Posted by
Jim Brown-10 on
Oct 27, 2010; 12:44am
URL: http://elecraft.85.s1.nabble.com/APF-For-K3-tp5671688p5677080.html
On 10/26/2010 5:28 PM, The Smiths wrote:
> If find that in Noisy conditions I like to lower my side tone down to 380Hz, yet when I'm in a casual QSO I find that I receive better at about 450Hz.
Yes. There's another psychoacoustic principle at work here, as well as
an electronic one. 50 Hz is a larger percentage of 350 Hz than of 600
Hz. This gives the ear/brain more to work with in discriminating tones
(and noise) that are closer in Hz, and it also makes the filter have
less percentage bandwidth, which means that, all things being equal, it
has better performance than a filter designed for the higher audio
frequency.
Ah, you say, these are digital filters, so it doesn't matter. Wrong --
digital filters are simply digital emulations of analog filters, and the
math that makes analog filters do what they do has the same effect on
the emulations! So there's no free lunch -- the digital filters are
simply far more flexible, because you're building with bits, not Ls and
Cs. :)
And there's a third VERY important operational principle, which i think
you and others have alluded to -- all of this must be done VERY QUICKLY
-- the entire QSO may only last 15 seconds, and you can easily lose a CQ
frequency while taking too long to dig a weak one out of the mud.
73, Jim K9YC
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