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APF and audio limiting

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Mike Reublin

APF and audio limiting

I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
volume cranked up pretty good, and a REALLY strong station throws in their call. I
thought my speakers had blown. Glad I wasn't wearing cans.

My CONFIG:AF is 18, AGC = F.

Was I doing something wrong? Anybody else experience this? Do we need/can we have
better audio limiting?

73, Mike NF4L

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Mike Reublin

Re: APF and audio limiting

Anybody keeping track of the longest time for an unanswered post? Over over. ;->

On 11/4/2010 9:48 PM, Mike wrote:

> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
> volume cranked up pretty good, and a REALLY strong station throws in their call. I
> thought my speakers had blown. Glad I wasn't wearing cans.
>
> My CONFIG:AF is 18, AGC = F.
>
> Was I doing something wrong? Anybody else experience this? Do we need/can we have
> better audio limiting?
>
> 73, Mike NF4L
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
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N5GE

Re: APF and audio limiting

On Sat, 06 Nov 2010 18:04:18 -0400, Mike <[hidden email]> wrote:

Sounds normal to me.

Audio up too loud and APF on, then a strong signal transmits on the frequency
you are listening to....

What do you think it SHOULD have done? You didn't say.

Tom
Radio Amateur N5GE

>On 11/4/2010 9:48 PM, Mike wrote:
>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
>> thought my speakers had blown. Glad I wasn't wearing cans.
>>
>> My CONFIG:AF is 18, AGC = F.
>>
>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
>> better audio limiting?
>>
>> 73, Mike NF4L

Amateur Radio Operator N5GE

Joe Subich, W4TV-4

Re: APF and audio limiting

AF LIM only applies when AGC is off.
The answer is in the manual.

73,

... Joe, W4TV

On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:

> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
>
> Sounds normal to me.
>
> Audio up too loud and APF on, then a strong signal transmits on the frequency
> you are listening to....
>
> What do you think it SHOULD have done? You didn't say.
>
> Tom
> Radio Amateur N5GE
>
>> On 11/4/2010 9:48 PM, Mike wrote:
>>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
>>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
>>> thought my speakers had blown. Glad I wasn't wearing cans.
>>>
>>> My CONFIG:AF is 18, AGC = F.
>>>
>>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
>>> better audio limiting?
>>>
>>> 73, Mike NF4L
>
> ______________________________________________________________
> 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
>

Mike Reublin

Re: APF and audio limiting

In reply to this post by N5GE

Thanks Tom.

Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T* up too
loud for the signal I was after. Maybe I don't understand what AGC does. That's why I
asked the questions I did.

On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:

Mike Reublin

Re: APF and audio limiting

In reply to this post by Joe Subich, W4TV-4

Thanks Joe.

Well, AN answer is in the manual, I'm not sure it's the only one possible. Software
(up to a point, but I don't know what that point is in this case) is flexible :-P .

On 11/6/2010 6:53 PM, Joe Subich, W4TV wrote:

> AF LIM only applies when AGC is off.
> The answer is in the manual.
>
> 73,
>
> ... Joe, W4TV
>
> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
>> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
>>
>> Sounds normal to me.
>>
>> Audio up too loud and APF on, then a strong signal transmits on the frequency
>> you are listening to....
>>
>> What do you think it SHOULD have done? You didn't say.
>>
>> Tom
>> Radio Amateur N5GE
>>
>>> On 11/4/2010 9:48 PM, Mike wrote:
>>>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
>>>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
>>>> thought my speakers had blown. Glad I wasn't wearing cans.
>>>>
>>>> My CONFIG:AF is 18, AGC = F.
>>>>
>>>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
>>>> better audio limiting?
>>>>
>>>> 73, Mike NF4L
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

The Smiths

Re: APF and audio limiting

In reply to this post by Mike Reublin

I think that your understanding of the AGC is probably pretty good. I also think that most people don't know how to set their AGC properly. Yes, there should have been SOME control over the loudness of the other signal, but because the Peak filter brings everything up as it does it can also take an S9 signal and make it sound like an S40 over signal too, even when the AGC is compressing things..

Remember, the AGC is only supposed to bring things to the level of your AF output setting. Therefore if you have your AF all the way up, well, that's as loud as the AGC will put it under Sloping conditions.. It doesn't mean that EVERY weak signal will also be within your AGC Threshold. What "sounds loud" because of the APF is on doesn't mean that it's opening your threshold control in the AGC. There in lies your problem I think.. What you thought was under AGC control, really wasn't!. What you were actually hearing is proper Dynamic range you should have. So the volume control still comes into play.

I'll send you a copy of my AGC tutorial offline. I hope this helps you out some.

> Date: Sat, 6 Nov 2010 19:46:11 -0400
> From: [hidden email]
> To: [hidden email]
> Subject: Re: [Elecraft] APF and audio limiting
>
> Thanks Tom.
>
> Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T* up too
> loud for the signal I was after. Maybe I don't understand what AGC does. That's why I
> asked the questions I did.
>
> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
> > On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
> >
> > Sounds normal to me.
> >
> > Audio up too loud and APF on, then a strong signal transmits on the frequency
> > you are listening to....
> >
> > What do you think it SHOULD have done? You didn't say.
> >
> > Tom
> > Radio Amateur N5GE
> >
> >> On 11/4/2010 9:48 PM, Mike wrote:
> >>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
> >>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
> >>> thought my speakers had blown. Glad I wasn't wearing cans.
> >>>
> >>> My CONFIG:AF is 18, AGC = F.
> >>>
> >>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
> >>> better audio limiting?
> >>>
> >>> 73, Mike NF4L
> >
>
>
> ______________________________________________________________
> 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

Joe Subich, W4TV-4

Re: APF and audio limiting

>> Remember, the AGC is only supposed to bring things to the level of
>> your AF output setting.

