APF (audio peaking filter) on the K3/K3S/KX3

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APF (audio peaking filter) on the K3/K3S/KX3

wayne burdick
Administrator
Hi all,

This morning I was hearing lots of very weak signals in the 40-meter CW band, right at today's noise floor of about S-5. (Among others, I copied BG4GOV in Shanghai.)

Many of the signals were not copyable until I turned on APF (audio peaking filter). This filter's center peak is very narrow (around 30 Hz), but the response broadens out quickly below the 3-dB points in the curve. This brings up the desired signal without allowing noise to cause ringing--something often heard with narrow filters of the "brick-wall" variety. On a noisy band, the effect is just short of magic.

APF is very narrow, so you'll need to tune in 1-Hz increments when it is turned on. Also, APF works best when used with a DSP/crystal filter WIDTH setting of 300-500 Hz.

Use of APF differs for the three transceivers.

KX3: 1-Hz tuning is selected automatically on the when the APF switch is pressed.

K3/K3S: APF is accessed via a hold of the XFIL switch. This function is labeled "APF" on a K3S, or "DUAL PB" on the K3). Use CONFIG:DUAL PB to make sure the selected filter function is APF. See the K3/K3S owner's manual for a description of the alternate setting. 1-Hz tuning can be selected by tapping FINE.

You might want to give APF a try if you haven't already.

73,
Wayne
N6KR

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Re: APF (audio peaking filter) on the K3/K3S/KX3

Bob McGraw - K4TAX
As a new K3S owner {since last August}, I agree.   The APF seems to lift
signals out of the noise when otherwise, one would not know they are
present.  I've used it successfully many times on weak signal QSO's.

Thanks for designing a great radio for the ham market.

73
Bob, K4TAX
K3S, s/n 10163


On 2/2/2016 8:34 AM, Wayne Burdick wrote:

> Hi all,
>
> This morning I was hearing lots of very weak signals in the 40-meter CW band, right at today's noise floor of about S-5. (Among others, I copied BG4GOV in Shanghai.)
>
> Many of the signals were not copyable until I turned on APF (audio peaking filter). This filter's center peak is very narrow (around 30 Hz), but the response broadens out quickly below the 3-dB points in the curve. This brings up the desired signal without allowing noise to cause ringing--something often heard with narrow filters of the "brick-wall" variety. On a noisy band, the effect is just short of magic.
>
> APF is very narrow, so you'll need to tune in 1-Hz increments when it is turned on. Also, APF works best when used with a DSP/crystal filter WIDTH setting of 300-500 Hz.
>
> Use of APF differs for the three transceivers.
>
> KX3: 1-Hz tuning is selected automatically on the when the APF switch is pressed.
>
> K3/K3S: APF is accessed via a hold of the XFIL switch. This function is labeled "APF" on a K3S, or "DUAL PB" on the K3). Use CONFIG:DUAL PB to make sure the selected filter function is APF. See the K3/K3S owner's manual for a description of the alternate setting. 1-Hz tuning can be selected by tapping FINE.
>
> You might want to give APF a try if you haven't already.
>
> 73,
> Wayne
> N6KR
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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Re: APF (audio peaking filter) on the K3/K3S/KX3

Jim Rodenkirch
In reply to this post by wayne burdick
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Re: APF (audio peaking filter) on the K3/K3S/KX3

David Kuechenmeister
In reply to this post by wayne burdick
I tried this the other day with no success. That is, the weak signal that was barely detectable, became so buried in ringing that I couldn't detect it at all. I think I followed the procedure outlined in Wayne's email below...
Noise was around S5 on 40m and the K3 was configured with APF active. I had my 500 Hz filter selected and varied the DSP WIDTH from 500 to 300 without substantial improvement. FINE tuning selected.
What am I forgetting?
vy 73,Dave N4KD

    On Tuesday, February 2, 2016 9:36 AM, Wayne Burdick <[hidden email]> wrote:
 

 Hi all,

This morning I was hearing lots of very weak signals in the 40-meter CW band, right at today's noise floor of about S-5. (Among others, I copied BG4GOV in Shanghai.)

Many of the signals were not copyable until I turned on APF (audio peaking filter). This filter's center peak is very narrow (around 30 Hz), but the response broadens out quickly below the 3-dB points in the curve. This brings up the desired signal without allowing noise to cause ringing--something often heard with narrow filters of the "brick-wall" variety. On a noisy band, the effect is just short of magic.

APF is very narrow, so you'll need to tune in 1-Hz increments when it is turned on. Also, APF works best when used with a DSP/crystal filter WIDTH setting of 300-500 Hz.

Use of APF differs for the three transceivers.

KX3: 1-Hz tuning is selected automatically on the when the APF switch is pressed.

K3/K3S: APF is accessed via a hold of the XFIL switch. This function is labeled "APF" on a K3S, or "DUAL PB" on the K3). Use CONFIG:DUAL PB to make sure the selected filter function is APF. See the K3/K3S owner's manual for a description of the alternate setting. 1-Hz tuning can be selected by tapping FINE.

You might want to give APF a try if you haven't already.

73,
Wayne
N6KR

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Re: APF (audio peaking filter) on the K3/K3S/KX3

N1EU
The receiver has to be tuned precisely to the signal in question for APF to
work.

73, Barry N1EU

On Fri, Feb 5, 2016 at 9:53 AM, David Kuechenmeister <[hidden email]>
wrote:

> I tried this the other day with no success. That is, the weak signal that
> was barely detectable, became so buried in ringing that I couldn't detect
> it at all. I think I followed the procedure outlined in Wayne's email
> below...
> Noise was around S5 on 40m and the K3 was configured with APF active. I
> had my 500 Hz filter selected and varied the DSP WIDTH from 500 to 300
> without substantial improvement. FINE tuning selected.
> What am I forgetting?
> vy 73,Dave N4KD
>
>     On Tuesday, February 2, 2016 9:36 AM, Wayne Burdick <[hidden email]>
> wrote:
>
>
>  Hi all,
>
> This morning I was hearing lots of very weak signals in the 40-meter CW
> band, right at today's noise floor of about S-5. (Among others, I copied
> BG4GOV in Shanghai.)
>
> Many of the signals were not copyable until I turned on APF (audio peaking
> filter). This filter's center peak is very narrow (around 30 Hz), but the
> response broadens out quickly below the 3-dB points in the curve. This
> brings up the desired signal without allowing noise to cause
> ringing--something often heard with narrow filters of the "brick-wall"
> variety. On a noisy band, the effect is just short of magic.
>
> APF is very narrow, so you'll need to tune in 1-Hz increments when it is
> turned on. Also, APF works best when used with a DSP/crystal filter WIDTH
> setting of 300-500 Hz.
>
> Use of APF differs for the three transceivers.
>
> KX3: 1-Hz tuning is selected automatically on the when the APF switch is
> pressed.
>
> K3/K3S: APF is accessed via a hold of the XFIL switch. This function is
> labeled "APF" on a K3S, or "DUAL PB" on the K3). Use CONFIG:DUAL PB to make
> sure the selected filter function is APF. See the K3/K3S owner's manual for
> a description of the alternate setting. 1-Hz tuning can be selected by
> tapping FINE.
>
> You might want to give APF a try if you haven't already.
>
> 73,
> Wayne
> N6KR
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>
>
>
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Re: APF (audio peaking filter) on the K3/K3S/KX3

David Kuechenmeister
Thanks. I'll try again and be very careful this time.
vy 73,Dave N4KD

    On Friday, February 5, 2016 10:08 AM, Barry N1EU <[hidden email]> wrote:
 

 The receiver has to be tuned precisely to the signal in question for APF to
work.

