Patent GB-467771-A (GB)
Title: Improved arrangements for assisting the tuning of superheterodyne receiving sets
IPC: H03J3/12
Filed: 1936-07-01
Abstract: 467,771. Valve circuits for wireless reception. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. July 1, 1936, Nos. 18268, 18270, 18271, 18272, and 18273. Convention dates, Aug. 20, 1935, Oct. 26,1935, Nov. 8, 1935, Nov. 8, 1935, and Nov. 8,1935. [Class 40 (v)] Exact tuning of a superheterodyne receiver is facilitated by means of two rectifiers coupled to the intermediate-frequency stage, one by a highly selective coupling and the other by a circuit of lower selectivity, the latter rectifier preventing operation of the former until the receiver is a predetermined but small amount off tune. The rectifier 11, Fig. 1, is coupled to the T.F. amplifier 3 through a sharply-tuned circuit 9, the corresponding circuit 4 of the second rectifier 6 being of lower selectivity. The load resistances 12, 7 of the two diodes are in series opposition in the grid biassing circuit of a relay valve 16, a second valve 15 being biassed only by the resistance 7. The output circuits of valves 15, 16 include coils 18, 19 wound in opposing sense on an electromagnet 17, the armature of which is a magnetic disc 20 mounted on the tuning spindle 21 of the receiver. With no signal, valves 15, 16 pass full current but the magnet 17 remains unenergized ; when a signal is just tuned in circuit 4 energizes diode 6 and valves 15 and 16 both cease to pass current, the relay still being inoperative. When the receiver is almost exactly in tune with the signal, circuit 9 energizes diode 11 ; the resulting potential across resistance 12 releases valve 16 and the electromagnet 17 is energized attracting disc 20' to prevent further rotation of the tuning knob 21. The valve 15 and coil 18 may be dispensed with by including a voltage source, such as a battery, in series with resistance 7, Fig. 2 (not shown). The brake-disc relay 17, 20 may also act as a switch by providing suitable contacts for muting the low - frequency stages until the brake is energized. The two diodes may be mounted in one envelope with a common cathode, Fig. 8 (not shown) ; the intermediatefrequency amplifier 3 may also function as the braking valve, replacing valve 16, Fig. 9, (not shown). Fig. 3 shows a further system employing an electromagnetic brake, in which the rectifiers 6, 11, associated respectively with the lowselectivity circuit 4 and sharply selective circuit 9 are combined in one envelope, part of the load resistance 24, 13, of diode 6 being included in the load circuit of diode 11. By this means the latter rectifier cannot operate until the voltage across circuit 9 exceeds the voltage drop across resistance 13 which provides a kind of delay voltage. In Fig. 3 the magnetizing current due to valve 16 is compensated by a second winding fed from the supply source. The brake thus operates on cessation of current in valve 16. This arrangement may be modified by using the I.F. amplifier 3 as the braking valve, a glow discharge lamp being provided in shunt with circuit 4 to act as a voltage limiter, Fig. 5 (not shown). In order to increase the band-width over which the control system is operative after operation has taken place, part of resistance 24 or resistance 13 may be shortcircuited by a switch which is opened when the braking device has operated, Fig. 6 (not shown). Specification 451,346 is referred to. The Specification as open to inspection under Sect. 91 also shows the application of the invention to muting of a low-frequency amplifier, Fig. 3, (Cancelled). The demodulated signal is applied to the amplifier 16 from resistance 12 over condenser 43. Circuits 4, 9, of low and high selectivity respectively, form a band-pass filter, and the circuit operates in the same manner as that of Fig. 1. The potentials across resistances 7, 12 are in opposition so that valve 16 is blocked by negative bias from 7 when the receiver is just off-tune ; when almost exactly in tune, circuit 9 is operative and the voltage across 12 releases valve 16. The volume control 44 cannot be regulated to zero owing to the residual p.d. across condenser 43 ; this may be overcome by employing a resistance bridge, of which 12 forms one limb, Fig. 4, (Cancelled, not shown). The rectifier 6 also functions as an A.V.C. rectifier. This subjectmatter does not appear in the Specification as accepted.