[Elecraft] KAF2 or KDSP2 for K2 #5287

[Vic K2VCO]

Darwin, Keith wrote:

> Let's widen the question to make it KAF2 or KDSP2 or NOTHING?  Does the
> basic K2's crystal filtering work well enough that you (any of you)
> would be happy with no AF filtering or does the AF/DSP filtering add
> enough that you wouldn't want to be without it?

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.
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco