GB855308A - Improvements in or relating to multi-channel transceivers - Google Patents

Abstract

855,308. Combined radio receiving and transmitting systems; automatic frequency control systems PHILIPS ELECTRICAL INDUSTRIES Ltd. Jan. 21, 1958 [Jan. 21, 1957], No. 2024/58. Class 40(5). A transceiver includes a crystal controlled transmitter, and a double superhet receiver with crystal controlled first and second local oscillators, and tunable second IF amplifier, and means for selecting one of a plurality of spot frequencies comprising a channel generator common to both transmitter and receiver, capable of selecting one of a plurality of adjacent auxiliary intermediate frequencies corresponding to the spot frequencies, and a first auxiliary frequency changer connected immediatelybefore the transmitter p.a., and a second auxiliary frequency changer connected between the first local oscillator and first mixer of the receiver, an input circuit of the two auxiliary frequency changers being coupled to the output circuit of the channel generator, thus changing the transmitter and receiver frequencies by an amount equal to that of the channel generator. In an embodiment Fig. 1, the transmitter 1 and receiver 2 are connected to hybrid unit 5 and antenna 6. The transmitter employs a crystal controlled oscillator of frequency 7À889 mc/s, multiplied 18 times in circuit 10. In the receiver, an input circuit 12 passes all the frequencies in the 157-158 mc/s band, suppressing image frequencies, the signal being applied to mixer 13, having a first crystal controlled local oscillator 14, 15, of frequency 131À3 mc/s. The IF is 10À7 mc/s. A second crystal controlled frequency changer 17 and 18 produces an IF of 455 kc/s. which is amplified and detected and applied to the loudspeaker 21 in known manner. The transmitter and receiver share a common channel generator 22 producing 20 crystal stabilised frequencies having a 50 kc/s. spacing, the central frequency being 15À5 mc/s. Auxiliary frequency changers 23, 24 are connected in the transmitter and receiver circuits respectively and the output of the channel-generator 22, whence by addition the transmitter-receiver frequencies are equalized. For duplex operation the receiver includes a further HF input circuit 12<SP>1</SP>, crystal 15<SP>1</SP> and connecting switches 25, 25<SP>1</SP> whereby the frequency of signal derived from local oscillator 14 after multiplication is raised by 4À5 mc/s. A practical form of channel generator 22 comprises a tunable main oscillator 29, Fig. 3, the frequency of which is changed in mixer 30, by auxiliary oscillator 31 and stabilized by an AFC loop comprising frequency doubler 32, phase discriminator 33 and pulse generator 34. The output of oscillator 29 is applied through inductor 40 to a twin diode frequency doubler 32. Pulse generator 34 is a known 100 kc/s. oscillator, feeding a blocking oscillator 44 converting the sine output of triode 41 into pulses, which are supplied together with the frequency doubler output to the phase discriminator 33. The output of the phase discriminator across winding 46 produces across capacitor 48 a stabilising voltage for oscillator 29. The auxiliary oscillator 31 includes a switch whereby its frequency is either 13À5 or 14À0 mc/s. Thus by mixing in stage 30, twenty crystal controlled frequencies between 15 and 16 mc/s may be selected. The channel generator Fig. 4 comprises a main AFC loop 51, and an auxiliary AFC loop 52, the auxiliary oscillator 53 being tuned in ten steps of 50 kc/s. between 1 and 1À5 mc/s, and after frequency doubling its output is fed to mixer 56, supplied with 0.1 mc/s pulses, from source 57. When the auxiliary oscillator frequency corresponds with a higher harmonic of the 0.1 mc/s pulses a D.C. voltage appears at the output of mixer 56, which is used to stabilize oscillator 53, In the main AFC loop comprising the main oscillator 60, first mixer 61, IF amplifier 62, second mixer 63, the frequency corrector 65 is coupled to the main oscillator 60. The output signal of oscillator 53 is fed to the first mixer 61. 0À5 mc/s. pulses derived from source 67 are applied to the second mixer 63. The main AFC loop 51 supplies frequencies adjustable between 14 mc/s. and 16 mc/s. and IF amplifier 62 is tunable in 0À5 mc/s steps from 13 mc/s. to 14À5 mc/s. Thus the output at terminal 68 is adjustable in four steps of 500 kc/s. and ten steps of 50 kc/s. by adjustment of auxiliary oscillator 53.