Patent GB-642696-A (GB)
Title: Improvements in or relating to interference suppression systems for radio receivers and the like
Inventor: BLAKE KENNETH
IPC: G01S1/24
Filed: 1948-04-01
Abstract: 642,696. Radio interference suppression. MINISTER OF SUPPLY. April 1, 1948, No. 9198. [Class 40 (v)] Relates to the suppression of interfering pulse signals in radio reception, in which the receiver is muted coincidently with the interference signals and comprises means for generating a train of muting pulses having a recurrence frequency above the limiting audio frequency of the receiver, certain pulses of the train being coincident with the interference pulses. The invention is applicable to cases in which this requires that the frequency of the muting pulses shall be many times greater than the frequency of the interference pulses. In Fig. 1, a typical radio communication receiver comprising stages 1, 2, 3, 4 is muted by pulses at a frequency of say 15 kc/s. The muting pulses are produced by units 5 to 13. Interference pulses, which may be from a neighbouring radar transmitter, are received amplified and detected in units 5 and 6, and used to trigger a multivibrator 7 which supplies pulses of predetermined duration to the control circuit 8. Control circuit 8 operates during each pulse to suppress oscillator 9 for one cycle, these oscillations always stopping and starting at the same point in their cycle, so that the phase of the oscillations is locked to that of the interference impulses. The output from oscillator 9 is supplied to resonant amplifier 10 which supplies continuous phase-controlled oscillations to pulse forming and shaping network 11. The pulses from unit 11 are used to suppress the R.F. amplifier 1. Unit 13 includes a filter for suppressing the higher harmonics and a pulse amplitude adjusting device. A pulse length adjusting device is provided in unit 11, so that the receiver may be muted long enough to suppress interference from short-range echoes as well as the main interference pulse. Fig. 2 shows the circuits for control oscillator 8, oscillator 9 and resonant amplifier 10. The oscillator comprises valve 17 with its associated tuned circuit in screen 21. Valve 16 has its suppressor and control grids negatively biassed so that it is normally non- conducting. A pulse from multivibrator 7, Fig. 1, is applied to terminal 34 to raise the potential of the suppressor grid and also that of the control grid which however rises more slowly due to the effect of condenser 41. The anode of valve 17 is also connected to the control grid through condenser 41, the arrangement being such that valve 16 commences to conduct just at the end of an oscillation in the valve 17 circuit. Valve 16 then suppresses these oscillations, the length of the pulse from multivibrator 7, Fig. 1, being just sufficient to maintain suppression for a period equal to one cycle. When the pulse ceases, valve 16 is again cut-off, thereby removing the shunt across valve 17 and also shock exciting the tuned circuit 21 so that oscillations immediately recommence from the same point in the cycle at which they ceased. The output from the oscillator is applied to resonant amplifier 18 which thus supplies continuous oscillations of locked phase to terminal 27. Terminal 27 is fed via a transformer 28, 30, and also via condensers 33, 32 which provides a phaseadjusting arrangement by varying condenser 32. The Specification discusses the length of multivibrator pulse, and the phase relationships of the different stages necessary to achieve the desired object. Specification 604,719 is referred to.