Patent GB-568747-A (GB)
Title: Improvements in radio receivers
IPC: H04N5/455
Filed: 1943-08-06
Abstract: 568,747. Wireless receiving apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. Aug. 6, 1943, No. 12699. Convention date, Aug. 6, 1942. [Classes 40 (iii) and 40 (v)] [Also in Group XXXVII] A detector circuit for a radio receiver capable of receiving a frequency modulated carrier wave of short wave-length or an amplitude modulated carrier wave of short or longer wavelength, comprising a pair of unilateral conducting devices, and a load resistance having an intermediate point connected through the different unilateral conducting devices to respective terminals thereof, said devices being so poled as to pass current oppositely through the load resistance, frequency modulated short waves to be detected being supplied through an amplitude limiting electron discharge device across each of said devices so as to varv the short wave electromotive force on the devices oppositely in response to variation in frequency of the electromotive force, and amplitude modulated long waves being supplied directly in series with one of the devices. The invention is embodied in a receiver for amplitude and frequency modulation, together with television and phonograph. Keys 14 ... 20 may be moved either up or down from a central neutral position to perform all the switching operations necessary to the various functions of the receiver. In the up positions, there are provided manual tuning for frequency modulation and short wave amplitude modulation, as well as four television stations and phonograph. The down positions give five selected broadcast stations, manual tuning for the broadcast range, and OFF. The lowermost set of contacts 14a, b ... 19b corresponding to keys 14-19 serve to connect the appropriate antenna 10 ... 12 through the corresponding input circuit 50, 41a ... 41d, 215, to line 44 which is connected to the input grid 46, Fig. 2, of frequency converter 45. Dial lights 64 are also energized. The input circuits for manual keys 14 and 19 include respectively tuning condensers 205 and 233. The middle set of contacts 14c ... 19c serve to adjust the frequency of the local oscillator 52, Fig. 2, either by inserting-trimming inductances as 55a ... d or tunable condensers 204, 232 which are ganged for control with the corresponding input tuning condensers 205, 233 by knobs 21, 22. The uppermost set of contacts 14d ... 19d serve to connect in circuit only those valves required for the particular function controlled by the corresponding key. The local oscillator 52 has its frequency determined by inductance 58 for F.M. and television reception, and the output is fed through condenser 61 to the control grid of the frequency converter 45. For the short wave band, an inductance 77 is used, and the output is fed to the suppressor grid 69 of the frequency converter. For the broadcast band an inductance 75 is used and the output, taken from the lower part of 75, is connected between the cathode of the frequency converter and ground. By this arrangement no switching is required in the oscillator feed to the converter. The converter 45 produces, according to which of the keys 14-19 are operated, three intermediate frequencies corresponding to : (1) television picture signals ; (2) television sound and frequency modulation signals ; (3) signals in the short-wave and broadcast ranges. After amplification at 82, the video I.F. is selected at 84 and fed through line 90 for amplification and detection at 95, Fig. 3; and thence to a cathode-ray tube 96. The unit 95 also feeds a synchronizing pulse separator and clipper 97 and horizontal and vertical sweep circuits 103, 106. The I.F. for television sound and for frequency modulation is selected at 85 and fed by line 120 to an I.F. amplifier 123, Fig. 4, limiter 126, and signal detector. The detector is of the phase-shift type, comprising diodes 132, 133 oppositely connected between load resistances 140a, 140b and coupled circuits 137, 138 tuned to the I.F. for television sound and frequency modulation. The connection of the cathode of diode 132 to the lower end of resistance 140a is, however, completed through a circuit 135 tuned to the broadcast I.F. This has negligible impedance at the television I.F. and so the F.M. signals produce an audio output across 140a, 140b which is fed by lines 36, 37 to audio amplifiers 142-144 and loud-speaker 39. Frequency control voltages are fed from resistance 141 after filtering at 156, 157 by line 158 through smoothing resistances 160 and 154, Fig. 2, to the grid of a thermionic reactance 150 to maintain the frequency of oscillator 52 constant. A.V.C. voltages may be fed from 141 to the grids of amplifier 123 and converter 45. For short-wave and broadcast reception having amplitude modulation, the I.F. is selected at 222, Fig. 2, and fed through circuit 85 and lead 120 to the I.F. amplifier 123, Fig. 4. The output appears in circuits 124, 135 tuned to this I.F. and the signal is applied directly to diode 132 and load resistance 140a, coil 137 having negligible impedance at this frequency. The audio output is fed through resistances 140b, 141, leads 36, 37 to the output stages as before. When key 20 is moved to the upper position, contact 20a serves to energize the turntable motor 27, while contact 20b connects audio amplifier line 37 to a pickup 13, Fig. 1. When key 20 is in its down or off position, contact 20a breaks the main circuit from supply plug 30, Fig. 4, over lines 33, 34. Fig. 10 shows the construction of the switch keys, only 14 and 15 being shown. Each key is of bellcrank form pivoted at 110 and biassed by springs 117 to a mid-position. The lower end of the key operatively engages a rectilinearly moving member 114 of insulating material which carries a number of contacts as 14d, 15d for engaging fixed contacts 115 on the base 116. Each key has an aperture 168 which, in the displaced position, engages a hooked part 167 on a longitudinally slidable locking plate 164, biassed to the left by a spring 165. Thus, movement of a key to the operated position, releases any key previously operated. Reference has been directed by the Comptroller to Specification 559,967.