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K3 AGC THR doesn't go low enough

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John Chappell G3XRJ

K3 AGC THR doesn't go low enough

I like to listen to a receiver with the rf gain set to just below
antenna atmospheric noise and AGC on - and not raising the rf gain when
it is switched on.

My K3 is srl 46xx and the only way I get the quiet background I desire
is to turn the AGC off. This necessitates having the AF limiter turned
on to save my ears and hopefully the speaker output chip.

I've played around with various AGC settings and in particular the
AGC THR - which if it would go 2 or 3 points lower would appear to
address the problem.

Anyway, to save a thousand words, this recording sets the scene
http://tinyurl.com/38qo9ud

- made from Main Rx on 3670khz with 2.8khz filter passband set to
Normal, NR and NB Off.
Sub Rx is identical in performance in this respect.

In all other respects that I use it the K3 is a stunner.

John G3XRJ
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alsopb

Re: K3 AGC THR doesn't go low enough

Interesting. Many of us have wanted just the opposite. The ability to
hold off AGC action until even high levels than the THR value allows
now. Perhaps in the future....

73 de Brian/K3KO

On 10/8/2010 12:22, John Chappell G3XRJ wrote:

> I like to listen to a receiver with the rf gain set to just below
> antenna atmospheric noise and AGC on - and not raising the rf gain when
> it is switched on.
>
> My K3 is srl 46xx and the only way I get the quiet background I desire
> is to turn the AGC off. This necessitates having the AF limiter turned
> on to save my ears and hopefully the speaker output chip.
>
> I've played around with various AGC settings and in particular the
> AGC THR - which if it would go 2 or 3 points lower would appear to
> address the problem.
>
> Anyway, to save a thousand words, this recording sets the scene
> http://tinyurl.com/38qo9ud
>
> - made from Main Rx on 3670khz with 2.8khz filter passband set to
> Normal, NR and NB Off.
> Sub Rx is identical in performance in this respect.
>
> In all other respects that I use it the K3 is a stunner.
>
> John G3XRJ
> ______________________________________________________________
> 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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Steve Wedge

Re: K3 AGC THR doesn't go low enough

In reply to this post by John Chappell G3XRJ

John, I've noticed the same thing: the AGC does seem to make the receiver - in the absence of signals - roar quite a bit with my early (#770) K3.

I've attributed a lot of the noise to computer and suburban hash, but listening with my old Drake receiver shows things much quieter. Noise reduction does help, but it would be nice to quiet this down as John suggests.

My .02

Steve, W1ES

-----Original Message-----

>From: John Chappell G3XRJ <[hidden email]>
>Sent: Oct 8, 2010 8:22 AM
>To: [hidden email]
>Subject: [Elecraft] K3 AGC THR doesn't go low enough
>
>I like to listen to a receiver with the rf gain set to just below
>antenna atmospheric noise and AGC on - and not raising the rf gain when
>it is switched on.
>
>My K3 is srl 46xx and the only way I get the quiet background I desire
>is to turn the AGC off. This necessitates having the AF limiter turned
>on to save my ears and hopefully the speaker output chip.
>
>I've played around with various AGC settings and in particular the
>AGC THR - which if it would go 2 or 3 points lower would appear to
>address the problem.
>
>Anyway, to save a thousand words, this recording sets the scene
>http://tinyurl.com/38qo9ud
>
>- made from Main Rx on 3670khz with 2.8khz filter passband set to
>Normal, NR and NB Off.
>Sub Rx is identical in performance in this respect.
>
>In all other respects that I use it the K3 is a stunner.
>
>John G3XRJ
>______________________________________________________________
>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: K3 AGC THR doesn't go low enough

Steve,

The solution is to RAISE the threshold. I run mine at 008 which is the
max. I also run the slope at 002 which makes the K3 AGC response more
like my K2 - weak signals sound weaker than stronger signals. You can
alter the slope without running into the situation where the K3 sounds
noisy, but the signals will sound more nearly the same as the slope
numbers get larger.

