GB211512A - Improvements in radio receivers - Google Patents

Abstract

211,512. Marconi's Wireless Telegraph Co., Ltd., (Assignees of Ranger, R. H.). Feb. 16, 1923, [Convention date]. Atmospherics, eliminating or limiting. - In order to reduce the difficulty of reading signals in the presence of static disturbance, the actual signal is caused to operate a cut-off device so that the dots and dashes of the Morse code are manifested as silent interludes (or marking periods) upon a background of heterogeneous noise (or non- marking periods) due to the static. In order to ensure a continuous noisy background, a local note may be.imparted to the receiver by a " chopper " so as to augment the static effect, this, in turn, being silenced by the signal energy. As shown in Fig. 2, a local source 6 modulates the received energy at a frequency of 3,000, this note being amplified and then passed through a double rectifier to emerge as a note of 6000 frequency. After amplification the 6000 cycle variation is applied to an impulse balancer comprising two thermionic tubes 16, 17 arranged in opposition across the secondary of the output transformers 18. Initial impulses are largely balanced out, but persistent signals reappear in the plate coil 24 as a 6000 cycle note. This output is applied to a coil 26 which feeds the limiting or cut-off galvanometer 25. The galvanometer mirror is initially adjusted so that when no signal is present, light from a source 27 is reflected directly on to a photoelectric cell. The light source is interrupted at a frequency of 1000 per second by an obturator 28, so that a corresponding note is normally delivered to the relay or recorder. When a dot or dash is received the galvanometer deflection swings the light-ray off the sensitive cell and the recorder is silenced. Fig. 3 shows a spacing period followed by a Morse dash, then a second spacing period interrupted by an impulse f<1> of static, followed by a dash broken by a momentary static impulse f<2>, the alternate light and dark zones representing the obturator rote frequency. Either the transmitter or the relay may be reversed in order to facilitate the reading of the inverted signals. Fig. 4 shows a magnetron tube used as a limiter or cut-off. One control winding 32 is fed from a local source with a frequency of 500, creating a control voltage which oscillates between the points V<1>, V<2> on the characteristic curve shown in Fig. 6, and giving rise to a frequency of 1000 in the output circuit. Incoming signals are applied to a second control winding 31, which biases the firts control, moving it either to the points V<4>, V<5> where the output is completely cut off, or else to the points V<7>, V<8> where the output frequency is reduced to 500 and is practically eliminated in the subsequent circuits, which are tuned to 1000. In a modified arrangement a local current of 1000 frequency is applied to the grid of a three-electrode magnetron, the signal currents being carried as before by an external coil.