Patent GB-588193-A (GB)
Title: Improvements in or relating to apparatus for tuning a variable electrical oscillator
IPC: H03J5/24
Filed: 1945-01-22
Abstract: 588,193. Oscillator tuning circuits. GENERAL ELECTRIC CO., Ltd., BLIGH, N. R., HELLER, D. M., STENNING, L. C., and CHUBB, A. A. Jan. 22, 1945, No. 1755. Addition to 576,161. [Class 40 (v)] [Also in Group XXXVIII] The parent Specification describes apparatus for tuning a variable oscillator, comprising a set of standard frequencies spaced at major intervals, and a second set of standard frequencies stated at minor intervals, the sum of all the minor intervals equalling one major interval, wherein driving means change the frequency of the oscillator continuously and as coincidences occur with each major standard frequency, a mixer circuit provides a pulse which moves a uniselector wiper to make contact with the next standard frequency. A major selector switch is set to control the number of coincidences which occur in this manner before change-over means operate to substitute the minor standard frequencies in the coincidence circuit. The setting of a minor selector switch then determines the number of steps which the uniselector wiper must take under minor coincidences before stopping means operate to prevent further change in the frequency of the variable oscillator. A discriminator circuit is associated with high and low pass filters which serve to keep the frequency of the variable oscillator stabilised in the small common passband of the filters, which is at a constant, displacement from the final standard frequency chosen by the uniselector. The minor frequency interval for a given number of tuning positions may be increased by (i) providing reversing means for the connection to the discriminator to stabilise the frequency of the oscillator at either of two values symmetrically above or below the final standard frequency ; (ii) adding each standard frequency successively to heterodyning frequencies which are harmonic sub-multiples of the minor frequency interval, to produce the required sub-division. To improve the ease and rapidity of tuning, especially when a large number of possible tuning positions is employed, the number of contact positions of each stud of the minor selector switch is increased by a factor C and the number of heterodyning oscillators associated with these contacts is increased accordingly. In this manner, the major interval required is increased by a factor C so that a smaller number of standard frequencies is required for a given number of tuning positions for the variable oscillator. As a further economy, the major standard frequencies are joined together in batches of C to each major interval stud on the uniseleotor, and although a corresponding increase in minor interval studs is required to accommodate the increased number of contact positions on the minor selector switch, the arrangement results in an overall reduction in uniselector studs. The Figure shows the case where factor C=2. Heterodyning oscillators are associated with contacts ABCD, IJKL &c. while contacts EFGH, MNOP; &c. are associated with the discrimmator in reverse polarity to provide interlacing frequencies as described in the parent Specification. Each stud of the minor selector switch N1 is now associated with two minor studs on the uniselector I, stud A of switch N1 being coupled to studs 20-23 of uniselector I, stud I to studs 21-24 and stud Q to studs 22-25. The change-over means always operate at the first major frequency associated with uniselector stud 19, but cams and contacts associated with the switch N1 are so arranged that if the second major frequency associated with stud 19 is required, the relay operating circuit which stops the movement of the wiper is only completed on the second uniselector minor stud coupled to the stud chosen on switch N1. In this manner, the second major interval is made up by one rotational sequence of switch N1, while the uniselector wiper passes over studs 20-22,2, 21-23 or 22-24. As in the parent Specification, one filter in the discriminator is used to produce coincidence pulses for operating the uniselector when beats between the variable frequency and the final standard frequency lie within the pass-band of the filter. In a modification, the second filter is used to hold the uniselector inoperative during periods when there is no output from the first filter in order to eliminate the effect of spurious pulses on the uniselector.