GB524225A - Improvements in or relating to electric oscillators - Google Patents

Abstract

524,225. Valve generating circuits. STANDARD TELEPHONES & CABLES, Ltd., BARNARD, R. M. Jan. 24, 1939, No. 2480. [Class 40 (v)] In a beat-frequency generator for producing a wide band of frequencies, the wide band is divided into a series. of limited ranges related to one another by a constant ratio e.g. 300 cycles-3 Kc., 3 Kc.-30 Kc., 30 Kc.-300 Kc. &c. by the provision of interchangeable tuning circuits which vary the frequency of both oscillators in the same ratio so that the beat frequencies will also vary in the same ratio and the frequency in any of the limited ranges may be read off from a single scale associated with a variable condenser in one of the oscillators which provides tuning within any of the ranges. In the example shown, one oscillator V2 provides a number of fixed frequencies 10 Kc., -100 Kc., 1 Mc., 10 Me., determined by interchangeable crystal elements X (or in the lower range by a tuned circuit L2, C4 only), and the other oscillator V1 has interchangeable tuning elements L1, C3 which with a variable condenser C5 provide frequency ranges of 7 Kc.-9.7 Kc., 70 Kc.-97 Kc., 700 Kc.-970 Kc., 7 Mc.-9.7 Mc. These fundamental frequencies are combined, after amplification, in a valve V5 and the difference frequencies corresponding to ranges of 300 cycles-3 Kc., 3 Kc.-30 Kc., 30 Kc.- 300 Kc., 300 Kc.-3 Mc. are selected by a bandpass filter F which is also interchangeable. The interchangeable units may be of plug-in type. The difference frequency produced may be checked in a cathode-ray oscillograph CRO with a standard frequency or, by changing over a switch S, with one of the frequencies of the crystal-controlled oscillator V2, any required adjustment being made by means of condenser C3.