[Elecraft] K3 AGC THR doesn't go low enough
Don Wilhelm
w3fpr at embarqmail.com
Tue Oct 12 13:39:39 EDT 2010
Carl,
Backing off the RF Gain will preserve the dynamic range of the receiver,
and will move the AGC response further from the threshold (but it will
do nothing for the slope).
So, yes, that can be quite effective for reducing noise. Many do not
like to back off the RF Gain. I have heard two valid reasons - one is
that a modern receiver's AGC should take care of the need to change the
RF Gain - and secondly, some object to the fact that the S-meter goes up
when the RF Gain is reduced.
Also, backing off the RF Gain is the best way to reduce the "no signal"
band noise, but the AGC will handle things differently when there are
signals on the band and pauses in the signal. If the AGC is set to be
agressive (low threshold and high slope), there will still be little
difference between the signal and the rise of noise during pauses in the
signal. The only way to change that is to adjust the AGC parameters.
73,
Don W3FPR
On 10/8/2010 11:54 PM, Carl Clawson wrote:
> 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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