[time-nuts] "Best" GPSDO

Chris Albertson albertson.chris at gmail.com
Fri Sep 28 20:44:45 UTC 2012


how important is the close in phase noise of a 10MHz reference?  I
means after all, the oscillator you are measuring, say the local
oscillator in a receivers or whatever,  is likely not running at 10MHz
so you have some step where you convert your t-bolt reference to the
desired freq. using either DDS or a synthesizer and I'd bet that step
introduces more noise and is the weak link.

I did mean this as a question because I really don't know how to
compute the effect.  Say my DDS needs 120MHz clock and I PLL  that
120Mhz clock to my t-bolt and then the DDS as asked to outout 14.5MHz.
 How do phase noise in the 10MHz t-bolt output effect the DDS' 14.5
output.   Or does it even matter compared to all the noise from other
sources.  Is there a simple rule of thumb?

OK, maybe we are not really doing any real-measurements, just
comparing 10MHz standards to each other? But the above assumes the end
goal is some real-world device who performance we want to determine.



On Fri, Sep 28, 2012 at 11:50 AM, Murray Greenman <denwood at orcon.net.nz> wrote:
> Ulrich,
> I think this is a bit like discussing one's favourite wine or favourite
> stereo! Especially since many of the participants here will not have the
> capability to compare GPSDO performance reliably.
>
> I have a few GPSDOs, and it's my impression that of them all the Agilent
> Z3815A with MTI260 DOCXO has the best phase noise. Of course these units
> were originally equipped with an E1938A, and the later MTI260 version is not
> as common.
>
> I also have an E1938A, which I operate standalone. It is very impressive,
> excellent AD, in fact my best source now that I've given away my HP 5065A.
> There is some phase noise well away from the carrier, but I've put that down
> to my own construction (switching power supply noise).
>
> Another of my favourites with low phase noise is the Trimble/Nortel
> NTGS50AA, which has a CMAC/Rakon CFPO-DO OCXO. I've had no opportunity to
> measure the AD apart from what Lady Heather reports. This unit is physically
> large but is not power hungry and talks to LH very well.
>
> I also own a Z3801A, a Samsung GCRU-D and a small homebrew GPSDO with a
> CFPO-DO. Sorry, no Timepod for comparisons.
>
> 73,
> Murray ZL1BPU
>
>
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-- 

Chris Albertson
Redondo Beach, California



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