Patent GB-566906-A (GB)
Title: Improvements in frequency measuring or indicating devices for use with oscillation generators
IPC: G01R23/00
Filed: 1943-07-14
Abstract: 566,906. Superheterodyne circuits for wireless reception. COSSOR, Ltd., A. C., and WYNN, A. H. A. July 14, 1943, No. 11451. [Class 40 (v)] [Also in Group XXXVI] A wavemeter for indicating the frequency of a tunable electric oscillator comprises a stable oscillator producing a desired range of harmonics, an intermediate frequency amplifier tunable over a range equal in width to the fundamental frequency of the stable oscillator, a tunable filter to select a desired harmonic from the stable oscillator means to mix that harmonic with the output of the tunable oscillator and to apply the resultant difference frequency to an I.F. amplifier which is tunable over a range equal in width to the fundamental frequency of the stable oscillator, and means to indicate when the I.F. output is a maximum. As shown, the wavemeter is combined with a standard superheterodyne receiver, and switches 13, 14, 15 are provided for switching from the reception to the metering condition. When the switches are thrown to the right, the aerial 11 feeds a mixer 17 through an amplifier 10 which is gang-tuned with the local oscillator 16. The difference frequency is fed to a fixed-tuned I.F. stage 22 and thence to a detector 19 and phones 20. In order to ascertain the frequency to which the set is tuned, the switches are thrown to the left-hand position. In a typical example, the stable oscillator 12 has a fundamental frequency of 100 kc/s. and produces harmonics covering the whole range of frequencies to which the set can be tuned. The filter amplifier 10 selects the nearest harmonic which beats with the oscillation from the local oscillator 16 and gives a difference frequency in the I.F. circuit 23. This circuit is then adjusted to give maximum output in the meter 21. If the fixed tuning of the circuit 22 is 400 kc /s., the circuit 23 tunes from 400 to 500 kc/s., and is graduated from 100 to 0 in thereverse direction. The true tuning of the set may then be read in kc/s. by taking the first two figures from the graduation of the control dial of the elements 10, 16 and the last two figures from the control dial of the circuit 23. The tunable circuit 23 may be used as a fixedtuned circuit during signal reception, the circuit 22 being omitted ; and a single valve may serve alternatively as an element of the meter 21 and the detector 19. The I.F. amplifiers for signal reception may be separate from that used for metering, both being permanently connected to the mixer output, and the switching effected by cutting out the filament or anode supply for the unwanted amplifier. Separate radio frequency amplifiers 10 may also be employed, both being gangtuned with the oscillator 16. The wavemeter may be used independently of the radio receiver, and the frequency of an outside source may be measured by adjusting the oscillator 16 until zero beat is obtained between the oscillator 16 and the outside source. According to the Provisional Specification, the tuning control of the circuit 23 may be geared to give a small adjustment to the normally stationary calibrated member of the local oscillator control 16. Alternatively, a mask with an opening may be mounted over the disc carrying the calibration of the local oscillator. The mask moves radially over the disc as the tuning control 16 is adjusted, so that the radial distance of the window is proportional to the rate of change of frequency with angular movement. The mask is also moved circumferentially or tangentially by the movement of the tuning control of the circuit 23.