Patent GB-602037-A (GB)
Title: Improvements in or relating to electrical signal transmission systems
IPC: G01S1/02
Filed: 1945-09-13
Abstract: 602,037. Thermionic valve circuits. BAILEY, A. E., GIRLING, F. E, J., and PLETTS, .T. W. Sept. 13, 1945, No. 23687. [Classes 40 (v) and 40 (vi)] An electrical signal transmission circuit having a non-linear characteristic is arranged that over a successively increasing range of input levels, the output level first rises to a maximum value, then falls to zero as the input is increased, and on a still further increase of input, rises again to a maximum so that within the range the characteristic exhibits two peaks and a trough. Fig. 1 shows an ideal characteristic for such a transmission circuit, in which the maximum desired input range is OA and the desired output range is OB. With this arrangement, a given small variation of input level such as C-D, G-H, or J-K occurring anywhere in the input range gives a corresponding variation in output level which is a large proportion of the total range. This is especially suitable for use in radar systems such as that described in Specification 602,030, in which Doppler effect due to a moving target produces amplitude modulation of the echo pulses. If these pulses are fed through a circuit having the characteristic of Fig. 1, then, whether the pulses are of large or small amplitude. the amplitude variations in the pulses will produce large variations in the output. These variations are used to modulate the intensity of the beam of a cathode-ray tube to produce a characteristic striated pattern. Fig. 2 shows an amplifier having a characteristic as in Fig. 1. The input, in the form of positive pulses, is fed in at 1 to the grid of a cathode follower V1 biassed from potentiometer P2 fed from a constant voltage source. A diode V2 ensures that in the absence of input pulses, the grid of V1 never falls below the voltage set by P2. The cathode follower V1 has a load resistance R1 in series with a condenser C2 shunted by resistances R2, R3, R4. Thus, since the current for V1 flows through R2 ... R4, the signal will appear with different biasses on lines 3, 4, 5, 6. These differences are arranged to be about 14 volts. Line 3 feeds the signal the inner grid of a valve V3A which is of a type in which the inner and outer grids have the same degree of control over the anode current. For no signal, the inner grid is about 5 volts negative to the cathode and the outer grid is about 4.5 volts positive, which is near cut-off point. As the input increases from zero (0 in Fig. 1), the anode current of V3A increases until the cathode voltage has risen to that of the outer grid, (P in Fig. 1). On a further increase in input, the cathode voltage rises farther and the outer grid being negative relative to the cathode reduces the anode current. This causes an increase in screen current. This continues until a value of the input is reached, (Q in Fig. 1), which causes the anode current to be entirely cut-off, the valve current being entirely screen current. A further increase in input does not affect the anode current of V3A, but the input voltage is now sufficient to overcome the additional negative bias on line 4 and so the signal is effectively passed to valve V3B identical with V3A. A further increase in input then produces an anode current characteristic for V3B, corresponding to the second triangle QRS of Fig. 1, and so on for valves V3C, V3D. As all four valves have a common load R5, the combined output characteristic is as in Fig. 1, these being a peak for each valve. The negative signal on line 8 is reversed and amplified in valve V4 and the output taken at 9 for controlling the intensity of a cathode-ray beam.