Patent GB-598948-A (GB)
Title: Improvements in or relating to radio object-detecting apparatus
IPC: G01S7/34
Filed: 1944-01-18
Abstract: 598,948. Radiolocation; radio receiving apparatus. SPERRY GYROSCOPE CO., Inc. Jan. 18, 1944, No. 986. Convention date, Jan. 22, 1943. [Class 40 (v)] In a radiolocation system the gain of the receiver is varied in synchronism with the pulse recurrence frequency, to provide selective amplification, according to the time interval between the transmission and reception of pulses, of signals received during an adjustable portion of the cycle, so that weaker signals from more distant reflecting objects receive greater amplification. The radiation system R, Fig. 1, comprises an aerial 15 in a reflector 17, so arranged that the whole system is rotated about a horizontal axis by the mechanism 18, while a slower speed oscillation or nodding about a transverse axis 19 is produced by a connecting rod 23 and crank 24, the beam scanning in spiral fashion. A master oscillator 12, producing sinusoidal waves 12<1>, controls a pulse circuit 13, generating short pulses 13<1> which are used to modulate the transmitter 14, the radio-frequency pulses 14' being fed over a wave-guide 16 to the radiating system. Reflected pulses P', received on the aerial, are fed through a waveguide 16<1> to the receiver S comprising a first detector 41, i.f. amplifier 39, second detector 42 and amplifier 43 which feeds signals as intensity modulation to the cathode-ray-tube indicator 1. A T-R box, 25, is provided in the waveguide 16<1> and protects the receiver from the directly transmitted energy. The beam of the cathode-ray-tube indicator is caused to move in a path corresponding with the motion of the beam of the radiating system by feeding the deflecting plates from a two-phase generator, synchronized with the scanning rotation frequency and having an amplitude varying in synchronism with the nodding frequency. Intensity modulation by signals thus produces a bright spot on the indicator screen in a position corresponding to the orientation of the target with'respect to the radiation system R. The receiver is blocked except for the interval following each transmitted pulse during which signals are received, and if the blocking voltage is neutralized by means of a square gating wave such as 29, Fig. 6, the receiver would be equally responsive to all received pulses so that the signals from greater ranges would be of smaller amplitude as indicated in Fig. 5. The compensating variation of receiver gain is produced by the signal compensator C which comprises a trigger circuit 33 producing a square wave 33' which is converted in the gate network 37 to the gaincontrolling voltage 37' fed to the i.f. amplifier. A cut-off circuit 38 develops a voltage to cause rapid blocking of the receiver at the end of the desired reception period. The trigger circuit 33 consists of an Eccles-Jordan circuit comprising valves 45, 46, Fig. 2 (not shown), the first valve being made conducting by the transmitter pulse 13' while the second valve is rendered conducting by the pulse from circuit 34 adjustably delayed by phase shifter 35. The square wave produced is fed through condenser 55 to the gate network which may consist of condenser 56, inductance 57 and resistance 58 arranged as in Fig. 3 or 4. The circuit elements may be adjustable and may be proportioned to produce a gain-controlling wave of parabolic shape as shown in Fig. 7 which will produce full compensation for the range attenuation of signals, as shown in Fig. 8, if applied to the screen grid of a pentode amplifier in which the gain is a substantially-linear function of screen voltage. The gain-control curve may be adjusted to some empirical form, Fig. 10, to produce partial compensation as indicated in Fig. 11 so that signals denoting more distant targets may be weaker. The cut-off circuit 38 comprises, Fig. 2 (not shown), a gas-filled discharge tube which is triggered by the end of the pulse from the trigger circuit 33 to discharge the gate network rapidly and reduce the receiver gain. As an alternative to the gate network 37 a saw-tooth generator, Fig. 1A (not shown), may be employed, synchronised from the pulse circuit 13, and feeding a saw-tooth voltage of the form shown in Fig. 9 to the screen grid or other electrode of a pentode or tetrode signal amplifier. This arrangement gives a linear correction of signal amplitude, but a parabolic increase of gain with time may be obtained by applying the saw-tooth voltage to two amplifier stages in cascade.