73, Barry N1EU

On Fri, Feb 5, 2016 at 9:53 AM, David Kuechenmeister <[hidden email]>
wrote:

> I tried this the other day with no success. That is, the weak signal that
> was barely detectable, became so buried in ringing that I couldn't detect
> it at all. I think I followed the procedure outlined in Wayne's email
> below...
> Noise was around S5 on 40m and the K3 was configured with APF active. I
> had my 500 Hz filter selected and varied the DSP WIDTH from 500 to 300
> without substantial improvement. FINE tuning selected.
> What am I forgetting?
> vy 73,Dave N4KD
>
>    On Tuesday, February 2, 2016 9:36 AM, Wayne Burdick <[hidden email]>
> wrote:
>
>
>  Hi all,
>
> This morning I was hearing lots of very weak signals in the 40-meter CW
> band, right at today's noise floor of about S-5. (Among others, I copied
> BG4GOV in Shanghai.)
>
> Many of the signals were not copyable until I turned on APF (audio peaking
> filter). This filter's center peak is very narrow (around 30 Hz), but the
> response broadens out quickly below the 3-dB points in the curve. This
> brings up the desired signal without allowing noise to cause
> ringing--something often heard with narrow filters of the "brick-wall"
> variety. On a noisy band, the effect is just short of magic.
>
> APF is very narrow, so you'll need to tune in 1-Hz increments when it is
> turned on. Also, APF works best when used with a DSP/crystal filter WIDTH
> setting of 300-500 Hz.
>
> Use of APF differs for the three transceivers.
>
> KX3: 1-Hz tuning is selected automatically on the when the APF switch is
> pressed.
>
> K3/K3S: APF is accessed via a hold of the XFIL switch. This function is
> labeled "APF" on a K3S, or "DUAL PB" on the K3). Use CONFIG:DUAL PB to make
> sure the selected filter function is APF. See the K3/K3S owner's manual for
> a description of the alternate setting. 1-Hz tuning can be selected by
> tapping FINE.
>
> You might want to give APF a try if you haven't already.
>
> 73,
> Wayne
> N6KR
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>
>
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>
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Re: APF (audio peaking filter) on the K3/K3S/KX3

Dave-7
In reply to this post by David Kuechenmeister

I'd agree. My experience with APF is that it will indeed pop a signal
that is already copyable, if a bit weak, out of the noise. Makes for
easier copy. However the ringing is so bad on a really weak signal
that it is of no help. I guess it depends on what you view as 'weak'
and your noise level. I was hoping it would make previously
un-copyable signals copyable, but that does not happen. Instead it
improves the copyability of weak but already copyable signals.

I find that simply narrowing the filters to 50, 100, or 150 Hz will
give essentially identical results as using the APF and is much easier
to do.

As for the super critical tuning, I do not find it to be all that
critical. The signal can be improved somewhat by going to the 'fine'
tuning, but it makes only a small difference. 10 Hz steps are OK and
much quicker. The APF has a BW of about 30 Hz so tuning cannot be all
that critical. +/- 5 Hz out of 30 is not that big of a deal.

This has been one of my biggest disappointments with the K3. After
reading all the hype about APF I was hoping for a real improvement.
But does not happen. OTOH, the narrow filters of the K3 are outstanding.

73 de dave
ab9ca/4



On 2/5/16 8:53 AM, David Kuechenmeister wrote:

> I tried this the other day with no success. That is, the weak
> signal that was barely detectable, became so buried in ringing that
> I couldn't detect it at all. I think I followed the procedure
> outlined in Wayne's email below... Noise was around S5 on 40m and
> the K3 was configured with APF active. I had my 500 Hz filter
> selected and varied the DSP WIDTH from 500 to 300 without
> substantial improvement. FINE tuning selected. What am I
> forgetting? vy 73,Dave N4KD
>
> On Tuesday, February 2, 2016 9:36 AM, Wayne Burdick
> <[hidden email]> wrote:
>
>
> Hi all,
>
> This morning I was hearing lots of very weak signals in the
> 40-meter CW band, right at today's noise floor of about S-5. (Among
> others, I copied BG4GOV in Shanghai.)
>
> Many of the signals were not copyable until I turned on APF (audio
> peaking filter). This filter's center peak is very narrow (around
> 30 Hz), but the response broadens out quickly below the 3-dB points
> in the curve. This brings up the desired signal without allowing
> noise to cause ringing--something often heard with narrow filters
> of the "brick-wall" variety. On a noisy band, the effect is just
> short of magic.
>
> APF is very narrow, so you'll need to tune in 1-Hz increments when
> it is turned on. Also, APF works best when used with a DSP/crystal
> filter WIDTH setting of 300-500 Hz.
>
> Use of APF differs for the three transceivers.
>
> KX3: 1-Hz tuning is selected automatically on the when the APF
> switch is pressed.
>
> K3/K3S: APF is accessed via a hold of the XFIL switch. This
> function is labeled "APF" on a K3S, or "DUAL PB" on the K3). Use
> CONFIG:DUAL PB to make sure the selected filter function is APF.
> See the K3/K3S owner's manual for a description of the alternate
> setting. 1-Hz tuning can be selected by tapping FINE.
>
> You might want to give APF a try if you haven't already.
>
> 73, Wayne N6KR
>
> ______________________________________________________________
> 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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> [hidden email]
>
>
>
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>
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Re: APF (audio peaking filter) on the K3/K3S/KX3

Stephen G4SJP
In reply to this post by David Kuechenmeister
I've seen it written that it helps to offset the IF slightly, although to
be honest I have never myself got the APF to work to my satisfaction.
Oddly, and I communicated with Wayne about this at the time, the first beta
(I think) implementation of it was stunning, but a later release lost it
for me.  Wayne told me there had been no change in code, but I have never
understood that.  With my XYL away in London for the weekend, I might
devote some more time to it :-)

73 Stephen G4SJP

On 5 February 2016 at 15:27, David Kuechenmeister <[hidden email]>
wrote:

