GB253152A - Improvements in or relating to wireless telegraphy and telephony - Google Patents

Abstract

253,152. Marconi's Wireless Telegraph Co., Ltd., (Assignees of Peterson, H. O.). June 8, 1925, [Convention date]. Transmitting systems; heterodyne receiving systems.-In order to overcome the effects of fading, static, and other disturbances, the short carrier wave on which the signal is imposed is periodically varied in frequency, and at the receiver is heterodyned with a locally-produced wave having the same periodic frequency variations. The variation in frequency may be of the order of 1 in 3000, and these variations may occur 100 times per second. As shown in Fig. 2, a long-wave oscillator 57 at the transmitter station B has its frequency periodically varied by the rotation of the movable plates, of a small condenser 59 connected in parallel with the main condenser 58. The long wave is amplified and radiated bv the aerial 68 and is also combined with a short wave from the oscillator 44 in the grid circuit of a modulator 48. From the resultant frequencies in the output circuit 51, the sum frequency is selected and radiated by the aerial 52. The shorter radiated wave is broken up by a signal key 45 or modulated by a microphone in any usual way. At the receiving station C the shorter wave with its periodic frequency variations is picked up by the tuned aerial 20, and transferred to the detector valve 23. The longer wave with its periodic frequency variations is picked up by a second tuned aerial 27 and is combined in the modulator 36 with a local short wave of a steady frequency differing from that of the source 44. The resulting sum frequency is selected at 37 and passed into the grid circuit of the valve 23. The two inputs to this valve thus bear synchronous frequency variations,. and their difference is a steady frequency to which the output circuit 25 is tuned. This steady frequency is interrupted or modulated according to the signals imposed by the key 45 or equivalent microphone. In a modification shown in Fig. 1, the long wave with its periodic frequency variations is generated at a separate station A and is radiated to the transmitter station D where it is picked up by the aerial 11. From this long wave a short wave is generated by an harmonic-producer or frequency-multiplier 14 and is radiated from the aerial 18. At the. receiving station C, one aerial 27 picks up the long wave, and a second aerial 20 the short wave. The long wave is multiplied in frequency by an apparatus 31 similar to that at the station D and is then combined in the valve 36 with a steady frequency from a local source 35. The output of the valve 36 is combined in the valve 23 with the short wave received on the aerial 20, and from the output a wave of the steady difference frequency is selected by the tuned circuit 71, and passed to the detector 40. For multiple working, a single long-wave source may be used for imposing its frequency variations on a number of short-wave channels.