[Elecraft] [K3] High internal noise level

[Don Wilhelm]

  Pete,

Don't tell me we are going to get into this "the K3 is noisy" discussion 
again - it is one of those that comes around once in a while.  The fact 
is that the K3 has adequate gain to enable the user to hear its internal 
noise floor - it can also hear everything above that noise floor.  If 
connecting an antenna results in an increase in the noise level (you are 
then hearing the atmospheric noise picked up by the antenna), then the 
internal noise floor will not get in the way of hearing weak signals.

The AGC settings will influence this effect.   When you disconnect the 
antenna, the AGC sets the K3 to full gain.  If you have the pre-amp on, 
you will be hearing the output noise level of the preamp too.  The MDS 
of a proper functioning K3 is very good, and that is the indicator of 
the signal level which can be discerned above the receiver noise floor.  
If you believe your K3 may be sub-par, I encourage you to use an 
Elecraft XG2 signal generator or a suitable low level generator to 
measure the MDS of your K3.

A 12 o'clock setting on the AF Gain is higher than usual, so yes, in 
that condition, you will begin to hear the internal noise floor of the 
receiver - turn back the AF Gain until the internal noise is just barely 
audible.

As far as your concern about the S-meter reading - the S-meter response 
can be altered by changing the AGC characteristics on your K3.  Jack 
Smith (www.cliftonlaboratories.com) has done measurements of the K3 AGC 
settings, so if you want to customize your AGC response, I suggest you 
use his charts for reference.  S-meter ABS setting can also influence 
your S-meter response and make it 'imune' to the ATT and PRE in/out 
condition.

73,
Don W3FPR

On 8/28/2010 6:18 AM, Pete Smith wrote:
> Ever since I got my K3, I have been a little surprised at what seems to
> be a relatively high noise level with no antenna connected (or on a
> dummy load).  Very unscientifically described, on 20m it registers 1-2
> bars on the S meter, and the background is quite loud on the speaker
> with the audio gain set at 12 o'clock (RF gain full, AGC - fast,
> bandwidth 200Hz with a 500 Hz roofing filter in, no noise blanker or
> noise reduction).
>
> The radio seems to perform fine, and I have not had the feeling that I
> was missing many signals because they were being masked by receiver
> noise.  Nonetheless, I wonder how this compares with others' experience,
> or with the factory expectation?
>
> 73, Pete N4ZR
>