APF

[todd ruby-2]

I have received 2 inquiries about how to use the APF. Well, I’ll put it to you this way. I used to be a photographer and used a 5X7 view camera. The image on the viewing glass was upside down, both the front (lens board) and rear (view glass) board swiveled from side to side and up and down. It was very frustrating for a 20 year old perfectionist to figure out how to manuever either of the boards together or individually to get the desired image. My teacher was very Zen about it. He said “F….k with it until it looks right.

Basically this is what I did to pull in Zorro in Myanmar who was a hair above the noise level. Every time I used the APF previously I got too much ringing and couldn’t hear the signal I wanted to zero in on. Truly, today it was a matter of opening up the width and lowering the shift to get rid of the ring, then playing with the two until I could hear his signal at its best. Switching back to the regular roofing filter (400 hz) didn’t cut it. The APF isolated Zorro enough to copy him Q5.

So my answer and my future technique will rely on messing with both the width and the shift until you can get rid of the ring and eke out the signal.

I am sure Don Wilhelm, Wayne and Jim Brown will weigh in on me being overly simplistic but it worked for me and we are both in each others log!

73
todd
WB2ZAB
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[Don Wilhelm-4]

Todd,

I am not going to "weigh in" on anything you said.  In the case of APF,
the instructions by your very Zen instructor may the best appropriate
answer.

Before you need to use it, give it a try on some weak signals and play
with the width and shift controls until you get a feel for it. It will
not seem to work very well on signals that can be copied without the
APF, so concentrate on the weak ones.

73,
Don W3FPR

On 3/16/2014 6:33 PM, todd ruby wrote:
> I have received 2 inquiries about how to use the APF. Well, I’ll put it to you this way. I used to be a photographer and used a 5X7 view camera. The image on the viewing glass was upside down, both the front (lens board) and rear (view glass) board swiveled from side to side and up and down. It was very frustrating for a 20 year old perfectionist to figure out how to manuever either of the boards together or individually to get the desired image. My teacher was very Zen about it. He said “F….k with it until it looks right.
>
> Basically this is what I did to pull in Zorro in Myanmar who was a hair above the noise level. Every time I used the APF previously I got too much ringing and couldn’t hear the signal I wanted to zero in on. Truly, today it was a matter of opening up the width and lowering the shift to get rid of the ring, then playing with the two until I could hear his signal at its best. Switching back to the regular roofing filter (400 hz) didn’t cut it. The APF isolated Zorro enough to copy him Q5.
>
> So my answer and my future technique will rely on messing with both the width and the shift until you can get rid of the ring and eke out the signal.
>
> I am sure Don Wilhelm, Wayne and Jim Brown will weigh in on me being overly simplistic but it worked for me and we are both in each others log!
>
>

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[Brian Hunt]

My "formula" for tuning very weak signals - almost can't see them on the P3 - is as follows:

- Set the WIDTH to 700 Hz to 1 KHz QRM permitting.

- Turn on NR and set to 5m3 or there about.

- Turn on APF and tune for best audio. Setting the rate to FINE sometimes helps.

This almost completely eliminates noise ringing the filter although the signal does ring a little. YMMV.

73,
Brian, K0DTJ
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[Don Wilhelm-4]

Brian,

Yes, using APF with a wider bandwidth helps, but a width more narrow
than 700 Hz should be usable - 400 Hz and more narrow may be "iffy".
FINE tuning with APF turned on is a necessity.

73,
Don W3FPR

On 3/16/2014 8:44 PM, Brian Hunt wrote:

> My "formula" for tuning very weak signals - almost can't see them on the P3 - is as follows:
>
> - Set the WIDTH to 700 Hz to 1 KHz QRM permitting.
>
> - Turn on NR and set to 5m3 or there about.
>
> - Turn on APF and tune for best audio. Setting the rate to FINE sometimes helps.
>
> This almost completely eliminates noise ringing the filter although the signal does ring a little. YMMV.
>
> 73,
> Brian, K0DTJ
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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[Brian Hunt]

Thanks, Don. My choice of 700-1000 Hz is more for the NR than for the APF. The idea is to get the noise going into the NR routine  as uncorrelated as practical. The knee of that curve seems to be around 700 Hz. Any lower and the NR doesn't work as well. It's a bit subjective.  Also using the "mix" mode of the NR is key because it gives the APF some "pure" signal to work on.

73,
Brian, K0DTJ
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