GB1499474A - Circuits for radio navigation system receivers - Google Patents

Abstract

1499474 Radio navigation systems; automatic phase control INTERNATIONAL STANDARD ELECTRIC CORP 13 Jan 1976 [21 Jan 1975] 01166/76 Headings H4D and H3A The invention relates to circuits for obtaining phase-corrected sinusoidal modulation frequencies (15 Hz and 135 Hz) from a video signal amplitude-modulated with these frequencies, especially for TACAN receivers, in which the video signal is rectified by a pulse-peak rectifier 1, and the modulation frequencies are filtered-out by means of filters 2, 2<SP>1</SP>. The phase error caused by the active filter 2 is eliminated automatically by a regulating loop. A multiplier 5 receives the output signal D of the pulse-peak rectifier 1 and the output signal G of the sine-to-square-wave converter 4, the filter output signal F being displaced 90 degrees in phase in a phase-shifter 3 and converted into the squarewave signal G in converter 4. Any phase error results, after integration in an integrator 6, in a D.C. voltage signal which is fed back via a line 8 to the filter 2, and a field-effect transistor used as a variable resistor 42, Fig. 4, receives the D.C. voltage signal from the integrator 6 and slightly detunes the filter 2, sufficiently to eliminate the phase shift. The phase error introduced by the pulse-peak rectifier 1 is eliminated by adding up the filter output signals in a mixer or summing circuit 14 and feeding back to the rectifier 1 over line 9, (see also Fig. 3, not shown), to regulate its phase response.