If your local noise is high, increase the AGC threshold and the K3 will
quiet down.
There is yet another way - turn off the preamp, and even turn on the
attenuator. You will have to increase your normal AF Gain a bit, but
the noise will be reduced. If you can still hear an increase in the
audio output when the antenna is connected, you can even reduce the RF
gain. You are not increasing the USABLE receiver sensitivity by running
everything at full right controls - in the presence of atmospheric
noise, that will only reduce the usable dynamic range and will make the
receiver sound noisy.

73,
Don W3FPR

On 10/8/2010 10:25 AM, Steve Wedge wrote:
> John, I've noticed the same thing: the AGC does seem to make the receiver - in the absence of signals - roar quite a bit with my early (#770) K3.
>
> I've attributed a lot of the noise to computer and suburban hash, but listening with my old Drake receiver shows things much quieter. Noise reduction does help, but it would be nice to quiet this down as John suggests.
>
> My .02
>
> Steve, W1ES
>
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WA1NTA

Re: K3 AGC THR doesn't go low enough

Ok, now I've done it...
I had resigned myself to living with the AGC off because I can't stand the
sound of the audio with it on in CW mode (I've come close to selling it
because of that many times), but with all this chatter about the AGC
settings, I got in there and messed around again (still not happy) but now
when I shut of the AGC, my audio shuts off too... ARGHH. Can anyone tell me
what I can do to undo my "adjustments" and get the option to shut of this
cursed AGC off without losing my audio?

Many thanks in advance and I better stop reading these postings :-)

George
WA1NTA...73

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Don Wilhelm
Sent: Friday, October 08, 2010 11:03 AM
To: Steve Wedge
Cc: [hidden email]
Subject: Re: [Elecraft] K3 AGC THR doesn't go low enough

Steve,

The solution is to RAISE the threshold. I run mine at 008 which is the
max. I also run the slope at 002 which makes the K3 AGC response more
like my K2 - weak signals sound weaker than stronger signals. You can
alter the slope without running into the situation where the K3 sounds
noisy, but the signals will sound more nearly the same as the slope
numbers get larger.

If your local noise is high, increase the AGC threshold and the K3 will
quiet down.
There is yet another way - turn off the preamp, and even turn on the
attenuator. You will have to increase your normal AF Gain a bit, but
the noise will be reduced. If you can still hear an increase in the
audio output when the antenna is connected, you can even reduce the RF
gain. You are not increasing the USABLE receiver sensitivity by running
everything at full right controls - in the presence of atmospheric
noise, that will only reduce the usable dynamic range and will make the
receiver sound noisy.

73,
Don W3FPR

On 10/8/2010 10:25 AM, Steve Wedge wrote:
> John, I've noticed the same thing: the AGC does seem to make the receiver
- in the absence of signals - roar quite a bit with my early (#770) K3.
>
> I've attributed a lot of the noise to computer and suburban hash, but
listening with my old Drake receiver shows things much quieter. Noise
reduction does help, but it would be nice to quiet this down as John
suggests.
>
> My .02
>
> Steve, W1ES
>
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David Gilbert

Re: K3 AGC THR doesn't go low enough

In reply to this post by Steve Wedge

You guys are headed in the wrong direction ... crank the AGC threshold
UP and you will come closer to getting what you want. I have mine set
to 008 and if it would go higher I would set it there.

73,
Dave AB7E

On 10/8/2010 7:25 AM, Steve Wedge wrote:

