GB1338569A - Receivers for frequency modulated oscillations - Google Patents

Abstract

1338569 Frequency demodulators LICENTIA PATENT-VERWALTUNGS-GmbH 4 Dec 1970 [15 Dec 1969] 57690/70 Heading H3A A frequency demodulator comprises a counting discriminator, such as 1, in which the incoming F.M. signals are initially limited to obtain rectangular pulses from which pulses of equal width are generated by differentiation, the latter pulses being used to generate a waveform (Fig. 3, not shown), e.g. by the charge and discharge of a capacitor 5, which contains the modulation information, an amplitude threshold circuit 7-9 for rejecting components of the waveform of amplitude below a given value which represents interference signals and an arrangement 10, 11 for extracting the modulation information. The demodulated output may be amplified at 13-16. In the alternative embodiment of Fig. 5 (not shown), the low-pass filter 10, 11 is interposed between the discriminator 1 and the threshold circuit. In a further embodiment (Fig. 6, not shown) the amplifying transistor 13 has its bias adjusted to provide the required threshold. The combination of the discriminator 1 and the threshold circuit 7-9 provides better selectivity (Fig. 4, not shown) against interfering signals than that provided by the discriminator 1 alone.