Patent GB-594403-A (GB)
Title: Radiant-energy-receiver
IPC: G01S1/02
Filed: 1944-08-09
Abstract: 594,403. Radio direction-finding. HAZELTINE CORPORATION. Aug. 9, 1944, No. 15192. Convention date, Sept. 20, 1943. [Class 40 (v)] In a direction-finding receiver including a detector with a load circuit for operating a direction indicator, alternative load circuits of different time-constant are provided to render the receiver responsive either to a pulse radiation in which the pulse recurrence period is long compared with the pulse duration or to a continuous-wave transmission. When operating on a pulse radiation, the time-constant of the load circuit is long compared not only with the pulse period t, Fig. 2, but also with the pulserecurrence period T so that a relatively-steady output B, Fig. 3, is obtained. In the system shown in Fig. 1, a dipole 10 mounted in a reflector 12 feeds the receiver through a pair of inductively coupled loops 18 and 19. The aerial system together with the loop 18 is rotated by a driver 13. The receiver comprises a radio-frequency amplifier 20, frequency changer 21, intermediate frequency amplifier 22 and a detector stage 23, the output of which is fed through a low-pass filter 24 to an indicator 15. The indicator may be a cathode-ray tube in which a circular path is traced in synchronism with the rotation of the aerial system, the output of the receiver modulating the radius of the circular pattern and causing the device to trace the aerial directive pattern. Any other suitable form of indicator, e.g. a voltmeter, may be used. The intermediate frequency amplifier 22 is provided with separate wide and narrow band-pass circuits 70 and 74, tuned to the intermediate frequency' of the receiver, for use respectively with pulse or C.W. transmissions, the circuits being selected by a pair of switches 66 and 67. The signals from either circuit 70 or 74 are fed to an amplifier 65, the output of which includes a flatly tuned circuit 77. The detector stage 23 comprises a diode 80 having a load circuit which, as adapted for use with a pulse signal, includes a condenser 81 and a resistance 32. The value of the resistance 82 is high and gives a long time constant as regards the discharge of the condenser 81. For use with a C.W. signal, the time constant is shortened by shunting a resistance 83 of relatively low value across the resistance 82 by means of a switch 68. A low resistance choke 79 is provided which has a value ensuring rapid charging of the condenser 81. For the purpose of providing A.V.C. and for monitoring purposes, a separate auxiliary receiver is provided. This receiver is fed through inductively coupled plates 46 and 47 from a non-directive aerial 45 and comprises a radio-frequency amplifier 48, a frequency changer 49, intermediate frequency amplifier 50 and a detector stage 51, including a double diode 91, 80<1>. The section 80<1> is similar to the detector stage 23 of the main receiver and its load circuit includes a high resistance 82<1> for use with pulse transmission and an additional low resistance 83<1> which may be shunted across the resistance 82<1> for use with continuous wave transmissions. The A.V.C. voltage builds up either across the resistance 82<1> alone or across the two resistance 82<1>, 83<1> in parallel and is fed through a lowpass filter 24<1> to the stages 20, 21 and 22 of the main receiver in the conventional manner. The rectifying section 91 includes a load resistance 92 across which an audio-frequency voltage builds up, this voltage being applied through an audio-frequency amplifier 52 to headphones 53. The switches 66, 67, 68 controlling the two channels of the main receiver may be ganged together and with corresponding switches in the auxitiary receiver.