Kenwood TS-990S In-Depth Manual page 40

06 DSP
In conventional transceivers, slopes (shoulders) by the IF filter were sharply formed regardless of the slope tuning
and passband width setting. The TS‑990S employs choices of filter shapes. For the shape characteristics, "Sharp",
"Medium", or "Soft" can be selected for the main band and the sub band respectively in the RX Filter screen.
Demodulation Mode
SSB (Slope Tuning)
SSB (WIDTH), FSK, PSK
CW
SSB IF Filter (Low-cut 2000 Hz, High-cut 2600 Hz/Sharp, Medium, Soft)
Fig. 60 Comparison of the Filter Shape Characteristics in
SSB Mode (Blue and Dark Green: Sharp, Red and Blue‑
Green: Medium, Purple and Yellowish Green: Soft)
The shape factors during the adjustment of the passband width and center frequency shift are designed with a reference
of a 2400 Hz bandwidth in SSB, FSK, and PSK modes and that of a 500 Hz bandwidth in CW mode. Such a sharp filter
tends to cause ringing by bandwidth narrowing and influence to the sound quality by group delay in SSB mode.
On the TS‑990S, with the digital filter design skills we have accumulated, the filter and AGC design is devised so that the
ringing and influence on the sound quality are minimized. However, the roofing filters for the analog circuit are linked with
specified filter bandwidth characteristics, that is, for example, if a narrow band of 250 Hz or lower is set in CW mode, the
roofing filter bandwidth is set to 270 Hz (if "Auto" is configured for "Roof" in the RX Filter screen). If a narrow band such
as 270 Hz is configured for the roofing filter, there is an advantage of insusceptibility to interference by adjacent signals
while there is a disadvantage of susceptibility of ripples and group delay characteristics.
Because of the relationship with the analog filter characteristics, only devising the digital filter does not attain practical
listening sensation in sound quality refining. The tuning of the IF AGC processing described above serves to gain the
effective filter characteristics.
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Table 11 Shape Factors by Shape Switching
Shape Factors (-60 dB BW/-3 dB BW)
1.6/ 1.8/ 2.0 (Low‑cut filter: 200 Hz, High‑cut filter: 2600 Hz)
1.5/ 1.8/ 2.0 (Bandwidth: 2400 Hz)
1.5/ 1.8/ 2.0 (Bandwidth: 500 Hz)
Frequency (Hz)
Fig. 61 Comparison of the Filter Shape Characteristics in
CW mode (Blue: Sharp, Green: Medium, Red: Soft)
Stop Band Attenuation
110 dB
110 dB
110 dB