Topband: noise

[John Kaufmann]

Tom Rauch wrote:

>3.) The system can't subtract random "white" noise from 
>random "white" noise. It can only eliminate it by adding 
>selectivity or adding the coherent signal. 

Absolutely correct.  The engineering definition of white noise is that the noise is statistically uncorrelated at any two different frequencies.  Ambient background noise is generally white.  In practical terms this means that you cannot sample white noise in your receiver at one frequency and subtract it from signal plus noise at another frequency to cancel the noise and leave only signal.  In fact it will increase the noise.

If you took a dual-trace oscilloscope and looked at high resolution waveforms of white noise at two different frequencies simultaneously, you would see the noise waveforms are never the same.  For this reason you cannot subtract one from the other to cancel them.

73, John W1FV