[Elecraft] K3: listening to both rcvrs - Reduced receiver noise floor

[Jim Brown]

On Tue, 18 Nov 2008 08:03:53 +0000, David Woolley (E.L) wrote:

>In this case, there is no splitting loss, and the noise is uncorrelated 
>because it is being received at different locations.

It's a risky to assume that ALL RX noise is uncorrelated after being 
detected. While there may be differences in RF level due to antenna 
displacement and transmission line length, the detected audio may be 
correlated if some specific noise source is heard by both receivers. 

In other words, noise can be random or correlated. Examples: an impulse 
noise generated from a power line or hash generated by a swithing power 
supply. While both are broadband sources, they are NOT random. If both 
antennas hear a source like them, the detected audio will be correlated 
between the two receivers! So in that case, there's no advantage from 
combining the two RX outputs. The 3 dB advantage arises when the noise is 
truly random, like the noise preamps that are not common to the two 
receivers. 

73,

Jim Brown K9YC