Patent GB-665924-A (GB)
Title: Improvements in or relating to electric variable frequency oscillation generators
Inventor: STEPHENS CEDRIC JOHN
IPC: H03B21/04
Filed: 1949-03-25
Abstract: 665,924. Generating oscillations. STANDARD TELEPHONES & CABLES, Ltd. March 25, 1949, No. 8155/49. Classes 40 (v) and 40 (vi). An oscillation generator adjustable between 0-5 Mc/s. comprises an adjustable lowfrequency interpolation oscillator followed by one or more intermediate frequency changers to which selectable carriers of higher frequency derived as harmonics of a standard frequency source are applied to produce in the output a successively higher frequency, and is characterized in that the control i.e. selector means for the intermediate frequency changers partly controls the selection of carrier frequencies by the next frequency changer. The invention is characterized by employing both the upper and lower sidebands of modulator outputs to reduce the number of carriers necessary, and reinverting the inversion previously produced by lower sidebands. The output band-pass filters of each stage are moreover halved in number. The intermediate frequency changers Fig. 2, comprise two modulators A, B and switches 17, 18 which select a particular combination of integrally related harmonics of the same order derived by filters 11-14 from the standard source, and switches 24, 28 selecting particular band-pass filters associated with the modulators so that only a particular sideband, upper or lower, is selected. The second and later intermediate frequency changers also comprise reversing switches 19, 20 for re-inverting previous frequency inversion if the later frequency changer itself does not call for frequency inversion. Push-button keys corresponding to the successive digits in the frequency to be produced operate through relays of the various switches. At a particular second or later intermediate frequency changer stage the upper sideband is selected by the first modulator A for digits 0-4 and lower sideband (inversion) for digits 5-9 unless the previous digit of the previous stage was in the range 5-9 in which case lower and upper sidebands are automatically selected for ranges 0-4 and 5-9 respectively. The second modulator B always selects an upper sideband. It is thus ensured that the final output of each stage comprising, e.g. the frequency component (D 1 +10D 2 +10<SP>2</SP>D 3 +10<SP>3</SP>D 4 +10 4 D 5 ), corresponding to the successive digits D 1  ... D 5  operated, is wholly uninverted (all terms D 1  ... D 5 +) or inverted (all terms -), depending on whether D 5  is within the range 0-4 or 5-9. The final frequency changer differs from the intermediate and produces an uninverted output. The carrier sources of each frequency changer are harmonics of a basic frequency 1, 10, 100 ... Kc/s. derived from a standard source of 1 Kc/s. The interpolation oscillator is of resistance-capacity type adapted by push-button digit keys to shunt decade resistances across the main oscillator resistance, and may be checked against the standard source. The final frequency changer (Fig. 6, not shown) may comprise in parallel a cascade modulator system fed by either of two stable oscillators each differing by 1000 c/s. in frequency from the two carrier sources feeding the first modulator so that two outputs differing by 1000 c/s. may be obtainable. These may be used for beating down two oscillations of variable phase difference to a low frequency of 1000 c/s before measuring phase deviations between the two oscillations.