[time-nuts] Equipment question: OCXO versus GPSDO + XTAL

WB6BNQ wb6bnq at cox.net
Sat Mar 19 05:34:19 UTC 2011


Well Wolfgang,

You’re A/B scenario does not make sense to me.  I am getting the impression that
you think there is a third oscillator in the “Timebase” selection.  From reading
the manual I only see two selections; the first is the standard supplied
oscillator which is the “TCXO” and the only selectable option is the high quality
OCXO.  BUT, as you stated the question, NO, I cannot think of a scenario where
“B” would exceed “A.”  Cases do exist where having an oscillator wander around a
bit can be used as a dither function, but the circumstances where I seen it used
would negate having 12 digits of resolution.

In reviewing the specification of the 53230A, the internal 53230A timebase is
phase locked by the external reference source when using the external or auto
modes.  So you do not have a “direct-drive” function when using the external
reference (i.e., a distinctly separate source).  I wonder about the added noise
the PLL circuitry could possibly add.  I would suspect it to be worse with the
TCXO compared to the OCXO option.  After buying such a sophisticated instrument,
it would be a shame to settle for the cheap hubcaps.

Just my two cents !  I could be all wet.  Maybe we all will lucky and Bruce will
chime in here and give us a well educated response.  If he does it would be worth
paying attention to.

73....Bill....WB6BNQ



Wolfgang Wieser wrote:

> Hello all,
>
> first, thanks for all the answers!
>
> Maybe let me ask the more fundamental question: Completely independent
> of use scenarios and so on: Assume device A uses standard reference tied
> to ultra-stable zero-drift magic 10 MHz refclock. Device B uses TXCO option.
>
> Is there any measurement type with any strange setup that you could imagine
> where B outperforms A just because the combo "standard XO + refclock"
> is inferior in any respect compared to "TXCO". (Lab/shop equipment,
> no portability needed.)
>
> I mean - not necessarily for this particular Agilent 53230A but for anything
> of this type and class.
>
> @Bill:
> thanks - exactly the type of advice/opinion I was hoping to get.
>
> @Paul Swed:
> > Unfortunately in the first round of the thread you did not say what you are
> > actually doing with the system and whats important to you.
> Measuring time and frequency? Maybe there are some unknown issues that I am
> not aware of but what I would like to know is whether for any usual
> measurement made with a timer/freq counter the choice of XO+refclock could
> be inferior to TXCO. If there are significantly different scenarios in
> your mind - it would be nice to let me know for what type of measurement
> you think that the one is better and for what not.
> Anything except portability issues?
>
> > The last answers actually the best considering the base system initial
> > investment.
> Well, once a year I buy something more expensive...
> However, while 2500 EUR seems reasonable for the counter, additional
> 1000 EUR seems a bit much for the OCXO option.
>
> @Joe
> > You will have to look at the stability measurements of the OCXO versus the
> > GPSDO to choose that one.
> OK, do you have an educated guess about the outcome of that?
> Because acutally doing this comparison exceeds my scope ATM.
>
> @Greg
> > My opinion is that first you need to tell more about how you
> > are going to use this counter. For work in the shop where
> > a distributed reference is always available (...)
> >
> Hm.. OK.. I re-formulated into the question on the top.
>
> > I am suspicious of the note that this OCXO upgrade can only
> > be done at the factory.  See if you can get the control sequence
> > to cause reference autocal.
> I've got a test unit ATM and there actually is a security code to
> unlock the calibration. I don't know the code right now.
>
> - Wolfgang, DL1SKY
>
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