the amplitude-modulated sub-carrier, and are fed via the terminals A, B to an ordinary receiver tuned to the subcarrier. The high-frequency circuits through the rectifiers are completed by the guide wall and by capacities present where the leads from the rectifier 17 and the loop 19 pass through the wall. In a modification, the rectifiers are placed a half-wave apart along the guide, and pick-up from the resonant cavity is by a probe connected to a coaxial line which is branched to feed the wave energy to the respective rectifiers (Fig. 4, not shown).