No. AGC should never "bring up" the level. AGC *REDUCES* the level of
signals above the AGC threshold. One normally sets the audio level for
signals *at the AGC threshold* or below and AGC keeps stronger signals
from exceeding that level (by the amount of the "slope" if one is not
using a "hard" threshold).

The difference with an *AUDIO PEAK FILTER* is that the APF is in the
AUDIO circuit *AFTER* the detector and *OUTSIDE* the AGC loop. Since
the PEAK gain of the K3 APF is roughly 10 dB - see the response here:
http://n1eu.com/K3/K3_apf.htm - this can cause an issue with strong
signal but is a big advantage with signals at or near the noise level
(and below the AGC threshold). Of course, the gain is exactly why APF
can be turned on and off ... you don't want it on with strong signals -
only with those at the noise signals where it makes a difference!

73,

... Joe, W4TV

On 11/6/2010 8:20 PM, The Smiths wrote:

>
> I think that your understanding of the AGC is probably pretty good. I also think that most people don't know how to set their AGC properly. Yes, there should have been SOME control over the loudness of the other signal, but because the Peak filter brings everything up as it does it can also take an S9 signal and make it sound like an S40 over signal too, even when the AGC is compressing things..
>
> Remember, the AGC is only supposed to bring things to the level of your AF output setting. Therefore if you have your AF all the way up, well, that's as loud as the AGC will put it under Sloping conditions.. It doesn't mean that EVERY weak signal will also be within your AGC Threshold. What "sounds loud" because of the APF is on doesn't mean that it's opening your threshold control in the AGC. There in lies your problem I think.. What you thought was under AGC control, really wasn't!. What you were actually hearing is proper Dynamic range you should have. So the volume control still comes into play.
>
> I'll send you a copy of my AGC tutorial offline. I hope this helps you out some.
>
>
>> Date: Sat, 6 Nov 2010 19:46:11 -0400
>> From: [hidden email]
>> To: [hidden email]
>> Subject: Re: [Elecraft] APF and audio limiting
>>
>> Thanks Tom.
>>
>> Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T* up too
>> loud for the signal I was after. Maybe I don't understand what AGC does. That's why I
>> asked the questions I did.
>>
>> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
>>> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
>>>
>>> Sounds normal to me.
>>>
>>> Audio up too loud and APF on, then a strong signal transmits on the frequency
>>> you are listening to....
>>>
>>> What do you think it SHOULD have done? You didn't say.
>>>
>>> Tom
>>> Radio Amateur N5GE
>>>
>>>> On 11/4/2010 9:48 PM, Mike wrote:
>>>>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
>>>>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
>>>>> thought my speakers had blown. Glad I wasn't wearing cans.
>>>>>
>>>>> My CONFIG:AF is 18, AGC = F.
>>>>>
>>>>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
>>>>> better audio limiting?
>>>>>
>>>>> 73, Mike NF4L
>>>
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

The Smiths

Re: APF and audio limiting

If I said black you would say white. What's the difference. Fine, it's not bringing the level UP to the AF Output, it's setting it TO the AF output according to the slope setting.. Unless of course the manual is written improperly too. Stop being such a nit pick Joe, you don't ALWAYS have to correct everyone.. My point is still the same. He heard the loud signal LOUD because that's where his AF Output was set to.
Perhaps you can spend more time helping this person than knocking down those that DO try to help others. It would be time better spent. END OF.

Sorry Eric, but I just feel like Joe is out here like a shark circling around looking for someone to bite.

> Date: Sat, 6 Nov 2010 20:48:14 -0400
> From: [hidden email]
> To: [hidden email]
> Subject: Re: [Elecraft] APF and audio limiting
>
>
> >> Remember, the AGC is only supposed to bring things to the level of
> >> your AF output setting.
>
> No. AGC should never "bring up" the level. AGC *REDUCES* the level of
> signals above the AGC threshold. One normally sets the audio level for
> signals *at the AGC threshold* or below and AGC keeps stronger signals
> from exceeding that level (by the amount of the "slope" if one is not
> using a "hard" threshold).
>
> The difference with an *AUDIO PEAK FILTER* is that the APF is in the
> AUDIO circuit *AFTER* the detector and *OUTSIDE* the AGC loop. Since
> the PEAK gain of the K3 APF is roughly 10 dB - see the response here:
> http://n1eu.com/K3/K3_apf.htm - this can cause an issue with strong
> signal but is a big advantage with signals at or near the noise level
> (and below the AGC threshold). Of course, the gain is exactly why APF
> can be turned on and off ... you don't want it on with strong signals -
> only with those at the noise signals where it makes a difference!
>
> 73,
>
> ... Joe, W4TV
>
>
> On 11/6/2010 8:20 PM, The Smiths wrote:
> >
> > I think that your understanding of the AGC is probably pretty good. I also think that most people don't know how to set their AGC properly. Yes, there should have been SOME control over the loudness of the other signal, but because the Peak filter brings everything up as it does it can also take an S9 signal and make it sound like an S40 over signal too, even when the AGC is compressing things..
> >
> > Remember, the AGC is only supposed to bring things to the level of your AF output setting. Therefore if you have your AF all the way up, well, that's as loud as the AGC will put it under Sloping conditions.. It doesn't mean that EVERY weak signal will also be within your AGC Threshold. What "sounds loud" because of the APF is on doesn't mean that it's opening your threshold control in the AGC. There in lies your problem I think.. What you thought was under AGC control, really wasn't!. What you were actually hearing is proper Dynamic range you should have. So the volume control still comes into play.
> >
> > I'll send you a copy of my AGC tutorial offline. I hope this helps you out some.
> >
> >
> >> Date: Sat, 6 Nov 2010 19:46:11 -0400
> >> From: [hidden email]
> >> To: [hidden email]
> >> Subject: Re: [Elecraft] APF and audio limiting
> >>
> >> Thanks Tom.
> >>
> >> Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T* up too
> >> loud for the signal I was after. Maybe I don't understand what AGC does. That's why I
> >> asked the questions I did.
> >>
> >> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
> >>> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
> >>>
> >>> Sounds normal to me.
> >>>
> >>> Audio up too loud and APF on, then a strong signal transmits on the frequency
> >>> you are listening to....
> >>>
> >>> What do you think it SHOULD have done? You didn't say.
> >>>
> >>> Tom
> >>> Radio Amateur N5GE
> >>>
> >>>> On 11/4/2010 9:48 PM, Mike wrote:
> >>>>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
> >>>>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
> >>>>> thought my speakers had blown. Glad I wasn't wearing cans.
> >>>>>
> >>>>> My CONFIG:AF is 18, AGC = F.
> >>>>>
> >>>>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
> >>>>> better audio limiting?
> >>>>>
> >>>>> 73, Mike NF4L
> >>>
> >>
> >>
> >> ______________________________________________________________
> >> Elecraft mailing list
> >> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >> Help: http://mailman.qth.net/mmfaq.htm
> >> Post: mailto:[hidden email]
> >>
> >> This list hosted by: http://www.qsl.net
> >> Please help support this email list: http://www.qsl.net/donate.html
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> >
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Don Wilhelm-4

