Patent GB-576161-A (GB)
Title: Improvements in means for tuning an electrical oscillator
IPC: H03L7/20
Filed: 1942-12-14
Abstract: 576,161. Electric selective signalling. GENERAL ELECTRIC CO., Ltd., BLIGH, N. R., HELLER, D. M., STENNING, L. C., and CHUBB, A. A. Dec. 14, 1942, No. 17775. [Class 40 (i)] [Also in Group XL] The invention relates to apparatus for tuning a variable frequency oscillator to a particular frequency determined by selecting a key N2 individual to a particular harmonic of the standard frequency, say 900 Kc/s. giving harmonics at major intervals and a key N1 individual to a particular harmonic of a second standard frequency, say 90 Kc/s. spaced at minor intervals. A method of tuning of this type is described in Specification 572,918, [Group XL], but is modified to provide an arrangement by which a predetermined frequency can be selected by keys N1, N2 in contrast to an arrangement in which the frequency to which the oscillator is tuned is indicated by a counter. Selector driving arrangement.-The depressing of the " start " key connects voltage to the apparatus with the result that the wiper W is driven to the "home" position where the circuit is open at contact 1. Also the tracking elements associated with the variable oscillator are cut out by the operation of relay OT. In the " home position relay RP is operated so that the inputs from both the variable and the control oscillators feed the relay Y through the. rectifier 17SS, 18SS. Relay S also operates when the tuning condenser of the variable oscillator is returned to its starting position by the release of the clutches by the spring bias when relay S locks itself. This prepares contact S1 to apply earth to the arm of the switch N1 and at the contact S2 caused magnet M to drive the wiper W. Further, contact S3 applies earth to switch N2 and thus marks the stud of the selector chosen while S4 prepares self-locking relays SA, SC, and closes the circuit of the motor driving the condenser of the variable oscillator. On the marked contact relay SC is operated and locks itself. In this way the " master clutch " is operated and the condenser driven through the "fast clutch " since relay RP2 is operated. Meanwhile magnet M remains operated until contact Y1 breaks and the contact SC4 completes the circuit so that the switch N1 marks the stud of the selector chosen. Relay Y caused the wiper W to be driven one step on each coincidence in frequency between the second set of standard frequencies and the variable oscillator until on stud 20 contact 20-25 opens so that relay RP releases on the next step. In this way the pulses from the rectifiers 17SS, 18SS, are applied separately to relays Y, Z and the "medium clutch" is brought into use and the last coincidence moves the wiper to stud 21 and closes 21-25 to operate relay MIN to bring in the first set of standard frequencies. Stepping continues until the contact marked by Nl is reached whereupon relay SA is operated, thus de-energising the " fast " and " medium " clutches and preparing relay ME to be under joint control of relays Y, Z. Provision for selecting quarter minor intervals. -The filters feeding the rectifiers 17SS, 18SS each pass a frequency of “fo where fo is the interval between the minor frequencies, but one filter passes also frequencies above “fo and the other passes also frequencies lower. The rectifiers control the Y and Z relays respecively. The arrangement is effective by the multiplied contacts A, B, C, D and is such that when the wiper passes from the contacts A, B to the contacts C, D of selector N1 a change in the function of the two sets of beats is effected by switches DR1, DR2. In addition the frequency of an oscillator whose output is mixed with the standard frequencies is changed by “fo when the wiper passes from contact A to contact B so that the variable oscillator is set on contact A to a frequency equal to (nfo-“fo), on contact B to nfo, on contact C to (nfo+“fo), on contact D to (nfo+¢fo), and on contact E to [(n+1)fo-“fo]. Automatic and fine tuning adjustment.-After the operation of relay SA, the motor is energised only when one of the contacts Y1, Z1 is operated in a direction depending on which of these contacts is operated. In this way the condenser is driven to adjust the tuning through the " slow clutch " when relay ME is energised. On the first de-energisation of the motor this relay causes the operation of relay R and the lighting of the " ready " lamp. At the same time the release of relay OT reinserts the tracking elements in circuit so that these elements are under the control of the " push to transmit " key. The "change" key enables the relays to be released sufficiently to enable the variable oscillator to be tuned to a new standard frequency by the release of relay S.