> Thanks. I'll try again and be very careful this time.
> vy 73,Dave N4KD
>
>     On Friday, February 5, 2016 10:08 AM, Barry N1EU <[hidden email]>
> wrote:
>
>
>  The receiver has to be tuned precisely to the signal in question for APF
> to
> work.
>
> 73, Barry N1EU
>
> On Fri, Feb 5, 2016 at 9:53 AM, David Kuechenmeister <[hidden email]>
> wrote:
>
> > I tried this the other day with no success. That is, the weak signal that
> > was barely detectable, became so buried in ringing that I couldn't detect
> > it at all. I think I followed the procedure outlined in Wayne's email
> > below...
> > Noise was around S5 on 40m and the K3 was configured with APF active. I
> > had my 500 Hz filter selected and varied the DSP WIDTH from 500 to 300
> > without substantial improvement. FINE tuning selected.
> > What am I forgetting?
> > vy 73,Dave N4KD
> >
> >    On Tuesday, February 2, 2016 9:36 AM, Wayne Burdick <
> [hidden email]>
> > wrote:
> >
> >
> >  Hi all,
> >
> > This morning I was hearing lots of very weak signals in the 40-meter CW
> > band, right at today's noise floor of about S-5. (Among others, I copied
> > BG4GOV in Shanghai.)
> >
> > Many of the signals were not copyable until I turned on APF (audio
> peaking
> > filter). This filter's center peak is very narrow (around 30 Hz), but the
> > response broadens out quickly below the 3-dB points in the curve. This
> > brings up the desired signal without allowing noise to cause
> > ringing--something often heard with narrow filters of the "brick-wall"
> > variety. On a noisy band, the effect is just short of magic.
> >
> > APF is very narrow, so you'll need to tune in 1-Hz increments when it is
> > turned on. Also, APF works best when used with a DSP/crystal filter WIDTH
> > setting of 300-500 Hz.
> >
> > Use of APF differs for the three transceivers.
> >
> > KX3: 1-Hz tuning is selected automatically on the when the APF switch is
> > pressed.
> >
> > K3/K3S: APF is accessed via a hold of the XFIL switch. This function is
> > labeled "APF" on a K3S, or "DUAL PB" on the K3). Use CONFIG:DUAL PB to
> make
> > sure the selected filter function is APF. See the K3/K3S owner's manual
> for
> > a description of the alternate setting. 1-Hz tuning can be selected by
> > tapping FINE.
> >
> > You might want to give APF a try if you haven't already.
> >
> > 73,
> > Wayne
> > N6KR
> >
> > ______________________________________________________________
> > 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
> > Message delivered to [hidden email]
> >
> >
> >
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> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
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Re: APF (audio peaking filter) on the K3/K3S/KX3

w5sum
In reply to this post by Dave-7
I went from a TenTec Orion to my K3 ( whose box I opened almost the very day the K3S was announced which is total BS) and I really mis the SAF feature in the Orion. The APF in my K3 doesn't touch it.

W5SUM

Sent from Ronnie's IPhone

> On Feb 5, 2016, at 09:56, dave <[hidden email]> wrote:
>
>
> I'd agree. My experience with APF is that it will indeed pop a signal that is already copyable, if a bit weak, out of the noise. Makes for easier copy. However the ringing is so bad on a really weak signal that it is of no help. I guess it depends on what you view as 'weak' and your noise level. I was hoping it would make previously un-copyable signals copyable, but that does not happen. Instead it improves the copyability of weak but already copyable signals.
>
> I find that simply narrowing the filters to 50, 100, or 150 Hz will give essentially identical results as using the APF and is much easier to do.
>
> As for the super critical tuning, I do not find it to be all that critical. The signal can be improved somewhat by going to the 'fine' tuning, but it makes only a small difference. 10 Hz steps are OK and much quicker. The APF has a BW of about 30 Hz so tuning cannot be all that critical. +/- 5 Hz out of 30 is not that big of a deal.
>
> This has been one of my biggest disappointments with the K3. After reading all the hype about APF I was hoping for a real improvement. But does not happen. OTOH, the narrow filters of the K3 are outstanding.
>
> 73 de dave
> ab9ca/4
>
>
>
>> On 2/5/16 8:53 AM, David Kuechenmeister wrote:
>> I tried this the other day with no success. That is, the weak
>> signal that was barely detectable, became so buried in ringing that
>> I couldn't detect it at all. I think I followed the procedure
>> outlined in Wayne's email below... Noise was around S5 on 40m and
>> the K3 was configured with APF active. I had my 500 Hz filter
>> selected and varied the DSP WIDTH from 500 to 300 without
>> substantial improvement. FINE tuning selected. What am I
>> forgetting? vy 73,Dave N4KD
>>
>> On Tuesday, February 2, 2016 9:36 AM, Wayne Burdick
>> <[hidden email]> wrote:
>>
>>
>> Hi all,
>>
>> This morning I was hearing lots of very weak signals in the
>> 40-meter CW band, right at today's noise floor of about S-5. (Among
>> others, I copied BG4GOV in Shanghai.)
>>
>> Many of the signals were not copyable until I turned on APF (audio
>> peaking filter). This filter's center peak is very narrow (around
>> 30 Hz), but the response broadens out quickly below the 3-dB points
>> in the curve. This brings up the desired signal without allowing
>> noise to cause ringing--something often heard with narrow filters
>> of the "brick-wall" variety. On a noisy band, the effect is just
>> short of magic.
>>
>> APF is very narrow, so you'll need to tune in 1-Hz increments when
>> it is turned on. Also, APF works best when used with a DSP/crystal
>> filter WIDTH setting of 300-500 Hz.
>>
>> Use of APF differs for the three transceivers.
>>
>> KX3: 1-Hz tuning is selected automatically on the when the APF
>> switch is pressed.
>>
>> K3/K3S: APF is accessed via a hold of the XFIL switch. This
>> function is labeled "APF" on a K3S, or "DUAL PB" on the K3). Use
>> CONFIG:DUAL PB to make sure the selected filter function is APF.
>> See the K3/K3S owner's manual for a description of the alternate
>> setting. 1-Hz tuning can be selected by tapping FINE.
>>
>> You might want to give APF a try if you haven't already.
>>
>> 73, Wayne N6KR
>>
>> ______________________________________________________________
>> 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 Message delivered to
>> [hidden email]
>>
>>
>>
>> ______________________________________________________________
>> 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 Message delivered to
>> [hidden email] .
>>
> ______________________________________________________________
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> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
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Re: APF (audio peaking filter) on the K3/K3S/KX3

Bob McGraw - K4TAX
In reply to this post by Dave-7
While I find the APF works really nice, one must also discover the
artful use of the RF Gain control as well.   Most hams seem to use
excessive RF Gain which will force noise through the filter and all of
those undesirable artifacts will be heard.  If in doubt, reduce the RF Gain.

Using this technique, I can tune the band with the APF engaged,
adjusting the RF Gain a bit, and actually hear signals with this
configuration which without the APC no signal could be heard.  I view
this gives one the ability to actually "dig signals out of the noise".

