GB737613A - Improvements in the automatic frequency control of oscillators - Google Patents

Abstract

737,613. Automatic frequency control systems. SOC. FRANCAISE RADIO-ELECTRIQUE. June 17, 1953 [June 17, 1952], No. 16786/63. Class 38 (4). [Also in Group XL (c)] An oscillator tunable over a relatively wide band, e.g. as the local oscillator in a single sideband receiver, has its frequency determining circuit inductively coupled to a second circuit comprising a capacitor and inductance variable under the control of a discriminator responsive to any deviation in frequency of the oscillator. The first and second circuits may be coupled by mutual inductance or, Fig. 3, by an inductance L4 common to the first circuit L3, C1, L4 and second circuit L4, C2, L2<SP>11</SP>. This Figure shows the arrangement applied to a tuned anode oscillator with frequency tuning variable capacitor C1 and with variable frequency correcting inductance L2" and with the inductances L3, L4 coupled to the grid circuit by mutual inductances M1, M2 of opposite sign, to ensure a constant amplitude as the tuning is varied. It is shown mathematically that if w o =1/#5.w, where w o and w are the frequencies of the secondary and primary circuits per se, then ##/#L2, the ratio of the change in frequency of the primary circuit to the change in inductance of the secondary circuit is a minimum value with respect to w, i.e. is nearly constant. A fixed value for w o is given which makes this relation hold approximately over the frequency range between the minimum and maximum values of the tuned frequency of the primary circuit and with the value of##/#L2 less than at the extreme limits of the frequency range. The secondary circuit inductance L2" may be variable by an iron core displaceable under motor control, or by a pair of non- magnetic metal vanes on a common spindle rotated to overlap on each side the inductance, or by a single vane rotated to a position between two inductance portions connected in series.