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APF For K3

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Bob K6UJ

Re: APF For K3

The APF does as you say, builds a narrow filter around an audio signal, and it does this
down to a razor sharp peak.
But what really makes it so great (and distinguishes it from just an audio filter) is that it adds another dimension. In addition It peaks or boosts the
narrowed down audio signal.
That is why we users say that it pulls the signal up out of the mud. The FT-1000's APF
and my TS-930S (I wish I still had her, sniff, sniff) did this very effectively.
The CW signal can be right down at the noise level, you know it is in there but cannot copy. By adjusting the
APF you can pull the signal up out of the mud and copy the signal.

Bob
K6UJ

On Oct 24, 2010, at 12:14 PM, Don Wilhelm wrote:

> I have never used a receiver with a button labeled APF, but I have
> used my K2 with an audio filter. It seems to me the only other
> characteristic of APF is that the center frequency can be changed.
> On the K3, we have the Dual Passband that may work in a similar manner.
> Set the width to the lowest value 50 Hz and turn on Dual PB and you have
> a wide filter with a peak at your sidetone pitch. You can change the
> Pitch if you wish to peak a different audio frequency, but for the life
> of me, I cannot imagine why anyone would want to peak any pitch other
> than his preferred sidetone pitch.
>
> If you want a little more peaking, turn on NR and set it to an
> aggressive setting. The way NR works is that it builds a narrow filter
> around a signal that it thinks is a valid signal - so you have a filter
> at the audio pitch where you have set the VFO.
>
> Yes, the K3 is different than those receiver that have APF, but in my
> opinion, it accomplishes the same thing, but differently.
>
> 73,
> Don W3FPR
>
> On 10/24/2010 2:47 PM, Paul Christensen wrote:
>>> I found the APF in my Icom 7800 worthless.
>> Same here. Icom's implementation of APF in the '7700/'7800 is really an
>> "Audio Passband Filter" with low Q. It's really no different than narrowing
>> a DSP passband filter.
>>
>> What's unique about the FT-1000D's APF is that the Q is very high, although
>> its affected with APF tuning. The high Q of the circuit forms a very narrow
>> filter with fixed gain, and variable peaking frequency.
>>
>> Paul, W9AC
>>
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Bill W4ZV

Re: APF For K3

In reply to this post by Roy Morris-6

Roy Morris-6 wrote

I used APF in the past on CW contacts when needed. This feature seems to have been lost on some of todays modern radios. Because I haven't pounded the brass as much as I used to, I had forgotten about this wonderful APF feature. Those of us who have used it on CW know how really great this feature is. Weak CW signals that are unreadable are enhanced with APF making some QRP contacts possible that otherwise wouldn't be heard. Wayne has said he is putting this feature on the K3 list. I am thrilled that Elecraft is considering this feature. I am looking forward to having APF on my K3s.

APF was discussed extensively in August 2009 (check the archives) including a simulation of the exact FT-1000D APF circuit I sent to Al W6LX. It has always been "on the list" but Wayne has now made no less than 3 promises on the Yahoo Groups K3 list in the past few days that "we're working on it". Maybe something will actually come to pass this time!

In the meantime:

W6LX's simulation (PowerPoint with several graphs):
http://sites.google.com/site/ft1000apf/w6lxanalysisoftheapfcircuitintheft-1000

How to emulate APF in the K3 if you have a 200 Hz filter:
http://www.mail-archive.com/elecraft@mailman.qth.net/msg88687.html

73, Bill

73, Bill

GW0ETF

Re: APF For K3

In reply to this post by N8XPQ

Be aware though that the DSP 'switches off' the EQ once you get to 100Hz and below bandwidth. If you raise your cw sidetone frequency band as you suggest and then wind down the bandwidth your signal will take a dive as you cross the 100Hz point.

73,

Stewart Rolfe, GW0ETF

N8XPQ wrote

I have found that using the receive EQ for this works quite nicely. I raise the frequency matching that of my side-tone and attenuate all others. The K3 will automatically switch to this EQ setting when you enable the CW mode and switch to the SSB setting when that mode is enabled.