Re: APF and audio limiting

In reply to this post by Mike Reublin

Mike,

The AGC works at the IF level, not the audio level.
What that means is if you crank the AF gain way up to listen to a very
weak signal, AGC action is probably not even started because the signal
level is at or near the level of the band noise - In other words, the
receiver is operation at "full gain, all stops removed".

Under those conditions, if a very strong signal suddenly comes into your
passband, yes, it will be loud simply because the AF Gain is advanced.
Yes, the AGC will respond to that new signal - just how much depends on
how you have the AGC menu parameters set. If it does cause an AGC
response, it will reduce the gain of the receiver, and you will no
longer be able to copy the signal at or near the band noise floor.

So perhaps what I am saying is that everyone might run their AGC
parameters so that all stations, no matter what their relative strengths
will have the same audio level - that would cure the condition you have
stated - but I do not really believe that is a good solution - for one,
it will make band noise the same audio level as the signals - result is
"noisy K3", and we have been there before.

Myself, I prefer to be able to determine the relative strength of
various signals "by ear" rather than "by S-meter" - that means the
strong signals will have greater audio levels than weaker stations -
that is just the way it is.

Since very weak signals (which is what APF is all about) are well below
the level that AGC action starts, when trying to dig out such a weak
station, it may be wise to turn off AGC altogether (provided you have
set the AF limiter beforehand). With AGC off, the Audio limiter is
active to protect you from ear-shattering events such as a strong signal
suddenly coming on frequency.

An additional benefit to copying very weak signals with AGC off is that
a strong signal coming on within the passband will not de-sense the
receiver (as it would with AGC on), so you may be able to use the
"filter between the ears" to continue copying the weak signal.

73,
Don W3FPR

On 11/6/2010 7:46 PM, Mike wrote:

> Thanks Tom.
>
> Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T* up too
> loud for the signal I was after. Maybe I don't understand what AGC does. That's why I
> asked the questions I did.
>
> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
>> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
>>
>> Sounds normal to me.
>>
>> Audio up too loud and APF on, then a strong signal transmits on the frequency
>> you are listening to....
>>
>> What do you think it SHOULD have done? You didn't say.
>>
>> Tom
>> Radio Amateur N5GE
>>
>>> On 11/4/2010 9:48 PM, Mike wrote:
>>>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
>>>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
>>>> thought my speakers had blown. Glad I wasn't wearing cans.
>>>>
>>>> My CONFIG:AF is 18, AGC = F.
>>>>
>>>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
>>>> better audio limiting?
>>>>
>>>> 73, Mike NF4L
>
> ______________________________________________________________
> 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
>

GREG WILSON

Re: APF and audio limiting

In reply to this post by The Smiths

I think you're the one who is out of line, Mr. Smith...Joe is being
accurate; you're not. If you're going to try to help someone, then give
them accurate information...not information that is "sort of" correct...and
then complain when someone does correct the information. I learn a lot from
Joe's posts and appreciate that he is a knowledgeable guy who is willing to
share with the group. 73 de Greg-N4CC

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of The Smiths
Sent: Saturday, November 06, 2010 7:13 PM
To: [hidden email]; Elecraft Reflector
Subject: Re: [Elecraft] APF and audio limiting

If I said black you would say white. What's the difference. Fine, it's not
bringing the level UP to the AF Output, it's setting it TO the AF output
according to the slope setting.. Unless of course the manual is written
improperly too. Stop being such a nit pick Joe, you don't ALWAYS have to
correct everyone.. My point is still the same. He heard the loud signal
LOUD because that's where his AF Output was set to.
Perhaps you can spend more time helping this person than knocking down those
that DO try to help others. It would be time better spent. END OF.

Sorry Eric, but I just feel like Joe is out here like a shark circling
around looking for someone to bite.

also think that most people don't know how to set their AGC properly. Yes,
there should have been SOME control over the loudness of the other signal,
but because the Peak filter brings everything up as it does it can also take
an S9 signal and make it sound like an S40 over signal too, even when the
AGC is compressing things..
> >
> > Remember, the AGC is only supposed to bring things to the level of your
AF output setting. Therefore if you have your AF all the way up, well,
that's as loud as the AGC will put it under Sloping conditions.. It doesn't
mean that EVERY weak signal will also be within your AGC Threshold. What
"sounds loud" because of the APF is on doesn't mean that it's opening your
threshold control in the AGC. There in lies your problem I think.. What you
thought was under AGC control, really wasn't!. What you were actually
hearing is proper Dynamic range you should have. So the volume control still
comes into play.
> >
> > I'll send you a copy of my AGC tutorial offline. I hope this helps you
out some.