> John, I've noticed the same thing: the AGC does seem to make the receiver - in the absence of signals - roar quite a bit with my early (#770) K3.
>
> I've attributed a lot of the noise to computer and suburban hash, but listening with my old Drake receiver shows things much quieter. Noise reduction does help, but it would be nice to quiet this down as John suggests.
>
> My .02
>
> Steve, W1ES
>
> -----Original Message-----
>> From: John Chappell G3XRJ<[hidden email]>
>> Sent: Oct 8, 2010 8:22 AM
>> To: [hidden email]
>> Subject: [Elecraft] K3 AGC THR doesn't go low enough
>>
>> I like to listen to a receiver with the rf gain set to just below
>> antenna atmospheric noise and AGC on - and not raising the rf gain when
>> it is switched on.
>>
>> My K3 is srl 46xx and the only way I get the quiet background I desire
>> is to turn the AGC off. This necessitates having the AF limiter turned
>> on to save my ears and hopefully the speaker output chip.
>>
>> I've played around with various AGC settings and in particular the
>> AGC THR - which if it would go 2 or 3 points lower would appear to
>> address the problem.
>>
>> Anyway, to save a thousand words, this recording sets the scene
>> http://tinyurl.com/38qo9ud
>>
>> - made from Main Rx on 3670khz with 2.8khz filter passband set to
>> Normal, NR and NB Off.
>> Sub Rx is identical in performance in this respect.
>>
>> In all other respects that I use it the K3 is a stunner.
>>
>> John G3XRJ
>> ______________________________________________________________
>> 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
>

hf4me

Re: K3 AGC THR doesn't go low enough

In reply to this post by Steve Wedge

My first thought on comments about noise on a receiver is that the radio
they are comparing it to just can't hear as well.

73, Jim

----- Original Message -----
From: "Steve Wedge" <[hidden email]>
To: "John Chappell G3XRJ" <[hidden email]>; <[hidden email]>
Sent: Friday, October 08, 2010 9:25 AM
Subject: Re: [Elecraft] K3 AGC THR doesn't go low enough

> John, I've noticed the same thing: the AGC does seem to make the
> receiver - in the absence of signals - roar quite a bit with my early
> (#770) K3.
>
> I've attributed a lot of the noise to computer and suburban hash, but
> listening with my old Drake receiver shows things much quieter. Noise
> reduction does help, but it would be nice to quiet this down as John
> suggests.
>
> My .02
>
> Steve, W1ES
>
> -----Original Message-----
>>From: John Chappell G3XRJ <[hidden email]>
>>Sent: Oct 8, 2010 8:22 AM
>>To: [hidden email]
>>Subject: [Elecraft] K3 AGC THR doesn't go low enough
>>
>>I like to listen to a receiver with the rf gain set to just below
>>antenna atmospheric noise and AGC on - and not raising the rf gain when
>>it is switched on.
>>
>>My K3 is srl 46xx and the only way I get the quiet background I desire
>>is to turn the AGC off. This necessitates having the AF limiter turned
>>on to save my ears and hopefully the speaker output chip.
>>
>>I've played around with various AGC settings and in particular the
>>AGC THR - which if it would go 2 or 3 points lower would appear to
>>address the problem.
>>
>>Anyway, to save a thousand words, this recording sets the scene
>>http://tinyurl.com/38qo9ud
>>
>>- made from Main Rx on 3670khz with 2.8khz filter passband set to
>>Normal, NR and NB Off.
>>Sub Rx is identical in performance in this respect.
>>
>>In all other respects that I use it the K3 is a stunner.
>>
>>John G3XRJ
>>______________________________________________________________
>>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
>

John Chappell G3XRJ

Re: K3 AGC THR doesn't go low enough

In reply to this post by Don Wilhelm-4

Don,

What I should have mentioned in my initial post was that the recording
was made at midday on 80m and the noise from the antenna was only s1.
For a given setting of the rf gain, increasing the threshold to 8
increases the noise, as can be heard in the recording.