73
Bob, K4TAX

On 2/5/2016 9:56 AM, dave wrote:

>
> I'd agree. My experience with APF is that it will indeed pop a signal
> that is already copyable, if a bit weak, out of the noise. Makes for
> easier copy. However the ringing is so bad on a really weak signal
> that it is of no help. I guess it depends on what you view as 'weak'
> and your noise level. I was hoping it would make previously
> un-copyable signals copyable, but that does not happen. Instead it
> improves the copyability of weak but already copyable signals.
>
> I find that simply narrowing the filters to 50, 100, or 150 Hz will
> give essentially identical results as using the APF and is much easier
> to do.
>
> As for the super critical tuning, I do not find it to be all that
> critical. The signal can be improved somewhat by going to the 'fine'
> tuning, but it makes only a small difference. 10 Hz steps are OK and
> much quicker. The APF has a BW of about 30 Hz so tuning cannot be all
> that critical. +/- 5 Hz out of 30 is not that big of a deal.
>
> This has been one of my biggest disappointments with the K3. After
> reading all the hype about APF I was hoping for a real improvement.
> But does not happen. OTOH, the narrow filters of the K3 are outstanding.
>
> 73 de dave
> ab9ca/4
>
>
>
> On 2/5/16 8:53 AM, David Kuechenmeister wrote:
>> I tried this the other day with no success. That is, the weak
>> signal that was barely detectable, became so buried in ringing that
>> I couldn't detect it at all. I think I followed the procedure
>> outlined in Wayne's email below... Noise was around S5 on 40m and
>> the K3 was configured with APF active. I had my 500 Hz filter
>> selected and varied the DSP WIDTH from 500 to 300 without
>> substantial improvement. FINE tuning selected. What am I
>> forgetting? vy 73,Dave N4KD
>>
>> On Tuesday, February 2, 2016 9:36 AM, Wayne Burdick
>> <[hidden email]> wrote:
>>
>>
>> Hi all,
>>
>> This morning I was hearing lots of very weak signals in the
>> 40-meter CW band, right at today's noise floor of about S-5. (Among
>> others, I copied BG4GOV in Shanghai.)
>>
>> Many of the signals were not copyable until I turned on APF (audio
>> peaking filter). This filter's center peak is very narrow (around
>> 30 Hz), but the response broadens out quickly below the 3-dB points
>> in the curve. This brings up the desired signal without allowing
>> noise to cause ringing--something often heard with narrow filters
>> of the "brick-wall" variety. On a noisy band, the effect is just
>> short of magic.
>>
>> APF is very narrow, so you'll need to tune in 1-Hz increments when
>> it is turned on. Also, APF works best when used with a DSP/crystal
>> filter WIDTH setting of 300-500 Hz.
>>
>> Use of APF differs for the three transceivers.
>>
>> KX3: 1-Hz tuning is selected automatically on the when the APF
>> switch is pressed.
>>
>> K3/K3S: APF is accessed via a hold of the XFIL switch. This
>> function is labeled "APF" on a K3S, or "DUAL PB" on the K3). Use
>> CONFIG:DUAL PB to make sure the selected filter function is APF.
>> See the K3/K3S owner's manual for a description of the alternate
>> setting. 1-Hz tuning can be selected by tapping FINE.
>>
>> You might want to give APF a try if you haven't already.
>>
>> 73, Wayne N6KR
>>
>> ______________________________________________________________
>> 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 Message delivered to
>> [hidden email]
>>
>>
>>
>> ______________________________________________________________
>> 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 Message delivered to
>> [hidden email] .
>>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>


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Re: APF (audio peaking filter) on the K3/K3S/KX3

Dave-7

> one must also discover the
> artful use of the RF Gain control as well

Adjustment of the RF gain control is not mentioned in Wayne's note on
using APF.

When I tried it here, the RF gain might have made some small
difference but it still did not allow un-copyable signals to be
copied. When testing APF I have made all adjustments the I thought
might affect signal quality. IIRC correctly I also tinkered with the
AGC parameters. But the APF never produced results any better than
simply narrowing the filters. Usually the regular narrow filters
worked better. I know I had not switched APF on for months. I did
switch it on to recheck before sending my note. But the noise is not
currently high enough to give it a good test.

I have found, in general, that careful adjustment of the RF gain
control can be useful. This applies to all receivers I have tried it on.

I'm wondering if the difference is in the type of noise. I have mostly
tried APF at times of high lightning activity. I think we in the SE
get more of that than other parts of the country. The higher noise
level means more weak signals. You need all the help you can get. But
that noise differs from the usual band noise.

And it may depend on each individual's hearing.

I have always puzzled over why some rave about how great APF is while
for myself, and obviously others, it is of no help at all.

73 de dave
ab9ca/4



On 2/5/16 10:13 AM, Bob McGraw K4TAX wrote:

> While I find the APF works really nice, one must also discover the
> artful use of the RF Gain control as well.   Most hams seem to use
> excessive RF Gain which will force noise through the filter and all of
> those undesirable artifacts will be heard.  If in doubt, reduce the RF
> Gain.
>
> Using this technique, I can tune the band with the APF engaged,
> adjusting the RF Gain a bit, and actually hear signals with this
> configuration which without the APC no signal could be heard.  I view
> this gives one the ability to actually "dig signals out of the noise".
>
> 73
> Bob, K4TAX
>
> On 2/5/2016 9:56 AM, dave wrote:
>>
>> I'd agree. My experience with APF is that it will indeed pop a
>> signal that is already copyable, if a bit weak, out of the noise.
>> Makes for easier copy. However the ringing is so bad on a really
>> weak signal that it is of no help. I guess it depends on what you
>> view as 'weak' and your noise level. I was hoping it would make
>> previously un-copyable signals copyable, but that does not happen.
>> Instead it improves the copyability of weak but already copyable
>> signals.
>>
>> I find that simply narrowing the filters to 50, 100, or 150 Hz will
>> give essentially identical results as using the APF and is much
>> easier to do.
>>
>> As for the super critical tuning, I do not find it to be all that
>> critical. The signal can be improved somewhat by going to the 'fine'
>> tuning, but it makes only a small difference. 10 Hz steps are OK and
>> much quicker. The APF has a BW of about 30 Hz so tuning cannot be
>> all that critical. +/- 5 Hz out of 30 is not that big of a deal.
>>
>> This has been one of my biggest disappointments with the K3. After
>> reading all the hype about APF I was hoping for a real improvement.
>> But does not happen. OTOH, the narrow filters of the K3 are
>> outstanding.
>>
>> 73 de dave
>> ab9ca/4
>>
>>
>>
>> On 2/5/16 8:53 AM, David Kuechenmeister wrote:
>>> I tried this the other day with no success. That is, the weak
>>> signal that was barely detectable, became so buried in ringing that
>>> I couldn't detect it at all. I think I followed the procedure
>>> outlined in Wayne's email below... Noise was around S5 on 40m and
>>> the K3 was configured with APF active. I had my 500 Hz filter
>>> selected and varied the DSP WIDTH from 500 to 300 without
>>> substantial improvement. FINE tuning selected. What am I
>>> forgetting? vy 73,Dave N4KD
>>>
>>> On Tuesday, February 2, 2016 9:36 AM, Wayne Burdick
>>> <[hidden email]> wrote:
>>>
>>>
>>> Hi all,
>>>
>>> This morning I was hearing lots of very weak signals in the
>>> 40-meter CW band, right at today's noise floor of about S-5. (Among
>>> others, I copied BG4GOV in Shanghai.)
>>>
>>> Many of the signals were not copyable until I turned on APF (audio
>>> peaking filter). This filter's center peak is very narrow (around
>>> 30 Hz), but the response broadens out quickly below the 3-dB points
>>> in the curve. This brings up the desired signal without allowing
>>> noise to cause ringing--something often heard with narrow filters
>>> of the "brick-wall" variety. On a noisy band, the effect is just
>>> short of magic.
>>>
>>> APF is very narrow, so you'll need to tune in 1-Hz increments when
>>> it is turned on. Also, APF works best when used with a DSP/crystal
>>> filter WIDTH setting of 300-500 Hz.
>>>
>>> Use of APF differs for the three transceivers.
>>>
>>> KX3: 1-Hz tuning is selected automatically on the when the APF
>>> switch is pressed.
>>>
>>> K3/K3S: APF is accessed via a hold of the XFIL switch. This
>>> function is labeled "APF" on a K3S, or "DUAL PB" on the K3). Use
>>> CONFIG:DUAL PB to make sure the selected filter function is APF.
>>> See the K3/K3S owner's manual for a description of the alternate
>>> setting. 1-Hz tuning can be selected by tapping FINE.
>>>
>>> You might want to give APF a try if you haven't already.
>>>
>>> 73, Wayne N6KR
>>>
>>> ______________________________________________________________
>>> 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 Message delivered to
>>> [hidden email]
>>>
>>>
>>>
>>> ______________________________________________________________
>>> 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 Message delivered to
>>> [hidden email] .
>>>
>> ______________________________________________________________
>> 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
>> Message delivered to [hidden email]
>>
>
>
> ______________________________________________________________
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> Post: mailto:[hidden email]
>
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> Message delivered to [hidden email]
>
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Re: APF (audio peaking filter) on the K3/K3S/KX3

