Pulse or digital communications – Repeaters – Testing
Patent
1986-03-06
1987-12-29
Griffin, Robert L.
Pulse or digital communications
Repeaters
Testing
375 88, 375119, 375120, 455260, 329124, H03D 300, H03D 324
Patent
active
047165790
ABSTRACT:
A simple radio receiver for FSK signals is described in which the signals from the aerial are mixed in two high-gain mixers respectively with local oscillator signals in phase quadrature and at the signals' nominal center frequency. The outputs from the mixers are low-pass filtered to get the difference frequencies. The filter outputs are amplified and one applied to the D input of a D-type flip-flop to the clock input of which the other is applied. The flip-flop output gives the FSK modulation. It is highly desirable that the local oscillator's outputs, called Io and Qo should be in accurate phase quadrature, and the circuit described herein is intended to achieve this. To do this, the Io and Qo signals are applied to a quadrature phase sensitive detector (10) which, if the phase relation is wrong, gives an error signal. This is applied to an adjustable phase shifter (12) in one of the oscillator outputs, in this case the Qo output. Alternatively, the phase adjustment can be applied to both Io and Qo lines. The detector can be analogue, or digital, in which case it could be based on an EXCLUSIVE OR circuit.
REFERENCES:
patent: 4105975 (1978-08-01), Sanders et al.
patent: 4570125 (1986-02-01), Gibson
patent: 4580101 (1986-04-01), Lax
Griffin Robert L.
Huseman Marianne
STC PLC
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