[Elecraft] K3 AGC THR doesn't go low enough

[Terry]

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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