[Elecraft] New K4 feature: Dual APF bandwidths (audio peaking filter)

[Victor Rosenthal 4X6GP]

I use the APF in my K3 all the time. The wide base with a sharp
peak are very helpful for CW intelligibility. I would like the peak to
have a little more gain, though. Maybe it could be adjustable in the K4?

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/

On 16/05/2020 1:11, Wayne Burdick wrote:
> CW ops, especially those doing weak-signal DXing and DXpedition work,
> will now benefit from a second APF filter bandwidth in the K4. The
> original bandwidth is 30 Hz, which is good for code speeds up to
> about 30 WPM. The second bandwidth selection is 50 Hz, which allows
> copy up to about 50 WPM.
> 
> On the air, I'm finding this a great addition to the receiver
> toolbox, especially for close-spaced, fast CW contests. Adjacent
> signals just seem to disappear.
> 
> APF has a narrow bandwidth only for the first several dB from its
> peak, then flares wider below that. This can dramatically improve S/N
> for weak signals right at the noise floor: it brings up the signal
> without "boxing up" band noise into a very narrow bandwidth. That's
> what causes ringing with "brick wall" filters.
> 
> 73, Wayne N6KR