Kenwood TS-990S In-Depth Manual page 52

06 DSP
When the speech processor is on, the modulated wave in the IF stage is processed by the compressor and bandpass
filter, and a signal is then diverted. With a speech processor placed in the IF stage, the TX monitoring audio is present as
the monitored audio after the modulated wave has been detected. This enables audio monitoring with the audio close to
the practical audio to be transmitted.
● CW Mode
A CW keying signal is waveform shaped by filtering the rising and falling waveforms so as to optimize the amplitude
change to prevent the occupied bandwidth from expanding. With the rise time setting, the rise time is switchable in 4
steps (1, 2, 4, and 6 ms). The lower the value, the steeper the rise and sound is exaggerated. The higher the value, the
slower the rise and sound is softened.
Using the waveform‑shaped keying signal as the baseband signal, a modulated wave in the IF stage is generated
through multiplication with the 24 kHz carrier. Additionally, through multiplication with a carrier with an accurate tone
frequency linking with the CW pitch frequency, a sidetone is generated. The rising and falling waveforms become the
same shape as those of the modulated wave in the IF stage.
● FSK Mode
A signal generated by FSK keying is processed in the baseband filter, and a 24 kHz modulated wave by 170 Hz shift
width modulation is generated. Additionally, using the audio mark frequency as a reference, the frequency is shifted and
the signal is then audible or sent as monitored audio.
For operation with the RTTY encoder, the signal contains the ASCII code transferred from a USB keyboard and
message memory and is converted to Baudot code to which the start bit and stop bit are added, and the signal is
modulated as the keying signal the same way as described above.
● PSK Mode
In PSK mode, a modulated wave is sent out only if the PSK31 or PSK63 encoder is active. If the PSK31 or PSK63
encoder is inactive, no modulated wave is sent out.
With the PSK31 or PSK63 encoder, BPSK or QPSK can be selected for PSK31, and only BPSK can be used for PSK63.
The ASCII code from a USB keyboard or message memory is converted to a code called Varicode, and convolutional
encoding is also processed in QPSK mode. After processing by the baseband filter, it is subject to quadrature
modulation with a 24 kHz carrier to generate a modulated wave in the IF stage. Separately, it is subject to quadrature
modulation with the carrier of the tone frequency in PSK mode, and is then audible or sent as monitored audio.
● AM Mode
In AM mode, audio from the microphone or external input terminal is processed by the TX DSP equalizer, microphone
gain control and TX filter and adds a DC signal following the factor of modulation to the audio. A modulated wave in the
IF stage is then generated after multiplication with the 24 kHz carrier. The demodulated wave is detected in the same
manner as in SSB mode, and is then audible or sent as monitored audio.
● FM Mode
In FM mode, audio from the microphone or external input terminal is processed by the TX DSP equalizer and microphone
gain control, and after the 3 kHz band limitation, passes through the pre‑emphasis filter which adds a CTCSS tone.
Additionally, the frequency characteristics are corrected following the modulation characteristics of the analog stage.
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