Posted by
P.B. Christensen on
Oct 25, 2010; 1:09pm
URL: http://elecraft.85.s1.nabble.com/APF-For-K3-tp5671688p5670573.html
> "Dual PB" (press and hold XFIL) allows one, as the manual says, to "focus"
> on a given signal that is matched to the sidetone frequency while hearing
> other callers above and below that frequency at reduced level (the
> "context"). Doesn't that do what the waveforms described on AB4OJ's
> website
> depict?
Icom's use of APF is different than that used in the FT-1000/D. Icom more
closely emulates the Dual PB feature in the K3 but without the "context"
feature. What's missing is high "Q" of the centered frequency. The
FT-1000/D's Q of the audio circuit varies with the tuning control, but it's
generally greater than 10. When the Dual PB tuning is enabled on the K3,
and with aggressive NR engaged, I don't hear what sounds like a high Q
equivalent. The FT-1000/D's APF is more closely associated with a
single-channel of a multi-band parametric equalizer where Q, amplitude, and
frequency are all variable. In the FT-1000/D, Q is mostly fixed, but
amplitude and frequency are variable.
Although the FT-1000/D adds amplification of the centered frequency -- and
even allows changing the peaking frequency, I think the most desirable
attribute of the circuit is the high Q ability. Fixed gain and variable
peaking frequency may be a nice added feature to the K3 if APF is
implemented, but these are secondary to achieving emulation of the high Q
portion of the analog circuit in DSP.
Paul, W9AC
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