Discussion:
[Elecraft] APF vs 10 Hz DSP, why they don't sound the same
Guy Olinger K2AV
2009-08-16 00:18:27 UTC
Permalink
After watching spectrogram on a noise signal and noting a much sharper shape
on 50 Hz DS as an audio peak filter, I began to wonder about some of the
posts I was seeing asking for APF. What was going on? After some
measurements...

1) the 50 Hz DSP bandwidth is *narrower* at the top than any APF I have
used. The 100 or 150 Hz DSP is more like it.

2) the 50/100 Hz DSP has *far* steeper skirts than the APF.

3) the APF *sounds to the ear* to drop off a signal more, but that is
because the signal as it moves outside the APF is still controlling the IF
AGC off the APF center, holding the input to the APF constant. In the
50/100 Hz DSP the AGC opens up the gain when one tunes off the signal,
giving the *appearance* of no skirts. Watching the S meter will show what is
going on. This effect dissappears entirely with the AGC *off*, where the
signal falls off the table on the DSP skirts as one tunes away.

If one simply measures the amount of discrimination between two close
signals, the 50 Hz DSP can beat the APF by 10, 20 db or more. Listening to
two S9 signals only 150 Hz apart, the 50 Hz DSP can completely isolate
them. In run situation, the shift and 50 Hz DSP would allow me to pick up
just one and then the other by remembering their respective tones, without
changing my transmit or RX reference.

The SOUND of tuning across a signal with APF in a 500 Hz IF bandwidth is
illusory in close signal discrimination, even if it is one's favorite analog
sound. Isn't this just dumbing down a superior DSP function to "sound like"
an analog result?

And reversing myself in one of my earlier posts, the modulation "pops"
produced by the sharp skirt drops on 10 Hz shift increments off a strong
signal are annoying, and perhaps the shift can be damped just a tiny bit to
remove them.
--
73, Guy K2AV
Merv Schweigert
2009-08-16 02:03:54 UTC
Permalink
Guy, your missing the whole point of what APF is and what is does,
has nothing to do with selectivity, nothing to do with skirts at all,
it is in the audio chain and there for no effect or cause with AGC
Is rarely if ever used on a signal that is loud enough to copy,
its mainly used for signals that are at the noise level or very weak.
Narrow bandwidth can be the enemy of APF. Many
times copy at wider width is the best with APF.
APF never drops off the signal, it enhances it.
APF = Audio Peak Filter not DSP or some other
manipulation to try and fake it.
To say that DSP beats APF in the proper use of APF
by 10 or 20 db is proof that there is a lack of understanding
of what APF does or even is.
APF is not used as a selectivity tool.
Its not a Q-multiplier type function, or a filter as in xtal
filter or DSP filter.
There were many reiterations of APF in various radios, the FT-1000
being one, and with the 1000 there were various versions even, the
one that works correctly is the old original circuit, many ops had to
change components to the older circuit to get the APF to function,
so unless you had one of the correct versions you have not heard
APF work.
Post by Guy Olinger K2AV
After watching spectrogram on a noise signal and noting a much sharper shape
on 50 Hz DS as an audio peak filter, I began to wonder about some of the
posts I was seeing asking for APF. What was going on? After some
measurements...
1) the 50 Hz DSP bandwidth is *narrower* at the top than any APF I have
used. The 100 or 150 Hz DSP is more like it.
2) the 50/100 Hz DSP has *far* steeper skirts than the APF.
3) the APF *sounds to the ear* to drop off a signal more, but that is
because the signal as it moves outside the APF is still controlling the IF
AGC off the APF center, holding the input to the APF constant. In the
50/100 Hz DSP the AGC opens up the gain when one tunes off the signal,
giving the *appearance* of no skirts. Watching the S meter will show what is
going on. This effect dissappears entirely with the AGC *off*, where the
signal falls off the table on the DSP skirts as one tunes away.
If one simply measures the amount of discrimination between two close
signals, the 50 Hz DSP can beat the APF by 10, 20 db or more. Listening to
two S9 signals only 150 Hz apart, the 50 Hz DSP can completely isolate
them. In run situation, the shift and 50 Hz DSP would allow me to pick up
just one and then the other by remembering their respective tones, without
changing my transmit or RX reference.
The SOUND of tuning across a signal with APF in a 500 Hz IF bandwidth is
illusory in close signal discrimination, even if it is one's favorite analog
sound. Isn't this just dumbing down a superior DSP function to "sound like"
an analog result?
And reversing myself in one of my earlier posts, the modulation "pops"
produced by the sharp skirt drops on 10 Hz shift increments off a strong
signal are annoying, and perhaps the shift can be damped just a tiny bit to
remove them.
Jan Babinec
2009-08-17 08:03:49 UTC
Permalink
Hi there,
the APF in TS930S is very effective too. It saved me MANY
TopBand QSOs! Especially thru rough summer QRN,
switch AGC off, wide filters plus APF allowed to hear the weak ones.
Such a filter is VERY high on my K3 wish list.