Brian Hunt
In reply to this post by wayne burdick
The technique I'm using with the APF also involves NR like so:

On an uncrowded band, set the DSP BW to 700 to 1000 Hz. If you have a roofing filter in that range stay within it.

Turn on NR set to mF5-3 or there about. The wide BW helps the NR work well. The "mix" mode lets a little unprocessed signal+noise through. This is a good weak signal search mode.

When you find a signal you want to copy, turn on APF and peak it in the filter. Fine tuning helps. There is little ringing because NR has reduced the noise amplitude. You can decrease the DSP BW a little but the NR is more effective with uncorrelated noise.

This technique has gotten me many pelts in the QRP Fox Hunts.

73,
Brian, K0DTJ
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Re: APF (audio peaking filter) on the K3/K3S/KX3

Bob McGraw - K4TAX
In reply to this post by Dave-7
Lightning has dramatic effect on the AGC system of many to most
receivers.   Rob Sherwood has had a lot to say about this.  Elecraft has
taken steps to minimize the effect.

Yes different types of noise clearly have different characteristics and
thus the reason for suggesting reducing the RF Gain, it reduces the
noise.  Fortunately this time of year in our location in TN the noise is
quite low, unless a line of thunder storms is located within 500 or so
miles.

Hear this morning no thunder storms close by, the neighborhood is
reasonably quiet, and the noise on 40M is about -103 dBm.  With the APF
a signal at -113 dBm can be easily copied, yet without the APF nothing
but noise is heard.

My technique is to observe the S meter, no signal, RF Gain at max for
the given band and antenna.  Then with the antenna disconnected,
actually by a switch, I adjust the RF Gain until the S meter indicates
the same value as the noise coming in on the antenna. Then switch the
antenna back to the receiver.  Also the AUTO SPOT feature is a big aid
to optimum tuning.  The result is signal present and no noise.

73
Bob, K4TAX



On 2/5/2016 10:49 AM, dave wrote:

>
>> one must also discover the
>> artful use of the RF Gain control as well
>
> Adjustment of the RF gain control is not mentioned in Wayne's note on
> using APF.
>
> When I tried it here, the RF gain might have made some small
> difference but it still did not allow un-copyable signals to be
> copied. When testing APF I have made all adjustments the I thought
> might affect signal quality. IIRC correctly I also tinkered with the
> AGC parameters. But the APF never produced results any better than
> simply narrowing the filters. Usually the regular narrow filters
> worked better. I know I had not switched APF on for months. I did
> switch it on to recheck before sending my note. But the noise is not
> currently high enough to give it a good test.
>
> I have found, in general, that careful adjustment of the RF gain
> control can be useful. This applies to all receivers I have tried it on.
>
> I'm wondering if the difference is in the type of noise. I have mostly
> tried APF at times of high lightning activity. I think we in the SE
> get more of that than other parts of the country. The higher noise
> level means more weak signals. You need all the help you can get. But
> that noise differs from the usual band noise.
>
> And it may depend on each individual's hearing.
>
> I have always puzzled over why some rave about how great APF is while
> for myself, and obviously others, it is of no help at all.
>
> 73 de dave
> ab9ca/4
>


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Re: APF (audio peaking filter) on the K3/K3S/KX3

Elecraft mailing list
In reply to this post by wayne burdick
 
In the last month of listening to really weak signals here in 9 land  I've
found it helpful but not radical.
 
Just for fun I tried tuning some of the same VP8SGI signals on a Drake  
2B/2BQ and found adding the 2BQ in the mix more user friendly and making a  
bigger difference, but hey, the 2B was starting from a worse spot.
 
Still it would be nice if the APF was user adjustable like the 2BQ or  the
old outbaord audio filters, peak magnitude, and maybe even frequency, within
 a selected passband.
 
Not sure why Wayne picked only 3 db - I'd like it to be user adustable to  
try a bit more peak if conditions permit.
 
If APF is user adjustable in that way and I missed it somebody please  
point out the page number....or if the experiment's been done and it's not  
workable would like to know that too.
 
73 Scott ka9p

 
 
In a message dated 2/5/2016 11:08:53 A.M. Central Standard Time,  
[hidden email] writes:


>  one must also discover the
> artful use of the RF Gain control as  well

Adjustment of the RF gain control is not mentioned in Wayne's note  on
using APF.

When I tried it here, the RF gain might have made  some small
difference but it still did not allow un-copyable signals to be  
copied. When testing APF I have made all adjustments the I thought  
might affect signal quality. IIRC correctly I also tinkered with the  
AGC parameters. But the APF never produced results any better than  
simply narrowing the filters. Usually the regular narrow filters  
worked better. I know I had not switched APF on for months. I did  
switch it on to recheck before sending my note. But the noise is not  
currently high enough to give it a good test.

I have found, in  general, that careful adjustment of the RF gain
control can be useful.  This applies to all receivers I have tried it on.

