GB871148A - Improvements in and relating to discriminators and limiters for use therewith - Google Patents

Abstract

871,148. Frequency discriminators; valve limiting circuits. BRITISH BROADCASTING CORPORATION. May 14, 1958 [May 14, 1957; Sept. 17, 1957], Nos. 15323/57 and 29298/57. Classes 40(5) and 40(6) In a frequency discriminator an input circuit is coupled to a tuned circuit 19, 28 inductively coupled to a tuned circuit 20, 29, one tuned circuit being connected to the centre tap of the other to form vector sum and difference pairs of outputs which are rectified and differentially combined in series connected load circuits 23, 25 and 24, 26 to produce a detected output at 27. A diode limiter 18 is also connected across the input circuit 17, 13 without producing distortion at the discriminator output and may be back biased by the voltage produced by the anode current of the amplifier tube 12. The inductors 19, 20 may be of low and high impedance respectively. Alternatively, the coupling between the input circuit and first tuned circuit may be capacitive. Also limiting may be produced by automatic gain control from a rectifier connected to the input circuit, or the diode limiter circuit 18 may be connected between anode and control grid of the valve 12 or across a further inductor coupled to the input circuit inductor 13. The limiter bias may also depend on signal voltage. Further, the limiter may be connected between the anodes of the two valves preceding the discriminator, and may be back biased by an R-C circuit in the anode circuit of the first of the two valves.