[Elecraft] APF (audio peaking filter) on the K3/K3S/KX3

[Bob McGraw K4TAX]

As a new K3S owner {since last August}, I agree.   The APF seems to lift 
signals out of the noise when otherwise, one would not know they are 
present.  I've used it successfully many times on weak signal QSO's.

Thanks for designing a great radio for the ham market.

73
Bob, K4TAX
K3S, s/n 10163


On 2/2/2016 8:34 AM, Wayne Burdick wrote:
> Hi all,
>
> This morning I was hearing lots of very weak signals in the 40-meter CW band, right at today's noise floor of about S-5. (Among others, I copied BG4GOV in Shanghai.)
>
> Many of the signals were not copyable until I turned on APF (audio peaking filter). This filter's center peak is very narrow (around 30 Hz), but the response broadens out quickly below the 3-dB points in the curve. This brings up the desired signal without allowing noise to cause ringing--something often heard with narrow filters of the "brick-wall" variety. On a noisy band, the effect is just short of magic.
>
> APF is very narrow, so you'll need to tune in 1-Hz increments when it is turned on. Also, APF works best when used with a DSP/crystal filter WIDTH setting of 300-500 Hz.
>
> Use of APF differs for the three transceivers.
>
> KX3: 1-Hz tuning is selected automatically on the when the APF switch is pressed.
>
> K3/K3S: APF is accessed via a hold of the XFIL switch. This function is labeled "APF" on a K3S, or "DUAL PB" on the K3). Use CONFIG:DUAL PB to make sure the selected filter function is APF. See the K3/K3S owner's manual for a description of the alternate setting. 1-Hz tuning can be selected by tapping FINE.
>
> You might want to give APF a try if you haven't already.
>
> 73,
> Wayne
> N6KR
>
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