Jan OM2XW
Date: Sat, 15 Aug 2009 16:03:54 -1000
From: k9fd at flex.com
To: olinger at bellsouth.net
CC: elecraft at mailman.qth.net
Subject: Re: [Elecraft] APF vs 10 Hz DSP, why they don't sound the same
Guy, your missing the whole point of what APF is and what is does,
has nothing to do with selectivity, nothing to do with skirts at all,
it is in the audio chain and there for no effect or cause with AGC
Is rarely if ever used on a signal that is loud enough to copy,
its mainly used for signals that are at the noise level or very weak.
Narrow bandwidth can be the enemy of APF. Many
times copy at wider width is the best with APF.
APF never drops off the signal, it enhances it.
APF = Audio Peak Filter not DSP or some other
manipulation to try and fake it.
_________________________________________________________________
Presun my?ou - z?skajte jednoduch? zdie?anie fotografi? v slu?be Windows LiveT Fotografie.
http://www.microsoft.com/windows/windowslive/products/photos.aspx
William Carver
2009-08-16 04:35:42 UTC
Permalink
The "DUAL PASSBAND" makes a pass at providing an APF type of function
where you make the DSP passband as narrow as you choose, but there's a
wider passband that's 20 dB down. Undoubtedly it isn't the same shape as
APF amplitude v.s. frequency, but conceptually "a signal peak floating
on a sea of weaker undesired signals" is similar.

G3XJP implementated a DUAL PASSBAND function (that terminology hadn't
been invented then) in his STAR transceiver, but there the amplitude of
the wider passband can be dialed to be -20, -30, -40, .... -60 dB. It
probably isn't too big a deal to make the "skirt attenuation" number a
user-adjustable variable but I enjoyed being able to dial it up and down
as QRM changed....which would ite up another programmable functio
button.

For those who suggested kicking the gain compensation up when narrower
roofing filters are switched in, that's exactly what I did. I'm well
aware that IF the roofing filter is setting the IMD capability of
the receiver adding pre-filter gain reduces the intercept/increases IMD
WHEN that IMD happens to occur, and IF it happens to fall into the
passband with the desired signal. I intentionally emphasized the string
of IF..WHEN..IF.. because depending upon you penchant for living in
pileups, or turning the rig off on big contest weeks, a 4 dB IMD
increase IF all of those things happened to occur may, or may not, be
that big a deal.

A post-roofing filter gain increment would not affect intercept or IMD
and could be a smoothly varying increase that could conceivably be
matched to a users memory of APF or Heath QF-1 function.

Bill
Eric Swartz -WA6HHQ, Elecraft
2009-08-16 06:08:42 UTC
Permalink
The filter gain compensation is -post- crystal filter. Its done inside
the DSP.

If this is set well above what is really needed, the DSP may generate
some distortion on really strong signals. We usually recommend +4 dB max.

