[Elecraft] Noisy K3 receiver

[Don Wilhelm]

Ian,

You are quite correct - the K3 does have a LOT of gain.  It is capable 
of bringing the level of even a small amount of band noise up to a large 
amount of audio output. 

While AGC *can* accomplish that task, it will not be active when there 
are pauses in the speech or between CW characters (or words), so the AGC 
will return the K3 to full gain.  You are correct in reducing the RF 
Gain to the point where the band noise is reduced.  I trust you are also 
using the attenuator and have the preamp off because these are stages 
prior to the mixer and will have a greater impact on the band noise 
reduction than the RF Gain which operates at the IF.

For those who have noisy reception, do a trial at a spot in each HF band 
where there are no signals present - first turn off the preamp, and then 
if noise is still present and bothersome, turn on the attenuator, then 
lastly reduce the RF Gain.

For the majority of those objecting to the K3 noise level, I do not 
believe that the K3 is generating the noise (there may be exceptions 
where the K3 has a fault), but it is faithfully demodulating the entire 
passband contents, whether that be noise or signal.  With enough gain 
combined with an aggressive AGC, the noise will be heard when there are 
no signals present.  The *cure* is to alter either the receiver gain or 
alter the AGC behavior (or both).  The K3 has reserve gain for those 
times when it is required, but must be "tamed" a bit in many cases.  My 
analogy is a sports car with a powerful engine - one does not operate 
that sports car all the time with the "pedal to the metal".

73,
Don W3FPR


Ian Maude wrote:
> Hi all,
> I have been following this thread with interest.  My experience is that my
> K3 seems noisy at home where my ambient RF noise floor can be anything up to
> s9 at times with the amount of RF producing electrical junk all around me.
>  However, when I use it at a 'quiet' location such as our DXpedition to the
> Isle of Jura or our contest site, the RX is extremely quiet.  This leads me
> to believe that I am simply suffering from a RX with a *lot* of gain.  At
> home, I simply turn down the RF gain and it is amazing how quickly the noise
> lowers significantly!  There is only about 30dB of isolation between antenna
> 1 and antenna 2 off the tuner which does not help the noise floor and as
> such I have simply stopped putting an antenna in ant2 for HF, I only have my
> 6m log periodic in there.
> I think in a lot of ways we are chasing our tails here.
>
> 73 Ian
>   
>