APF in CQWW; and DXing in general w/K3

[John Harper AE5X]

The past weekend's CQWW was the first time I've had the opportunity to use my new K3 in those types of band conditions and I'd been looking forward to doing just that. I S&P'ed the whole 'test and used it to tweak and twiddle with the K3's various functions, notably the NB settings.

I didn't use APF that much due to the pace of the contest but there were two occassions where an On/Off comparison was the difference between me copying the stations or not copying. There were probably more than two but these stick out in my mind because they were both new band-countries on 80m (KH2, UA0), so I was motivated and thankful to be able to get them logged.

The real amazement to me wasn't the APF but the ability to tune to a pile-up at 500Hz, hearing an amalgam of callsigns, then dial the selectivity down and hear the target revealed in splendid isolation. Pile-ups were fun and I think of them as a cross between chess and fishing. I'm at a loss as to how to explain the ability to get thru a pile-up on 80m with 100W and a dipole but I'm beginning to believe it's due to the abilty to precisely zero-beat, as opposed to the more general way I was doing it before with the wider selectivity necessitated by my previous rig. Results in the contest seem to confirm that for me.

John AE5X
http://www.ae5x.com/blog

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[k.igor]

You nailed the proverbial nail on the head. The combination of narrow
roofing filter, great DSP filtering, cut-off and the feature of zero-beat
the pitch to the other station works magic in those pile-ups. Unfortunately,
the CWT is not really useful when the DX working SPLIT. In this case you
have to rely on your ears to match the tone of the station currently in QSO
with the DX using the SUB. After practicing for a while I am able to come
pretty close to call on the same frequency where the last QSO was just
ended. Works almost every time.
In my opinion, the APF is the work in progress, just too much ringing when
the frequency is noisy. When the band is quiet and the signal is just very
weak, the APF works fine. Somebody mentioned to add Q adjustment. I agree. I
would even propose to add this adjustment INSTEAD of APF position adjustment
with the SHIFT knob. The position is better adjusted with main VFO in FINE
mode. Just an opinion.

73,
Igor, N1YX

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of John Harper
Sent: Monday, November 29, 2010 7:25 PM
To: Elecraft
Subject: [Elecraft] APF in CQWW; and DXing in general w/K3

The past weekend's CQWW was the first time I've had the opportunity to use
my new K3 in those types of band conditions and I'd been looking forward to
doing just that. I S&P'ed the whole 'test and used it to tweak and twiddle
with the K3's various functions, notably the NB settings.

I didn't use APF that much due to the pace of the contest but there were two
occassions where an On/Off comparison was the difference between me copying
the stations or not copying. There were probably more than two but these
stick out in my mind because they were both new band-countries on 80m (KH2,
UA0), so I was motivated and thankful to be able to get them logged.

The real amazement to me wasn't the APF but the ability to tune to a pile-up
at 500Hz, hearing an amalgam of callsigns, then dial the selectivity down
and hear the target revealed in splendid isolation. Pile-ups were fun and I
think of them as a cross between chess and fishing. I'm at a loss as to how
to explain the ability to get thru a pile-up on 80m with 100W and a dipole
but I'm beginning to believe it's due to the abilty to precisely zero-beat,
as opposed to the more general way I was doing it before with the wider
selectivity necessitated by my previous rig. Results in the contest seem to
confirm that for me.

John AE5X
http://www.ae5x.com/blog

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[Bob K6UJ]

It is interesting that some of us do not experience "too much
ringing" with the APF when the band is noisy.  It works perfectly
for me,  I wouldn't change a thing.  I think the ringing syndrome
is a function of how we each use our settings and what we perceive as
ringing. I had a combination of heavy noise and very heavy QRM this last weekend
during the CQ WW contest and the APF worked quite well, yes there is a distinct
sharp, hollow sounding effect when the APF is engaged, just like listening to a narrow
audio filter (go figure) but this is normal for a narrow audio peaking filter.
As Yaesu learned when they dumbed down the APF in the FT1000 to reduce the
sharp audio filter sound to please some operators, the reduction to the Q they made
rendered the APF almost useless. They later came out with a mod to restore it
to its original design which worked great again.   The Elecraft K3 APF design is
a derivative of this excellent APF circuit.
 
73,
Bob
K6UJ

 
On Nov 29, 2010, at 10:03 PM, Igor Kosvin wrote:

> You nailed the proverbial nail on the head. The combination of narrow
> roofing filter, great DSP filtering, cut-off and the feature of zero-beat
> the pitch to the other station works magic in those pile-ups. Unfortunately,
> the CWT is not really useful when the DX working SPLIT. In this case you
> have to rely on your ears to match the tone of the station currently in QSO
> with the DX using the SUB. After practicing for a while I am able to come
> pretty close to call on the same frequency where the last QSO was just
> ended. Works almost every time.
> In my opinion, the APF is the work in progress, just too much ringing when
> the frequency is noisy. When the band is quiet and the signal is just very
> weak, the APF works fine. Somebody mentioned to add Q adjustment. I agree. I
> would even propose to add this adjustment INSTEAD of APF position adjustment
> with the SHIFT knob. The position is better adjusted with main VFO in FINE
> mode. Just an opinion.
>
> 73,
> Igor, N1YX
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of John Harper
> Sent: Monday, November 29, 2010 7:25 PM
> To: Elecraft
> Subject: [Elecraft] APF in CQWW; and DXing in general w/K3
>
> The past weekend's CQWW was the first time I've had the opportunity to use
> my new K3 in those types of band conditions and I'd been looking forward to
> doing just that. I S&P'ed the whole 'test and used it to tweak and twiddle
> with the K3's various functions, notably the NB settings.
>
> I didn't use APF that much due to the pace of the contest but there were two
> occassions where an On/Off comparison was the difference between me copying
> the stations or not copying. There were probably more than two but these
> stick out in my mind because they were both new band-countries on 80m (KH2,
> UA0), so I was motivated and thankful to be able to get them logged.
>
> The real amazement to me wasn't the APF but the ability to tune to a pile-up
> at 500Hz, hearing an amalgam of callsigns, then dial the selectivity down
> and hear the target revealed in splendid isolation. Pile-ups were fun and I
> think of them as a cross between chess and fishing. I'm at a loss as to how
> to explain the ability to get thru a pile-up on 80m with 100W and a dipole
> but I'm beginning to believe it's due to the abilty to precisely zero-beat,
> as opposed to the more general way I was doing it before with the wider
> selectivity necessitated by my previous rig. Results in the contest seem to
> confirm that for me.
>
> John AE5X
> http://www.ae5x.com/blog
>
> ______________________________________________________________
> 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
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html

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[Barry N1EU]

I agree.  If you want a lower Q APF, just use 50hz dsp selectivity without APF.  

50hz dsp selectivity is an amazing contesting tool to isolate dx from the calling pileup.

73, Barry N1EU

Robert Harmon wrote

It is interesting that some of us do not experience "too much
ringing" with the APF when the band is noisy.  It works perfectly
for me,  I wouldn't change a thing.