This number one that bothers me about the K3.  The fact that there is noise that comes up before any signals as you advance the RF gain.

The following measurements clearly show the issue.  This is not an AGC problem - no AGCs are being activated with the 1 uV signal I am using (coming from an XG3 on 160 meters).  

First - the K3.  Here is the audio output of the radio with the RF gain all the way down and the AF gain around 9 O'clock.  Things are as they should be - nice and quiet.

Here is the plot with the RF gain advanced to about 12 O'clock.  A very noticable increase of receiver noise can be heard and seen:

Yes - there is a weak carrier in there - but you can't really hear it.

Now - let's turn the RF gain up even more...

There's my signal!!  It is easy to hear - some 30 db above the noise.  However, notice that there background noise level is almost identical to what it was before.  

This is a very nagging issue.  I often "ride the RF gain" back to the point where I can just hear some band noise and this improves the IMD performance of the receiver.  However, I am often fooled into thinking I have it at the right setpoint as I will back off until I start hearing the band noise start to go down.  However, this often happens at a point where I am not longer hearing any signals from the antenna.  

Here is a TS850S with the same test.  RF gain all the way down:

RF gain where I start seeing the noise come up:

Note - the signal is clearly audible at this point - some 40 db above the noise level.  

Now - with the RF gain all the way up:

The signal to noise ratio remains about the same.  This feels like how a radio should behave.

Tree N6TR 02-Dec-2011