> >
> >
> >> Date: Sat, 6 Nov 2010 19:46:11 -0400
> >> From: [hidden email]
> >> To: [hidden email]
> >> Subject: Re: [Elecraft] APF and audio limiting
> >>
> >> Thanks Tom.
> >>
> >> Well, I kinda thought it shouldn't blast my ears that hard. Audio
> >> *WASN'T* up too loud for the signal I was after. Maybe I don't
> >> understand what AGC does. That's why I asked the questions I did.
> >>
> >> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
> >>> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
> >>>
> >>> Sounds normal to me.
> >>>
> >>> Audio up too loud and APF on, then a strong signal transmits on
> >>> the frequency you are listening to....
> >>>
> >>> What do you think it SHOULD have done? You didn't say.
> >>>
> >>> Tom
> >>> Radio Amateur N5GE
> >>>
> >>>> On 11/4/2010 9:48 PM, Mike wrote:
> >>>>> I'm playing with the new APF, and trying to get a REALLY weak
> >>>>> QSO to pop. I have the volume cranked up pretty good, and a
> >>>>> REALLY strong station throws in their call. I thought my speakers

had blown. Glad I wasn't wearing cans.

> >>>>>
> >>>>> My CONFIG:AF is 18, AGC = F.
> >>>>>
> >>>>> Was I doing something wrong? Anybody else experience this? Do we
> >>>>> need/can we have better audio limiting?
> >>>>>
> >>>>> 73, Mike NF4L
> >>>
> >>
> >>
> >> ______________________________________________________________
> >> Elecraft mailing list
> >> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >> Help: http://mailman.qth.net/mmfaq.htm
> >> Post: mailto:[hidden email]
> >>
> >> This list hosted by: http://www.qsl.net Please help support this
> >> email list: http://www.qsl.net/donate.html
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net Please help support this
> > email list: http://www.qsl.net/donate.html
> >
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AC7AC

Re: APF and audio limiting

In reply to this post by Joe Subich, W4TV-4

CONTENTS DELETED

The author has deleted this message.

Joe Subich, W4TV-4

Re: APF and audio limiting

In reply to this post by Don Wilhelm-4

>> Since very weak signals (which is what APF is all about) are well below
>> the level that AGC action starts, when trying to dig out such a weak
>> station, it may be wise to turn off AGC altogether (provided you have
>> set the AF limiter beforehand).

It might be wise to ask Wayne and Lyle to consider activating the AF
Limiter when APF is turned on just to prevent a problem it a strong
signal jumps on top of the weak one we're trying to copy. It is not
much of a stretch to think that a local might call that weak UA0 on
160 or 5R on 80 while we're running "all knobs to the right" trying
to dig it out of the noise.

Looking at W8OZA's AGC test data, it appears that the audio output
can vary more than 40 dB from a -140 dBm (MDS) signal to a -43 dBm
signal (S9 +30 dB) depending on the user's selection of AGC slope
and threshold. If one adds another 10 dB of APF gain, a sudden 40
to 50 dB audio "shot" can be quite dangerous depending on the initial
listening level.

In addition, given reports of damage to the speaker amplifier with
sudden noise bursts with AGC off, enabling AF LIM with APF *might*
prevent some potential amplifier damage.

73,

... Joe, W4TV

On 11/6/2010 9:20 PM, Don Wilhelm wrote:

> Mike,
>
> The AGC works at the IF level, not the audio level.
> What that means is if you crank the AF gain way up to listen to a very
> weak signal, AGC action is probably not even started because the signal
> level is at or near the level of the band noise - In other words, the
> receiver is operation at "full gain, all stops removed".
>
> Under those conditions, if a very strong signal suddenly comes into your
> passband, yes, it will be loud simply because the AF Gain is advanced.
> Yes, the AGC will respond to that new signal - just how much depends on
> how you have the AGC menu parameters set. If it does cause an AGC
> response, it will reduce the gain of the receiver, and you will no
> longer be able to copy the signal at or near the band noise floor.
>
> So perhaps what I am saying is that everyone might run their AGC
> parameters so that all stations, no matter what their relative strengths
> will have the same audio level - that would cure the condition you have
> stated - but I do not really believe that is a good solution - for one,
> it will make band noise the same audio level as the signals - result is
> "noisy K3", and we have been there before.
>
> Myself, I prefer to be able to determine the relative strength of
> various signals "by ear" rather than "by S-meter" - that means the
> strong signals will have greater audio levels than weaker stations -
> that is just the way it is.
>
> Since very weak signals (which is what APF is all about) are well below
> the level that AGC action starts, when trying to dig out such a weak
> station, it may be wise to turn off AGC altogether (provided you have
> set the AF limiter beforehand). With AGC off, the Audio limiter is
> active to protect you from ear-shattering events such as a strong signal
> suddenly coming on frequency.
>
> An additional benefit to copying very weak signals with AGC off is that
> a strong signal coming on within the passband will not de-sense the
> receiver (as it would with AGC on), so you may be able to use the
> "filter between the ears" to continue copying the weak signal.
>
> 73,
> Don W3FPR
>
> On 11/6/2010 7:46 PM, Mike wrote:
>> Thanks Tom.
>>
>> Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T* up too
>> loud for the signal I was after. Maybe I don't understand what AGC does. That's why I
>> asked the questions I did.
>>
>> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
>>> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
>>>
>>> Sounds normal to me.
>>>
>>> Audio up too loud and APF on, then a strong signal transmits on the frequency
>>> you are listening to....
>>>
>>> What do you think it SHOULD have done? You didn't say.
>>>
>>> Tom
>>> Radio Amateur N5GE
>>>
>>>> On 11/4/2010 9:48 PM, Mike wrote:
>>>>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
>>>>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
>>>>> thought my speakers had blown. Glad I wasn't wearing cans.
>>>>>
>>>>> My CONFIG:AF is 18, AGC = F.
>>>>>
>>>>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
>>>>> better audio limiting?
>>>>>
>>>>> 73, Mike NF4L
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
>

Mike Reublin

Re: APF and audio limiting

In reply to this post by The Smiths

Thanks.