I'm wondering if the  difference is in the type of noise. I have mostly
tried APF at times of  high lightning activity. I think we in the SE
get more of that than other  parts of the country. The higher noise
level means more weak signals. You  need all the help you can get. But
that noise differs from the usual band  noise.

And it may depend on each individual's hearing.

I have  always puzzled over why some rave about how great APF is while
for myself,  and obviously others, it is of no help at all.

73 de  dave
ab9ca/4



On 2/5/16 10:13 AM, Bob McGraw K4TAX  wrote:

> While I find the APF works really nice, one must also discover  the
> artful use of the RF Gain control as well.   Most hams  seem to use
> excessive RF Gain which will force noise through the  filter and all of
> those undesirable artifacts will be heard.  If  in doubt, reduce the RF
> Gain.
>
> Using this technique, I  can tune the band with the APF engaged,
> adjusting the RF Gain a bit,  and actually hear signals with this
> configuration which without the  APC no signal could be heard.  I view
> this gives one the ability  to actually "dig signals out of the noise".
>
> 73
> Bob,  K4TAX
>
> On 2/5/2016 9:56 AM, dave wrote:
>>
>>  I'd agree. My experience with APF is that it will indeed pop a
>>  signal that is already copyable, if a bit weak, out of the noise.
>>  Makes for easier copy. However the ringing is so bad on a really
>>  weak signal that it is of no help. I guess it depends on what you
>>  view as 'weak' and your noise level. I was hoping it would make
>>  previously un-copyable signals copyable, but that does not happen.
>>  Instead it improves the copyability of weak but already copyable
>>  signals.
>>
>> I find that simply narrowing the filters to  50, 100, or 150 Hz will
>> give essentially identical results as  using the APF and is much
>> easier to do.
>>
>> As  for the super critical tuning, I do not find it to be all that
>>  critical. The signal can be improved somewhat by going to the  'fine'
>> tuning, but it makes only a small difference. 10 Hz steps  are OK and
>> much quicker. The APF has a BW of about 30 Hz so tuning  cannot be
>> all that critical. +/- 5 Hz out of 30 is not that big of  a deal.
>>
>> This has been one of my biggest  disappointments with the K3. After
>> reading all the hype about APF  I was hoping for a real improvement.
>> But does not happen. OTOH,  the narrow filters of the K3 are
>>  outstanding.
>>
>> 73 de dave
>>  ab9ca/4
>>
>>
>>
>> On 2/5/16 8:53 AM,  David Kuechenmeister wrote:
>>> I tried this the other day with no  success. That is, the weak
>>> signal that was barely detectable,  became so buried in ringing that
>>> I couldn't detect it at all.  I think I followed the procedure
>>> outlined in Wayne's email  below... Noise was around S5 on 40m and
>>> the K3 was configured  with APF active. I had my 500 Hz filter
>>> selected and varied  the DSP WIDTH from 500 to 300 without
>>> substantial improvement.  FINE tuning selected. What am I
>>> forgetting? vy 73,Dave  N4KD
>>>
>>> On Tuesday, February 2, 2016 9:36 AM,  Wayne Burdick
>>> <[hidden email]>  wrote:
>>>
>>>
>>> Hi  all,
>>>
>>> This morning I was hearing lots of very  weak signals in the
>>> 40-meter CW band, right at today's noise  floor of about S-5. (Among
>>> others, I copied BG4GOV in  Shanghai.)
>>>
>>> Many of the signals were not  copyable until I turned on APF (audio
>>> peaking filter). This  filter's center peak is very narrow (around
>>> 30 Hz), but the  response broadens out quickly below the 3-dB points
>>> in the  curve. This brings up the desired signal without allowing
>>>  noise to cause ringing--something often heard with narrow  filters
>>> of the "brick-wall" variety. On a noisy band, the  effect is just
>>> short of magic.
>>>
>>>  APF is very narrow, so you'll need to tune in 1-Hz increments  when
>>> it is turned on. Also, APF works best when used with a  DSP/crystal
>>> filter WIDTH setting of 300-500  Hz.
>>>
>>> Use of APF differs for the three  transceivers.
>>>
>>> KX3: 1-Hz tuning is selected  automatically on the when the APF
>>> switch is  pressed.
>>>
>>> K3/K3S: APF is accessed via a hold of  the XFIL switch. This
>>> function is labeled "APF" on a K3S, or  "DUAL PB" on the K3). Use
>>> CONFIG:DUAL PB to make sure the  selected filter function is APF.
>>> See the K3/K3S owner's manual  for a description of the alternate
>>> setting. 1-Hz tuning can be  selected by tapping FINE.
>>>
>>> You might want to  give APF a try if you haven't already.
>>>
>>> 73,  Wayne N6KR
>>>
>>>  ______________________________________________________________
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Re: APF (audio peaking filter) on the K3/K3S/KX3

N1EU
I suspect that when the K3 APF was first engineered, the Yaesu FT-1000D APF
(original hi-Q version) was used as the model because many prominent
dx'ers/topbanders always raved about it.

73, Barry N1EU

On Fri, Feb 5, 2016 at 12:37 PM, Scott via Elecraft <
[hidden email]> wrote:

