| 摘要 |
<p>This invention relates to a frequency converter for use in a receive-transmit ground station in a satellite communication system, having improved frequency control characteristics and reduced cost. The converter is comprised of apparatus for generating a first local oscillator signal, and adding the first signal to a transmit baseband signal to form a first sum signal. A second local oscillator signal is generated, and the second signal is added to the first sum signal to form a second sum signal. A third local oscillator signal is generated and the third signal is added to the second sum signal to form a third sum transmission frequency signal. A signal is received at a receive frequency which is different from the transmit frequency, and the receive frequency signal is subtracted from the third local oscillator signal to form a first difference signal. The second local oscillator signal is subtracted from the first difference signal to form a second difference signal, and the first local oscillator signal is added to the second difference signal to obtain a receive baseband signal. The receive baseband signal includes a pilot frequency signal component. It is preferred that the apparatus should include a filter for filtering the receive baseband signal to obtain a pilot frequency signal. A reference oscillator having a normal frequency similar to that of the pilot frequency signal has its frequency compared with that of the pilot frequency in a frequency comparator and provides a control signal representative of the frequency difference, which is applied to the first or third local oscillator signal generator for controlling its frequency in response or frequency drift of the pilot frequency signal relative to that of the reference oscillator.</p> |
