Patent GB-633071-A (GB)
Title: Improvements in multi-frequency generating and selecting systems
IPC: H03B21/02
Filed: 1946-09-09
Abstract: 633,071. Valve generating circuits. COLLINS RADIO CO. Sept. 9, 1946, No. 27060. Convention date, Feb. 27. [Class 40 (vi)] A selective multi-frequency producing system for obtaining any one of a large series of closely spaced frequencies each having the stability of a crystal-controlled oscillator, comprises a number of frequency selector channels controlled from a common master oscillator characterised in that each channel has a number of frequency convertors each fed by an adjustable local oscillator and by oscillations controlled from the master source to produce a selected stable frequency at the output of each channel, these outputs being combined in a common mixer circuit from which a particular output frequency is selected. The Figure shows such a system for use in producing in successive 10 kc/s. steps any one of,2000 desired frequencies in the range from 20 to 40 mc/s., each having the same stability as the crystal controlled oscillator 10. The output from the 100 kc/s. crystal oscillator 10 is halved in frequency in divider 13 and harmonics of the 50 kc/s. output are produced in the distorting valve 21 and passed through a band-pass filter 22 which passes any desired narrow band of frequencies in the range 6.7-8.7 mc/s. The output of filter 22 is mixed with the output of a variable local oscillator 24 which is set to any frequency within the range 3-4 mc/s. and which has an output circuit selectively amplifying the second harmonic of its fundamental frequency the " difference " frequency of 700 kc/s. which is set by the ganging of oscillator 24 and filter 22 is amplified in the I.F. amplifier 27. The output of this amplifier is mixed in mixer 28 with the output of a further band-pass filter 29 which selects a narrow band of frequencies within the range 6-8 mc/s. to give the " sum " frequency which is selected by a further tuned band-pass filter 31 which passes a narrow band of frequencies within the range 6.7-8.7 mc/s. The output frequency of this filter, the stability of which depends only upon that of the master oscillator 10, is multiplied ten times in stage 33 and passed through an adjustable band-pass filter 34 which covers the range of 67-87 mc/s. The tuning controls of filters 22, 29, 31, 34 and of oscillator 24 are ganged and controlled by one knob 36 which may be calibrated to cover the range of 67-86.5 mc/s. in 500 kc/s. steps. The selector channel " B " which is controlled by the 10 kc/s. output of divider 14 is substantially the same as channel " A " as far as filter 31 except that it is arranged to select in 50 successive steps of 10 kc/s. spacing any frequency in the range of 3-3.5 mc/s. For use in a carrier generating system the switches 50, 51 are set in the position shown, the crystal oscillator output frequency after successive multiplication and filtering in the stages 15 to 19 is passed through the 50 mc/s. filter 52 and mixed in stage 53 with the output of channel B, the " difference " frequency being selected by the band-pass filter 54 which covers the range of 46.5-47 mc/s. The output of filter 54 is then mixed in stage 55 with the output of channel " A " and the " difference " frequency selected by filter 56 to give any frequency in successive steps of 10 kc/s. within the range of 20-40 mc/s. When the switches 50, 51 are moved to the lower position a 55 mc/s. signal is selected by filter 58 and the band-pass filter 59 adjusted to pass a band of frequencies in the range 51.5-52 mc/s., thus enabling any frequency in successive 10 kc/s. steps within the range 15-35 mc/s. to be selected at the output 57.