John G3XRJ

>
> The solution is to RAISE the threshold. I run mine at 008 which is the
> max. I also run the slope at 002 which makes the K3 AGC response more
> like my K2 - weak signals sound weaker than stronger signals. You can
> alter the slope without running into the situation where the K3 sounds
> noisy, but the signals will sound more nearly the same as the slope
> numbers get larger.
>
> If your local noise is high, increase the AGC threshold and the K3 will
> quiet down.
> There is yet another way - turn off the preamp, and even turn on the
> attenuator. You will have to increase your normal AF Gain a bit, but the
> noise will be reduced. If you can still hear an increase in the audio
> output when the antenna is connected, you can even reduce the RF gain.
> You are not increasing the USABLE receiver sensitivity by running
> everything at full right controls - in the presence of atmospheric
> noise, that will only reduce the usable dynamic range and will make the
> receiver sound noisy.
>
> 73,
> Don W3FPR
>
>

Don Wilhelm-4

Re: K3 AGC THR doesn't go low enough

John,

I find that true too - but ONLY under the following conditions:
1 - the preamp is turned on
2 - the attenuator is off
3 - I set the K3 to hear only noise (no signal)

If I set the preamp off and attenuator on (normal operation with my 80
meter antenna) and then set the AF gain to listen to normal signals, the
K3 is less noisy with no signal than using other settings for the AGC
Threshold.
In other words, you cannot listen only to the noise level and make a
valid comparison.

73,
Don W3FPR

On 10/8/2010 12:08 PM, John Chappell G3XRJ wrote:

> Don,
>
> What I should have mentioned in my initial post was that the recording
> was made at midday on 80m and the noise from the antenna was only s1.
> For a given setting of the rf gain, increasing the threshold to 8
> increases the noise, as can be heard in the recording.
>
> John G3XRJ
>
>> The solution is to RAISE the threshold. I run mine at 008 which is the
>> max. I also run the slope at 002 which makes the K3 AGC response more
>> like my K2 - weak signals sound weaker than stronger signals. You can
>> alter the slope without running into the situation where the K3 sounds
>> noisy, but the signals will sound more nearly the same as the slope
>> numbers get larger.
>>
>> If your local noise is high, increase the AGC threshold and the K3 will
>> quiet down.
>> There is yet another way - turn off the preamp, and even turn on the
>> attenuator. You will have to increase your normal AF Gain a bit, but the
>> noise will be reduced. If you can still hear an increase in the audio
>> output when the antenna is connected, you can even reduce the RF gain.
>> You are not increasing the USABLE receiver sensitivity by running
>> everything at full right controls - in the presence of atmospheric
>> noise, that will only reduce the usable dynamic range and will make the
>> receiver sound noisy.
>>
>> 73,
>> Don W3FPR
>>
>>
> ______________________________________________________________
> 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 Scott-7

Re: K3 AGC THR doesn't go low enough

In reply to this post by John Chappell G3XRJ

I have thought about John's wish for more AGC control. The K3 has a lot of
gain, I wonder if greater attenuator control would be more useful. I would
like to rotate in another 10 or 20 dB attenuation at times when operating
lower bands. I would guess my that wishes would require hardware
modifications and John's may not.

AE6WA

Mike Scott

K3, KX1

>John G3XRJ said: I've played around with various AGC settings and in
particular the

AGC THR - which if it would go 2 or 3 points lower would appear to

address the problem.

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Bill K9YEQ

Re: K3 AGC THR doesn't go low enough

In reply to this post by Don Wilhelm-4

I would concur with Don. I do not use the preamp unless the noise level is
very low. I use the attenuator on load bands or when there is a substantial
noise level. I use AGC as I don't want to damage my hearing accidentally.

Bill
K9YEQ

John,

I find that true too - but ONLY under the following conditions:
1 - the preamp is turned on
2 - the attenuator is off
3 - I set the K3 to hear only noise (no signal)

If I set the preamp off and attenuator on (normal operation with my 80 meter
antenna) and then set the AF gain to listen to normal signals, the
K3 is less noisy with no signal than using other settings for the AGC
Threshold.
In other words, you cannot listen only to the noise level and make a valid
comparison.

73,
Don W3FPR

On 10/8/2010 12:08 PM, John Chappell G3XRJ wrote:

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Don Wilhelm-4

Re: K3 AGC THR doesn't go low enough

In reply to this post by Mike Scott-7

I seem to have trouble convincing some to raise the threshold to
combat the noisy effect. Please read all below carefully, and I believe
I can offer some explanation.

