AGC THR and noise

[Steven.Zabarnick]

I'm somewhat puzzled by the behavior of the AGC THR adjustment with respect
to band noise. My understanding is that the AGC THR setting adjusts the
level at which the AGC is activated. Thus, I would expect when listening to
band noise (QRN) that if the noise is activating the AGC, using a higher
number would prevent AGC activation, resulting in a lower background band
noise. But, my experience with the K3 is just the opposite. When adjusting
the AGC THR setting I get lower background band noise with a lower setting
-- as a matter of fact, a setting of 2 (the lowest AGC THR) signficantly
reduces the background noise relative to higher settings.

Can someone explain this to me?

Steve N9SZ
K3 #1672

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[Barry N1EU]

Steven.Zabarnick wrote

I'm somewhat puzzled by the behavior of the AGC THR adjustment with respect
to band noise. My understanding is that the AGC THR setting adjusts the
level at which the AGC is activated. Thus, I would expect when listening to
band noise (QRN) that if the noise is activating the AGC, using a higher
number would prevent AGC activation, resulting in a lower background band
noise.

A higher number means that AGC compression begins at a higher signal level, so a higher number means you'll hear more noise.

take a look at the graphs at http://www.cliftonlaboratories.com/elecraft_k3_agc_and_s-meter.htm#AGC_SLP_and_AGC_THR

73,
Barry N1EU

[Barry N1EU]

Barry N1EU wrote

Steven.Zabarnick wrote

I'm somewhat puzzled by the behavior of the AGC THR adjustment with respect
to band noise. My understanding is that the AGC THR setting adjusts the
level at which the AGC is activated. Thus, I would expect when listening to
band noise (QRN) that if the noise is activating the AGC, using a higher
number would prevent AGC activation, resulting in a lower background band
noise.

A higher number means that AGC compression begins at a higher signal level, so a higher number means you'll hear more noise.

Expressed in another way:  ALL signals, including noise, >-115dBm will be louder as you increase threshold from 2 to 8.

73,
Barry N1EU

[Don Wilhelm-4]

Steve,

Yes, I know it sounds counter-intuitive, but if you establish the right
frame of mind, it does become clear.

You might want to consider that the audio level from the K3 is what is
heard after the AGC is applied.
If you set the threshold so low that the band noise activates the AGC,
then the noise will reduce the gain of the radio.

The point where the noise increases can be an indication that the AGC
threshold is now set above the band noise - of course you would do that
check in an area where there are no signals present.

73,
Don W3FPR

[hidden email] wrote:

> I'm somewhat puzzled by the behavior of the AGC THR adjustment with respect
> to band noise. My understanding is that the AGC THR setting adjusts the
> level at which the AGC is activated. Thus, I would expect when listening to
> band noise (QRN) that if the noise is activating the AGC, using a higher
> number would prevent AGC activation, resulting in a lower background band
> noise. But, my experience with the K3 is just the opposite. When adjusting
> the AGC THR setting I get lower background band noise with a lower setting
> -- as a matter of fact, a setting of 2 (the lowest AGC THR) signficantly
> reduces the background noise relative to higher settings.
>
> Can someone explain this to me?
>
> Steve N9SZ
> K3 #1672
>
> _______________________________________________
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