| 摘要 |
<p>The Doppler radio direction-finding system with rotational or quasi-rotational antenna consists of an array of antennae (1) in which two, 180 deg. apart (1a-b), are switched in rotation to receiver circuits, one for each channel, (4a-b). One is tuned to the upper sideband and the other to the lower as produced in two mixer stages (6a-b) (8a-b). The mixer frequency for the second stage is derived from a third receiver (9) fed from a single omnidirectional aerial (10). The received frequencies are eliminated in the two second-stage mixers whose outputs are added (11) and the phase-shift effect due to the aerial system is balanced out. The demodulated output (12) is twice the amplitude of that at one of the inputs, representing an increase in sensitivity of 3 dB.</p> |
