International Standard Electric Corporation

John K Goatcher

Ian A Vance

A radio receiver for FM signals having a demodulation system to produce an approximation to an analog output by either measuring the time intervals between successive zero crossings in the I.F. (FIG. 1, FIG. 2B) or by filtering pulses produced at each zero crossing of the I.F. (FIG. 1, FIG. 2A). The demodulator includes two signal pathways in quadrature phase relation, the second signal either lagging or leading the first signal in dependence on whether the received signal frequency is above or below a local oscillator frequency. The modulation frequency can carry analog information separate and apart from the on-off (digital) information.

Direct conversion radio receiver for FM signals

A multi-mode radio receiver divides the radio frequency input into two channels and in each channel mixes it with the carrier wave frequency. A quadrature shift in the mixing carrier wave frequencies enables base band signals to be filtered from the mixer outputs. The analogue quadrature signals are converted to digital form and processed digitally to reproduce the original modulating signal for am, fm or pm transmissions. For ssb modulation the mixing frequency is the side band center frequency instead of carrier frequency.

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Harlow, United Kingdom

John K Goatcher