Patent GB-223267-A (GB)
Title: Improvements in wireless receiving systems
IPC: H03G3/22
Filed: 1923-06-04
Abstract: 223,267. Soc. Francaise Radio-Electrique, and Regnauld de Bellescize, H. J. J. M. de. June 4, 1923. Atmospherics, eliminating or limiting; thermionic amplifiers, detectors, and heterodyne receivers.-A receiving system for eliminating strong damped atmospherics comprises a series of high-frequency resonators of normally low damping but arranged to be highly damped as soon as the received current exceeds that of the normal signal. By this means an atmospheric giving a rectified current Q<1>, Fig. 4, large compared with the normal signal (shown in dotted lines), is shortened in duration and acquires the form Q<2>. By passing this current through a suitably-adjusted currentlimiter, it assumes the shape Q<3>. Its amplitude is then reduced below that of the signal, as shown at Q<4>, by passing it through an aperiodic circuit, or a circuit tuned to tone frequency, the time constant of this circuit being adjusted to as high a value as is permitted by the speed of sending the signals. The difference in amplitude between signal and atmospheric is then increased, as shown at Q<5>, by applying them to the grid of a valve adjusted to a point of zero plate current, the signal carrying the point up to the straight portion of the characteristic. while the atmospheric hardly carries the point beyond the lower bend. Referring to Fig. 7, an aerial or other resonant circuit 1, 2 is coupled to another resonator 3, 4 forming the input of a high-frequency amplifier 11, the output of which is applied to a detecting-valve 14 having a resistance 21 in its plate circuit. The voltages arising from the flow of rectified current in the resistance 21 are applied through a biassing battery 7 and a low-pass filter 8, 9, 10 to the grids of damping valves 5. The plates and filaments of these valves are connected across the respective resonant circuits 1. 2 and 3. 4 and their normal grid potential is such that the ordinary signals do not cause the valves to become conductive. A strong atmospheric, such as Q<1>, Fig. 4. renders the valves 5 conductive and damps the resonators, thus shortening the duration of the disturbance. The received energy passes forward through valves 23, 26 the first having its grid voltage so biassed by the battery 7 that the positive potential pulses applied to its grid by the plate of valve 14 are reproduced without disortion as negative potentials on the plate of the valve 23. The valve 26 has its grid voltage adjusted so that normal signals just annul the plate current. Strong atmospherics are thus reduced to the same amplitude as signals, as shown at Q<3>, Fig. 4. The disturbance is further reduced in amplitude and lengthened in duration, as indicated at Q<4>, Fig. 4, by connecting a condenser 31 shunted bv a resistance 32 in the plate circuit of the valve 26. The capacity of the condenser 31 is as large as the speed of working will allow, without causing the signals to merge into each other. The disturbance is thus reduced to an amplitude less than that of the signal. Both are applied to the grid of a valve 43 which has its normal grid potential adjusted slightly more negative than that required to annul the plate current. The weaker disturbance hardlv carries the grid potential beyond the lower band of the characteristic, whilst the stronger signal reaches up the straight portion. A resistance 42 may be connected in the grid circuit of the valve 43. The plate, circuit includes a signal indicator 51 in series with a resistance 52, a telephone and audiofrequency interrupter being connected across the resistance. In a modification. the signals are heterodyned by a local source before passing into the amplifier 11. The first limitation in amplitude is obtained by connecting a resistance between the grid of the valve 23 and the battery 7, the high voltage of the disturbance causing grid current to flow through this resistance, thus reducing the grid potential and the plate current. The output circuit of this valve is coupled to a circuit tuned to the beat frequency, which is connected in the grid circuit of a back-coupled valve serving to reduce the damping of this tuned circuit. This reduction of damping is carried as far as the working speed will allow, and has the effect of extending the duration of the disturbance, whilst reducing its amplitude relatively to the signal amplitude. The signals may be heard in a telephone in the plate circuit of this valve, or passed on to a rectifier with a signal indicator in its output circuit. The voltages applied to the grids of the damping valves 5 may be of highfrequency, obtained from the circuits of one of the high-frequency amplifiers; or it may be of low-frequency obtained from a transformer in the plate circuit of the detector, when a local heterodyne source is provided.