[Kenwood] TS-570 filter for use with CW

[Ted Champagne]

Hello Tom --

If you want to have a pleasant CW experience with the '570, I strongly
recommend that you install the CW filter rather than a narrow SSB
filter.  The DSP is only in the AF chain, not in the IF chain, so it is
possible for signals which are within the crystal-filtered IF passband
and at the same time outside of the DSP-filtered AF passband to activate
the IF-derived AGC.  If these signals are much stronger than the desired
signal in the AF passband, the audio level will vary with the signal you
can't hear rather than with the one you are trying to hear.  This is
commonly known as "pumping", and it is very annoying to me.

The bottom line is that the narrower your IF passband, the less likely
this "pumping" is to happen.  

After installing the filter, you need to set the receiver to CW mode and
go to menu 46 to select the bandwidth closest to the filter you
installed.  The Kenwood filters correspond to the choices for menu 46 in
the (G) model (1800, 500, and 270 Hz).  I have the Inrad 400-Hz filter,
so I set menu 46 to 500 Hz.  In the CW mode, at the DSP filter settings
above 600 Hz, the stock (wider) IF filtering is used, while at the 600
Hz and narrower positions, the radio switches to the narrow IF filter
(see page 38 in the Instruction Manual).

While IF DSP might be more desirable, it is more expensive.  I have used
an Icom IC-746 with IF DSP at a friend's station, and I think it handles
a crowded band better than the '570.  It also costs more.  I think
Kenwood has made a decent tradeoff between cost, performance, and
complexity with this setup (and no, I don't work for or own stock in
Kenwood).  I find it works well for me for all but the most crowded
contest conditions.

Hope this helps.  73,
--Ted Champagne, N4TW
  Madrid, NY
  trustee, Northern New York Contest Club station W2NNY
  (a little southwest of the junction of W2, VE2, and VE3)