Patent GB-620481-A (GB)
Title: Improvements in or relating to radio frequency receiving apparatus
IPC: G01S1/30
Filed: 1945-08-24
Abstract: 620,481. Radio navigation; testing radio apparatus. O'BRIEN, W. J. Aug. 24, 1945, No. 21690. [Class 40 (vii)] A radio receiver for determining the phase relationships between a number of signals of unlike but related frequencies consists of amplifiers tuned to each received frequency and frequency changing or multiplying means associated with the amplifiers to provide two or more pairs of signals of like frequency, together with phase difference measuring means for each pair. The receiver may be used with the navigation system described in Specification 620,479, wherein intersecting equiphase displacement contours are created by three synchronized spaced transmitters using different but harmonically related frequencies so that by measuring the phase difference between two pairs of transmissions on a moving craft its geographical position can be determined. In a receiver, three signals of, say, 60 kc., 80 kc. and 90 kc. from the spaced transmitters are received by antenna 5 and applied to three transformers 17, 18 and 19 tuned to 90 kc., 60 kc., and 80 kc., and passing signals at these frequencies to amplifiers 21, 22, 23, respectively. The phase changes in the transformers are made equivalent as is more fully described, in divisional Specincation 620,508, by making the tuning capacitors and relative degrees of coupling equal and the respective voltage gains proportional to frequency. The amplifiers are provided with automatic gain control systems to maintain constant output levels and amplifier 21 is, coupled to frequency doubler 24 which applies a 180 kc. signal to. one input of phase discriminator 35. Similarly amplifier 23 feeds frequency trebler 37 which applies a 240 kc. signal to phase discriminator 40. The .output of amplifier 22 is fed to frequency trebler 43 and also to frequency quadrupler 44, applying 180 kc. and 240 kc. signals to the other inputs of discriminators 35 and 40 respectively. The outputs of each of the discriminators consists of two direct currents proportional to the sine and the cosine of the phase difference angle and these currents are fed to the field coils of two indicating goniometers. Preferably the goniometers are of the integrating type, as described in Specification 620,480, [Group XXXVI], so that once they are set when the craft is in a known position they continuously indicate its location in terms of the equiphase contours. The discriminators form the subject matter of divisional Specification 620,507, [Group XXXVI]. Testing. The receiver may be checked by means of a 10 kc. pulse generator 103 whose output signal consists not only of the 10 kc. fundamental but all the odd and even harmonics thereof. This may be connected to the input by switch 7 and the channels of the receiver pass the particular harmonic to which they are tuned. As the multiple phase relationship between any two harmonics is the same as that between any other two, the indicators 52 and 54 will give the same readings if the apparatus is in order. It is preferred to adjust the circuits so that these check readings are zero. Specification 584,727 also is referred to.