| 摘要 |
L-band tuner stage is combined with a quadrature downconverter stage in a single shielded enclosure as an L-band-to-baseband PSK tuner suitable for receiving L-band signals from an LNB and converting the signals directly to signals in a desired digital format. The bandwidths within the two stages are optimized for digital PSK demodulation, and certain functions are shared, such as automatic gain control and carrier tracking information. Electronically switchable attenuators and voltage-variable gain controlled amplifiers, in connection with a low-phase-noise local oscillator employing a microstrip resonator, provide for over 70 dB of dynamic range. The IF frequency and bandwidth are selected so that voltage-variable tunable bandpass filters of conventional design may be used to obtain over 40 dB of radio frequency (RF) image rejection necessary for reception of PSK signals. The IF signal from an L-band tuner stage is passed to the quadrature downconverter stage within the same enclosure, where the signal is split, and an IF local oscillator signal is injected into double balanced mixers to mix with the IF output of the L-band downconverter stage. The output of the mixers is the desired baseband I and Q data signals for PSK demodulation, which is fed directly to a PSK demodulator stage, which may also be a part of the same unit.
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