[time-nuts] Housing LPRO and Thunderbolt together

[brent evers]

Somewhat related to this, someone posted a link for 1U chassis a while
back.  I thought I saved the link, but can't find it, and since the
text of posts can't be searched from the archives, can't find mention
of it that way either.  If anyone has a decent source for 1U chassis
that I could mount a pair of tbolts in, I would appreciate it.  These
were generic 1U rackmount chassis - not 'server' chassis with a bunch
of preplanned holes.

Brent

On Fri, Apr 22, 2011 at 5:37 PM, WB6BNQ <wb6bnq at cox.net> wrote:
> Hi Pete,
>
> As Bob, K6RTM, pointed out the Thunderbolt and the Rubidium are two different
> animals all together.
>
> True, you can treat a Rubidium like it was a normal crystal oscillator, but it is
> not the same.  The Rubidium has a definite life span, the more you run it the less
> the life.  A high quality crystal oscillator, on the other hand, just gets better
> the longer you leave it on.  Aside from nominal electrical component failures, the
> crystal blank in a properly designed circuit has no short term failure mechanism and
> will last for decades with constant applied power.  The Rubidium’s life span is, at
> best, 10 years.  The question is how long was it running before you got it ?
>
> A high quality crystal oscillator has excellent short term specs but does have drift
> and aging functions that severely limit its use for long term purposes.  Long term
> meaning more than a few hours for the best.  That is where the Rubidium oscillator
> takes over as its drift function is measured in days to a month or more.
>
> For high quality measurements, the crystal excels for measurement times of less than
> 10 seconds, as the Rubidium is noisier in that time frame.  That is, for taking
> readings on a one second to second basis, such as with a high resolution time
> interval counter, the crystal excels.  However, if the period of the measurement is
> longer, then the Rubidium would be a better choice.  For portable purposes the
> Rubidium also excels as its retrace is much better than a crystal oscillator.  You
> also do not need to wait the thirty to sixty days for the crystal to stabilize.  The
> Rubidium will be very close to its original set point in about 20 minutes.
>
> Adding GPS to mix has its own issues.  First, you need to know the coordinates
> precisely or spend a couple of days getting a damn good fix.  The GPS is quite noisy
> in the short term and the oscillator that is steered by the GPS has that noise show
> up in its output.  That is mitigated by having a high quality crystal oscillator
> where the GPS control loop seldom makes corrections; perhaps once an hour or more.
> That is how the Thunderbolt works and depending upon its internal crystal
> oscillator, it may possibly be tweaked to perform better then the standard factory
> settings.
>
> As for use, it all depends upon what and how you’re making measurements.  With a
> nominal 8 or 9 digit counter, for example, you may not notice all of the above
> issues because they are typically beyond the resolution of the equipment in most
> cases.  In other measurement processes it may be of major concern.
>
> As for your project boxes, I would use the rack mounted box to house the
> Thunderbolt, distribution amps and perhaps a couple of other oscillators (like the
> hp 10811) along with quality power sources.  Because crystal oscillators like a
> constant operating condition, do consider battery power for the lab to handle those
> occasional mains power drops.
>
> I would use the portable box for the Rubidium oscillator and include a battery
> option depending upon your intent.  The emphasis should be to have very quiet and
> stable power supplies for both projects.  Even batteries have a fair amount of noise
> so make the mains power (and battery) voltage high enough to allow for running a
> quality regulation circuit.
>
> My two cents !
>
> 73....Bill....WB6BNQ
>
>
> g4gjl at btopenworld.com wrote:
>
>> I have a dilemma and wish to access the collective wisdom of the group to advise
>> a solution.
>>
>> I am building a clock generator based on a Thunderbolt. I have an LPRO and would
>> also locate this in the same enclosure. I will also add a distribution amp and a
>> divide chain in due course.
>>
>> The ultimate purpose of the set up is to provide a self contained clock
>> generator set for my other test equipment, and also an experimental workstation
>> for Rubidium and GPS disciplined experiments.
>>
>> Most of my other equipment is for 19-inch rack mounting.
>>
>> I have two potential solutions for housing the timing kit:
>>
>> 1. An old dismantled HP 4U scope chassis which will fit in with my other
>> equipment physically, and can be racked if necessary. The PSU would have to be
>> built into the same enclosure.
>>
>> 2. A pair of Anritsu instrument cases which once house a bit error test set. The
>> two units clip together beautifully, and are free standing. As there are two
>> units, this solution would allow me to build the PSUs in one case and the more
>> sensitive timing electronics in the other. These units cannot be racked on
>> account of their form factors.
>>
>> Both solutions will require me to do some bespoke metalwork, but that is no
>> problem for me and amounts to about the same amount of work for either solution.
>>
>> So what does the group advise? Is it vitally important to keep PSU components
>> isolated from the timing electronics? I want to create the least noisy clock
>> source given the components I have.
>>
>> Looking forward to hearing some opinions...
>>
>> Pete
>> G4GJL
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