Almost every glitch I've had has been a misunderstanding of how things work. Enjoyed
your other tutorials.

Mike

On 11/6/2010 8:20 PM, The Smiths wrote:

> I think that your understanding of the AGC is probably pretty good. I also think
> that most people don't know how to set their AGC properly. Yes, there should have
> been SOME control over the loudness of the other signal, but because the Peak
> filter brings everything up as it does it can also take an S9 signal and make it
> sound like an S40 over signal too, even when the AGC is compressing things..
>
> Remember, the AGC is only supposed to bring things to the level of your AF output
> setting. Therefore if you have your AF all the way up, well, that's as loud as the
> AGC will put it under Sloping conditions.. It doesn't mean that EVERY weak signal
> will also be within your AGC Threshold. What "sounds loud" because of the APF is
> on doesn't mean that it's opening your threshold control in the AGC. There in lies
> your problem I think.. What you thought was under AGC control, really wasn't!. What
> you were actually hearing is proper Dynamic range you should have. So the volume
> control still comes into play.
>
> I'll send you a copy of my AGC tutorial offline. I hope this helps you out some.
>
>
> > Date: Sat, 6 Nov 2010 19:46:11 -0400
> > From: [hidden email]
> > To: [hidden email]
> > Subject: Re: [Elecraft] APF and audio limiting
> >
> > Thanks Tom.
> >
> > Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T* up too
> > loud for the signal I was after. Maybe I don't understand what AGC does. That's
> why I
> > asked the questions I did.
> >
> > On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
> > > On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
> > >
> > > Sounds normal to me.
> > >
> > > Audio up too loud and APF on, then a strong signal transmits on the frequency
> > > you are listening to....
> > >
> > > What do you think it SHOULD have done? You didn't say.
> > >
> > > Tom
> > > Radio Amateur N5GE
> > >
> > >> On 11/4/2010 9:48 PM, Mike wrote:
> > >>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I
> have the
> > >>> volume cranked up pretty good, and a REALLY strong station throws in their
> call. I
> > >>> thought my speakers had blown. Glad I wasn't wearing cans.
> > >>>
> > >>> My CONFIG:AF is 18, AGC = F.
> > >>>
> > >>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
> > >>> better audio limiting?
> > >>>
> > >>> 73, Mike NF4L
> > >
> >
> >
> > ______________________________________________________________
> > 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

Mike Reublin

Re: APF and audio limiting

In reply to this post by Don Wilhelm-4

Thanks Don.

No, I wouldn't want all sigs to have the same audio level. I'll play with AGC off,
and the limiter, and the AGC settings.

Mike

On 11/6/2010 9:20 PM, Don Wilhelm wrote:

> Mike,
>
> The AGC works at the IF level, not the audio level.
> What that means is if you crank the AF gain way up to listen to a very weak signal,
> AGC action is probably not even started because the signal level is at or near the
> level of the band noise - In other words, the receiver is operation at "full gain,
> all stops removed".
>
> Under those conditions, if a very strong signal suddenly comes into your passband,
> yes, it will be loud simply because the AF Gain is advanced. Yes, the AGC will
> respond to that new signal - just how much depends on how you have the AGC menu
> parameters set. If it does cause an AGC response, it will reduce the gain of the
> receiver, and you will no longer be able to copy the signal at or near the band
> noise floor.
>
> So perhaps what I am saying is that everyone might run their AGC parameters so that
> all stations, no matter what their relative strengths will have the same audio
> level - that would cure the condition you have stated - but I do not really believe
> that is a good solution - for one, it will make band noise the same audio level as
> the signals - result is "noisy K3", and we have been there before.
>
> Myself, I prefer to be able to determine the relative strength of various signals
> "by ear" rather than "by S-meter" - that means the strong signals will have greater
> audio levels than weaker stations - that is just the way it is.
>
> Since very weak signals (which is what APF is all about) are well below the level
> that AGC action starts, when trying to dig out such a weak station, it may be wise
> to turn off AGC altogether (provided you have set the AF limiter beforehand). With
> AGC off, the Audio limiter is active to protect you from ear-shattering events such
> as a strong signal suddenly coming on frequency.
>
> An additional benefit to copying very weak signals with AGC off is that a strong
> signal coming on within the passband will not de-sense the receiver (as it would
> with AGC on), so you may be able to use the "filter between the ears" to continue
> copying the weak signal.
>
> 73,
> Don W3FPR
>
> On 11/6/2010 7:46 PM, Mike wrote:
>> Thanks Tom.
>>
>> Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T* up too
>> loud for the signal I was after. Maybe I don't understand what AGC does. That's why I
>> asked the questions I did.
>>
>> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
>>> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
>>>
>>> Sounds normal to me.
>>>
>>> Audio up too loud and APF on, then a strong signal transmits on the frequency
>>> you are listening to....
>>>
>>> What do you think it SHOULD have done? You didn't say.
>>>
>>> Tom
>>> Radio Amateur N5GE
>>>
>>>> On 11/4/2010 9:48 PM, Mike wrote:
>>>>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I
>>>>> have the
>>>>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
>>>>> thought my speakers had blown. Glad I wasn't wearing cans.
>>>>>
>>>>> My CONFIG:AF is 18, AGC = F.
>>>>>
>>>>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
>>>>> better audio limiting?
>>>>>
>>>>> 73, Mike NF4L
>>
>> ______________________________________________________________
>> 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
>>
>

Mike Reublin

Re: APF and audio limiting

In reply to this post by Joe Subich, W4TV-4

Yes!