>
> In the last month of listening to really weak signals here in 9 land  I've
> found it helpful but not radical.
>
> Just for fun I tried tuning some of the same VP8SGI signals on a Drake
> 2B/2BQ and found adding the 2BQ in the mix more user friendly and making a
> bigger difference, but hey, the 2B was starting from a worse spot.
>
> Still it would be nice if the APF was user adjustable like the 2BQ or  the
> old outbaord audio filters, peak magnitude, and maybe even frequency,
> within
>  a selected passband.
>
> Not sure why Wayne picked only 3 db - I'd like it to be user adustable to
> try a bit more peak if conditions permit.
>
> If APF is user adjustable in that way and I missed it somebody please
> point out the page number....or if the experiment's been done and it's not
> workable would like to know that too.
>
> 73 Scott ka9p
>
>
>
> In a message dated 2/5/2016 11:08:53 A.M. Central Standard Time,
> [hidden email] writes:
>
>
> >  one must also discover the
> > artful use of the RF Gain control as  well
>
> Adjustment of the RF gain control is not mentioned in Wayne's note  on
> using APF.
>
> When I tried it here, the RF gain might have made  some small
> difference but it still did not allow un-copyable signals to be
> copied. When testing APF I have made all adjustments the I thought
> might affect signal quality. IIRC correctly I also tinkered with the
> AGC parameters. But the APF never produced results any better than
> simply narrowing the filters. Usually the regular narrow filters
> worked better. I know I had not switched APF on for months. I did
> switch it on to recheck before sending my note. But the noise is not
> currently high enough to give it a good test.
>
> I have found, in  general, that careful adjustment of the RF gain
> control can be useful.  This applies to all receivers I have tried it on.
>
> I'm wondering if the  difference is in the type of noise. I have mostly
> tried APF at times of  high lightning activity. I think we in the SE
> get more of that than other  parts of the country. The higher noise
> level means more weak signals. You  need all the help you can get. But
> that noise differs from the usual band  noise.
>
> And it may depend on each individual's hearing.
>
> I have  always puzzled over why some rave about how great APF is while
> for myself,  and obviously others, it is of no help at all.
>
> 73 de  dave
> ab9ca/4
>
>
>
> On 2/5/16 10:13 AM, Bob McGraw K4TAX  wrote:
> > While I find the APF works really nice, one must also discover  the
> > artful use of the RF Gain control as well.   Most hams  seem to use
> > excessive RF Gain which will force noise through the  filter and all of
> > those undesirable artifacts will be heard.  If  in doubt, reduce the RF
> > Gain.
> >
> > Using this technique, I  can tune the band with the APF engaged,
> > adjusting the RF Gain a bit,  and actually hear signals with this
> > configuration which without the  APC no signal could be heard.  I view
> > this gives one the ability  to actually "dig signals out of the noise".
> >
> > 73
> > Bob,  K4TAX
> >
> > On 2/5/2016 9:56 AM, dave wrote:
> >>
> >>  I'd agree. My experience with APF is that it will indeed pop a
> >>  signal that is already copyable, if a bit weak, out of the noise.
> >>  Makes for easier copy. However the ringing is so bad on a really
> >>  weak signal that it is of no help. I guess it depends on what you
> >>  view as 'weak' and your noise level. I was hoping it would make
> >>  previously un-copyable signals copyable, but that does not happen.
> >>  Instead it improves the copyability of weak but already copyable
> >>  signals.
> >>
> >> I find that simply narrowing the filters to  50, 100, or 150 Hz will
> >> give essentially identical results as  using the APF and is much
> >> easier to do.
> >>
> >> As  for the super critical tuning, I do not find it to be all that
> >>  critical. The signal can be improved somewhat by going to the  'fine'
> >> tuning, but it makes only a small difference. 10 Hz steps  are OK and
> >> much quicker. The APF has a BW of about 30 Hz so tuning  cannot be
> >> all that critical. +/- 5 Hz out of 30 is not that big of  a deal.
> >>
> >> This has been one of my biggest  disappointments with the K3. After
> >> reading all the hype about APF  I was hoping for a real improvement.
> >> But does not happen. OTOH,  the narrow filters of the K3 are
> >>  outstanding.
> >>
> >> 73 de dave
> >>  ab9ca/4
> >>
> >>
> >>
> >> On 2/5/16 8:53 AM,  David Kuechenmeister wrote:
> >>> I tried this the other day with no  success. That is, the weak
> >>> signal that was barely detectable,  became so buried in ringing that
> >>> I couldn't detect it at all.  I think I followed the procedure
> >>> outlined in Wayne's email  below... Noise was around S5 on 40m and
> >>> the K3 was configured  with APF active. I had my 500 Hz filter
> >>> selected and varied  the DSP WIDTH from 500 to 300 without
> >>> substantial improvement.  FINE tuning selected. What am I
> >>> forgetting? vy 73,Dave  N4KD
> >>>
> >>> On Tuesday, February 2, 2016 9:36 AM,  Wayne Burdick
> >>> <[hidden email]>  wrote:
> >>>
> >>>
> >>> Hi  all,
> >>>
> >>> This morning I was hearing lots of very  weak signals in the
> >>> 40-meter CW band, right at today's noise  floor of about S-5. (Among
> >>> others, I copied BG4GOV in  Shanghai.)
> >>>
> >>> Many of the signals were not  copyable until I turned on APF (audio
> >>> peaking filter). This  filter's center peak is very narrow (around
> >>> 30 Hz), but the  response broadens out quickly below the 3-dB points
> >>> in the  curve. This brings up the desired signal without allowing
> >>>  noise to cause ringing--something often heard with narrow  filters
> >>> of the "brick-wall" variety. On a noisy band, the  effect is just
> >>> short of magic.
> >>>
> >>>  APF is very narrow, so you'll need to tune in 1-Hz increments  when
> >>> it is turned on. Also, APF works best when used with a  DSP/crystal
> >>> filter WIDTH setting of 300-500  Hz.
> >>>
> >>> Use of APF differs for the three  transceivers.
> >>>
> >>> KX3: 1-Hz tuning is selected  automatically on the when the APF
> >>> switch is  pressed.
> >>>
> >>> K3/K3S: APF is accessed via a hold of  the XFIL switch. This
> >>> function is labeled "APF" on a K3S, or  "DUAL PB" on the K3). Use
> >>> CONFIG:DUAL PB to make sure the  selected filter function is APF.
> >>> See the K3/K3S owner's manual  for a description of the alternate
> >>> setting. 1-Hz tuning can be  selected by tapping FINE.
> >>>
> >>> You might want to  give APF a try if you haven't already.
> >>>
> >>> 73,  Wayne N6KR
> >>>
> >>>  ______________________________________________________________
> >>>  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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> >>> email  list: http://www.qsl.net/donate.html Message delivered to
> >>>  [hidden email]
> >>>
> >>>
> >>>
> >>>  ______________________________________________________________
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> >>>  http://mailman.qth.net/mmfaq.htm Post:
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Re: APF (audio peaking filter) on the K3/K3S/KX3

K9ZTV
In reply to this post by Stephen G4SJP
Stephen is correct.

Several of us lobbied for an APF feature shortly after the K3 debuted in
2007, drawing on our experiences with the FT-1000D. There /were/ two
firmware versions that Wayne developed, and the consensus among some of
us was that the first one was better than the second.  As I recall, the
second version cleaned up some artifacts and unintended consequences,
but, we felt, at the cost of diminished "peaking."  Wayne was adamant
that the APF part of the code was not touched.  We eventually chalked up
the difference between the two versions to subjectivity among the
testers and left it at that.

Barry, by the way, is also correct in saying there were two versions of
the APF circuit in the FT-1000D over the years.  It has been the
consensus of owners that the earlier version was superior to the later
version.

The APF in both the K3 and KX3 is excellent, in my opinion.

73,

Kent  K9ZTV
K3/KX3  s.n. 21



On 2/5/2016 10:03 AM, Stephen Prior wrote:
> I've seen it written that it helps to offset the IF slightly, although to
> be honest I have never myself got the APF to work to my satisfaction.
> Oddly, and I communicated with Wayne about this at the time, the first beta
> (I think) implementation of it was stunning, but a later release lost it
> for me.  Wayne told me there had been no change in code, but I have never
> understood that.

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Re: APF (audio peaking filter) on the K3/K3S/KX3

Nr4c
In reply to this post by David Kuechenmeister
Also, you can move the "peak" left/right by rotating the SHIFT knob. You will see APF setting appear in the VFO B area and the ref point is denoted by an "*" next to 45.