Let's study what the AGC SLP and AGC THR settings do and try to relate
them to the perception that the K3 is noisy.

IF --
the threshold is so low that the noise triggers the AGC (and that will
be happening if the noise is causing the S-meter to have a reading with
no signal)
AND --
If the slope is set to a high value which makes all the signals have
more or less the same audio volume,
THEN --
The noise will appear at about the SAME audio volume as the signals.
RESULT --
A K3 that sounds noisy :-( ! It is a combination of both the threshold
and the slope that create this condition.

The cure for that situation is to increase the threshold and reduce the
slope.
How much?
That is an individual decision, but I have mine set to the extremes of
THR at 008 and SLP at 002.
I really believe the defaults are OK for a band where the ambient noise
level is lower, but certainly gives problems on a band that is
inherently noisy.

Please make your evaluation while listening to signals and the breaks
between signals - if you are hearing only noise, you will naturally turn
the AF Gain up, and yes the noise will increase - not only that, with
only noise, the perception is that one should use a lower threshold setting.
That is because as you lower the threshold, the AGC response to the
noise gets stronger, and the audio level is reduced by the AGC - what
you are perceiving is exactly the opposite of what you wish to achieve.

In addition, turn the attenuator on and the preamp off - again, if you
hear an increase in the band noise when the antenna is connected, you
have all the sensitivity that you can use for that band and antenna.
The K3 remembers those settings by band, so you don't have to make
changes as you switch bands.

73,
Don W3FPR

On 10/8/2010 2:23 PM, Mike Scott wrote:

> I have thought about John's wish for more AGC control. The K3 has a lot of
> gain, I wonder if greater attenuator control would be more useful. I would
> like to rotate in another 10 or 20 dB attenuation at times when operating
> lower bands. I would guess my that wishes would require hardware
> modifications and John's may not.
>
>
>
> AE6WA
>
> Mike Scott
>
> K3, KX1
>
>
>
>> John G3XRJ said: I've played around with various AGC settings and in
> particular the
>
> AGC THR - which if it would go 2 or 3 points lower would appear to
>
> address the problem.
>

Bill K9YEQ

Re: K3 AGC THR doesn't go low enough

Don,

I tried your recommendations and it makes the setup sound better than where
I had it. The threshold increase makes quite a listening difference for me
personally. Thank you for sharing.

Bill
K9YEQ

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Don Wilhelm
Sent: Friday, October 08, 2010 1:56 PM
To: [hidden email]
Cc: [hidden email]
Subject: Re: [Elecraft] K3 AGC THR doesn't go low enough

I seem to have trouble convincing some to raise the threshold to combat
the noisy effect. Please read all below carefully, and I believe I can
offer some explanation.

Let's study what the AGC SLP and AGC THR settings do and try to relate them
to the perception that the K3 is noisy.

IF --
the threshold is so low that the noise triggers the AGC (and that will be
happening if the noise is causing the S-meter to have a reading with no
signal) AND -- If the slope is set to a high value which makes all the
signals have more or less the same audio volume, THEN -- The noise will
appear at about the SAME audio volume as the signals.
RESULT --
A K3 that sounds noisy :-( ! It is a combination of both the threshold and
the slope that create this condition.

The cure for that situation is to increase the threshold and reduce the
slope.
How much?
That is an individual decision, but I have mine set to the extremes of THR
at 008 and SLP at 002.
I really believe the defaults are OK for a band where the ambient noise
level is lower, but certainly gives problems on a band that is inherently
noisy.

Please make your evaluation while listening to signals and the breaks
between signals - if you are hearing only noise, you will naturally turn the
AF Gain up, and yes the noise will increase - not only that, with only
noise, the perception is that one should use a lower threshold setting.
That is because as you lower the threshold, the AGC response to the noise
gets stronger, and the audio level is reduced by the AGC - what you are
perceiving is exactly the opposite of what you wish to achieve.

In addition, turn the attenuator on and the preamp off - again, if you hear
an increase in the band noise when the antenna is connected, you have all
the sensitivity that you can use for that band and antenna.
The K3 remembers those settings by band, so you don't have to make changes
as you switch bands.

