Adding a cw filter to the 570 eliminates the problem that occurs when the 
AGC circuit is being tripped by signals which are outside the audio 
passband. This shows up as a pop, and a reduction in the signal that you are 
actually trying to copy. It happens no matter where you have the narrow 
audio filter set in the cw mode.

In my 570, I have the 400 hz filter from IRAD. While their specs are 
somewhat better than those of Kenwood filters, the real reason that I have 
it is that I caught them on sale the year I went to Dayton, and brought one 
home, since I went there planning to buy a Kenwood filter anyway.

Based on my previous experience with the Kenwood filters for earlier rigs, 
the 500 hz filter will do nicely for all but the most challenging contest 
pile ups.

If you operate cw even casually, they make the 570 a much nicer cw rig.


Mike Duke, K5XU