Patent GB-755433-A (GB)
Title: Direct reading very-high-frequency meter and signal generator
Inventor: CUTLER LEONARD S
IPC: G01R23/00
Filed: 1954-02-10
Abstract: 755,433. Frequency measuring. GERTSCH PRODUCTS, Inc. Feb. 10, 1954, No. 3943/54. Class 37. [Also in Group XL (c)] A direct reading heterodyne type V.H.F. frequency meter and signal generator comprises side - by - side coarse and fine adjustment and a lattice-type modulator. Frequency measuring.-In Fig. 1, crystal oscillator (1 mc/s.) 10 cooperates with harmonic multiplier 12 so that multiplier 12 and interpolation oscillator 18 feed selected frequencies into lattice type modulator 16 which transmits only the sum and difference frequencies. The L.F. oscillator 18 (1-2 mc/s.) covers adjacent harmonic frequencies. The gang-tuner control coarse dial 170 is adjusted to zero-beat (in detector/amplifier 20/26) the incoming signal 24 (e.g. value: 24.557 mc/s.) with the output frequency of a transfer oscillator 14 and select the appropriate harmonic at 12 tracking 1.5 mc/s. above the 24-25 mc/s. zero-beat value output of transfer oscillator 14 (i.e. the 26th harmonic is selected). Vernier and geared dial/tuner control 172, 174 for interpolation oscillator 18 is now adjusted for zero-beat of the output of modulator 16 against the output of transfer oscillator 14. The frequency output of oscillator 18 is from 2 to 1 mc/s. whilst geared dial 172, 174 goes from 0 to 1 so that the frequency generated is 2 minus the dial reading and this frequency is subtracted from the 26th harmonic to zero-beat the signal from transfer oscillator 14. Thus: 24.557 = 26.000 - (2 -.557) =24+0.557. The sum frequency which would be 26.000+(2-0.557)=27.443 cannot be obtained with any setting of dials 172, 174 because.the 27th and all other harmonics except the 26th are strongly attenuated in the multiplier 12. The Specification includes a detailed circuit, Fig. 2, comprising a 4-position, 6-gang selector switch 130, 132 ... 140, in which a (beat) produces conditions for setting coarse dial 170 for zero-beat of oscillator 14 output with the signal 24 and b sets up for Read " or setting of vernier dial 172. Use of device as signal generator (output from transfer oscillator 14).-For an unmodulated frequency the selector switch 130-140 is positioned at band dial 170/transfer oscillator 14 is set as nearly as possible to the desired frequency (and this also selects the appropriate harmonic in 12); next the L.F. oscillator 18 is tuned by dial 172, 174 to indicate in conjunction with dial 170 the exact frequency desired after which the transfer oscillator 14 is returned as necessary to indicate the zero-beat condition. The d or " Modulate " position of switch 130-140 converts amplifier 26 into an audio Hartley oscillator for anode modulating the output of transfer oscillator 14. Calibrating L.F. oscillator 18 using crystal standard 10.-This is done using switch position c-the " Calibrate " position-which isolates transfer oscillator 14 and connects the output of 10/12 to detector/amplifier 20/26 so that the fundamental of 10 may be compared in mixer 16 with the output of oscillator 18 for the 1.000 reading to be marked; calibration at 0.500 and 0.000 readings can also be carried out in the same manner but using second and third harmonics. Additional marker or calibration frequencies may be obtained by taking the output of oscillator 18 through a suitable harmonic producing network. Also a larger number of check points could be made available by using instead of 10 a 50 kc/s. standard feeding into a multiplier to produce a stable 1 mc/s. and supplying the latter to the multiplier 12. This would provide marker frequencies spaced 50 kc. apart. Circuit details, Fig. 2.-Transfer oscillator 14 is an electron-coupled Hartley type whose fundamental range of 20-40 gives with harmonics a coverage from 20-480 mc/s. of input signal 24 through coaxial line 22. The harmonic multiplier 12 has tuning condenser 60 ganged to tuning condenser 65 of transfer oscillator 14 and as required, 60 selects the resonant condition for producing a particular harmonic of crystal standard 10 at high level and in predetermined correlation with setting of condenser 65. The lattice type modulator 16 employs germanium crystal diodes 90-93 for operation in known manner and the interpolation oscillator 18 is also a known Hartley arrangement. Modifcations.-The oscillator 10 having a single fundamental frequency with harmonics via unit 12 may be replaced by a plurality of stabilized reference oscillators of different frequencies or a single oscillator with a plurality of interchangeable frequency-controlling elements (crystals or the like) to supply the desired carriers to the modulator 16. The transfer oscillator 14 may be an H.F. butterfly type.