Patent GB-529542-A (GB)
Title: Improvements in or relating to radio direction finders
IPC: G01S1/02
Filed: 1939-06-02
Abstract: 529,542. Directive wireless systems. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE. June 2, 1939, No. 16304. Convention date, June 4. 1938. [Class 40 (v)] A radio direction finder of the kind having a continuously rotating coil and indicating visually on an oscillograph or other indicator is provided with manual or automatically operated regulating means for maintaining the two side bands produced by the rotation of the goniometer at equal amplitudes, thereby sharpening the minimum signal indication. In the apparatus shown in Fig. 2, the receiver comprises a high frequency portion c followed by an intermediate frequency portion d feeding a crystal filter e which separates the two side bands and applies them to separate amplitude limiters f, g, which make the output amplitudes of the two side band frequencies always equal to each other. The equal voltages are then applied to the remainder h of the receiver. Alternatively the amplitude limiters f, g may provide amplitude dependent back coupling of the side band frequencies to a preceding high or intermediate frequency stage through phase shifters. Regulation is effected by superposing the separated side band frequencies in opposite phase on the received frequencies so that the weaker side band is damped less than the stronger one thus making the side band amplitudes of equal value independently of each other. In a modification the output voltages from the amplitude limiters f, g are applied to a differential arrangement with a rectifier which, according to whether the side band amplitude of f or g predominates, supplies positive or negative D.C. voltage to a valve grid in the limiter f or g in such a manner that the amplifier stage f or g with greater output voltage is given a negative bias to reduce its gain while that with the weaker output voltage is given a positive bias. The differential arrangement may be a bridge circuit, or the two voltages may be supplied by the regulating amplifiers f, g to the windings of a polarized relay which switches in the required D.C. biases. In the arrangement shown in Fig. 5 the outputs from the amplitude limiters f, g are applied to a valve circuit n. If the transmitted frequency is correct current flows in the output circuit of the valve arrangement n and a relay o is energized which switches in the quartz filter e and amplitude limiters f, g as shown into the signal reception channel. If the output of the limiters f, g is zero due to fluctuation of the transmitting frequency, the relay o is de-energized and the switching device r switches out the filter e and regulating amplifiers f, g. The receiver h can in this case be of normal band width and can also indicate a transmitting station even with inaccurate tuning, in which case no voltage is passed through the quartz filter e. In a modification the quartz filter e and regulating members f, g are arranged in a subsidiary circuit and the regulators f, g may supply a back coupling voltage to a previous amplifier stage according to the amplitudes of the side bands, by means of a differential arrangement and rectifier.