73, Eric WA6HHQ
Post by William Carver
The "DUAL PASSBAND" makes a pass at providing an APF type of function
where you make the DSP passband as narrow as you choose, but there's a
wider passband that's 20 dB down. Undoubtedly it isn't the same shape as
APF amplitude v.s. frequency, but conceptually "a signal peak floating
on a sea of weaker undesired signals" is similar.
G3XJP implementated a DUAL PASSBAND function (that terminology hadn't
been invented then) in his STAR transceiver, but there the amplitude of
the wider passband can be dialed to be -20, -30, -40, .... -60 dB. It
probably isn't too big a deal to make the "skirt attenuation" number a
user-adjustable variable but I enjoyed being able to dial it up and down
as QRM changed....which would ite up another programmable functio
button.
For those who suggested kicking the gain compensation up when narrower
roofing filters are switched in, that's exactly what I did. I'm well
aware that IF the roofing filter is setting the IMD capability of
the receiver adding pre-filter gain reduces the intercept/increases IMD
WHEN that IMD happens to occur, and IF it happens to fall into the
passband with the desired signal. I intentionally emphasized the string
of IF..WHEN..IF.. because depending upon you penchant for living in
pileups, or turning the rig off on big contest weeks, a 4 dB IMD
increase IF all of those things happened to occur may, or may not, be
that big a deal.
A post-roofing filter gain increment would not affect intercept or IMD
and could be a smoothly varying increase that could conceivably be
matched to a users memory of APF or Heath QF-1 function.
Bill
_..._
David Woolley (E.L)
2009-08-16 10:24:51 UTC
Permalink
Post by Eric Swartz -WA6HHQ, Elecraft
If this is set well above what is really needed, the DSP may generate
some distortion on really strong signals. We usually recommend +4 dB max.
I wonder if distorting the audio is really what APF is about. With a
narrow enough filter, the distortion products will only be based on the
signal. Alternatively, and more worrying, it may be about defeating the
ear's defences against load sounds, by making the spectrum too narrow,
in which case there may be a risk of burning out the hair cells for the
chosen frequency.

More generally, the APF proponents seem to have the problem that they
treat it almost as magic. If they could characterise what it does in
terms of filtering, AF gain adjustment, distortion etc. it should be
possible to simulate it in DSP, subject only to having enough processing
power. In particular, peaking just seems to me to mean turning up the
AF gain in parallel with reducing the bandwidth. If that is all that it
is doing, and if the K3 has soft AF gain controls, a plugin box could
issue both commands in parallel.

