[time-nuts] Symmetricom X72

Steve Rooke sar10538 at gmail.com
Sun Jul 25 08:02:22 EDT 2010


Sage advice Bill!

Heathkid, you don't need another Rb unit when you have 3 perfectly
decent ones! You really need a standard to calibrate your Rb units to,
a Trimble Thunderbolt is likely to be the cheapest choice for you. Bob
Mokia, fluke.l, on fleeBay sells them separately or as a starter kit
with everything there to get you going. Once you have this up and
running for quite some time and see that things are looking stable in
the Lady Heather application, then you can start to think about
calibrating the FEI-5680's but only after you have run them in well. I
don't know your counter but does it have an input for an external
reference source? If so you will be able to use the T'Bolt as an
external reference for it, providing the required reference is 10MHz.
If it's not, you can divide down the T'Bolt's output to match. If your
frequency counter has no reference input (apart from throwing it in
the bin) you should be able to engineer it into the instrument,
depending on your skill set.

So, first get yourself a frequency standard to work with, IE. a T'Bolt
or the like.

My 2c worth,
Steve

On 25/07/2010, WB6BNQ <wb6bnq at cox.net> wrote:
> 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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-- 
Steve Rooke - ZL3TUV & G8KVD
The only reason for time is so that everything doesn't happen at once.
- Einstein




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