And to avoid some potential ear damage as well. Normally I wear phones, and I think
that blast may have caused bleeding if I'd had them on then.... >:o

Mike NF4L

On 11/6/2010 11:51 PM, Joe Subich, W4TV wrote:

>>> Since very weak signals (which is what APF is all about) are well below
>>> the level that AGC action starts, when trying to dig out such a weak
>>> station, it may be wise to turn off AGC altogether (provided you have
>>> set the AF limiter beforehand).
> It might be wise to ask Wayne and Lyle to consider activating the AF
> Limiter when APF is turned on just to prevent a problem it a strong
> signal jumps on top of the weak one we're trying to copy. It is not
> much of a stretch to think that a local might call that weak UA0 on
> 160 or 5R on 80 while we're running "all knobs to the right" trying
> to dig it out of the noise.
>
> Looking at W8OZA's AGC test data, it appears that the audio output
> can vary more than 40 dB from a -140 dBm (MDS) signal to a -43 dBm
> signal (S9 +30 dB) depending on the user's selection of AGC slope
> and threshold. If one adds another 10 dB of APF gain, a sudden 40
> to 50 dB audio "shot" can be quite dangerous depending on the initial
> listening level.
>
> In addition, given reports of damage to the speaker amplifier with
> sudden noise bursts with AGC off, enabling AF LIM with APF *might*
> prevent some potential amplifier damage.
>
> 73,
>
> ... Joe, W4TV
>
>
> On 11/6/2010 9:20 PM, Don Wilhelm wrote:
>> Mike,
>>
>> The AGC works at the IF level, not the audio level.
>> What that means is if you crank the AF gain way up to listen to a very
>> weak signal, AGC action is probably not even started because the signal
>> level is at or near the level of the band noise - In other words, the
>> receiver is operation at "full gain, all stops removed".
>>
>> Under those conditions, if a very strong signal suddenly comes into your
>> passband, yes, it will be loud simply because the AF Gain is advanced.
>> Yes, the AGC will respond to that new signal - just how much depends on
>> how you have the AGC menu parameters set. If it does cause an AGC
>> response, it will reduce the gain of the receiver, and you will no
>> longer be able to copy the signal at or near the band noise floor.
>>
>> So perhaps what I am saying is that everyone might run their AGC
>> parameters so that all stations, no matter what their relative strengths
>> will have the same audio level - that would cure the condition you have
>> stated - but I do not really believe that is a good solution - for one,
>> it will make band noise the same audio level as the signals - result is
>> "noisy K3", and we have been there before.
>>
>> Myself, I prefer to be able to determine the relative strength of
>> various signals "by ear" rather than "by S-meter" - that means the
>> strong signals will have greater audio levels than weaker stations -
>> that is just the way it is.
>>
>> Since very weak signals (which is what APF is all about) are well below
>> the level that AGC action starts, when trying to dig out such a weak
>> station, it may be wise to turn off AGC altogether (provided you have
>> set the AF limiter beforehand). With AGC off, the Audio limiter is
>> active to protect you from ear-shattering events such as a strong signal
>> suddenly coming on frequency.
>>
>> An additional benefit to copying very weak signals with AGC off is that
>> a strong signal coming on within the passband will not de-sense the
>> receiver (as it would with AGC on), so you may be able to use the
>> "filter between the ears" to continue copying the weak signal.
>>
>> 73,
>> Don W3FPR
>>
>> On 11/6/2010 7:46 PM, Mike wrote:
>>> Thanks Tom.
>>>
>>> Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T* up too
>>> loud for the signal I was after. Maybe I don't understand what AGC does. That's why I
>>> asked the questions I did.
>>>
>>> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
>>>> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
>>>>
>>>> Sounds normal to me.
>>>>
>>>> Audio up too loud and APF on, then a strong signal transmits on the frequency
>>>> you are listening to....
>>>>
>>>> What do you think it SHOULD have done? You didn't say.
>>>>
>>>> Tom
>>>> Radio Amateur N5GE
>>>>
>>>>> On 11/4/2010 9:48 PM, Mike wrote:
>>>>>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
>>>>>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
>>>>>> thought my speakers had blown. Glad I wasn't wearing cans.
>>>>>>
>>>>>> My CONFIG:AF is 18, AGC = F.
>>>>>>
>>>>>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
>>>>>> better audio limiting?
>>>>>>
>>>>>> 73, Mike NF4L
>>>

David Gilbert

Re: APF and audio limiting

In reply to this post by The Smiths

It's not nit picking when someone corrects your incorrect description.
AGC action seems to be one of the least understood facets of the K3 and
putting bad information out there about it doesn't help. You were wrong
... Joe is correct. Don't take it personally.