Good luck,

Mike N8XPQ

AC7AC

Re: APF For K3

In reply to this post by Bob K6UJ

CONTENTS DELETED

The author has deleted this message.

Mike K2MK

Re: APF For K3

In reply to this post by Roy Morris-6

I am exited by the prospect of its arrival. The APF on my FT1000D was an excellent aid for weak signal work. I miss not having it on my K3. I'm sure Elecraft's firmware implementation of an APF will be quite unique and hopefully very useful. I'll gladly except every tool that Elecraft can add to the K3.

73,
Mike K2MK

Roy Morris-6 wrote

I used APF in the past on CW contacts when needed. This feature seems to have been lost on some of todays modern radios. Because I haven't pounded the brass as much as I used to, I had forgotten about this wonderful APF feature. Those of us who have used it on CW know how really great this feature is. Weak CW signals that are unreadable are enhanced with APF making some QRP contacts possible that otherwise wouldn't be heard. Wayne has said he is putting this feature on the K3 list. I am thrilled that Elecraft is considering this feature. I am looking forward to having APF on my K3s. Roy Morris W4WFB

Lu Romero - W4LT

Re: APF For K3

In reply to this post by Roy Morris-6

Guy:

I am admittedly not a CW maven, I'm sort of a CW "duffer", but your comment
kind of baffles me:

---------
At this point, I have no means of duplicating that in the K3. This is
NOT the same as running narrower bandwidth. If I narrow bandwidth,
then I don't hear the off-frequency callers, some of which are closer
to the up or down stations than me.
-----------

"Dual PB" (press and hold XFIL) allows one, as the manual says, to "focus"
on a given signal that is matched to the sidetone frequency while hearing
other callers above and below that frequency at reduced level (the
"context"). Doesn't that do what the waveforms described on AB4OJ's website
depict? It works that way for me.

Or, I could patch my decades old Autek QF-1 into the audio path and peak
audio tones to my hearts content.

What else is required to accentuate a CW signal better than the tools we
have on hand? A "pitch" control option like Icom Pro series rigs have
(which I ALWAYS seem to forget to reset when I use it!)? If so then put in
a way to restore it to "normal" like the CLR button for RIT/XIT.

I'm all for options!

-lu - w4lt-

Message: 10
Date: Sun, 24 Oct 2010 14:18:56 -0400
From: Guy Olinger K2AV <[hidden email]>
Subject: Re: [Elecraft] APF For K3
To: [hidden email]
Cc: Bruce Beford <[hidden email]>,
[hidden email]
Message-ID:
<AANLkTikpCXwaNXOb=yp+7LLVhb_nwVG-6bcjTL=[hidden email]>
Content-Type: text/plain; charset=ISO-8859-1

No, actually not.

The MP has something "like" APF, without calling it that. On CW if
you turn on EDSP and set contour to 11 oclock and set NR to D and then
set spot to 450, what you will get is a rounded AF response. This
works well running (as opposed to search and pounce) in a contest,
when you want to hear up and down a ways to catch the off-frequency
callers (seemingly about 25% of world population, equals entirely
common, typical tone-deaf to some degree), but don't want the entire
bandwidth of noise roaring in your ear.

At this point, I have no means of duplicating that in the K3. This is
NOT the same as running narrower bandwidth. If I narrow bandwidth,
then I don't hear the off-frequency callers, some of which are closer
to the up or down stations than me.

Throwing away up and down callers easily throws away 10% of run QSO's
depending on how tight you have to squeeze. This is why I have the
"250" roofing filter defined as 350 with the 400 defined as 450. I
will run at 450 if I can get away with it. When it gets crowded, 350
running is really as tight as I want to go, just so I can hear
off-frequency callers. I just need to hear them well enough to get
them in with shift or RIT. 450 with APF is having your cake and
eating it too.

For that matter, if Wayne sees this, a fixed to center mild
NR-generated APF that came out like the MP version but with an
automatic band-pass following center might be a big hit. Try the
above with an MP some time and see if you can mimmick that in K3
firmware. Once discovered, it was always a favorite. That's where I
got stuck on 450 Hz as a center frequency. Just got used to it.