PS the relevance of AGC here is whether or not it is applied pre- or
post- the ultimate selectivity. From what the APF people say, it is
normally applied pre-.
--
David Woolley
"we do not overly restrict the subject matter on the list, and we
encourage postings on a wide range of amateur radio related topics"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
Merv Schweigert
2009-08-16 17:15:26 UTC
Permalink
Post by David Woolley (E.L)
Post by Eric Swartz -WA6HHQ, Elecraft
If this is set well above what is really needed, the DSP may generate
some distortion on really strong signals. We usually recommend +4 dB max.
I wonder if distorting the audio is really what APF is about. With a
narrow enough filter, the distortion products will only be based on the
signal. Alternatively, and more worrying, it may be about defeating the
ear's defences against load sounds, by making the spectrum too narrow,
in which case there may be a risk of burning out the hair cells for the
chosen frequency.
APF does not distort the audio at all, its extremely simple, all it
does is peak
an audio freq by X amount. In older radios its done with a analog
circuit of
one or two chips and resistor capacitor sets to determine the freq of
the peak.
I assume there is some feedback loop to increase the audio gain at the
peaked
freq.
Post by David Woolley (E.L)
More generally, the APF proponents seem to have the problem that they
treat it almost as magic. If they could characterise what it does in
terms of filtering, AF gain adjustment, distortion etc. it should be
possible to simulate it in DSP, subject only to having enough processing
power. In particular, peaking just seems to me to mean turning up the
AF gain in parallel with reducing the bandwidth. If that is all that it
is doing, and if the K3 has soft AF gain controls, a plugin box could
issue both commands in parallel.
It does nothing as far as filtering, years ago it was used in cheap
receivers as a CW filter
but that is not the purpose in a radio that has xtal filters or DSp filters.
Yes it is like turning up the AF gain some amount, but at one particular
freq, usually the
freq you have the pitch set at on CW. but you do not want to reduce the
bandwidth,
many time you want to use the APF at wider bandwidth settings due to the
different
sound of the background noise at the wider bandwidth makes copy easier
than with
the narrow sound of narrow filters.
Post by David Woolley (E.L)
PS the relevance of AGC here is whether or not it is applied pre- or
post- the ultimate selectivity. From what the APF people say, it is
normally applied pre-.
Since APF is totally an audio function the gain and AGC is not effected
by its use
at all, unless you have a radio that has audio derived AGC.
As I stated before APF is for very weak signal detection, one would not
usually
use it on signals that are copyable with normal filters etc. It is
used for copying
signals you normally tune across because they are too weak to copy or you
perhaps dont even hear them.
It will take a signal that is at the noise level, and peak it to the
point of being
able to copy.
Some ops like it so much they use it for louder signals as well.
The closest thing is to outboard a audio filter like the Datong, I have
tried the
Autek and its not up to par, the Datong is fair but again not the same
as the
circuit in the 1000D radios. If there was a comparable outboard that worked
I would put one in the P3 empty space and go away laughing.
73 Merv KH7C
David Woolley (E.L)
2009-08-16 17:43:32 UTC
Permalink
Post by Merv Schweigert
APF does not distort the audio at all, its extremely simple, all it
does is peak
an audio freq by X amount. In older radios its done with a analog
circuit of
So how does that differ from the existing filters in the K3. What
people seem to be saying is that it actually boosts the audio, but that
is just equivalent to turning up the AF gain, so I was speculating that
the gain is actually turned up to the point where later stages overload,
and that is why people think it differs from a simple filter.
Post by Merv Schweigert
one or two chips and resistor capacitor sets to determine the freq of
the peak.
I assume there is some feedback loop to increase the audio gain at the
peaked
freq.
I.E. is a band bass FILTER!
Post by Merv Schweigert
It does nothing as far as filtering, years ago it was used in cheap
If it boost one frequency with respect to another, it is, by definition,
filter. This is what I mean by people claiming magical properties.
It is just a linear filter (although possibly followed by non-linear
output stages).
Post by Merv Schweigert
receivers as a CW filter
Since APF is totally an audio function the gain and AGC is not effected
by its use
The gain is influenced. The audio gain is part of the overall gain of
the receiver. People seem to be claiming that the "peak" part of the
name means that there is excess audio gain at the filter centre, over
that without the filter.

The reason people introduced AGC was to point out that, being post AGC,
the subjective effect of tuning through a signal was a much greater
change in amplitude than pre-AGC, where the AGC would keep the amplitude
more or less constant, although the signal to noise ratio would peak as
you tuned through the signal.
Post by Merv Schweigert
at all, unless you have a radio that has audio derived AGC.
As I stated before APF is for very weak signal detection, one would not
usually
use it on signals that are copyable with normal filters etc. It is
used for copying
signals you normally tune across because they are too weak to copy or you
perhaps dont even hear them.
It's just a normal filter and if it is better than the existing filters,
that is a matter of working out what it is about the filter shape
(considering the overall effect of all filters in the receiver), in
phase and frequency, that makes it subjectively better, and adjust the
DSP filter to reproduce that characteristic. If one understands exactly
why it seems better, the flexibility of a DSP filter may mean that by
designing a first principles solution, one can do even better.
Post by Merv Schweigert
It will take a signal that is at the noise level, and peak it to the
point of being
able to copy.
As does any narrow band pass filter.