73,
Don W3FPR

On 10/8/2010 2:23 PM, Mike Scott wrote:

> I have thought about John's wish for more AGC control. The K3 has a
> lot of gain, I wonder if greater attenuator control would be more
> useful. I would like to rotate in another 10 or 20 dB attenuation at
> times when operating lower bands. I would guess my that wishes would
> require hardware modifications and John's may not.
>
>
>
> AE6WA
>
> Mike Scott
>
> K3, KX1
>
>
>
>> John G3XRJ said: I've played around with various AGC settings and in
> particular the
>
> AGC THR - which if it would go 2 or 3 points lower would appear to
>
> address the problem.
>

David Gilbert

Re: K3 AGC THR doesn't go low enough

In reply to this post by Don Wilhelm-4

Don,

That's a good explanation. Hopefully those folks will read it however
many times it takes for them to understand that lowering the threshold
is the opposite of what they want to do. I suspect that MANY of the
complaints about the K3 being a "noisy" rig are due to similar
misunderstandings of how AGC actually works. It appears that many folks
think of AGC as being only gain reduction, and while that's probably
true technically, it's probably much better to think of AGC as being
gain equalization when you're trying to use it.

For anyone still unclear about how the AGC in the K3 works, I also
recommend that study Jack Smith's page on the subject. It's a great
explanation with several very informative graphs, and not surprisingly
it is the very first link that is displayed when you Google "K3 AGC".
The page doesn't appear to have been updated to include the newer "SOFT"
AGC mode in the K3, but even so it is highly relevant.
http://www.cliftonlaboratories.com/elecraft_k3_agc_and_s-meter.htm

I do a lot of contesting so I don't even want all signals to sound the
same, and I certainly don't want the distortion issues that can
sometimes be caused by AGC attack/decay slopes in the presence of
multiple in-band signals. Linearity is my friend, and AGC is by
definition not linear over the range of interest. I have my AGC THR
set to 008 and I have my AGC SLP set to 000. Jack's curves show that at
even those settings, there is still some AGC action at low signals and
protection at high signals. For example, his data shows that even with
AGC SLP = 000 it takes a 10 db increase in signal strength to give a 4
db increase in audio level. That works fine for me ...

73,
Dave AB7E

On 10/8/2010 11:55 AM, Don Wilhelm wrote:

Julian, G4ILO

Re: K3 AGC THR doesn't go low enough

In reply to this post by John Chappell G3XRJ

John Chappell G3XRJ wrote

Don,

What I should have mentioned in my initial post was that the recording
was made at midday on 80m and the noise from the antenna was only s1.
For a given setting of the rf gain, increasing the threshold to 8
increases the noise, as can be heard in the recording.

It doesn't increase the noise, it just makes it sound louder. You need to turn down the AF gain to restore the noise to its original level. Or tune in a signal and adjust it to the same level as before, you should find you need less AF gain and the noise when the signal isn't present will be quieter.

As Don stated you probably have too much front end gain because the reason increasing the threshold makes the noise louder is because the noise is strong enough to activate the AGC when the threshold is set low. Any receiver will sound noisy if you use preamplification when you don't need it.

The important difference is that increasing the threshold and decreasing the slope increases the volume of signals relative to the noise and makes strong signals sound louder than weak ones. It's hard to explain and the adjustments are not very intuitive but a few months ago I tried different settings using my XG1 to generate 50uV and 1uV signals and observed the audio output on a scope, then it became clear what was happening and how the adjustments affected things.

Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com
* KComm - http://www.g4ilo.com/kcomm.html
* KTune - http://www.g4ilo.com/ktune.html

Don Wilhelm-4

Re: K3 AGC THR doesn't go low enough

In an effort to help those who perceive their K3 as noisy, and for
those who are not certain their AGC slope and threshold settings are not
right for their operation, I have added a page to my website.

