GB909018A - Improvements in or relating to the tuning of radio receivers - Google Patents

Abstract

909,018. Radio receiving circuits; frequencychanging circuits. COLE Ltd., E. K., and WOODHALL, N. M. Aug. 14, 1961 [Aug. 20, 1960], No. 28909/60. Classes 40 (5) and 40 (6). A radio receiver for three V.H.F. signals which bear the relationship x-n, x, x+n consists of a double heterodyne system which comprises a first oscillator which will provide, with x a beat frequency f and with the other, signal frequencies f+n and f - n, a second oscillator tuned to frequency n and selective connecting means between the output of the first mixer circuit and the second mixer, whereby any one of the three intermediate frequency signals can be fed to the second mixer. In the embodiment the three V.H.F. signals are the Home, Light and Third programmes of the B.B.C. Sutton Coldfield station, the spacing n between the signals being 2.2 mc/s. The incoming signals are amplified by wideband amplifier 2 and then passed to an oscillator mixer 3, the oscillator section of which is tuned to 79.8 mc/s. This mixer produces three intermediate frequencies of 8.5, 10.7 and 12.9 mc/s. The required frequency is selected by the tuned circuit 5 and passed to a second mixer where if the I.F. frequency 10.7 mc/s. is selected the oscillator 7 may be switched off to avoid interference but if the 8.5 or the 12.9 mc/s. signals are selected the mixer beats the incoming signal with the 2.2 mc/s. oscillator 7 and the resultant 10.7 mc/s. signal is taken from the output to the I.F. stage of the receiver. The oscillators may be crystal controlled. In areas where the stated frequency relationships does not hold the frequency of the second oscillator may be changed to produce the required I.F. when the station selection means is actuated.