Kenwood TS-590S manual Modulation, 4 DSP

4 DSP

4.5 Modulation

Following is how the TX signal is processed. The audio signal captured from the microphone or an external terminal is first processed by the bandwidth-limiting filter, microphone gain control, speech processor or VOX, and then, in SSB and AM modes, the signal is modulated and output as an IF signal; in FM mode, a CTCSS tone signal is added.

In CW mode, the waveform of the keying input is shaped and then the signal is multiplied by the modulating carrier to be transmitted as an IF signal. At the same time, the signal is multiplied by a carrier for monitoring to produce a CW sidetone.

In FSK mode, the keying input is processed by a baseband filter for bandwidth limiting, and then the signal is processed by frequency modulation with the 24 kHz center frequency to obtain an FSK modulated wave. As in CW mode, for the purpose of monitoring, the audio center frequency based on the FSK tone frequency setting in the menu mode is processed by frequency modulation to obtain the monitoring audio.

In SSB mode, the proven PSN design continues to be adopted for modulation. Unlike for demodulation, for modulation enough sideband suppression must be provided for the bandwidth of the modulation input. The characteristics of the PSN are designed to deliver sufficient suppression according to the characteristics of the bandwidth-limiting filter (Figure 4-9).

Figure 4-9 Opposite Sideband Suppression Characteristics of the PSN for SSB Modulation

The bandwidth-limiting filter for transmission that can be set in the menu mode is applied to SSB and AM modes, but in SSB mode the filter is made sharper at 3 kHz.

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TS-590S