[time-nuts] Thunderbolt vs Motorola M12+T

Tijd Dingen tijddingen at yahoo.com
Thu Mar 17 14:01:26 EDT 2011

With regard to your mentioning of "a reference  is not 10MHz" ...
Suppose one is after a good quality ~ 375 MHz reference with low
jitter and high frequency accuracy, what would be the best bang
for buck time-nut approved way be?

For now I would settle for a 370 MHz reference, which would be
obtained by multiplying from a 10 MHz source from say a thunberbolt.
But possibly there are more economic ways to go about this...

----- Original Message ----
From: Chris Albertson <albertson.chris at gmail.com>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Sent: Thu, March 17, 2011 6:45:34 PM
Subject: Re: [time-nuts] Thunderbolt vs Motorola M12+T

On Thu, Mar 17, 2011 at 8:58 AM, Tijd Dingen <tijddingen at yahoo.com> wrote:
> Same here. A GPSDO like the thunderbolt is really nice from a system
> integration point of view. Buy an easy thingy kit on ebay, and you have
> your 10 MHz reference. However, cannot a lot be gained from using a
> more up-to-date design with newer gps engine?
> On the one hand we have a thunderbolt which you can view as blackbox
> that has a nice stable 10 MHz as output. On the other hand we have for
> example a Motorola M12+T where you have to do your own oscillator
> disciplining. At this point I am more inclined to go for the thunderbolt
> since it solves a lot of problems. However I feel that with a modern
> gps engine with better pps signal + a good quality XO you could get
> a better 10 MHz signal. Any thought/experience/tips?

I've only read reports of experiments and I think in general the
result is that there is an inherent limit to what you can expect from
a GPSDO that is around 10E-12 and that all the GPSDOs if you let them
run, get somewhat close to that limit.  What seems to matter the most
is the quality of the VXCO used.  So asking if the t-bolt or mt12 is
best may not be the important question as gps may not be not the weak
link, it's the oscillator.  That said I thing the quality of the GPS'
PPS determines how long you need to let the GPSDO run.

I've been thinking recently that if the ultimate goal is a reference
that is not 10MHz you might be best off building a GPDDO that runs at
the desired frequency then trying to lock to a 10MHz.

Chris Albertson
Redondo Beach, California

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