[Elecraft] K3: listening to both rcvrs

[Dr. James C. Garland]

I don't dispute the idea that adding uncorrelated noise degrades the s/n
ratio.  However, Fred's suggestion, as I understand it, pertained to
contesting, not digging a weak DX signal out of the background noise.
Typically, in a contest the problem is QRM from many other stations, with
the desired signal many dB above the receiver or atmospheric noise. This is
also the situation with much DXing, where the desired signal is plenty
strong, but is masked by the pileup.  

I doubt that physics arguments really pertain to this situation (and as a
physicist that's hard for me to admit!). I'd think the psychology of hearing
is more pertinent.

In any case, an interesting topic, with many interesting comments.

73,
Jim W8ZR

> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net [mailto:elecraft-
> bounces at mailman.qth.net] On Behalf Of Joe Subich, W4TV
> Sent: Sunday, November 16, 2008 5:06 PM
> To: 'Kok Chen'; 'Elecraft Reflector'
> Subject: RE: [Elecraft] K3: listening to both rcvrs
> 
> 
> > So the reduction in SNR (assuming equal noise power) is
> > 3.01 dB, not 6 dB.
> 
> That's the best case if the noise power is equal.  If the
> "other" receiver has higher noise power (wider bandwidth,
> more interfering signals, etc.) the S/N reduction is greater.
> Even 3 dB reduction in S/N is a big hit if the DX Station
> you're trying to hear is at or just below the noise level.
> 
> It would be a shame to turn a top performing radio into a
> mid-pack device by mixing the audio - because of some old
> wife's tail.  Let those who want mixing do it externally
> so it doesn't impose a S/N penalty otherwise.
> 
> 
> 
> > -----Original Message-----
> > From: elecraft-bounces at mailman.qth.net
> > [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Kok Chen
> > Sent: Sunday, November 16, 2008 5:10 PM
> > To: Elecraft Reflector
> > Subject: Re: [Elecraft] K3: listening to both rcvrs
> >
> >
> >
> > On Nov 16, 2008, at 1:52 PM, Joe Subich, W4TV wrote:
> > > Assuming equal volume settings and equal bandwidths in the two
> > > receivers, the S/N will degrade by 6 dB (twice the noise voltage).
> >
> > Unless the noise is correlated, the probability density
> > function from
> > summing two random variables causes variances (noise power), not the
> > standard deviations (noise amplitude), to add.  So the reduction in
> > SNR (assuming equal noise power) is 3.01 dB, not 6 dB.
> >
> > 73
> > Chen, W7AY
> >
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