On 11/22/19 2:29 PM, Hal Murray wrote:
[email protected] said:
I like the idea of inserting attenuation until the SNR or Cn values start to
go down. That may be the most practical solution.
Inserting attenuation is a good trick for the tool box. It is also used to
measure error rates on fiber links.
With a reasonable fiber setup, the error rate is so low that it is hard to
measure.
I don't know that this is the case all the time. On radio links, the
kind of coding affects the BER vs Eb/No curve - and there's a variety of
impairments that have the top part of the curve looking ok, and the low
BER part looking funny.
Figure 6 in this report (figure attached) shows this problem - "BER Flaring"
https://ntrs.nasa.gov/search.jsp?R=20140008859
Granted, that example is because there was a bug in the implementation
of the receiver software, however it can happen on other systems, due to
various non-ideal implementation aspects.
At low error rates, there is a simple relation between signal/noise
and error rate. So insert enough attenuation until you can easily measure the
error rate, then compute what it would be without the attenuation.
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