GB578151A - Improvements in high-frequency signal generators - Google Patents

Abstract

578,151. Valve generating circuits. HAZELTINE CORPORATION. July 17, 1941, No. 9075. Convention date, Sept. 30, 1940. [Class 40 (v)] A whole series of stabilized radio frequencies with equal frequency spacing are produced by heterodyning the selected outputs from two or more crystal-controlled oscillators, selection being effected either by switching-in any one of a series of crystals or by switching-in tuned circuits to select harmonics from a single crystal. Each frequency step of a lower-frequency oscillator corresponds to the whole range of ten steps of a higher-frequency oscillator so that decade indicators may be used. As shown, the smaller steps in frequency are provided by a series of crystals A1 ... A10 switched into the circuit of an oscillator valve 20 by an arm 31 under the control of an indicator drum 82. Oscillations of lower frequency are selected by a switch arm 59 which connects a number of condensers B1 ... B10 across a coil 53 so as to select particular harmonics of the oscillation generated by a crystal-controlled oscillator 40. The switch 59 is controlled by an indicator drum 83, and each step in frequency due to movement of the arm 59 corresponds to the whole range covered by the crystals A 1 ... A10. The outputs of the oscillators are mixed in a pair of valves 63, 64 being fed in push-pull to the grids and cathodes respectively. The anodes of the valves 63, 64 are joined in parallel to a broadly-tuned output circuit feeding an amplifier 76. The anode circuit of this amplifier is selectively tuned to pass a desired sum frequency by a switch 80 linked to the switch 59 and arranged to select one of the band-pass circuits C1 ... C10. The harmonic generator 40, or a following valve, may be arranged to have a limiting action so that a square-topped wave is produced rich in harmonics. Amplitude reduction of the higher harmonics may be countered by the use of an inductive output circuit 49 for the valve 40. In a modification, three generators are employed, that of the highest frequency having crystal selection and those of intermediate and lower frequency having harmonic selection. The two latter are mixed to produce sum frequencies which are then mixed with the first to produce the final frequency (Fig. 2, not shown). In a further modification, the first generator has a single frequency output which is mixed with the selected output of the second generator to derive difference frequencies. These are mixed with the selected output of the third generator to produce a desired sum frequency (Fig. 3, not shown).