I don't hate my MP. I just wish to H* that it had a K3 style
uncrushable RF IF string.

Yes, APF, and sooner than later, and with a scalar adjustment to how
deep it goes and the width.

73, Guy

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Lu Romero - W4LT

Re: APF For K3

In reply to this post by Roy Morris-6

Don:

Thanks for the tip on the NR and Dual Passband! Never thought about doing
that! Just tried it. The only thing is that its not variable, which is
sometimes useful in a contest pileup. And you can change the pitch, but,
like my previous post about Icom's pitch, you have to remember to set it
back to "normal" as there is no CLR button. But it does what I think APF
should do, which is peak a certain tone in the context of other signals.

Maybe I can finally pack up the ancient QF-1 and take it to the next
Hamfest!

-lu- w4lt-

Message: 17
Date: Sun, 24 Oct 2010 15:14:45 -0400
From: Don Wilhelm <[hidden email]>
Subject: Re: [Elecraft] APF For K3
To: Paul Christensen <[hidden email]>
Cc: [hidden email]
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

I have never used a receiver with a button labeled APF, but I have
used my K2 with an audio filter. It seems to me the only other
characteristic of APF is that the center frequency can be changed.
On the K3, we have the Dual Passband that may work in a similar manner.
Set the width to the lowest value 50 Hz and turn on Dual PB and you have
a wide filter with a peak at your sidetone pitch. You can change the
Pitch if you wish to peak a different audio frequency, but for the life
of me, I cannot imagine why anyone would want to peak any pitch other
than his preferred sidetone pitch.

If you want a little more peaking, turn on NR and set it to an
aggressive setting. The way NR works is that it builds a narrow filter
around a signal that it thinks is a valid signal - so you have a filter
at the audio pitch where you have set the VFO.

Yes, the K3 is different than those receiver that have APF, but in my
opinion, it accomplishes the same thing, but differently.

73,
Don W3FPR

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P.B. Christensen

Re: APF For K3

In reply to this post by Lu Romero - W4LT

> "Dual PB" (press and hold XFIL) allows one, as the manual says, to "focus"
> on a given signal that is matched to the sidetone frequency while hearing
> other callers above and below that frequency at reduced level (the
> "context"). Doesn't that do what the waveforms described on AB4OJ's
> website
> depict?

Icom's use of APF is different than that used in the FT-1000/D. Icom more
closely emulates the Dual PB feature in the K3 but without the "context"
feature. What's missing is high "Q" of the centered frequency. The
FT-1000/D's Q of the audio circuit varies with the tuning control, but it's
generally greater than 10. When the Dual PB tuning is enabled on the K3,
and with aggressive NR engaged, I don't hear what sounds like a high Q
equivalent. The FT-1000/D's APF is more closely associated with a
single-channel of a multi-band parametric equalizer where Q, amplitude, and
frequency are all variable. In the FT-1000/D, Q is mostly fixed, but
amplitude and frequency are variable.

Although the FT-1000/D adds amplification of the centered frequency -- and
even allows changing the peaking frequency, I think the most desirable
attribute of the circuit is the high Q ability. Fixed gain and variable
peaking frequency may be a nice added feature to the K3 if APF is
implemented, but these are secondary to achieving emulation of the high Q
portion of the analog circuit in DSP.

Paul, W9AC

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riese-k3djc

Re: APF For K3

In reply to this post by Roy Morris-6

I found this it be of some assistance
for either ssb or cw I will operate the
notch in manual mode and by placing it
on the high / low side of a signal it will
help make the signal a bit more readable

Bob K3DJC

On Mon, 25 Oct 2010 09:09:51 -0400 "Paul Christensen" <[hidden email]>
writes:

> > "Dual PB" (press and hold XFIL) allows one, as the manual says, to
> "focus"
> > on a given signal that is matched to the sidetone frequency while
> hearing
> > other callers above and below that frequency at reduced level
> (the
> > "context"). Doesn't that do what the waveforms described on
> AB4OJ's
> > website
>

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Lu Romero - W4LT

Re: APF For K3

In reply to this post by Roy Morris-6

Paul:

Do the 1000MP's have this feature as you describe it, or
only the 1000D models?

