GB620668A - An improved arrangement for reducing the frequency band in the heterodyne reception of frequency-modulated oscillations - Google Patents

Abstract

620,668. Frequency modulation. PATELHOLD PATENTVERWERTUNGS- & ELEKTRO-HOLDING AKT.-GES. Jan. 25, 1946, No. 2566. Convention date, Jan. 27, 1945. [Classes 40 (v) and 40 (vi)] In a frequency-modulation receiver, the received wave is divided in frequency by a heterodyne mixer, the second input of which is derived from the I.F. output through a limiter, a frequency-multiplier and a band-filter. The incoming wave, or preferably a wave of lower frequency derived therefrom, is fed to a mixer M2, the output of which is amplified at ZF2 and is fed through a limiter B to F.M. detector D. The limiter B also feeds a frequency-doubler or frequency-multiplier V, and the multiplied output is filtered and constitutes the second input to the mixer M2. If the multiplying factor of V is n, the mixer output is at 1/nŒ1 times the input frequency. The output from the multiplier V may be used to synchronize a local oscillator which feeds the mixer M2 (Fig. 3, not shown). As shown, the frequencydividing stage M2, ZF2, B, V follows an ordinary heterodyne stage M1 in which the local oscillator O is of the magnetron type and has its frequency automatically adjusted by the output of the discriminator D fed through a low-pass filter TP. Two or more frequencydividing stages may be arranged in cascade (Fig. 4, not shown). The frequency multiplier V may comprise a multi-vibrator circuit (Fig. 6, not shown). Specifications 554,914 and 556,171 are referred to.