GB626325A - Receiving and indicating system for a variable-frequency rotary beacon - Google Patents

Abstract

626,325. Frequency measurements. STANDARD TELEPHONES & CABLES, Ltd. Sept. 20, 1946, No. 28304. Convention date, June 11, 1945. [Class 37] [Also in Group XL (c)] A frequency-meter in a receiver used in radio beacon system, wherein the radio or modulation frequency of the transmitted signal varies with the direction of a rotating directive beam, comprises two channels, in one of which the attenuation varies with frequency according to a sine function and in the other of which the attenuation varies with frequency according to a cosine function so that, by a comparison of the outputs of the channels, the input frequency, and hence the azimuth of the receiver with respect to the beacon, may be determined. The beacon transmitter 1 comprises a variable frequency source ganged to the rotating aerial system whereby the modulation or radio frequency is made to vary with azimuth. At the receiver, the received signals, amplified at 8 and limited at 9, are applied in parallel to filters 10 and 11. The attenuation of filter 10 depends upon the received frequency in such a manner that the output thereof varies linearly with the cosine of the azimuth angle, as illustrated at 15, Fig. 2. Similarly, the output of filter 11 is made to vary linearly with the sine of the azimuth angle, as illustrated at 13, Fig. 2. Integrating circuits 17 and 18 provide continuous signals from the intermittent signals which are delivered from 10 and 11. A similar continuous signal is delivered from circuit 22 and is used to convert the signals from 17 and 18, which are always of the same sign, into signals which may be eithor positive or negative according to the appropriate sine or cosine function, i.e. the constant amplitude level superimposed on the variable level is removed. These operations are performed in circuits 19 and 20, the outputs of which are directly proportional to the sine and cosine respectively of the azimuth angle, and are applied to ratioineter 21 to indicate its value. Specifications 581,201 and 606,264 are referred to.