The only difference between filtering at audio and at IF, is that
distortion products will remain in band, and it is more likely that it
will be done post-AGC.
--
David Woolley
"we do not overly restrict the subject matter on the list, and we
encourage postings on a wide range of amateur radio related topics"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
Steve Ellington
2009-08-16 18:00:15 UTC
Permalink
The DSP in the original Omni 6 was a low pass filter intended to eliminate
white noise from the IF stage. Later, the Omni 6 Plus used the DSP as a CW
Peaking filter. It really sounded great without the typical ringing so
common in narrow analog audio filters.
Steve
N4LQ
N4LQ at carolina.rr.com
----- Original Message -----
From: "David Woolley (E.L)" <forums at david-woolley.me.uk>
To: <Elecraft at mailman.qth.net>
Sent: Sunday, August 16, 2009 1:43 PM
Subject: Re: [Elecraft] APF vs 10 Hz DSP, why they don't sound the same
Post by David Woolley (E.L)
Post by Merv Schweigert
APF does not distort the audio at all, its extremely simple, all it
does is peak
an audio freq by X amount. In older radios its done with a analog
circuit of
So how does that differ from the existing filters in the K3. What
people seem to be saying is that it actually boosts the audio, but that
is just equivalent to turning up the AF gain, so I was speculating that
the gain is actually turned up to the point where later stages overload,
and that is why people think it differs from a simple filter.
Post by Merv Schweigert
one or two chips and resistor capacitor sets to determine the freq of
the peak.
I assume there is some feedback loop to increase the audio gain at the
peaked
freq.
I.E. is a band bass FILTER!
Post by Merv Schweigert
It does nothing as far as filtering, years ago it was used in cheap
If it boost one frequency with respect to another, it is, by definition,
filter. This is what I mean by people claiming magical properties.
It is just a linear filter (although possibly followed by non-linear
output stages).
Post by Merv Schweigert
receivers as a CW filter
Since APF is totally an audio function the gain and AGC is not effected
by its use
The gain is influenced. The audio gain is part of the overall gain of
the receiver. People seem to be claiming that the "peak" part of the
name means that there is excess audio gain at the filter centre, over
that without the filter.
The reason people introduced AGC was to point out that, being post AGC,
the subjective effect of tuning through a signal was a much greater
change in amplitude than pre-AGC, where the AGC would keep the amplitude
more or less constant, although the signal to noise ratio would peak as
you tuned through the signal.
Post by Merv Schweigert
at all, unless you have a radio that has audio derived AGC.
As I stated before APF is for very weak signal detection, one would not
usually
use it on signals that are copyable with normal filters etc. It is
used for copying
signals you normally tune across because they are too weak to copy or you
perhaps dont even hear them.
It's just a normal filter and if it is better than the existing filters,
that is a matter of working out what it is about the filter shape
(considering the overall effect of all filters in the receiver), in
phase and frequency, that makes it subjectively better, and adjust the
DSP filter to reproduce that characteristic. If one understands exactly
why it seems better, the flexibility of a DSP filter may mean that by
designing a first principles solution, one can do even better.
Post by Merv Schweigert
It will take a signal that is at the noise level, and peak it to the
point of being
able to copy.
As does any narrow band pass filter.
The only difference between filtering at audio and at IF, is that
distortion products will remain in band, and it is more likely that it
will be done post-AGC.
--
David Woolley
"we do not overly restrict the subject matter on the list, and we
encourage postings on a wide range of amateur radio related topics"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
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DM4iM
2009-08-16 10:33:37 UTC
Permalink
I once owned a FT-107, it had APF, i sure miss that feature.
If you are looking for a good analog Audio-filter, go to

http://www.eurofrequence.de/filtereing/

I own the predecessor with less features for more than 15 years.
I am a satisfied customer, no other relationship.

