[Elecraft] KAF2 or KDSP2 for K2 #5287

[Darwin, Keith]

When I had narrow filtering in my Omni V I found that S/N did not
increase as bandwidth decreased.  Instead, the noise began to sound like
signal since both were at the same frequency.  Add some filter ringing
to the mix and sometimes the narrowest settings made copy worse.

As always, I reserve the right to change my mind as I get more operating
time with various rigs :-)

- Keith KD1E - 

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Vic K2VCO
Sent: Thursday, April 06, 2006 12:54 PM
To: Elecraft Group
Subject: Re: [Elecraft] KAF2 or KDSP2 for K2 #5287

Selectivity has two functions: to reject QRM and to increase the
signal/noise ratio by narrowing the bandwidth.  The crystal filter in
the K2 is usually sufficient for QRM reduction, with the help of the
"built-in wetware filter" in the human brain.

However, it *is* advantageous to have the narrowest practical bandwidth
when receiving a weak CW signal; the signal's energy is concentrated in
a very narrow range of frequencies -- maybe 50 Hz is required for usual
CW speeds -- while the noise is evenly distributed over the bandpass of
the receiver.  I find it useful to have a narrow audio filter available
for this reason.