| 摘要 |
772,639. Radar; phase detectors. COLLINS RADIO CO. April 18, 1955, No. 11135/55. Classes 40(5) and 40(7) In a low altitude radio altimeter for aircraft the transmitter amplitude modulation signal and detected echo signal of frequency f.e.g. 25 kc/s, are respectively multiplied in frequency to (n-1)f and nf in frequency multipliers 17, 16, so that the difference frequency taken from a mixer 18 is of same frequency f, e.g. 25 kc/s, but phase difference i.e. n times that between the transmitted and detected signals relative to the transmitted modulating frequency. This difference frequency f is then beat in a phase detector 20 with the transmitted modulating frequency f to produce a D.C. output dependent on n times the original phase difference. The D.C. output at an altitude less than 100 feet is so small that a normally operated flag 22 is released to bring into circuit an indicate 25 energised by a similar phase difference amplifying a system comprising a frequency multiplier 27 multiplying the frequency f the input to the first phase detector 20 by n and combining it in a mixer 28 with the input at frequency (n-1) f to the first mixer 18, to derive again the frequency f from a filter 22 and in a phase detector 30 by recombining this frequency f, e.g. 25 kc/s, with the modulating frequency f to derive a D.C. output dependent on n<SP>2</SP>, e.g. 100, times the original phase difference. At altitudes below 100 feet contacts 23 are bridged by the flag 22 and the output of phase detector 30 acts on a pivoted aircraft indicia vertically movable over a scale, calibrated in feet in a vertical slot in the face of the indicator 25. |