Martin
--
73, DM4iM
Bill Tippett
2009-08-16 11:38:53 UTC
Permalink
Post by David Woolley (E.L)
More generally, the APF proponents seem to have the problem that they
treat it almost as magic. If they could characterise what it does in
terms of filtering, AF gain adjustment, distortion etc. it should be
possible to simulate it in DSP, subject only to having enough processing
power. In particular, peaking just seems to me to mean turning up the
AF gain in parallel with reducing the bandwidth. If that is all that it
is doing, and if the K3 has soft AF gain controls, a plugin box could
issue both commands in parallel.

The circuit in question is on page 54 of the FT1000 schematic below:

<http://www.radioamateur.eu/schemi/FT1000_user.pdf>http://www.radioamateur.eu/schemi/FT1000_user.pdf

The APF is around Q3016-2 (including Rs 3062, 3065, 3067 per the
"un-modification" sheet on N1EU's website below). The circuit
schematic above has *not* been modified to the (incorrect) values
shown in the Yaesu service bulletin.

http://n1eu.com/Mods/apf.pdf

The FT-1000's APF is generally regarded by many as the best APF ever
done. It should be possible to plug this into a circuit simulator
and generate a frequency response plot that Lyle can emulate in the
DSP. I have a feeling that this is a very narrow and high-Q response
that is on the verge of ringing, but it should be possible to
duplicate the circuit in the DSP.

73, Bill W4ZV
Paul Christensen
2009-08-16 11:52:51 UTC
Permalink
Post by Bill Tippett
DSP. I have a feeling that this is a very narrow and high-Q response
that is on the verge of ringing, but it should be possible to
duplicate the circuit in the DSP.
And only subject to the remaining DSP processing power within the K3. A
traditional, single parametric EQ channel with variable Q, amplitude, and
frequency range (e.g., 300 Hz - 1200 Hz), would work very well. A quick
measurement of the FT-1000's APF peaking gain and Q could be used to
establish initial parameters.

Paul, W9AC
Brian Alsop
2009-08-16 13:03:37 UTC
Permalink
Unlike the phone guys, most CW guys could care less about audio
distortion or quality for that weak one. They just want to be able to
copy it. The information is in the off's and on's, the rest doesn't
matter.

The old QF-1 Q-muliplier had an advertised Q of 4000 @ 455KHz. That's a
bandwidth of about 100Hz. There was some skill requiring adjusting
several knobs to make it work for you. Of course, any K3 implementation
would have to be knobless.

73 de Brian/K3KO
Post by David Woolley (E.L)
Post by David Woolley (E.L)
More generally, the APF proponents seem to have the problem that they
treat it almost as magic. If they could characterise what it does in
terms of filtering, AF gain adjustment, distortion etc. it should be
possible to simulate it in DSP, subject only to having enough processing
power. In particular, peaking just seems to me to mean turning up the
AF gain in parallel with reducing the bandwidth. If that is all that it
is doing, and if the K3 has soft AF gain controls, a plugin box could
issue both commands in parallel.
<http://www.radioamateur.eu/schemi/FT1000_user.pdf>http://www.radioamateur.eu/schemi/FT1000_user.pdf
The APF is around Q3016-2 (including Rs 3062, 3065, 3067 per the
"un-modification" sheet on N1EU's website below). The circuit
schematic above has *not* been modified to the (incorrect) values
shown in the Yaesu service bulletin.
http://n1eu.com/Mods/apf.pdf
The FT-1000's APF is generally regarded by many as the best APF ever
done. It should be possible to plug this into a circuit simulator
and generate a frequency response plot that Lyle can emulate in the
DSP. I have a feeling that this is a very narrow and high-Q response
that is on the verge of ringing, but it should be possible to
duplicate the circuit in the DSP.
73, Bill W4ZV
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drewko
2009-08-16 13:41:29 UTC
Permalink
I have one of those old QF-1 filters sitting in a drawer. I bought it
new years ago. It was certainly a lot of fun notching a signal then
switching it to peak and narrowing it down. And a very effective
accessory for my rig at the time, a Century-21 which had no such
refinements.