Go to www.w3fpr.com and click on the link in the left column referring
to K3 noise and AGC settings.
It is an expansion of the post I offered earlier today dealing with AGC
settings and their relationship to K3 noise.

73,
Don W3FPR

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Carl W Clawson

Re: K3 AGC THR doesn't go low enough

Nice writeup, Don. Thanks!

But the one thing I haven't seen mentioned in this month's installment of
the "noisy K3" discussion is setting the RF gain control. I got into the
habit long ago of using the RF gain to quiet the band noise to a reasonable
level -- after setting pre-amp, attenuator, and AF gain appropriately. We
didn't have AGC parameters to play with back then except maybe
Fast/Slow/Off.

If the K3's "RF" (actually IF) gain control works the way most rigs' do, it
is providing a bias to the AGC control voltage. In other words, it is
providing a maximum gain that will not be exceeded by the AGC's feedback
action. Is that not an equally valid way to control the level of band noise?
Apart from it being manual instead of automatic, is there any drawback to
it? I can imagine that it could interact with AGC dynamics in some
unpleasant way, but if so I haven't noticed it yet.

The K3 is only the second HF rig I've owned in 23 years as a ham. My first
was an Icom 735, and it is quite noisy on the low bands if the RF gain is
all the way up. I've heard quieter rigs, but it never occurred to me to
think of them as better just because of that.

73, Carl WS7L
K3 #486

> -----Original Message-----
> Go to www.w3fpr.com and click on the link in the left column
> referring to K3 noise and AGC settings.
> It is an expansion of the post I offered earlier today
> dealing with AGC settings and their relationship to K3 noise.
>
> 73,
> Don W3FPR

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g4amt

Re: K3 AGC THR doesn't go low enough

In reply to this post by Don Wilhelm-4

I`ve been following this thread with interest as I have the same
perceived problem as John - and think all K3s exhibit this symptom.

I do not believe anyone has mentioned signal to noise ratio and surely
this is fundamental ?
I work a lot on 160m trying to dig out extremely weak signals using a
K9AY loop array with pre-amp on (on the K3).
I have tried lots of AGC settings with the K3 but my conclusion is that
the best signal to noise ratio is achieved with the AGC off; turning it
on in whatever combination of settings introduces noise and degrades the
S:N.

This conclusion means setting the AF limiter at a suitable level to
protect my ears !

73

Terry
G4AMT

On 08/10/2010 19:55, Don Wilhelm wrote:

> I seem to have trouble convincing some to raise the threshold to
> combat the noisy effect. Please read all below carefully, and I believe
> I can offer some explanation.
>
> Let's study what the AGC SLP and AGC THR settings do and try to relate
> them to the perception that the K3 is noisy.
>
> IF --
> the threshold is so low that the noise triggers the AGC (and that will
> be happening if the noise is causing the S-meter to have a reading with
> no signal)
> AND --
> If the slope is set to a high value which makes all the signals have
> more or less the same audio volume,
> THEN --
> The noise will appear at about the SAME audio volume as the signals.
> RESULT --
> A K3 that sounds noisy :-( ! It is a combination of both the threshold
> and the slope that create this condition.
>
> The cure for that situation is to increase the threshold and reduce the
> slope.
> How much?
> That is an individual decision, but I have mine set to the extremes of
> THR at 008 and SLP at 002.
> I really believe the defaults are OK for a band where the ambient noise
> level is lower, but certainly gives problems on a band that is
> inherently noisy.
>
> Please make your evaluation while listening to signals and the breaks
> between signals - if you are hearing only noise, you will naturally turn
> the AF Gain up, and yes the noise will increase - not only that, with
> only noise, the perception is that one should use a lower threshold setting.
> That is because as you lower the threshold, the AGC response to the
> noise gets stronger, and the audio level is reduced by the AGC - what
> you are perceiving is exactly the opposite of what you wish to achieve.
>
> In addition, turn the attenuator on and the preamp off - again, if you
> hear an increase in the band noise when the antenna is connected, you
> have all the sensitivity that you can use for that band and antenna.
> The K3 remembers those settings by band, so you don't have to make
> changes as you switch bands.
>
> 73,
> Don W3FPR
>
> On 10/8/2010 2:23 PM, Mike Scott wrote:
>> I have thought about John's wish for more AGC control. The K3 has a lot of
>> gain, I wonder if greater attenuator control would be more useful. I would
>> like to rotate in another 10 or 20 dB attenuation at times when operating
>> lower bands. I would guess my that wishes would require hardware
>> modifications and John's may not.
>>
>>
>>
>> AE6WA
>>
>> Mike Scott
>>
>> K3, KX1
>>
>>
>>
>>> John G3XRJ said: I've played around with various AGC settings and in
>> particular the
>>
>> AGC THR - which if it would go 2 or 3 points lower would appear to
>>
>> address the problem.
>>
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John Chappell G3XRJ

