[time-nuts] Best choice for house 10MHz reference...??

John Miles jmiles at pop.net
Sun Jan 27 13:21:13 EST 2008

As unhappy as you may be to hear it, Mike, you're done upgrading, at least
for now.  Thunderbolts are about as good as they get.  Yes, some units like
the HP and Jackson Labs clocks can do somewhat better, and with
entirely-different equipment, you might be able to tell.  Not with the 49xP
analyzer, though.

Your 497P is limited by its 1-Hz counter LSD, not the Thunderbolt.  1E-10
accuracy from the Thunderbolt is 1 Hz at 10 GHz, and that's about what the
Thunderbolt does at tau=1s, even though the spec sheet shows it closer to
1E-9 at t=1s.

That means that there is no conceivable benefit to further upgrading the 10
MHz reference beyond where you already are.  I know, I know, that's the
worst news of all. :)

Focus on giving the Thunderbolt the best signal you can, via antenna

-- john, KE5FX

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Michael Baker
> Sent: Sunday, January 27, 2008 8:17 AM
> To: time-nuts at febo.com
> Subject: [time-nuts] Best choice for house 10MHz reference...??
> Hello, All--
> RE: Tom Van Baak's comments on his preference for a CNS-II
> for long-term, high -accuracy UTC measurements (against
> Cs or maser) included the statement:
>  > I don't use a GPSDO. Instead I use a plain, non-disciplined
>  > OEM GPS board or something like a CNS II"
> (http://www.cnssys.com/cnsclock/CNSClockII.html).
>  > High-end, short-term, or low phase noise, you always use
>  > quartz; long-term you always used GPS. The cool thing about
>  > a GPSDO is that you get (almost) the best of both in one box.
> --------------------------
> This got me to wondering.....:
> My primary need for a GPSDO is as a 10MHz house frequency
> reference to externally lock my spectrum analyzer up with.
> I currently have a Trimble Thunderbolt running and it seems
> to be working OK--
> Is this a good choice for a 10MHz long-term frequency
> reference that does not require hocking my wife's
> car to pay for...?  (she might notice if I did that...)
> I will be a happy camper if I can reliably measure up
> to the upper frequency limits of my Tek 497P/494P (21GHz)
> to within +/- a few hundred Hz...
> Any feedback on this will be most appreciated!!
> Mike Baker
> Micanopy, Florida

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