[Elecraft] Noisy K3 receiver

[W4GRJ]

Wes,

I am a brand new (3 days) K3 owner. My RF Gain control was acting exactly
like yours. I contacted Dale at Elecraft and he walked me thru a procedure
which completely fixed the problem. Suggest you give him a call.
Jack
W4GRJ


-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Wes Stewart
Sent: Friday, December 18, 2009 11:10 AM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Noisy K3 receiver

"The more you turn RF GAIN back, the higher the S-Meter will read."

Well, that's the way it should work, but I can assure you that with my K3
with the factory default RF Gain calibration, turning the control 
counterclockwise from max would cause the S-meter to increase at first, then
*decrease* and then increase again as the control reached minimum gain.

That is why I've said repeatedly, NOT ALL K3s BEHAVE THE SAME WAY with
respect to RF gain and AGC.

If you do not have a 50 uV signal source and you haven't run the latest
variant of the RF Gain calibration routine, then you are at the mercy of the
default settings.  

This endless discussion of the "proper" way to adjust your RF gain,
attenuator, preamp, et cetera is pointless when there is this variation.

Look at Jack Smith's analysis here:

http://www.cliftonlaboratories.com/elecraft_k3_and_manual_rf_gain_control.ht
m

and pay particular attention to the chart of gain reduction v. control
volts.  To be sure, this is a simulation, but Jack is a smart guy and his
lab measurements to back this up are second to none, plus I asked someone at
Elecraft whether this was accurate and the reply was, "pretty much".

Now introduce into this FET characteristic variations that
are---well---variable, such as Gm having a 2 to 1 tolerance, and you should
be able see how easily one radio can be different from another.

Wes  N7WS

--- On Fri, 12/18/09, Bill W4ZV <btippett at alum.mit.edu> wrote:

Bill W4ZV wrote:
> 
>   
> 4.  Now adjust the RF GAIN knob counterclockwise until the antenna noise
> on the meter just stops flickering on the meter.  This will be familiar to
> OTs since this is the way we set RF GAIN many years ago on analog radios.
> 

Someone just questioned this step.  I didn't mean the S-meter should read
ZERO.  I meant that you decrease the RF GAIN setting until the noise level
on the S-meter stops flickering.  For example if your noise is flickering
S4-5 (as mine typically is on 160m), turn RF GAIN counterclockwise until you
get a steady S5 with no flicker.  The more you turn RF GAIN back, the higher
the S-Meter will read.

73,  Bill
-l



      
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