GB864974A - Improvements in or relating to radio receivers - Google Patents

Abstract

864,974. Radio receiver circuits; radio receiving systems. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. Aug. 4, 1959 [Aug. 6, 1958], No. 26549/59. Class 40(5) [Also in Group XXXVI] A radio receiver comprises a double frequency changing reception channel including two mixers 2, 4 each with its own local oscillator 6, 13, that of the first being variable in frequency and a stabilising channel having two successive mixers 7, 10 with a tunable filter 9 between them and a second filter 12 following the second mixer. The first mixer of the stabilisation channel is connected to receive one input from the oscillator 6 and the other from a source of selectable stabilised frequencies 8, and the second mixer 10 receives one input from the filter 9 and a second input from a variable frequency oscillator 11. A switch 14 is provided for supplying either the output from the local oscillator 13 or the output from the filter 12 as a second input to the mixer 4. With the switch 14 connecting the local oscillator 13 to the mixer 4, the receiver may be tuned in the normal manner, and if the oscillator 11 is now tuned to make the output from the filter 12 equal in frequency to that from the oscillator 13, then the switch may be switched to its other position without effecting the operation of the receiver. The two frequencies are made equal by comparing them on a CRT indicator 15. With the switch 14 in this second position operation of the receiver is unaffected by variation in frequency of the first local oscillator 6. The frequency control of the local oscillator 6 is ganged to that of the oscillator 8 which is in the form of a crystal controlled harmonic generator, and also to a decade counter 16, so that the counter shows the three figures of the received frequency equal to or higher than tens of kc/s, the lower order figures being hidden by a shutter. A figure for the tens and lower orders of kc/s are controlled by the oscillator 11, and movement of the switch 14 to connect filter 12 exposes these figures and masks the previously exposed tens figure. Two indicator devices, for example lamps, are associated with the counter one being operated when the oscillator 11 is adjusted to within one part of its tuning range and the other when in the other part of the tuning range, the devices being arranged so that they indicate which of two numbers which the counter may show simultaneously is the correct one.