GB1379657A - Phase correcting circuits for diversity reception - Google Patents

Abstract

1379657 Radio receiving systems MARCONI CO Ltd 28 Feb 1973 [19 May 1972] 23550/72 Heading H4L A known phase-correcting arrangement for diversity signal combining is modified to take into account the noise on a diversity channel. As shown in Fig. 3, a diversity signal is supplied to balanced mixers 13, 14, mixer 14 receiving as its second input the difference output of mixer 13 via a narrow bandpass filter 15, components 18, 19 being omitted in the known arrangement. The output of mixer 14 is supplied via a filter 16 passing all the input information signals to a summing network where it is combined with the other diversity signals to provide an output 10. Mixer 13 receives its other input from the combined output signal and this ensures that all the diversity signals are in phase when combined. The overall characteristic of the phase-correcting circuit may be made to approximate to a square law to provide ratio square combining. In the modified arrangement an amplifier 18 receives the output of filter 15 and saturates for all normal signal levels, or is provided with A.G.C. to produce a level output, this output being supplied via a voltage-controlled attenuator 19 to the mixer 14. The control voltage applied at 20 is dependent on the noise in the diversity channel so that if the signal to noise ratio of one channel is worse than that of the others its contribution to the output signal will be decreased. Fig. 4 shows an arrangement for combining two diversity signals applied at 1 and 2 respectively, using phase correctors 6, 9 of the type described. The diversity signals are supplied to the phase correctors via attenuators 5, 8 controlled by A.G.C. developed at 11, 12 from the common output circuit in known manner. The output of attenuator 5 is also supplied to a gain-controlled amplifier 23 providing a level output to a discriminator 22 which provides a baseband signal from the frequency-modulated input. A noise slot just above the normal traffic band is filtered, amplified and detected at 21 to provide a D.C. voltage representing channel noise, these voltages being compared, as represented by dashed line 27, Fig. 5 (not shown), to produce a common reference voltage for application to terminals 20. Circuits 24, 25, 26 operate similarly for the other diversity channel.