One of the cool CW features that I discovered this summer on my KX3 is audio peak filtering. Somehow, turning this on, brings a signal right up out of the mud. This feature is available on a number of mid-level and high-level rigs, such as the K3, IC-7610, FT DX 1200, and my new (to me) Flex 6400. Unfortunately, it’s not available on the IC-7300, even though I’m pretty sure that it’s all done digitally now and should be relatively easy to implement.
It really does work well. Here’s a video demonstrating how the Flex Radio APF:
In the CW mode, the APF (Audio Peak Filter) function has an audio peak at the signal frequency; this improves the S/N and increases the readability of the CW signal. The APF peak frequency can be finely aligned.
It works so well that I always have it on when operating CW. I want more details on how it works, though. I wouldn’t think that it’s just a simple audio filter. If anyone can point me to a more detailed explanation of how audio peak filtering works, I’d appreciate it.
Yohei N8YQX says
Is it implemented as an inverse auto notch filter, with the time constant adjusted?
Dan KB6NU says
On Twitter, Rich, WD3C, replied:
Knew I’d heard of this year’s ago. Expect it’s easier in software. Have a look at the November 1983 73 magazine article, The Magical Audio Filter. What is old is new again.
chaz young says
my old yaesu FT902DM has an APF FREQ dial which i assume shifts the frequency or tunes the APF to make it clearer still as well as an APF switch to turn on of or monitor APF as i havnt yet picked up the manual for the FT902DM yet ( iwill be doing so tommoz) as i bought the radio from a friend whos husband who was a good friend sadly passed away several weeks ago and i wasnt sure what the function was for the APF so thank you for those who have passed on the info about APF and what it does
Joseph Anthony says
All I know is it rocks and essential for working QRP stations that otherwise would be impossible. That’s how good it is. AI5DD Joe
Paul Gonzalez says
I use the APF frequently on my DX3000.
It’s an amazing feature.