Re: K3 AGC THR doesn't go low enough

In reply to this post by Don Wilhelm-4

Don,
Thank you for your responses and for your efforts on your webpage.

However, I should have made it clear that I'm not in a noisy environment
and just to make it absolutely clear I've made another recording without
antenna connected to the K3.
Main and RX antenna physically removed, pre Amp off.
Att Off, SSB Bandwidth Normal ....
Recording made in LSB mode rather than my normal CW because it
demonstrates the point more clearly.

Recording here http://www.g3xrj.com/Recordings/K3_agc_part2.mp3

Finally I must point out that I'm not saying the K3 is a noisy receiver
but rather, whatever the AGC does in its present incarnation in the
digital stream, has the effect of increasing the 'rf gain' from 12
o'clock to nearly 3 o'clock on overall system noise.

73
John G3XRJ

> In an effort to help those who perceive their K3 as noisy, and for
> those who are not certain their AGC slope and threshold settings are not
> right for their operation, I have added a page to my website.
>
> Go to www.w3fpr.com and click on the link in the left column referring
> to K3 noise and AGC settings.
> It is an expansion of the post I offered earlier today dealing with AGC
> settings and their relationship to K3 noise.
>
> 73,
> Don W3FPR
>
>
> ______________________________________________________________
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> Please help support this email list: http://www.qsl.net/donate.html
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Richard Ferch

Re: K3 AGC THR doesn't go low enough

In reply to this post by John Chappell G3XRJ

G3XRJ wrote:

> Finally I must point out that I'm not saying the K3 is a noisy receiver
> but rather, whatever the AGC does in its present incarnation in the
> digital stream, has the effect of increasing the 'rf gain' from 12
> o'clock to nearly 3 o'clock on overall system noise.

Rather than comparing the noise level at identical gain control
settings, I believe you should be comparing the noise level at gain
control settings that result in the same loudness for a fixed-strength
signal (e.g. a 1 uV signal). After all, what matters is not the absolute
level of noise at some arbitrarily-chosen gain control setting, it is
the level of noise relative to the signals you want to listen to.

In your original posting, you were comparing AGC off to AGC on. In order
to reduce the disparity, you were requesting a lower AGC threshold. This
would be counter-productive; reducing the AGC threshold increases the
disparity between AGC on and off. To reduce the overall disparity
between AGC on and AGC off, you must raise the AGC threshold so the AGC
has as little effect as possible on weak signals. This may also require
a re-adjustment of the RF gain control in order to make overall system
gain on weak signals and noise the same between the two AGC settings (on
and off, or low and high threshold).

To put it another way, if you like the way the receiver operates with no
AGC but would like to have AGC protecting your ears for very strong
signals, set the AGC threshold as high as possible, adjust the rf gain
controls for the desired noise (and weak signal) level at your ears, and
then adjust the AGC "slope" setting to affect strong signals the way you
want it to. The least aggressive AGC action overall occurs with the
threshold set as high as possible and the "slope" setting as low as
possible.

There is a very good explanation of the effects of the K3's AGC settings at
<http://www.cliftonlaboratories.com/elecraft_k3_agc_and_s-meter.htm>.

73,
Rich VE3KI
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