[Elecraft] Elecraft DSP vs Audio Filter?

[Steven Pituch]

Hi Fred,
The K2 has one of the best IF sections around.  Because it is so good, it
does not need IF filtering. So they decided to make an AF DSP filter that
was a lot more affordable and had a real benefit to the K2.  Being single
conversion the K2's IF filter is close to the front end.  It narrows down
the signal before a lot of internally generated crap appears.  Triple and
quadruple conversion receivers need IF DSP because so much garabage is
introduced into the signal after the front end and before the IF filtering.
When you hear that an expensive radio has just been "improved" and had
roofing filters installed near its front end to clean up the garbage, I
think they should go back to the drawing board and dream up a cleaner radio.
But then the K2 is available so why would anyone want to consider anything
else?  
How is that for a "nontechnical " answer? ;o)   ( flame suit on)

The K2 IF variable width filter is very good.  It makes the K2 one of the
best radios for fighting adjacent interference.  When that 2000 W CW signal
camps out 300 Hz away from your QRP friend, its this filter that makes the
K2 the easiest radio to use to hear your contact.  It is ahead of the AGC so
you generally narrow down the IF filter until you can receive the other guy
and minimize the interference from the other station.  That way the
interfering station does not pump the AGC.

The audio DSP filters are much sharper.  Once you have maximized the IF
filter, you can get additional isolation by kicking in the audio DSP
filters.  It took me awhile to figure out the DSP but it is very nice and
apparently one of the best around.

I have even optimized the IF and DSP on my K2 for RTTY and as an example
have some waterfall displays of the filters at:
http://users.ev1.net/~spituch/Steve's%20Page/Radio/RTTY/RTTY.html
>From the photos you can see how well the DSP works.  Also you can center the
DSP filters very easily by just watching the waterfall display.

Regards,
Steve, W2MY

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