Dave AB7E

On 11/6/2010 6:12 PM, The Smiths wrote:

> If I said black you would say white. What's the difference. Fine, it's not bringing the level UP to the AF Output, it's setting it TO the AF output according to the slope setting.. Unless of course the manual is written improperly too. Stop being such a nit pick Joe, you don't ALWAYS have to correct everyone.. My point is still the same. He heard the loud signal LOUD because that's where his AF Output was set to.
> Perhaps you can spend more time helping this person than knocking down those that DO try to help others. It would be time better spent. END OF.
>
> Sorry Eric, but I just feel like Joe is out here like a shark circling around looking for someone to bite.
>
>
>> Date: Sat, 6 Nov 2010 20:48:14 -0400
>> From: [hidden email]
>> To: [hidden email]
>> Subject: Re: [Elecraft] APF and audio limiting
>>
>>
>>>> Remember, the AGC is only supposed to bring things to the level of
>>>> your AF output setting.
>> No. AGC should never "bring up" the level. AGC *REDUCES* the level of
>> signals above the AGC threshold. One normally sets the audio level for
>> signals *at the AGC threshold* or below and AGC keeps stronger signals
>> from exceeding that level (by the amount of the "slope" if one is not
>> using a "hard" threshold).
>>
>> The difference with an *AUDIO PEAK FILTER* is that the APF is in the
>> AUDIO circuit *AFTER* the detector and *OUTSIDE* the AGC loop. Since
>> the PEAK gain of the K3 APF is roughly 10 dB - see the response here:
>> http://n1eu.com/K3/K3_apf.htm - this can cause an issue with strong
>> signal but is a big advantage with signals at or near the noise level
>> (and below the AGC threshold). Of course, the gain is exactly why APF
>> can be turned on and off ... you don't want it on with strong signals -
>> only with those at the noise signals where it makes a difference!
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>>
>> On 11/6/2010 8:20 PM, The Smiths wrote:
>>> I think that your understanding of the AGC is probably pretty good. I also think that most people don't know how to set their AGC properly. Yes, there should have been SOME control over the loudness of the other signal, but because the Peak filter brings everything up as it does it can also take an S9 signal and make it sound like an S40 over signal too, even when the AGC is compressing things..
>>>
>>> Remember, the AGC is only supposed to bring things to the level of your AF output setting. Therefore if you have your AF all the way up, well, that's as loud as the AGC will put it under Sloping conditions.. It doesn't mean that EVERY weak signal will also be within your AGC Threshold. What "sounds loud" because of the APF is on doesn't mean that it's opening your threshold control in the AGC. There in lies your problem I think.. What you thought was under AGC control, really wasn't!. What you were actually hearing is proper Dynamic range you should have. So the volume control still comes into play.
>>>
>>> I'll send you a copy of my AGC tutorial offline. I hope this helps you out some.
>>>
>>>
>>>> Date: Sat, 6 Nov 2010 19:46:11 -0400
>>>> From: [hidden email]
>>>> To: [hidden email]
>>>> Subject: Re: [Elecraft] APF and audio limiting
>>>>
>>>> Thanks Tom.
>>>>
>>>> Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T* up too
>>>> loud for the signal I was after. Maybe I don't understand what AGC does. That's why I
>>>> asked the questions I did.
>>>>
>>>> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
>>>>> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
>>>>>
>>>>> Sounds normal to me.
>>>>>
>>>>> Audio up too loud and APF on, then a strong signal transmits on the frequency
>>>>> you are listening to....
>>>>>
>>>>> What do you think it SHOULD have done? You didn't say.
>>>>>
>>>>> Tom
>>>>> Radio Amateur N5GE
>>>>>
>>>>>> On 11/4/2010 9:48 PM, Mike wrote:
>>>>>>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
>>>>>>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
>>>>>>> thought my speakers had blown. Glad I wasn't wearing cans.
>>>>>>>
>>>>>>> My CONFIG:AF is 18, AGC = F.
>>>>>>>
>>>>>>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
>>>>>>> better audio limiting?
>>>>>>>
>>>>>>> 73, Mike NF4L
>>>>
>>>> ______________________________________________________________
>>>> Elecraft mailing list
>>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>>> Help: http://mailman.qth.net/mmfaq.htm
>>>> Post: mailto:[hidden email]
>>>>
>>>> This list hosted by: http://www.qsl.net
>>>> Please help support this email list: http://www.qsl.net/donate.html
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Joe Subich, W4TV-4

Re: APF and audio limiting

In reply to this post by Mike Reublin

Mike,

Don's explanation is good. Remember, AGC does not "bring up" the level
of any signal ... only the audio gain control will do that. AGC simply
*reduces the IF gain for signals above the AGC threshold*.

Although it is intended as an analysis of the K3's AGC behavior, the
study by Jack Smith, W8OZA is one of the best explanations of the way
an AGC system works:
http://cliftonlaboratories.com/elecraft_k3_agc_and_s-meter.htm

Notice that the audio output shows a 1:1 slope for increasing RF input
from the receiver's noise floor (MDS) to the AGC threshold at which
time the *rate of increase* is reduced to some value set by the AGC
SLOPE parameter. Setting the threshold to 2 (minimum) and slope to
15 (maximum flatness) will result in the least change in audio output
from the weakest to strongest signal but that lack of change is due
to *DECREASING* IF/RF gain as the input signal becomes stronger.
Based on Jack's measurements, the absolute differences in audio
output from noise floor to S9+40 dB can be as little as 10 dB
(AGC THR=2, AGC SLP=15) or as much as 45 dB! (AGC THR=8, AGC SLP=0)
- of course the input range is 100+ dB (-140 dBm to -33 dBm).

The goal is to find a set of parameters that allow the output audio
to reflect changes in signal strength - so the operator can separate
signals - without providing so much dynamic range that the appearance
of a strong signal on top of a weak one causes pain <G>.

The "problem" with APF (or when operating with AGC OFF) is that the
natural tendency of most operators is to "turn up the audio" in order
to hear a signal at or near the noise level. Without APF, the noise
tends to set a maximum comfortable AF gain level but with APF, not
only is the noise reduced but the level is enhanced. When a strong
signal shows up in the peak of the APF response, even if the AGC
reduces the IF gain, the "extra" audio gain allows the full difference
between a signal "at the noise" and one that may be "only" 60 dB
stronger to be reflected in the audio.

