Demodulation - Kenwood TS-590SG Manual

DSP 04

4.4 Demodulation

For the demodulation of the RX signal in SSB, CW, FSK and SSB-DATA modes, we have employed the proven PSN (Phase
Shift Network) design again.
In the previous models (TS-2000/X and TS-870S), the selection of the PSN s characteristics was interlocked with the
passband setting of the IF filter, and when the passband is narrow, a PSN with a good sideband suppression was selected.
On the other hand, on the TS-590S/SG, the order of the PSN is decreased by tuning the PSN only to the opposite side
band that was not fully removed by the digital IF filter.
In this way, the low frequency range of the PSN stretches out substantially and the poor group delay characteristics in the
lower frequency range, which is a drawback of a PSN, is also improved. As a result, the low range reaches farther with
less attenuation than that reached in the previous models.
In SSB mode, the digital IF filter has a setting of 0 Hz in LO CUT and this means the cutoff frequency is set to the carrier
point so that the low frequency range can be stretched out maximally. Enjoy distinctly different audio from that of previous
transceivers.
The same demodulation process is used in SSB, CW FSK and SSB-DATA modes, except that the selection of PSN
characteristics and of digital IF filters varies depending on the mode.
In AM mode, an absolute value detection circuit is used for demodulation as in the previous models.
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