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

[wayne burdick]

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

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[Vic Rosenthal]

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

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[Vic Rosenthal]

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

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