| 摘要 |
The receiver has a mixer (2) which receives the transmission frequencies (f and f+ DELTA f). A local oscillator (3) feeds a mixing signal to the mixer (2) and is switchable between two frequencies neither of which lies midway between the two transmission frequencies, the switching being controlled by the output. The low or band mass filtered signal to detector 8 thus comprises one of four frequencies which fall in respective upper and lower bands, which bands are distinguished by the detector to provide the binary output at (7). The local oscillator frequency is switched to its alternative frequency either when an upper band frequency is detected or alternatively in the absence of such a frequency. The receiver thus requires only one filter, and one mixer, with no quadrature local oscillator. <IMAGE> |
