[time-nuts] Newbie question about thunderbolts

John Miles jmiles at pop.net
Wed Feb 27 19:23:35 EST 2013

Sounds like a bad OCXO.  The crystal frequency jumps slightly, and the
disciplining loop then has to compensate by steering the DAC  voltage
through the loop filter.  If that's the problem it may get better if you
leave it running for a few more weeks.

The smoking gun is the attack/decay characteristic of the DAC adjustment.
At least in theory, no issues on the GPS side of the loop should result in a
fast leading edge at the DAC. 

I haven't seen any Thunderbolts with genuinely bad OCXOs yet, although some
of them are definitely better than others.  The Thunderbolt-E, however, is a
very different model than the ones that are normally found on eBay.  Almost
everything you hear about a "Thunderbolt" refers to the older non-E version.

I've heard (but can't exactly cite) that the Thunderbolt E models were a
reduced-cost, higher-volume product.  If that's true, you can assume that
they don't use the same OCXOs, because those OCXOs were much better -- and
would have been more expensive -- than they had to be.  

(The Thunderbolt E should not be confused with the more common Thunderbolts
running 'E'-level firmware.)

-- john, KE5FX

> Hi, Paul. Glad to see you made it here. For the time-nuts; Paul and I
> have spoken about these issues, and I have had similar experience. The
> only thing I would add is the the spikes to seem to occur less
> frequently with a better antenna placement, but when they start to
> cluster, they fire off one every two or three seconds, sometimes
> faster.
> JimT
> On Wed, Feb 27, 2013 at 2:08 PM, Paul Berger <phb.hfx at gmail.com> wrote:
> >
> > Hello all:
> >
> > I am an electronic technician with 30+ years experience fixing
> > computers.   In my spare time I like to play with old computers and
> > electronics.  Recently I got bit by the precision timing bug, partially
> > after running across the wonderful leapsecond.com site, which lead me
> > here.   First I got  a FE-5680A, then after reading some of the archives
> > here I bought a Nortel / Trimble 45000   GPSDO and still later a used
> > Thunderbolt-E...

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