APF Question

Norm - W7CK

During the last few evenings I decided to play around on CW.  Its been several years for me, and I've  been having a lot of fun.  Anyway, Can someone explain exactly how APF is to be used?  I've tried selecting it and playing with the slider on CW but it just doesn't seem to do much of anything.  It might even be making copy a little harder than without it!  

Anyone else having issues with APF?   I'm running a 6700 on v1.4.16

Duane_AC5AA

I think APF works great and I use it all the time on CW. It emphasizes the selected sidetone frequency and de-emphasizes other frequencies. Usually it will help a signal "pop" out of the background noise. I like it a lot

Norm - W7CK

I wonder what I'm doing wrong then.  The slider just doesn't seem to do much.  As I slide it to the right, the receiver gets quieter, but it doesn't really enhance the signal much if at all.   I seem to remember trying it months ago and it seemed like it added a heterodyne to the incoming signal and really made it ring out loud.   It just doesn't seem to be doing much for me now.  Are you using the latest SmartSDR and do you have any other settings specifically set to take advantage of APF?  Filter width etc....

I'm only using it on really weak signals....

Al_NN4ZZ

Norm,
You might be interested in adding a vote to this idea to improve the APF control. 

https://community.flexradio.com/flexradio/topics/ssdr_v1_2_apf_could_use_more_gain_it_seems_diminish...

I use APF along with setting the RX Equalizer controls to emphasize 500 HZ and reduce all the other frequencies.   It works but I'd like to see more user control of the APF parameters. 

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com

Barry N1EU

Norm, it's not going to do much unless you have the target signal tuned in with its pitch closely matching the sidetone frequency.

Steve N4LQ

Norm
Google the word "subjective". This word applies to how APF affects opinions. 

Rick Hadley - W0FG

The latest iteration of the APF is better.  I run APF at 90, sidetone at 500 Hz, and EQ peaked at 500 with 50 & 100 Hz filters.  The APF definitely improves readability on weak signals.

Duane_AC5AA

Norm, one of the comments here has asked a good question.  What filter bandwidth are you using when you try APF?  I find the 400 Hz default for CW is much too narrow for me in "general DXing" when I'm scanning the band for stations.  I primarily use 1000 Hz on CW, and with sidetone at 700 Hz and APF between 40-60, it works fine for me.  If you start with a narrow filter and then run APF, there is little you can de-emphasize because there is little besides the signal and the noise immediately adjacent to it.  There are a number of these default settings that I'd like to see Flex make user-adjustable.  Especially the one that automatically activates the B slice rather than the A slice when you change bands, but that's another topic entirely....

George KF2T

Here is a sequence of images depicting the progressively higher use of APF on a 1 kHz bandwidth slice. I notice APF can lead to a kind of ringing sound as the bandwidth is narrowed. Adjustment of the AGC-T and initial bandwidth is necessary for optimum use. To dig out the weak ones, I use a 250 Hz bandwidth, drop the AGC-T down as much as I can, and peak the desired signal with the APF. It does need to be in the middle of the passband.

Enjoy!