[time-nuts] Symmetricom X72

WB6BNQ wb6bnq at cox.net
Sat Jul 24 18:11:00 EDT 2010


To Bob and Stan (W1LE),
[p.s. But not just to you two alone]


Why complicate the answers to Heathkid (now Brice KA8MAV) with a bunch of different directions that should only be decided after one gains enough knowledge and understanding (they are not the same) to properly grasp the subject matter ? ? ? ?

Clearly Heathkid needs some guidance.  The form should be to start out with the very basics and get his feet on the ground.  He already has three (3) Rb sources that should keep him busy for quite some time.  However, his counter is really junk from a lab point of view.  Nonetheless, even it can be useful if it is understood how to apply it after understanding its limitations.

What Heathkid needs to understand is it is not about equipment.  It is all about how to measure and account for errors and unknowns.  Actually, quite a daunting task depending upon the level of achievement.

I agree he needs some kind of external reference and I agree the Trimble Thunderbolt (Tbolt) would be the right item for his true reference.  Even the Tbolt has its issues that need to be understood.

He will also need a method of comparison.   The oscilloscope is a good start but very tedious.  Here Burt's project would help him a lot when Burt gets it done.  I guess he is close.  I guess, also, the PICTIC II would fit the bill after he understands what it is.

Still he needs to understand how to apply and use this stuff.  Confusing him with suggesting all of the different Rb sources available is only making him think a better one { relative statement } would be the answer which is not true.  His FEI-5680's are so much better for his particular level, it is not even funny.

What has not been asked of him is what are his goals and intentions.  If it is to just say you have an atomic frequency reference, then sit the FEI-5680 on the coffee table; job done.  One cannot be properly guided if the goals are unknown.

Bill....WB6BNQ


Bob Camp wrote:

> Hi
>
> The only way to be sure of what's going on is to have several (hopefully) accurate references. With at least three you can begin to guess how good they are.
>
> The TBolt is different from the Rb in a couple of regards:
>
> 1) It's short term stability isn't as good when locked tightly to the GPS.
> 2) It's long term stability is much better than the Rb when it's locked.
> 3) It's easier to tell what's happening with it if you hook up a PC and the Lady Heather (free) program.
>
> The Rb will need a couple of things to make it play right:
>
> 1) It's got to have a pretty good heat sink on it. An 8 x 10" piece of 1/4" aluminum is a reasonable start
> 2) It's got to be run for a while (possibly 24 hours) before it will be stable
> 3) You need to watch the lock, and lamp voltages to be sure it's not doing something crazy.
>
> My recommendation based on cost is the Efratom LPRO for a cheap Rb. They are in the ~$60 range and seem to work pretty well.
>
> Setup wise, I would get a TBolt in addition to the Rb. You need something to calibrate the Rb (and your counter TCXO) against. Both are "secondary" standards. They (unlike a Cesium) are adjusted to match a known good reference.
>
> Once you have the Rb and the TBolt, next step is up to you. Cesium is always an alternative, so's a Hydrogen Maser ....
>
> Bob
>
> On Jul 24, 2010, at 3:32 PM, Heathkid wrote:
>
> > Hello Bob,
> >
> > What would you recommend?  I already have three FE-5680A Rb standards (which I'm quickly learning likely aren't worth the powder to blow them to (*insert your own word here*).  Okay, that was probably my first mistake (thoughts?).
> >
> > My frequency counter is one I built from a kit from aade.com that has the TCXO option (although I had to tweak it myself so I have NO idea how close it is to any accuracy or precision).  I have access to some really nice HP counters at work so that's my next step is to try one of those.  My DFD4 measured the output of one of my 5680A's to 10.000.007 MHz after about a 10 minute warm-up.  I don't know which one is off.  Reading the specs on the 5680A's before I bought them looked like they were pretty decent.  I'm learning...
> >
> > So, what "reasonably priced" Rb standard would you recommend?
> >
> > Should my next step in this process be a Trimble Thunderbolt?  Am I starting over?
> >
> > Thanks...
> >
> > ----- Original Message ----- From: "Bob Camp" <lists at rtty.us>
> > To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> > Sent: Saturday, July 24, 2010 9:31 AM
> > Subject: Re: [time-nuts] Symmetricom X72
> >
> >
> >> Hi
> >>
> >> At least looking at the spec sheet it's not really very impressive.
> >>
> >> Bob
> >>
> >>
> >> On Jul 23, 2010, at 11:06 PM, Heathkid wrote:
> >>
> >>> Hello.  Does anyone have any experience with the Symmetricom X72?
> >>>
> >>> Thanks...
> >>>
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> >>
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