Patent GB-503217-A (GB)
Title: Automatic tuning control system for radio receivers
IPC: H03J3/12
Filed: 1937-06-30
Abstract: 503,217. Adjusting wireless apparatus. MULLER, E. N. June 30, 1937,.No. 18179. Void. Convention date, July 1, 1936. [Class 37] [Also in Group XL] In a radio receiver of the kind in which the movement of the tuning shaft is effectively arrested on tuning in to a desired signal by means of a control voltage developed by the signal, the arresting device is released for a predetermined period by means of a switch operated by rotating the tuning knob through a predetermined angle. Fig. 1 shows a superheterodyne receiver in which part of the I.F. energy is applied to a control channel amplifier 19, thence through a rectifier 26 and d.c. amplifier 29 to the winding 30 of an electromagnet, the moving armature 33 of which carries a toothed member 35 which engages the toothed periphery of a disc 32 carried on the tuning shaft. The circuits 24, 25 are sharply tuned to the I.F. so that the magnet 30 is energized only when a signal is accurately tuned in, whereupon further movement of the tuning elements is prevented. The amplifier 29 is biassed back to such an extent that it only becomes operative when the signal is within 300 cycles off-tune, the A.V.C. device 16 ensuring approximately equal response for all signals of satisfactory field strength. To provide for the contingency of operation by a powerful signal off-tune, an auxiliary winding 31, opposing the winding 30, is provided on the electromagnet and is energized by a separate rectifier fed from a circuit of lower selectivity. The clutch interposed between the tuning shaft 64 and the condenser spindle 62 is shown in Figs. 4 and 4a. The drive is effected by a spring-loaded disc 67 carrying a half-ball 68 which engages any one of a series of circular depressions 661 in a cupshaped member secured to the toothed disc 32 on the condenser shaft 62. When the magnet 30 is energized, member 35 engages disc 32 and arrests shaft 62 ; further rotation of 64 causes the ball 68 to spring out of its notch 661 and thus actuates a switch 73, 74 operating contacts 38, 39. As shown in Fig. 1, this switch operation connects the condenser 40 across a battery by connecting contacts 39A and 39B. At the same time contact 38A is disconnected from 38C and connected to 38B ; the former removes an earthing connection from transformer 11 over condenser 12 and thus releases the muting, while the latter closes the circuit of an indicator lamp 15 fed from source 14 to indicate the station received. If the tuning knob is still further rotated, the' ball 68 springs into the next notch ; the low frequency amplifier is again muted and the condenser 40 discharges across part of the grid resistance 22 of triode 19 which is thereby paralysed, the magnet 30 is de-energized and the tuning condenser spindle is released to tune in the next station. In a modification, Fig. 2 (not shown) the filter 24, 25 is replaced by a two-circuit arrangement supplying two differential rectifiers, the resultant voltage being applied to bias the grid of amplifier 19, the anode circuit of which includes the electromagnet winding 30. Alternatively the low frequency amplifier of the receiver may serve as the magnet-operating stage, Fig. 3 (not shown). Other modifications of the clutch construction shown in Fig. 4 include the use of rollers on the disc 32 engaging circular depressions in a member carried by shaft 64, Fig. 5 (not shown) ; and the use of a planetary gear system employing a ball-race and rotatable cage, Fig. 6 (not shown).