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

[Kok Chen]

On Nov 17, 2008, at 10:06 AM, Tayloe Dan-P26412 wrote:

> Band noise from one receiver at
> any instant in time will look exactly like band noise from
> the second receiver.


That is true if the two receivers are tuned to the same passband and  
you are using an identical antenna for the two receivers.

In the case of receiving split, you are not looking at the same noise  
entering the two receivers.  In this case, by combining two different  
passbands, the desired signal would only come from one receiver but  
the summed noise would come from both receivers, dropping the SNR by 3  
dB.

An easy test is to subtract two receiver outputs (assuming the  
receivers are phase coherent).  You should get a "reasonable" null  
(sky noise and signals are nulled away, leaving just the receiver  
noise and any gain/phase mismatch in the two passbands) when looking  
at the same antenna.  When you tune one receiver away, the noise level  
should rise.

Come to think of it, it is an easy DSP experiment by looking at the  
output of two complex mixers using different (numerical) local  
oscillators.

73
Chen, W7AY