I will be around some MP's this weekend, so before the
"battle" begins, I will try it and see how this feature
works so I can get an understanding of it in person.

I have experience with K3, Kenwood and Icom in CW mode, but
zero experience piloting a 1000 series Yaesu in CW. Did
like the "shuttle" knob around the main VFO on the 1000MP,
reminds me of using videotape machines... My mind adjusted
to it instinctively. :)

-lu-w4lt-

Message: 5
Date: Mon, 25 Oct 2010 09:09:51 -0400
From: "Paul Christensen" <[hidden email]>
Subject: Re: [Elecraft] APF For K3
To: <[hidden email]>
Message-ID: <32E1515EF267466FAF1D1301843877C2@DBTOA000>
Content-Type: text/plain; format=flowed;
charset="iso-8859-1";
reply-type=original

> "Dual PB" (press and hold XFIL) allows one, as the manual
says, to
"focus"
> on a given signal that is matched to the sidetone
frequency while hearing
> other callers above and below that frequency at reduced
level (the
> "context"). Doesn't that do what the waveforms described
on AB4OJ's
> website
> depict?

Icom's use of APF is different than that used in the
FT-1000/D. Icom more
closely emulates the Dual PB feature in the K3 but without
the "context"
feature. What's missing is high "Q" of the centered
frequency. The
FT-1000/D's Q of the audio circuit varies with the tuning
control, but it's
generally greater than 10. When the Dual PB tuning is
enabled on the K3,
and with aggressive NR engaged, I don't hear what sounds
like a high Q
equivalent. The FT-1000/D's APF is more closely associated
with a
single-channel of a multi-band parametric equalizer where Q,
amplitude, and
frequency are all variable. In the FT-1000/D, Q is mostly
fixed, but
amplitude and frequency are variable.

Although the FT-1000/D adds amplification of the centered
frequency -- and
even allows changing the peaking frequency, I think the most
desirable
attribute of the circuit is the high Q ability. Fixed gain
and variable
peaking frequency may be a nice added feature to the K3 if
APF is
implemented, but these are secondary to achieving emulation
of the high Q
portion of the analog circuit in DSP.

Paul, W9AC

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wayne burdick

APF For K3: progress report

Administrator

In reply to this post by Roy Morris-6

We might have a field-test revision of K3 code that includes APF
sometime this week.

In this test version, APF is turned on by rotating the WIDTH control
counterclockwise past the 50-Hz setting ("BW 0.05") to the 30-Hz APF
setting ("APF 0.03"). This eliminates the need for a menu entry or a
new switch function. A new DSP graphic pattern shows that APF is in
effect. SHIFT can be used, with either 10- or 50-Hz steps.

The APF filter is an "IIR" (infinite impulse response) DSP filter that
accurately emulates the equivalent analog circuitry. There's a slight
ring to the filter, as expected. Gain is also increased when APF is
turned on, compensating for the loss of overall signal+noise that
occurs at this very narrow bandwidth.

73,
Wayne
N6KR

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Stephen Prior

Re: APF For K3: progress report

Great! Thanks Wayne.

73 Stephen G4SJP

On 25/10/2010 19:39, "Wayne Burdick" <[hidden email]> wrote:

>
> We might have a field-test revision of K3 code that includes APF
> sometime this week.
>
> In this test version, APF is turned on by rotating the WIDTH control
> counterclockwise past the 50-Hz setting ("BW 0.05") to the 30-Hz APF
> setting ("APF 0.03"). This eliminates the need for a menu entry or a
> new switch function. A new DSP graphic pattern shows that APF is in
> effect. SHIFT can be used, with either 10- or 50-Hz steps.
>
> The APF filter is an "IIR" (infinite impulse response) DSP filter that
> accurately emulates the equivalent analog circuitry. There's a slight
> ring to the filter, as expected. Gain is also increased when APF is
> turned on, compensating for the loss of overall signal+noise that
> occurs at this very narrow bandwidth.
>
> 73,
> Wayne
> N6KR
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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Scott Ellington

Re: APF For K3

In reply to this post by riese-k3djc

I've used both the APF filter in the FT-1000 and an external audio filter (Timewave DSP-599zx), but never found them useful for CW. The filter in my head always seems better at picking out the desired signal than the audio filter, so the audio filter just doesn't help. Others my find differently, of course, though the filter in my head probably isn't an exceptionally good one. There are some very good cw contest operators who do nearly all their operating using the SSB filter.

