GB628245A - Improvements in or relating to electric frequency coincidence indicators - Google Patents

Abstract

628,245. Frequency measurements. PHILCO RADIO & TELEVISION CORPORATION. May 30, 1945, No. 13560. Convention date, May 30, 1944. [Class 37] In calibrating a variable-frequency oscillator against a standard oscillator, the zero beat frequency is determined by producing two beat frequencies having a phase difference of 90 degrees, both beat frequencies being changed to variable amplitude signals which are applied to non-linear circuits whose outputs are added to produce a wave having maximum amplitude at zero beat frequency. The output of the variable frequency oscillator 8 is heterodyned with local oscillations from a source 4 to produce an intermediate frequency which is amplified at 10 and tripled and limited in amplitude at 11; to ensure constancy of the intermediate frequency an automatic retroactive circuit 14, 15 may be employed, and constancy of amplitude may be obtained by A.V.C. The standard oscillator 1, 2, produces a series of fixed frequencies, and the appropriate frequency is mixed with oscillations from 4 to produce an intermediate frequency which is tripled and limited at 6. The two intermediate frequencies are mixed at 7, while the output from 11 is given a 90 degrees phase shift at 12 and mixed with the output from 6 at 13. The mixed intermediate frequencies 'are integrated (or differentiated) at 16, 20, phase inverted at 17, 21, applied to square law rectifiers at 18, 22 and mixed at 19, whose output is a maximum at zero beat frequency. The output of 19 produces a pulse at 23 which at its maximum actuates a blocking oscillator 24 to energize a lamp 25 which illuminates the scale of the variable frequency oscillator 8 to produce a photographic record on a camera 25. The pulse from 24 is also applied over inverter 26 and amplifier 27 to step on the film in the camera 28. Specifications 628,246, [Group XIX], and 628,312 are referred to.