Patent GB-662693-A (GB)
Title: Angular-velocity-modulation wave-signal translating system
IPC: H03D11/06
Filed: 1949-06-09
Abstract: 662,693. Frequency and phase modulation. HAZELTINE CORPORATION. June 9, 1949 [June 25, 1948], No. 15408/49. Addition to 638,111. Class 40 (v). A receiver for frequency-modulated or phasemodulated waves comprises a pulse-modulated repeater for periodically sampling the phase of the received wave and developing an oscillation in that phase, means for comparing the phase of the received wave and of the oscillation at periods following the sampling periods to develop an output signal, and a control circuit responsive to the output signal for controlling a time component of the pulses. In Fig. 4, the received wave is applied to an amplifier 120, pulsed by a source 122, to shock-excite a resonator 141 giving a damped oscillation in the same phase as the momentary phase of the received wave. After a delay, the received wave is passed through a pulsed amplifier 121 to a comparator 140 where its phase is compared with that of the oscillation from the resonator 141, and the audio signal resulting from the comparison is taken off at terminals 150, 151. The time delay is effected by a multivibrator 123 pulsed from the source 122. The output pulse from 123 is differentiated and limited at 124 to give a delayed pip which times a pulse generated in 125 and applied to the amplifier 121. The width of the multivibrator pulse, and therewith the time delay, is varied in the rhythm of the demodulated signal by applying that signal to the multi-vibrator. Pulses, time-modulated by the audio signal, may be taken off at the output terminals T of the pulse source 125. In the arrangement shown in Fig. 1, the incoming wave is applied to the grid of a super-regenerative amplifier 21 to generate oscillations in the tuned circuit 22, 23 when a quenching-pulse from the anode of a second valve 43 periodically brings the circuit to maximum sensitivity. The phase of this oscillation is determined by the momentary phase of the incoming wave, and its frequency content includes a spectrum of side frequencies as shown by the ordinates of the curve A, Fig. 2, separated by the quench frequency. Curve C represents the frequency response of the amplifier unit 20, centred on the mean incoming frequency fr. A second self-quenching super-regenerator unit 40 comprising valve 43 and back-coupled circuit 41, 42 is arranged so that its oscillation persists through the quench period and its responsive curve represented at D and E is centred beyond the limit of the curve C but within the range of the side frequencies bounded by the curve A. The regenerator 40 is excited by the overlapping side frequencies, the phase of each of which is determined by the phase of the incoming wave at the moment of sampling by the unit 20. At the moment of maximum sensitivity of the unit 40, the valve grid has two voltage components, one due to the hang-over from the preceding burst of oscillation, and the other due to the side frequencies from the unit 20. As the latter shift in.phase relative to the former, their vectorial resultant shifts in phase and amplitude. The variation in amplitude changes the self-quench frequency of the unit 40, with the result that the anode voltage of the valve 43 comprises pulses frequency-modulated by the audio signal. This signal may be taken off through a filter 52, 54 designed to remove quench-frequency and higher frequency components. Specifications 654,887 and 657,329 are referred to.