I should give it a try with the K3. It is kind of a pain because there
is no bypass switch in the unit: it has to be powered on to hear
anything. Also a noticeable AC hum which was apparently a standard
feature of these units.

73,
Drew
AF2Z
Post by Brian Alsop
Unlike the phone guys, most CW guys could care less about audio
distortion or quality for that weak one. They just want to be able to
copy it. The information is in the off's and on's, the rest doesn't
matter.
bandwidth of about 100Hz. There was some skill requiring adjusting
several knobs to make it work for you. Of course, any K3 implementation
would have to be knobless.
73 de Brian/K3KO
Frank Ross W4NHJ
2009-08-16 13:37:19 UTC
Permalink
If you have an SDR type panadaptor using the IF out signal, you can try a
peaking filter by downloading and running WinRad software. WinRad has a
peaking filter that works great.

Frank - W4NHJ

----- Original Message -----
From: "Bill Tippett" <btippett at alum.mit.edu>
To: <elecraft at mailman.qth.net>
Sent: Sunday, August 16, 2009 7:38 AM
Subject: Re: [Elecraft] APF vs 10 Hz DSP, why they don't sound the same
Post by David Woolley (E.L)
Post by David Woolley (E.L)
More generally, the APF proponents seem to have the problem that they
treat it almost as magic. If they could characterise what it does in
terms of filtering, AF gain adjustment, distortion etc. it should be
possible to simulate it in DSP, subject only to having enough processing
power. In particular, peaking just seems to me to mean turning up the
AF gain in parallel with reducing the bandwidth. If that is all that it
is doing, and if the K3 has soft AF gain controls, a plugin box could
issue both commands in parallel.
<http://www.radioamateur.eu/schemi/FT1000_user.pdf>http://www.radioamateur.eu/schemi/FT1000_user.pdf
The APF is around Q3016-2 (including Rs 3062, 3065, 3067 per the
"un-modification" sheet on N1EU's website below). The circuit
schematic above has *not* been modified to the (incorrect) values
shown in the Yaesu service bulletin.
http://n1eu.com/Mods/apf.pdf
The FT-1000's APF is generally regarded by many as the best APF ever
done. It should be possible to plug this into a circuit simulator
and generate a frequency response plot that Lyle can emulate in the
DSP. I have a feeling that this is a very narrow and high-Q response
that is on the verge of ringing, but it should be possible to
duplicate the circuit in the DSP.
73, Bill W4ZV
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Merv Schweigert
2009-08-16 17:23:18 UTC
Permalink
Bill, thanks a million, I have difficulty explaining what is in the
brain cells,
this helps a lot, simple circuit, and agree that running this through a
simulator would give the answers.
I know some would not like the feature, but one does not have to use it.
Its the difference for me of making the contact or not, so a really
big deal.
For causal operators they may never use it.
73 Merv KH7C
Post by David Woolley (E.L)
Post by David Woolley (E.L)
More generally, the APF proponents seem to have the problem that they
treat it almost as magic. If they could characterise what it does in
terms of filtering, AF gain adjustment, distortion etc. it should be
possible to simulate it in DSP, subject only to having enough processing
power. In particular, peaking just seems to me to mean turning up the
AF gain in parallel with reducing the bandwidth. If that is all that it
is doing, and if the K3 has soft AF gain controls, a plugin box could
issue both commands in parallel.
<http://www.radioamateur.eu/schemi/FT1000_user.pdf>http://www.radioamateur.eu/schemi/FT1000_user.pdf
The APF is around Q3016-2 (including Rs 3062, 3065, 3067 per the
"un-modification" sheet on N1EU's website below). The circuit
schematic above has *not* been modified to the (incorrect) values
shown in the Yaesu service bulletin.
http://n1eu.com/Mods/apf.pdf
The FT-1000's APF is generally regarded by many as the best APF ever
done. It should be possible to plug this into a circuit simulator
and generate a frequency response plot that Lyle can emulate in the
DSP. I have a feeling that this is a very narrow and high-Q response
that is on the verge of ringing, but it should be possible to
duplicate the circuit in the DSP.
73, Bill W4ZV
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Al Lorona
2009-08-16 21:48:50 UTC
Permalink
?
The circuit surrounding op amp 3016-2 in the FT-1000 schematic?is nothing more than an active bandpass filter, center frequency of about 1025 Hz, Q = 35, with a gain of about 10.5 dB.