73,

... Joe, W4TV

On 11/7/2010 6:33 AM, Mike wrote:
> Thanks Don.
>
> No, I wouldn't want all sigs to have the same audio level. I'll play with AGC off,
> and the limiter, and the AGC settings.
>
> Mike
>
______________________________________________________________
Elecraft mailing list
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Post: mailto:[hidden email]

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The Smiths

Re: APF and audio limiting

In reply to this post by David Gilbert

No one is taking anything personally. It's not the information that bothers me, it's when Joe decides to CHANGE my wording, MISQUOTE me, and then Correct me based on what HE said, not me. I'm all about helping others with the PROPER information.. Not trying to correct others that are trying to be helpful. Now, this is enough of this topic. Thank you for your input. We'll leave it here. This doesn't even belong on the reflector.

> Date: Sun, 7 Nov 2010 09:04:35 -0700
> From: [hidden email]
> To: [hidden email]
> Subject: Re: [Elecraft] APF and audio limiting
>
>
> It's not nit picking when someone corrects your incorrect description.
> AGC action seems to be one of the least understood facets of the K3 and
> putting bad information out there about it doesn't help. You were wrong
> ... Joe is correct. Don't take it personally.
>
> Dave AB7E
>
>
>
> On 11/6/2010 6:12 PM, The Smiths wrote:
> > If I said black you would say white. What's the difference. Fine, it's not bringing the level UP to the AF Output, it's setting it TO the AF output according to the slope setting.. Unless of course the manual is written improperly too. Stop being such a nit pick Joe, you don't ALWAYS have to correct everyone.. My point is still the same. He heard the loud signal LOUD because that's where his AF Output was set to.
> > Perhaps you can spend more time helping this person than knocking down those that DO try to help others. It would be time better spent. END OF.
> >
> > Sorry Eric, but I just feel like Joe is out here like a shark circling around looking for someone to bite.
> >
> >
> >> Date: Sat, 6 Nov 2010 20:48:14 -0400
> >> From: [hidden email]
> >> To: [hidden email]
> >> Subject: Re: [Elecraft] APF and audio limiting
> >>
> >>
> >>>> Remember, the AGC is only supposed to bring things to the level of
> >>>> your AF output setting.
> >> No. AGC should never "bring up" the level. AGC *REDUCES* the level of
> >> signals above the AGC threshold. One normally sets the audio level for
> >> signals *at the AGC threshold* or below and AGC keeps stronger signals
> >> from exceeding that level (by the amount of the "slope" if one is not
> >> using a "hard" threshold).
> >>
> >> The difference with an *AUDIO PEAK FILTER* is that the APF is in the
> >> AUDIO circuit *AFTER* the detector and *OUTSIDE* the AGC loop. Since
> >> the PEAK gain of the K3 APF is roughly 10 dB - see the response here:
> >> http://n1eu.com/K3/K3_apf.htm - this can cause an issue with strong
> >> signal but is a big advantage with signals at or near the noise level
> >> (and below the AGC threshold). Of course, the gain is exactly why APF
> >> can be turned on and off ... you don't want it on with strong signals -
> >> only with those at the noise signals where it makes a difference!
> >>
> >> 73,
> >>
> >> ... Joe, W4TV
> >>
> >>
> >> On 11/6/2010 8:20 PM, The Smiths wrote:
> >>> I think that your understanding of the AGC is probably pretty good. I also think that most people don't know how to set their AGC properly. Yes, there should have been SOME control over the loudness of the other signal, but because the Peak filter brings everything up as it does it can also take an S9 signal and make it sound like an S40 over signal too, even when the AGC is compressing things..
> >>>
> >>> Remember, the AGC is only supposed to bring things to the level of your AF output setting. Therefore if you have your AF all the way up, well, that's as loud as the AGC will put it under Sloping conditions.. It doesn't mean that EVERY weak signal will also be within your AGC Threshold. What "sounds loud" because of the APF is on doesn't mean that it's opening your threshold control in the AGC. There in lies your problem I think.. What you thought was under AGC control, really wasn't!. What you were actually hearing is proper Dynamic range you should have. So the volume control still comes into play.
> >>>
> >>> I'll send you a copy of my AGC tutorial offline. I hope this helps you out some.
> >>>
> >>>
> >>>> Date: Sat, 6 Nov 2010 19:46:11 -0400
> >>>> From: [hidden email]
> >>>> To: [hidden email]
> >>>> Subject: Re: [Elecraft] APF and audio limiting
> >>>>
> >>>> Thanks Tom.
> >>>>
> >>>> Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T* up too
> >>>> loud for the signal I was after. Maybe I don't understand what AGC does. That's why I
> >>>> asked the questions I did.
> >>>>
> >>>> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
> >>>>> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<[hidden email]> wrote:
> >>>>>
> >>>>> Sounds normal to me.
> >>>>>
> >>>>> Audio up too loud and APF on, then a strong signal transmits on the frequency
> >>>>> you are listening to....
> >>>>>
> >>>>> What do you think it SHOULD have done? You didn't say.
> >>>>>
> >>>>> Tom
> >>>>> Radio Amateur N5GE
> >>>>>
> >>>>>> On 11/4/2010 9:48 PM, Mike wrote:
> >>>>>>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop. I have the
> >>>>>>> volume cranked up pretty good, and a REALLY strong station throws in their call. I
> >>>>>>> thought my speakers had blown. Glad I wasn't wearing cans.
> >>>>>>>
> >>>>>>> My CONFIG:AF is 18, AGC = F.
> >>>>>>>
> >>>>>>> Was I doing something wrong? Anybody else experience this? Do we need/can we have
> >>>>>>> better audio limiting?
> >>>>>>>
> >>>>>>> 73, Mike NF4L
> >>>>
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