GB1366365A - Disortion reduction in directional radio links - Google Patents

Abstract

1366365 Radio signalling LICENTIA PATENT - VERWALTUNGS - GmbH 9 Nov 1971 51908/71 Heading H4L In a system for reducing echo distortion at the receiver in a frequency modulation radio link, at the transmitter the frequency-modulated signal y 0 is additionally phase-modulated by a frequency-wobbled pilot signal Z(t) by multiplying at # 1 the pilot signal Z(t) with the frequency-modulated signal y 0 phase-shifted by 90 degrees and adding the resultant signal to the signal y 0 to provide a signal y 1 . At the receiver the distortion is removed by combining with the received signal y 1 several artificially produced echoes, in networks N 1 , N 2 &c., the different delays being produced by lines L1, L2, &c. controlled by resistive terminations R1, R2 &c. The pilot signal is selected via frequency demodulator FD, bandpass filter BP and integrator I, and amplitude modulation due to the echo distortion is detected at G1 and supplied via a high pass filter HP to a rectifier G2. The resulting voltage v controls an optimizer to adjust the mismatches of the lines L1, L2 &c. to produce the desired correction to reduce the voltage v to a minimum. The pilot signal at the output of integrator I is also supplied via an amplitude and phase correcting filter BP<SP>-1</SP> to a phase modulator #/2 where it is combined with the frequency-modulated signal phase-shifted by 90 degrees, the resultant signal being subtracted from the frequency-modulated signal to remove the pilot modulation.