From: Brian Kirby <[EMAIL PROTECTED]> Subject: [time-nuts] TI Counter Noise Floor/Resolution Date: Thu, 28 Jul 2005 15:06:50 -0500 Message-ID: <[EMAIL PROTECTED]>
Brian, Just back from a 4 day of music festival, so lagging behind somewhat. > Why we are talking about resolution and noise floor, I am looking for a > merit figure to say the data I have measured, is valid. > > As an example, when I worked in satellite communications, we had a > measurement called C/kt. This is a carrier to noise measurement, > normalized back to a 1 hertz bandwidth. When we made these measurements > with a spectrum analyzer, we had to account for the measurement > bandwidth of the instrument, the detector used (factors for sine wave > response vs. gaussian noise), etc. Basically if the reading was 6 db > above the noise floor, then we could believe the measurement. > > In my case, were I have baselined the HP53131A noise floor, I know my > readings have to be above this floor, to be valid. > > My question is how much should our readings be above the noise floor to > be considered valid, and what units/formulas should we use ? Can we > convert Allan variances to a decibel reading, and use similar techniques > as I described? Interesting view on things. A 10*log(AVAR(tau)) would be the appropriate thing to use, this would be equalent to a 20*log(ADEV(tau)) since ADEV(tau) = SQRT(AVAR(tau)). Again, a 6 dB margin is would render the right neighborhood, but then again, that is a rule-of-thumb rather than exact science. Cheers, Magnus _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
