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Old July 29th 19, 10:25 AM posted to
Jim Lesurf[_2_]
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Posts: 4,567
Default Derating factor.....

In article ,
Casey wrote:
In effect, if they are all packed together you end up with a SNR
determined by all the 'other' channels having the same power level as
the one carrying the Mux you want to pick up!

Interesting point but, with some obvious exceptions, DTV muxes were
grouped into a similar bandwidth to the 11 channel analogue groups, so
there wouldn't be much difference in levels across each group.

Must admit the comment only came to my mind because I'm currently writing
about a project a few decades ago to 'mask' a low-power transmission by
spreading it over a 1GHz bandwidth and use this to present any
'evesdropper' with a SNR that was well below unity.

The result was that you needed to know 'key' info to even tell the signal
was being transmitted. Steganography rather than crytography. :-)

In that case the assumed background was 'natural'. But this has set me
thinking about something similar for bands that are stuffed with 'normal'
signals like DVB muxes...


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