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[IW5CWC]

I am puzzled about the Audio Peak Filter (APF) for CW on my FT-891. It is not clear to me what parameter the setting (-250 Hz to +250 Hz, with default value of 250 Hz) refers to.

If it is some width I would not expect to be possible to set to a negative value. On the other hand, if it is some shift I would expect the default to be 0 Hz and not 250 Hz.

Moreover the manual says that “The APF bandwidth can be selected narrow/medium/wide with the menu item 12-01 [APF-WIDTH]." Which is the relationship between this setting and the -250 Hz to +250 Hz setting?

Does someone knows more about this function?

I usually don’t like just to try and see if a function works without knowing what it actually does! But this is a limit against ham radio, I know...

[KD6VXI]

It's pretty much an equalizer.

You can choose the center frequency and choose the sharpness of the eq.

--Shane
WP2ASS / ex KD6VXI

[K0UA]

OK. this is in the category of "this is how I think it works, vs. this is how I know it works."

Lets start with the CW pitch control.  It is defaulted to 700 hz. BUT you can adjust it up and down to suit your ear and style of operating. I always set mine to 600 hz.  NOW lets examine the CW Audio Peaking Filter width:  It can be adjusted to a medium or narrow or wide width. This determines how much of the bandwidth around that CW pitch you just set (or the default 700 hz.) gets "boosted" by the APF (Audio Peaking Filter) when it is on. So now lets look at the APF setting itself, I think it allows you to "boost" on the fly, or otherwise slide the boosted audio bandwidth around a bit by up to -250 hz or centered or +250 hz..  That is what I "think" it does. YMMV.  

[K0UA]

It's pretty much an equalizer.

You can choose the center frequency and choose the sharpness of the eq.

--Shane
WP2ASS / ex KD6VXI

yeah, I think you and I said about the same thing, only you said it with a lot less words.