Patent GB-102503-A (GB)
Title: Improvements in High Frequency Signalling, particularly applicable to wireless Telephony.
IPC: H04B1/68
Filed: 1916-11-30
Abstract: 102,503. Western Electric Co., (Assignees of Carson, J. R.). Dec. 1, 1915, [Convention date]. Wireless telephony and signalling.-In a method of signalling by means of modulated high-frequency waves, particularly applicable for wireless telephony, the oscillation-generator and the microphone are connected to the aerial circuit in such a manner that, when the microphone is inactive, no energy is radiated, while when the microphone is operative to vary the high-frequency current, the energy radiated has a frequency equal to that of the oscillation-generator, plus or minus the mean speech frequency. For signalling, the microphone is replaced by a key and a generator of audible frequency. At the receiving-station, the received waves may be combined with locallygenerated oscillations having a frequency equal to that of the oscillation-generator at the transmitting-station. In order to enable the transmitting and receiving circuits to be permanently connected to the same aerial, current-limiting devices are arranged between the aerial and the receiving circuits to prevent the energy absorbed by the receiv. ing circuits from exceeding a pre-assigned value. In the transmitting system shown in Fig. 1, the oscillation-generator 1 and microphone 2 are inductively coupled to a circuit 5, which is tuned to the frequency of the generator 1. Each terminal of the condenser 8 is connected to the grid of one, and the filament of the other, of two similar audions 9, 10, the output circuits 17, 18 of which contains coils 19, 20 coupled to an oscillation circuit 23, which is connected through an amplifier 27 to the aerial circuit. If the frequency of the generator 1 is O/2# and the mean speech frequency is P/2#, the resultant wave in the circuit 5 may be resolved into three components of frequency Q-P/2#, Q/2#, and Q+P/2#, of which only the first and last components contain a current of speech frequency. The currents of frequency Q/2# can therefore be eliminated without affecting the clearness of telephonic transmission; locally-produced oscillations of this frequency may be combined at the receiving-station with the received waves of frequency Q-P/2# or Q+P/2# The currents of frequency Q/2# are suppressed by the differential arrangement of audions shown, the circuits 17, 18, 23 and the aerial circuit being all tuned to the frequency Q-P/2# or Q+P/2# Waves of frequencies Q+P/2# and Q-P/2# may be simultaneously radiated. A similar arrangement is described in which the two audions 9, 10 are combined, the device having one filament and two grids and two anodes. In both arrangements, the audions do not act as amplifiers or repeaters, but as a modulating-device. In the receiving-system shown in Fig. 2, the aerial 31 and oscillatory circuit 32 are tuned to the frequency Q-P/2# (or Q+P/2#), and the received energy amplified by an audion 34 is conveyed to a circuit 36 tuned to the same frequency. A generator 37 producing waves of frequency Q/2# is also coupled to the circuit 36, and the combined energy influences an audion detector 39 connected to a telephone 41. In a combined transmitting and receiving station, the receiving circuit 32, shown in Fig. 2, is coupled to the aerial forming part of the transmitting system shown in Fig. 1, by two thermionic devices which act as current-limiting devices adapted to pass an amount of energy approximately equal to that received from the distant station.