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

[Victor Rosenthal 4X6GP]

I didn't mean "all the time" as "whenever I operate." I meant "a great 
deal of the time."
Sorry for the exaggeration. It's one of my favorite features.

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 16/05/2020 14:50, Victor Rosenthal 4X6GP wrote:
> 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