Patent GB-611728-A (GB)
Title: Improvements in variable-frequency radio signalling apparatus
IPC: H03J1/18
Filed: 1945-10-31
Abstract: 611,728. Selective control systems. GENERAL ELECTRIC CO., Ltd., FAIRBAIRN, E. P., and CHUBB, A. A. Oct. 31, 1945, No. 28959. [Class 40 (i)] [Also in Group XL (c)] Means for tuning radio apparatus of the kind depending on the counting of beats between two oscillations, are arranged so that the tuning operation cannot begin until the beating oscillations have reached a predetermined amplitude. Fig. 1 shows the general arrangement in which the output from an harmonic generator 13 is modulated at 12 on to the output of the oscillator 10 which is to be tuned to a desired frequency. The output from 12 after filtering at 14 is mixed at 15 with the output of a fixed crystal-controlled oscillator 16. As the frequency of oscillator 10 is varied throughout its range, the series of equally-spaced frequencies in the output of mixer 12 moves past the frequency of oscillator 16. As each coincidence is passed through, the output of mixer 15 includes frequencies in the range 0-60 kc. which are selected at 17 and fed to filter 18 which passes 22-50 kc. and filter 19 which passes 0-23 kc. Filters 18, 19 feed rectifiers 20, 21 to supply a D.C. input at each coincidence to terminals 31, 32 of a beat counting and tuning unit arranged to drive the tuning element of oscillator 10 through shaft 11 until the number of beats for which unit 22 has been set have been received. To expedite counting, harmonic generator 13 is arranged to give two series of harmonics, a major series having a fundamental frequency of 450 kc. and a minor series having a fundamental frequency of 90 kc. In the condition shown, oscillator 27 has a controlling crystal and an anode circuit both tuned to give 450 kc. which is fed to a multi-vibrator 29 to give the major series of harmonics. When relay contacts M1, M2, M3 are moved across, the crystal and anode circuit are changed to 90 kc. and the output is fed to a multi-vibrator 28 to generate the minor series of harmonics. Fig. 4 shows the apparatus in the unit 22 of Fig. 1 in the initial rest position. When power is switched on, such as by closing switch 26 of Fig. 1, positive potential is applied to terminal 33, Fig. 4. This operates relay M causing contacts M1, M2, M3, Fig. 1, to set the generator 13 to 90 kc. When the valves have warmed up, one of the harmonics from 13 will combine with the oscillations from 10 and 16 to give an output from 18 or 19 which is applied to terminals 31, 32 of units 22 to cause operation of relay CF. Contact CF1 causes operation of delay relay which locks on at D1. D2 deenergizes relay M, thus setting generator 13 to 450 kc. and D3 disconnects filter 19 and terminal 32 from relay CF. This test shows the apparatus to be ready for a tuning operation. QA, QB are major and minor harmonic setting switches, and if, for example, the tuning spindle is to be turned through the equivalent of thirtytwo minor harmonics, QA is set to contact 6 and QB to contact 2 to connect these contacts to earth. The contacts of QA, QB are connected as shown to contacts 1 ... 21 of a step-by-step selector SM1 controlled by winding SM. To start a tuning operation, switch B is closed to operate relay S which locks on at S1 and energizes relay coil SM causing selector arm SM1 to advance until it reaches earthed contact 5. At this stage the motor Z is connected to tuning spindle 11 through a fast clutch FA. Tuning proceeds at a rapid rate and at each coincidence of the 450 kc. series of harmonics with the output from oscillator 16, an output from filters 18, 19 applied to terminals 31, 32 causes operation of relay CF to cause selector SM1 to advance one step. At the end of the set number of major coincidences, arm 34 of SM1 is on contact 10. Then a switch SM2 is operated by a cam on the selector spindle 35 which causes the fast clutch FA to be de-energized and a medium speed clutch ME to be energized. Also relay M is energized to change the generator 13 over to 90 kc. Tuning proceeds more slowly and at each 90 kc. coincidence, relay CF is energized to advance selector SM1 one step until the selected earthed contact 12 is reached. This causes operation of relay SA which disconnects the selector operating coil SM, de-energizes the medium speed clutch ME and couples the motor through a slow speed clutch SL. The tuning now proceeds at a very slow rate until, at the next coincidence, the output from the filter 17 has a frequency between 22 and 23 kc., i.e. the overlap of filters 18, 19. Then both relays CF and RV operate since contacts D3 and RP2 are open and SA4 is closed. Both brushes of the motor are connected to earth by contacts CF1 and RV1 and the apparatus is then tuned. In a modification, Fig. 5 (not shown), the delay relay D is dispensed with and its functions are performed by relay S. In this case, a test for indicating the correct working of the beating oscillations is made at each tuning operation and not only when the apparatus is first switched on. An arrangement is also described, Fig. 7 (not shown), for tuning shaft 11 manually through the medium of a clutch which is energized only when the beating oscillations are present. Alternatively, rotation of the shaft may be prevented by an electricallycontrolled stop except when beating oscillations are present. Specification 572,918, [Group XL], is referred to.