[Elecraft] APF For K3: progress report

[Paul Christensen]

> There's a button labeled "RIT" and an associated knob especially for that 
> purpose.

Wes,

Here's an example of using APF in conjunction with RIT.  I normally leave my 
CW offset at 650 Hz.  Some of my CW operating is very weak signal DX on the 
low bands.  When copying extremely weak DX in the midst of static crashes, I 
need to temporarily shift pitch to less than 400 Hz.  Some ops, including 
W4ZV, have noted that weak CW copy can improve when low pitch is used.  I 
also don't want to tamper with my normal CW offset if I don't need to.

By engaging in RIT, I would like to temporally dip the incoming pitch, leave 
my CW offset alone where I want it 95% of the time, and then adjust the 
frequency of the APF to match/peak the incoming pitch selected by RIT.  If I 
want to experiment with different pitch settings based on band conditions, I 
also want the ability for the APF peak to track the pitch I've selected on 
RIT.  That requires a tunable APF.  This is precisely what the FT-1000/D 
gave its users.

Of course, the greater the departure of the RIT pitch from the offset may 
require a wider DSP filter setting and/or roofing filter.  But under these 
weak band conditions, wide DSP and roofing filters are just fine when band 
activity and adjacent interference is low or moderate.  When I'm working 
early morning grayline DX on 80m or 40m, I rarely encounter strong adjacent 
stations since conditions are long and stateside is not heard much of the 
time.  Because of this, my overall Rx bandwidth is generally set to 2.8 kHz 
or greater.  Even when weak DX is running split and listening up 2 kHz, 
there's ample separation to allow a filter settings wide enough to depart a 
few hundred Hz from the CW offset.

Paul, W9AC