Scott K9MA

Scott Ellington
Madison, Wisconsin
USA

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n7ws

Re: APF For K3: progress report

In reply to this post by wayne burdick

Not ever having a radio with APF, I've had this nagging question since this thread began. Does the Pitch track the center frequency of the BPF?

Wes

--- On Mon, 10/25/10, Wayne Burdick <[hidden email]> wrote:

> From: Wayne Burdick <[hidden email]>
> Subject: [Elecraft] APF For K3: progress report
> To: "Roy Morris" <[hidden email]>
> Cc: [hidden email]
> Date: Monday, October 25, 2010, 12:39 PM
> We might have a field-test revision
> of K3 code that includes APF
> sometime this week.
>
> In this test version, APF is turned on by rotating the
> WIDTH control
> counterclockwise past the 50-Hz setting ("BW 0.05") to the
> 30-Hz APF
> setting ("APF 0.03"). This eliminates the need for a menu
> entry or a
> new switch function. A new DSP graphic pattern shows that
> APF is in
> effect. SHIFT can be used, with either 10- or 50-Hz steps.
>
> The APF filter is an "IIR" (infinite impulse response) DSP
> filter that
> accurately emulates the equivalent analog circuitry.
> There's a slight
> ring to the filter, as expected. Gain is also increased
> when APF is
> turned on, compensating for the loss of overall
> signal+noise that
> occurs at this very narrow bandwidth.
>
> 73,
> Wayne
> N6KR
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Please help support this email list: http://www.qsl.net/donate.html
>

wayne burdick

Re: APF For K3: progress report

Administrator

It will in the K3 case. If you have SHIFT centered, the APF filter
will be at your sidetone pitch. So in most cases you won't even need
to do a SHIFT; just turn APF on using a full counterclockwise setting
of the WIDTH control. SHIFT can be used if you want to tune in a
station that is slightly off your sidetone pitch.

Wayne

On Oct 25, 2010, at 12:00 PM, Wes Stewart wrote:

> Not ever having a radio with APF, I've had this nagging question
> since this thread began. Does the Pitch track the center frequency
> of the BPF?

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Merv Schweigert

Re: APF For K3

In reply to this post by Scott Ellington

The benefit of APF is not selectivity to seperate signals at all. its
the
boost of a signal in the noise level that brings it up out of the noise
by peaking a particular audio freq. It is used to make copy of a signal
that is in the noise possible that is otherwise not possible to copy.

Also not all FT-1000D were created equal, early models were great,
middle and later models were not effective at all, so its all on which one
you tried at the time. Many operators converted the newer models to the
old circuit by changing a few component values.
Merv K9FD

> I've used both the APF filter in the FT-1000 and an external audio filter (Timewave DSP-599zx), but never found them useful for CW. The filter in my head always seems better at picking out the desired signal than the audio filter, so the audio filter just doesn't help. Others my find differently, of course, though the filter in my head probably isn't an exceptionally good one. There are some very good cw contest operators who do nearly all their operating using the SSB filter.
>
> Scott K9MA
>
> Scott Ellington
> Madison, Wisconsin
> USA
>
>
>
> ______________________________________________________________
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Jan Erik Holm

Re: APF For K3: progress report

In reply to this post by wayne burdick

Nice!

