Posted by
Don Wilhelm-4 on
Feb 02, 2010; 9:34pm
URL: http://elecraft.85.s1.nabble.com/Attenuator-and-RF-Gain-Settings-tp4503505p4503840.html
For ALL - a further explanation! The K3 does not make noise louder!
BUT one *can* make that happen with incorrect settings.
The AGC Threshold must be set above the level of the noise. If that is
not done, the AGC will activate on the noise and reduce the gain of the
receiver. The result is that signals which *should* stand out above the
noise will be buried closer to the noise because their level has been
reduced by the AGC action.
Reducing the RF Gain will normally accomplish the same thing.
Since all K3s are not at the same location with the same atmospheric
noise level, the correct settings for one may not be right for another.
It all depends on the local noise, the atmospheric noise coming into
your antenna.
I am not certain how a person can say that the atmospheric noise on his
antenna is S-2 to S-3, but the K3 S-meter reads the noise as S-5 to
S-7. I just don't understand that - what is the "standard of
comparison"? The noise is whatever it is, and the level indicated on
any one receiver will depend on the sensitivity of the receiver as well
as its S-meter response. A receiver with a better MDS *should* receive
that noise at a higher level than one with a lesser MDS. The answer is
to either add attenuation until the noise is reduced (preamp off,
Attenuator on, RF Gain backed off), or change the onset of AGC so the
noise does not trigger it - or both. Signals that are greater than the
noise will still be present and can be copied.
73,
Don W3FPR
juergen wrote:
> This problem with the K3's producing noise with AGC on is real problem. On my 40 meter 4 square I basically have a very low noise floor S1 -S2. With AGC on I am getting QRN that the K3 AGC makes thats not really at the level that the K3 is reporting. Yes there is QRN there, but its residual with occasional pops, not the S5 and S7 QRN crashes that the AGC produces. This is not a S meter calibration issue either. Like you my QRN level jumps up mysteriously. With the AGC is off this QRN is not there. I have the threshold set at 2. Even with the ATT on this QRN is being made much more apparent with the AGC on. I hope Elecraft has a fix for this because the K3 is unusable for me in its current form on the low bands.
>
>
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