Patent GB-397880-A (GB)
Title: Methods of and means for converting a range of electrical frequencies into a second range of electrical frequencies
IPC: H04B1/66
Filed: 1931-12-01
Abstract: 397,880. Transmission systems. WALTON, G. W., 2, Dean Street, London., Dec. 1, 1931, No. 33267. [Class 40 (iv).] Electric oscillations of a primary band of frequencies are converted into oscillations forming a secondary band of different width with the aid of two tuned circuits one of which automatically adjusts its resonance frequency to that of the incoming signal and at the same time alters the tuning of the other circuit. As shown, Fig. 2, a speech-modulated high-frequency current from 16 is delivered to a tuned circuit comprising inductances 3, 4 forming electrodes of a neon &c. tube. The discharge takes place at such a point along the inductances that the circuit is brought into resonance with the incoming currents and a 2nd discharge takes place at a corresponding point between the inductance '4 and a 3rd inductance 5 included in a 2nd oscillatory circuit having a different range of possible frequencies. The secondary oscillations are taken off at 17. An inductance may be included in series with the battery to prolong each discharge. Condensers 10, 14 are bridged by chokes &c. to provide a connection from the battery to the electrodes 3, 5. The inductance electrodes may be of various shapes to give different laws connecting the two groups of frequencies and one or more of them may be straight wires. Fig. 3 shows a practical arrangement. Speech &c. from '23 is fed to an oscillating triode 19 and the modulated oscillations are amplified and fed to the' primary circuit of the conversion apparatus. The secondary oscillations are rectified by the triode 24. The inductance 18 is provided to prolong each discharge. Direct radio transmission of secondary range. The output of the circuit shown in Fig. 2 consists of a side-band with no unmodulated carrier. It can be received bv a similar circuit with a source of carrier frequency oscillations associated with its output side. Where it is desired to send both side-bands the electrodes 3, 5 are split and connected as shown in Fig. 8 to inductances 33, 34 the midpoints of which are connected to supplementary discharge points 35, 36 co-operating with a point 37 connected with split electrode 4. The effect of this is to cause all frequencies in the primary circuit differing by less than 20 from the carrier frequency to produce the same frequency ir the secondary circuit. In a further arrange ment which allows the use of an ordinary re ceiving set, the width of the speech band is halved by halving each frequency, a carrier is modulated with this band and both side-bands are transmitted without any carrier. Systems with 2-electrode tubes. Tubes with 2-electrodes may be connected up as shown ir Fig. 11 the secondary band of frequencies then being inverted as well as compressed and shifted One electrode may be a wire parallel to or coincident with the axis of the coil electrode or it may be a cylinder coaxial with the coi and made of magnetic material with low mag netic losses and high specific resistance. A further circuit is shown in Fig. 16 in which only two connections are made to the discharge device. System with double tubes to avoid direct coupling between primary and secondary cir cuits. In the tube shown in Fig. 17 two pairs of electrodes each comprising a coil and a cylin der are arranged at right-angles. They are con nected up as shown in Fig. 18. The primary circuit comprises in series the elements 11, 49, 3, 45, 45a, 3a, 49a, and the secondary comprises coil 15 and condenser 13 and the two halves of the primary circuit in parallel. Applications. In addition to the use in radio systems referred to above the system may be used in multiplex telephony, a number of narrow secondary bands being sent over a telephone circuit or a single such band being sent over an unloaded line. Mechanical or optical sound records may be made of the secondary band, reconversion taking place in the reproducer.