Patent GB-453922-A (GB)
Title: Improvements in and relating to frequency determining means
IPC: G01R23/00
Filed: 1935-03-25
Abstract: 453,922. Frequency measurements. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London. March 25, 1935, No. 9268. Convention date, March 24, 1934. [Class 37] [See also Group XL] Apparatus for measuring the frequency of oscillations received from an external source comprises two discharge devices 1; 2, the device 1 being connected to a set of piezoelectric crystals or the like 29 and the device 2 to a circuit of adjustable frequency ; oscillations received in the device 1 may produce a beat note with oscillations produced in that device, which note is amplified in the device 2 and a third device 3 and received in the earphones 22 ; or the oscillations received in the device 1 may produce a beat note with oscillations produced in the device 2 ; or oscillations produced in the devices may be transferred to an output circuit 48. The grid 25 of the device 1 nearest to the cathode is connected to a movable contact 30 which can be applied to any one of the piezo-electric crystals 29 and, through a resistance 26, to the negative pole of a battery 4 ; the next grid 27 is connected to the positive pole of the battery through a fixed tuning inductance 271 giving a frequency outside of the range of the frequencies of the crystals 29 ; the grid 41 is connected to the receiving circuit and is provided with a screen grid 11. The cathode of the device 1 is connected through a condenser 49 to a grid 44 in the device 2 protected by a screen grid 12. The device 2 is also provided with a grid 37 connected to an oscillatory circuit and a grid 36 connected to the negative pole of the battery 4. The cathode of the device 2 is connected through an amplifying valve 3 and a transformer 10 to the earphones 22. To measure the frequency of incoming oscillations and adjust the transmitter producing them to a required frequency the contact 30 is connected to the crystal 29 the frequency of which is nearest to that required. According to the nature of the coupling between the two devices either beats are produced in the device 1, amplified in devices 2 and 3 and transmitted to the earphones 22, or the two sets of oscillations are transmitted to the device 2 which acts as a detector producing beats which are amplified in the valve 23 and are transmitted to the earphones 22. If the frequency required is that of the crystal the transmitting apparatus is then adjusted until the beats disappear. If the frequency required is intermediate between those of two of the crystals oscillations of the required frequency are produced in the device 2 by means of an oscillatory circuit comprising a tuning-condenser 31 and either of two inductances 32, 33, and beats produced between these oscillations and the incoming oscillations transmitted by the device 1, the crystals 29 being disconnected. In this case a preliminary calibration of the oscillating circuit may be made by causing it to produce beats with oscillations produced by the appropriate crystal and transmitted by the device 1. The earphones 22 are provided with a jack 21 which may be connected to one of several tappings of the secondary of the transformer 10 and at the same time close the heating-circuits of the cathodes of the devices 1, 2, 3.