[time-nuts] Measuring GPS noise floor (sort of)

Ulrich Bangert df6jb at ulrich-bangert.de
Mon Dec 3 08:30:56 UTC 2012


what you are doing is not wrong but must be interpreted in the correct way.
Please keep in mind that you are NOT comparing two naked GPS receivers. In
fact you are comparing the outputs of two GPSDOs. The deeper sense of a
GPSDO is to surpress the noise floor of the GPS receiver as good as

What you may get as a result out of your test is a sense of the overall
stability of your sources, not the GPS noise floor. With an AD of 1E-10 @ 1
s I fear however that you are currently measuring mainly the noise floor of
your counter. Can you give us a clue what instrument you are using?

Best regards

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Mark Spencer
> Gesendet: Sonntag, 2. Dezember 2012 23:38
> An: time-nuts at febo.com
> Betreff: [time-nuts] Measuring GPS noise floor (sort of)
> I'm wondering how useful it is to compare two different GPS 
> receivers to a single Rb to get a sense of the GPS noise 
> floor.   I've been collecting some data for the last week or 
> so seem be making some headway with this.
> Not having a cesium or an Hmaser I elected to compare two 
> different GPSDO's to a single Rb and then assuming the data 
> seemed sane, I thought I would then compute the Adev between 
> the two GPSDO's.   My assumption is that by comparing the two 
> GPSDO's to the Rb it should be possible to detect when one 
> GPSDO is mis behaving or possibly when the Rb mis behaves.  
> So far other than a bit of a glitch at the start of the 
> process things seem to be proceeding as I expected.   I hope 
> to collect another two weeks or so of data if all goes 
> according to plan.
> I'm really only interested in the longer term numbers and I 
> wouldn't put to much trust in the shorter term results.
> Comments would be welcome especially if there is a 
> fundamental flaw with this process.   
> Looking at the data gave me something to do this afternoon 
> during some down time on a business trip (:  I reazlize this 
> approach is probably not how the pros would do this.
> Regards Mark Spencer

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