Sent from my iPhone
...nr4c. bill


> On Feb 5, 2016, at 10:27 AM, David Kuechenmeister <[hidden email]> wrote:
>
> Thanks. I'll try again and be very careful this time.
> vy 73,Dave N4KD
>
>    On Friday, February 5, 2016 10:08 AM, Barry N1EU <[hidden email]> wrote:
>
>
> The receiver has to be tuned precisely to the signal in question for APF to
> work.
>
> 73, Barry N1EU
>
> On Fri, Feb 5, 2016 at 9:53 AM, David Kuechenmeister <[hidden email]>
> wrote:
>
>> I tried this the other day with no success. That is, the weak signal that
>> was barely detectable, became so buried in ringing that I couldn't detect
>> it at all. I think I followed the procedure outlined in Wayne's email
>> below...
>> Noise was around S5 on 40m and the K3 was configured with APF active. I
>> had my 500 Hz filter selected and varied the DSP WIDTH from 500 to 300
>> without substantial improvement. FINE tuning selected.
>> What am I forgetting?
>> vy 73,Dave N4KD
>>
>>     On Tuesday, February 2, 2016 9:36 AM, Wayne Burdick <[hidden email]>
>> wrote:
>>
>>
>>   Hi all,
>>
>> This morning I was hearing lots of very weak signals in the 40-meter CW
>> band, right at today's noise floor of about S-5. (Among others, I copied
>> BG4GOV in Shanghai.)
>>
>> Many of the signals were not copyable until I turned on APF (audio peaking
>> filter). This filter's center peak is very narrow (around 30 Hz), but the
>> response broadens out quickly below the 3-dB points in the curve. This
>> brings up the desired signal without allowing noise to cause
>> ringing--something often heard with narrow filters of the "brick-wall"
>> variety. On a noisy band, the effect is just short of magic.
>>
>> APF is very narrow, so you'll need to tune in 1-Hz increments when it is
>> turned on. Also, APF works best when used with a DSP/crystal filter WIDTH
>> setting of 300-500 Hz.
>>
>> Use of APF differs for the three transceivers.
>>
>> KX3: 1-Hz tuning is selected automatically on the when the APF switch is
>> pressed.
>>
>> K3/K3S: APF is accessed via a hold of the XFIL switch. This function is
>> labeled "APF" on a K3S, or "DUAL PB" on the K3). Use CONFIG:DUAL PB to make
>> sure the selected filter function is APF. See the K3/K3S owner's manual for
>> a description of the alternate setting. 1-Hz tuning can be selected by
>> tapping FINE.
>>
>> You might want to give APF a try if you haven't already.
>>
>> 73,
>> Wayne
>> N6KR
>>
>> __________________________
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Re: APF (audio peaking filter) on the K3/K3S/KX3

Bill Frantz
In reply to this post by K9ZTV
I followed my interpretation of Wayne's instructions when trying
to copy VP8SGI on 80M. I have an inverted V antenna with the
peak at about 12 meters (44').

When I started, I could barely hear him. When I got the APF
tuned in, I could hear him clearly, and actually managed to work
him with 100W. I had to send my call 5 0r 6 times before AA7A,
the op on the other end got it, but I could easily hear when he
got it. To pull me out of the muck means he must be really good.

When it worked well for me, there were no signals near the DX,
and it worked with less ringing than going to a 50 Hz DSP
bandwidth. I find when the CW gets up above about 25 WPM, the
ringing makes it more difficult to interpret, although honestly,
30 WPM is well above my CW speed of competency. 15 is more like
it for English text (W1AW practice).

On the other hand, if there are nearby signals -- and I am using
a 2.1KHz roofing filter when I have APF on -- then narrowing the
DSP to 50 or 100Hz with the 250Hz roofing filter seems to work better.

73 Bill AE6JV

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Re: APF (audio peaking filter) on the K3/K3S/KX3

Bill W4ZV
In reply to this post by N1EU
N1EU wrote
I suspect that when the K3 APF was first engineered, the Yaesu FT-1000D APF
(original hi-Q version) was used as the model because many prominent
dx'ers/topbanders always raved about it.
I lifted the "original" FT-1000D APF from the schematic in 2009 and Al W6LX did a circuit simulation on it.  Al's description provided the roadmap for what Elecraft eventually implemented in the K3's DSP in 2010.  

http://www.mail-archive.com/elecraft%40mailman.qth.net/msg105227.html

As Wayne has suggested previously, APF works best if you use a relatively wide DSP setting (I use 400 Hz).  I trick my K3 into using my 200 Hz XFIL at DSP=400 by setting the XFIL BW to 400 (similar idea to what Wayne recently suggested with the 2.7/2.8 XFIL for better NB).  The wider DSP BW keeps the ringing down and gives your ear/brain a better background to discriminate signals through the 30 Hz APF without ringing while the wide (5 pole) 200 Hz XFIL still gives good protection from nearby strong signal overload.  Setting the VFO is not as critical compared to narrow DSP settings, and I use APF virtually all the time...even in contests.  This signal path may help visualize what I'm doing:

signal >> 200 Hz XFIL >> 400 Hz DSP >> 30 Hz APF >>  ear/brain

73,  Bill  W4ZV
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Re: APF (audio peaking filter) on the K3/K3S/KX3

Deni F5VJC
Well actually I prefer copying CW with a certain amount of noise present.
 Pure tone, no noise CW, as from a practice oscillator or an S9++ signal
quickly becomes boring and I loose concentration(or something).
It's perhaps why I prefer to dig out weak signals (ESP) from the noise on
the band.
However I do really appreciate the tools available in the K3 to do this :)
APF works great if you really learn how to use it.

Any one else?


73,  Deni - F5VJC



On 6 February 2016 at 12:19, Bill W4ZV <[hidden email]> wrote:

> N1EU wrote
> > I suspect that when the K3 APF was first engineered, the Yaesu FT-1000D
> > APF
> > (original hi-Q version) was used as the model because many prominent
> > dx'ers/topbanders always raved about it.
>
> I lifted the "original" FT-1000D APF from the schematic in 2009 and Al W6LX
> did a circuit simulation on it.  Al's description provided the roadmap for
> what Elecraft eventually implemented in the K3's DSP in 2010.
>
> http://www.mail-archive.com/elecraft%40mailman.qth.net/msg105227.html
>
> As Wayne has suggested previously, APF works best if you use a relatively
> wide DSP setting (I use 400 Hz).  I trick my K3 into using my 200 Hz XFIL
> at
> DSP=400 by setting the XFIL BW to 400 (similar idea to what Wayne recently
> suggested with the 2.7/2.8 XFIL for better NB).  The wider DSP BW keeps the
> ringing down and gives your ear/brain a better background to discriminate
> signals through the 30 Hz APF without ringing while the wide (5 pole) 200
> Hz
> XFIL still gives good protection from nearby strong signal overload.
> Setting the VFO is not as critical compared to narrow DSP settings, and I
> use APF virtually all the time...even in contests.  This signal path may
> help visualize what I'm doing:
>
> signal >> 200 Hz XFIL >> 400 Hz DSP >> 30 Hz APF >>  ear/brain
>
> 73,  Bill  W4ZV
>
>
>
> --
> View this message in context:
> http://elecraft.365791.n2.nabble.com/APF-audio-peaking-filter-on-the-K3-K3S-KX3-tp7613416p7613632.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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