?
Al? W6LX
?
?
?
?

--- On Sun, 8/16/09, Bill Tippett <btippett at alum.mit.edu> wrote:


From: Bill Tippett <btippett at alum.mit.edu>
Subject: Re: [Elecraft] APF vs 10 Hz DSP, why they don't sound the same
To: elecraft at mailman.qth.net
Date: Sunday, August 16, 2009, 4:38 AM
Post by David Woolley (E.L)
More generally, the APF proponents seem to have the problem that they
treat it almost as magic.? If they could characterise what it does in
terms of filtering, AF gain adjustment, distortion etc. it should be
possible to simulate it in DSP, subject only to having enough processing
power.? In particular, peaking just seems to me to mean turning up the
AF gain in parallel with reducing the bandwidth. If that is all that it
is doing, and if the K3 has soft AF gain controls, a plugin box could
issue both commands in parallel.

? ? ? ???The circuit in question is on page 54 of the FT1000 schematic below:

<http://www.radioamateur.eu/schemi/FT1000_user.pdf>http://www.radioamateur.eu/schemi/FT1000_user.pdf

The APF is around Q3016-2 (including Rs 3062, 3065, 3067 per the
"un-modification" sheet on N1EU's website below).? The circuit
schematic above has *not* been modified to the (incorrect) values
shown in the Yaesu service bulletin.

http://n1eu.com/Mods/apf.pdf

The FT-1000's APF is generally regarded by many as the best APF ever
done.? It should be possible to plug this into a circuit simulator
and generate a frequency response plot that Lyle can emulate in the
DSP.? I have a feeling that this is a very narrow and high-Q response
that is on the verge of ringing, but it should be possible to
duplicate the circuit in the DSP.

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ???73,? Bill? W4ZV

? ? ? ? ?

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Paul Christensen
2009-08-16 23:39:02 UTC
Permalink
"The circuit surrounding op amp 3016-2 in the FT-1000 schematic is nothing
more than an active bandpass filter, center frequency of about 1025 Hz, Q
= 35, with a gain of about 10.5 dB."
The APF filter is active on the Main Rx, CW mode only. However, Fc is not
confined to 1025 Hz; with the front panel "APF" control, it's adjustable
roughly over the range of the CW BFO offset when the filter switch is
engaged.

Paul, W9AC
Al Lorona
2009-08-16 23:44:41 UTC
Permalink
Yes, I ran the analysis on the circuit as shown, without the tuning control. If anyone wants to pore through the schematics and tell me the value of the control as well as where to put it, I'll be happy to run the analysis at the two ends of the range of the control.
?
What I had wanted to do with my information was remove any mystery surrounding the topology of the circuit in the FT-1000. Now that we know what it is, it may help someone to try and duplicate it with hardware, software, or whatever.
?
Al? W6LX

--- On Sun, 8/16/09, Paul Christensen <w9ac at arrl.net> wrote:


From: Paul Christensen <w9ac at arrl.net>
Subject: Re: [Elecraft] APF vs 10 Hz DSP, why they don't sound the same
To: elecraft at mailman.qth.net
Date: Sunday, August 16, 2009, 4:39 PM
"The circuit surrounding op amp 3016-2 in the FT-1000 schematic is nothing
more than an active bandpass filter, center frequency of about 1025 Hz, Q
= 35, with a gain of about 10.5 dB."
The APF filter is active on the Main Rx, CW mode only.? However, Fc is not
confined to 1025 Hz; with the front panel "APF" control, it's adjustable
roughly over the range of the CW BFO offset when the filter switch is
engaged.

Paul, W9AC







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