| 摘要 |
<p>793,198. Radar; transponder apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 9, 1956 [July 12, I955], No. 20188/55. Drawings to Specification. Classes 40 (5) and 40 (7). In an amplitude-modulated C.W. secondary radar system in which.the distance between an airborne interrogation and a ground transponder is derived by phase comparison at the interrogation of the transmitted and received 350 c./s modulation signals, the interrogator and transponder radiate at the same carrier frequency F, e.g. 130 Mc/s, the transmitter and receiver at the interrogation are alternately operative at a switching frequency of 40 c/s. and the transmitter and receiver at the transponder are alternately operative at the same switching frequency such that the transponder receiver is operative when the interrogator is transmitting. In one embodiment, Fig. 1 (not shown), the 350 c/s. modulation signal received at the transponder is detected and applied to synchronize a stable 350 c/s. oscillator by means of a known automatic frequency control system, the oscillator output being applied to modulate a locally generated carrier of frequency F; alternatively, Fig. 2 (not shown), the modulation signal detected at the transponder is delayed for a period of 1/80 secs. by means of a delay line or magnetic recording cylinder and then applied to modulate the carrier. As described, the transponder switching is synchronized with the interrogator switching by deriving at the transponder a 40 c/s. trigger signal from the detected modulation signal and the phase comparison at the transponder is effected by a known form of servo-controlled phase meter. Any one of a plurality of different modulation frequencies may be selected to resolve phase ambiguities. When the transponder includes means for determining the bearing of the interrogator, the bearing data may be transmitted from the transponder as a phase shift on the modulation frequency in response to a special request signal from the interrogator; the difference between the reading of the interrogator phase meter before and after such a request then indicates the required bearing.</p> |
