Patent GB-592579-A (GB)
Title: Radio obstacle detection systems employing reflected pulses
IPC: G01S19/35
Filed: 1944-03-15
Abstract: 592,579. Radiolocation ; valve circuits. STANDARD TELEPHONES & CABLES, Ltd. March 15, 1944, No. 4871. Convention date, July 24,1942. [Class 40 (v)] In a pulse reflection obstacle detection system, to enable pulses of differing amplitudes to be kept in view on a cathode-ray oscillograph while providing all the necessary amplification to enable the aerial orientation for maximum amplitude of any pulse to be determined, an amplifier is employed comprising two amplifying means, one of which saturates at a predetermined input level while the second only becomes effective at an adjustable level greater than that at which the first saturates. In the conventional radiolocation system of Fig. 1 (not shown), comprising a pulse transmitter and receiver with a suitable blocking circuit associated with them, and a recurrence frequency oscillator controlling the transmitter modulator and a saw-tooth generator producing the sweep voltage for a cathode-ray oscillograph, the receiver contains an amplifier according to the invention which may comprise the final stage of the amplifier circuit of the receiver or may.be located directly after the detector stage. The amplifier, Fig. 2, comprises two valves 30, 31 with the input applied to their grids in parallel through condensers 34, 35- and the output obtained in parallel from their anodes through condenser 44. Valve 30 is provided with a fixed small negative bias C1 and provides a gain characteristic as indicated by slope 51 of curve A, Fig. 3, which becomes saturated at the output level X. Valve 31 is provided with a large negative bias from source C2 by means of potential divider 55 so that the valve commences to amplify at an input level 61 and provides the gain characteristic indicated by slope 53 of curve A, which reaches a saturation level Y. The upper portion of curve A may be moved to positions such as B and C by adjustment of the bias on valve 31 and the amplification of the valves may be controlled by variable resistances 56, 57 in the screen connection so that the slopes of portions 51, 53 of curve A and thus the input voltages necessary to produce saturation may be adjusted. A single variable resistance may be employed to obtain simultaneous amplification control for both valves. For the gain characteristic A, pulses such as 2, 4, 8 and 10 which do not extend to the input level 60 are not limited and their maximum values may be determined for direction-finding purposes. Pulse 9 which exceeds input level 61 may also have its maximum amplitude observed. Pulses 3, 5 and 6, however, which are limited by the saturation line X and pulse 7 which exceeds the level 62 and is limited by saturation line Y cannot be maximised. To observe the maximum of pulse 7 the gain characteristic B would have to be employed while for pulses 5 and 6 characteristic C would be used. A higher gain characteristic D, Fig. 7, which enables the weaker pulses 1, 2 and 4 to be maximised may be obtained by adjusting the bias of valve 31 to be substantially the same as the bias of valve 30, a resistance 63 in series with the potential divider 55 limiting the minimum bias on valve 31 to equality with the bias on valve 30.