/ Jim SM2EKM
--------------
On 2010-10-25 20:39, Wayne Burdick wrote:

> We might have a field-test revision of K3 code that includes APF
> sometime this week.
>
> In this test version, APF is turned on by rotating the WIDTH control
> counterclockwise past the 50-Hz setting ("BW 0.05") to the 30-Hz APF
> setting ("APF 0.03"). This eliminates the need for a menu entry or a
> new switch function. A new DSP graphic pattern shows that APF is in
> effect. SHIFT can be used, with either 10- or 50-Hz steps.
>
> The APF filter is an "IIR" (infinite impulse response) DSP filter that
> accurately emulates the equivalent analog circuitry. There's a slight
> ring to the filter, as expected. Gain is also increased when APF is
> turned on, compensating for the loss of overall signal+noise that
> occurs at this very narrow bandwidth.
>
> 73,
> Wayne
> N6KR
>

Merv Schweigert

Re: APF For K3: progress report

In reply to this post by n7ws

Not on the FT-1000D, the APF has an adjustable freq knob,
I find that I have it set 99 percent of the time the same pitch
as the side tone, so not sure that it needs to be adjustable.
Seems if it tracked the side tone freq that may be sufficient.

Problem is that APF should not be limited to use on extreme
narrow filter widths, many times there is no need to narrow
the filter width as there is no adjacent QRM on the weak
signal. The background "noise" on wider widths is easier
to copy through many times than the different pitch background
"noise" on narrow width.

Unless you have used it, it is hard to comprehend what it is
perhaps, but as many have posted, when working properly
it makes copy possible of signals in the noise that is not
possible without.

Merv K9FD

> Not ever having a radio with APF, I've had this nagging question since this thread began. Does the Pitch track the center frequency of the BPF?
>
> Wes
>
> --- On Mon, 10/25/10, Wayne Burdick<[hidden email]> wrote:
>
>> From: Wayne Burdick<[hidden email]>
>> Subject: [Elecraft] APF For K3: progress report
>> To: "Roy Morris"<[hidden email]>
>> Cc: [hidden email]
>> Date: Monday, October 25, 2010, 12:39 PM
>> We might have a field-test revision
>> of K3 code that includes APF
>> sometime this week.
>>
>> In this test version, APF is turned on by rotating the
>> WIDTH control
>> counterclockwise past the 50-Hz setting ("BW 0.05") to the
>> 30-Hz APF
>> setting ("APF 0.03"). This eliminates the need for a menu
>> entry or a
>> new switch function. A new DSP graphic pattern shows that
>> APF is in
>> effect. SHIFT can be used, with either 10- or 50-Hz steps.
>>
>> The APF filter is an "IIR" (infinite impulse response) DSP
>> filter that
>> accurately emulates the equivalent analog circuitry.
>> There's a slight
>> ring to the filter, as expected. Gain is also increased
>> when APF is
>> turned on, compensating for the loss of overall
>> signal+noise that
>> occurs at this very narrow bandwidth.
>>
>> 73,
>> Wayne
>> N6KR
>>
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>
>
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Joe Subich, W4TV-4

Re: APF For K3: progress report

In reply to this post by wayne burdick

Wayne,

1) Outside the 30 Hz APF "peak" what is the background DSP
bandwidth and can that be adjusted?

2) how does one prevent activation of a narrow CW filter (e.g.,
200 Hz) and excessively narrow DSP filtering when activating
APF? Remember, the desired behavior is primarily to peak
the desired signal while reducing the background bandwidth
is a secondary concern.

3) How does one move the APF "peak" (as in the case of the
old FT-1000D where the peak was tunable over most of the
audio range0?

Rather that lose ability to specify basic DSP (and IF) bandwidth
when activating APF, I would suggest overloading the "notch"
control- particularly since auto notch (tap) does not function
in CW - to activate APF.

73,

... Joe, W4TV

On 10/25/2010 2:39 PM, Wayne Burdick wrote:

wayne burdick

Re: APF For K3: progress report

Administrator

Joe,

We're still experimenting with both the UI and the underlying filter
function. I jumped the gun a bit in my proposed use of the WIDTH
control to activate APF, and we're looking at other ways to do that so
that the width can still be set independently.

One possibility is to overload the DUAL PB control (say, a long hold
of DUAL PB turns on APF, or the DUAL PB control has three settings).
When APF is selected, the SHIFT control could adjust the APF center
frequency, leaving the rig's normal passband unshifted.

More later--

Wayne

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