Patent GB-601154-A (GB)
Title: Improvements relating to frequency measurement
IPC: G01R23/00
Filed: 1945-03-05
Abstract: 601,154. Frequency measurements. STANDARD TELEPHONES & CABLES, Ltd., EARP, C. W., and KRAMSKOY, C. M. March 5, 1945, No. 5511. [Class 37] In a method of calibrating directly the screen of a cathode-ray oscillograph to measure directly the frequency of a signal wave, a plurality of auxiliary signal waves are produced, of stable frequency spread over the operating frequency range and applied to the screen of an oscillograph in alternation. with the signal wave so that the indications of both exist on the screen simultaneously. In an embodiment of the invention, Fig. 1, which determines the Doppler frequency of a moving object, electromagnetic waves are radiated from directive antenna 6, fed by transmitter 7 and after reflection from the moving object are received by directive antenna 8 and together with waves received directly from the transmitter are fed to receiver 9 from which the difference frequency is obtained. The output from 9 is passed through band-pass filter 24, to alternate noise and frequencies outside the operating band, to amplifier 25. The output of the latter together with the local injection frequency from master oscillator 20 is fed to frequency changer 21 and then to amplitude limiter 26 as a precaution against variations of the local injection voltages, and then to the low-pass filter 27. In unit 2, the output of multivibrator 17 is fed to integrating circuit 18 to produce a symmetrical saw-tooth waveform which controls the frequency of multivibrator 19 by biassing one or both of the grids of the multivibrator. The portion of the frequency range in the vicinity of the frequency to be measured is obtained by applying the saw-tooth to amplitude limiters suitably biassed. The output frequency of 19 is made to vary in precise steps over a frequency range by application to it of the output of 20, a crystal-controlled oscillator. The latter provides two stable frequencies which are connected alternately to control the frequency output of 19 which then. produces two series of frequencies in which coincidental frequencies cause brighter indica. tions on the screen of oscillograph 16. In. Fig. 2, which shows the construction of 20 and 17, valve V1 is a crystal-controlled oscillator giving an output of two sine waves, the amplitudes of which are separately controlled by valves V2 and V3. The two waves are applied alternately to the multivibrator 17 by an electronic switch, both multivibrator and switch being incorporated in the valves V4 and V5, In unit 3, Fig. 1, amplitude limiter 28, bandpass filter 29 and power amplifier 30 are connected in series. The size of the display on the screen is determined by 28 which deals with varying input levels due to different line conditions when units 3 and 4 are connected by a long length of transmission line to units 1 and 2. The output from 30 is fed to paths 10 and 11 and the power amplifier 13 follows and compensates for the loss in delay network 12. With switch 5 at the upper position, calibrator unit 2 is connected to units 3 and 4 and a succession of progressively varying frequencies is applied to the two paths 10 and 11, the phase difference between the waves in the two paths varies with frequency and corresponding indications are produced on the screen of 16. With switch 5 in the lower position, unit 1 is connected to 3 and 4 and the signal wave produces an indication on the screen, the frequency of which can be read directly from the calibration markings which persist on the screen from the application of the calibrator. Specifications 581,162, [Group XL], and 581,201 are referred to.