Patent GB-657329-A (GB)
Title: Angular-velocity-modulated wave-signal receiver
IPC: H03D11/06
Filed: 1948-10-22
Abstract: 657,329. frequency and phase modulation. HAZELTINE CORPORATION. Oct. 22, 1948, No. 27538. Convention date, Nov. 28, 1947. [Class 40 (v)] A received F.M. wave is broken up into a series of repetitive pulses from which one or more of the multiplicity of resulting frequencies is selected and applied to a frequency discriminating detector. The detected output is fed back to frequency-modulate (a) the local heterodyning oscillator, or (b) the pulse generator, or (c) the resonance frequency of a narrow pass filter, with the object of reducing the frequency deviation of the F.M. wave, and facilitating the isolation of a selected frequency. The breaking up into pulses may be effected by a super-regenerative amplifier, or by a gating amplifier controlled by a pulse generator. The pulse or quench frequency is higher than the maximum signal frequency, and is less than the maximum frequency deviation of the received wave. As shown in Fig. 5, the F.M. wave is mixed at 14 with a local] oscillator 15 and the resulting I.F. is fed to a super-regenerative amplifier 12<SP>1</SP>. Owing to the intermittent nature of the output, a number of side frequencies are produced having frequency intervals equal to the pulsing or quenching frequency, and each bearing the F.M. signal. One of these is selected by a filter 16 and applied to a F.M. detector 17 giving an audio output at 18. This output is passed to a reactance tube 20 associated with the local oscillator 15 to cause its frequency to follow that of the incoming wave and so reduce the frequency swing of the wave applied to the selector. Fig. 6 is a circuit diagram of a modified receiver. The incoming wave is amplified at 27 and applied to a super-regenerative frequency-changing stage 28, in which it is mixed with a local oscillation from 29 to provide a first I.F. in the tuned anode circuit 46 ... 49 of the mixing valve 45. The valve is intermittently quenched by the discharge of the condenser 47 through the valve, as described in Specifications 648,920 and 654,887, so that I.F. pulses are taken off through the condenser 54 to the outer grid of a second mixing valve 60. The cathode and first two grids of the valve 60 are back-coupled to the tuned circuit 66, 67 to oscillate at a frequency determined partly by the tuning of that circuit and partly by a quadrature feed-back from the valve anode through the damped coil 75. A circuit 77 tuned to the second I.F. feeds a phasing discriminator which detects the signal and applies it through resistors 82, 83 to the outer grid of the valve 60. This causes variation of the quadrature feed-back at 75 and varies the local oscillation frequency in the rhythm of the signal with the result that the deviation of the second I.F. is reduced. The signal is taken to an audio-frequency amplifier 31 across a resistor 78 in the anode circuit. The feed-back from the detector output so reduces the frequency swing that the phase variation in each pulse period is less than 180 degrees. In Fig. 8. the incoming wave is applied to the super-regenerator 12<SP>1</SP> and is then reduced in frequency by heterodyning at 14. The output is passed through a narrow-pass filter 100 to a wide-band detector 17. The filter 100 comprises a tuned circuit 101, 102 associated with a quadrature-phase thermionic reactance 105, the value of which is varied by the detected signal. In this way, the tuning of the filter 100 follows the frequency variations of the selected component of the pulsed wave supplied to it. Specification 657,328 also is referred to.