[time-nuts] Symmetricom X72

Bob Camp lists at rtty.us
Mon Jul 26 11:15:53 UTC 2010 

Hi

One issue with the FE's is they often show up as conversions. Various sellers take the 1 pps version and hack in a 10 MHz output. There is a lot of room for error in the conversion process.

Bob  



On Jul 26, 2010, at 7:06 AM, Steve Rooke <sar10538 at gmail.com> wrote:

> Brice,
> 
> On 26/07/2010, Heathkid <heathkid at heathkid.com> wrote:
>> Last night, as suggested by several people on this list... I ordered a
>> Trimble Thunderbolt from Bob Mokia, fluke.l so I should be in pretty good
>> shape there to get started once it arrives.
> 
> Sounds like your starting on the long path to time-nuttiness :) Bob
> has supplied a lot of stuff to people on this list and he will look
> after you if anything is amiss.
> 
>> The counter I mentioned (it's a DFD4 - modified with the tcxo as the "a"
> ...
>> anyway).  :)  By the way, when I built it, I calibrated it by zero beating
>> against WWV at 10 and 20 MHz.  That was the best way I had at the time and
>> if the DFD4 is now 7 Hz off after all these years... it's not doing so bad
>> (based on it's limitations).
> 
> Not bad considering it's a TCXO.
> 
>> So... that's what that counter is for and not for what I'm doing now.  I'm
>> currently looking for a nice/used HP counter.  Please don't think I'm going
>> to use the DFD4 for measuring my Rb standards.  It's a wonderful counter for
>> what it was designed for and that's it.
> 
> Dependant upon what your looking for in a counter, you could broaden
> your choices as there are other useful counters out there that may be
> more affordable but still as good. Try looking for a Racal-Dana 1992,
> preferably with the high stability option timebase (although these
> turn up seperately anyway and are a doddle to fit). It makes a nice
> footprint 1ns counter and can be referenced to your T'Bolt.
> 
>> I'm not giving up on the FEI's anytime soon.  I understand now that along
>> with the Trimble Thunderbolt (and a decent counter) I'll be on my way to
>> "getting started".
> 
> You'll have to see if those FEI's are the programmable types which can
> be set to produce frequencies up to 20MHz. Do they have jut the D'Sub
> connector or have an RF connector as well. There are different
> variants of these produced by FEI under the same product code.
> 
> 73 de Steve ZL3TUV & G8KVD
> 
>> 73 Brice KA8MAV
>> 
>> 
>> ----- Original Message -----
>> From: "Steve Rooke" <sar10538 at gmail.com>
>> To: "Discussion of precise time and frequency measurement"
>> <time-nuts at febo.com>
>> Sent: Sunday, July 25, 2010 8:40 AM
>> Subject: Re: [time-nuts] Symmetricom X72
>> 
>> 
>>> Excuse my replying to my own posting please.
>>> 
>>> This post is really about the DFD1 frequency counter.
>>> 
>>> Heathkid: You are comparing a Rb against a frequency counter with a
>>> TCXO that you tweaked yourself to calibrate it against no known
>>> frequency standard. Try running the three FEI-5660s for 24 hours and
>>> then measure the output of each with your frequency counter. Pick the
>>> mean of them and adjust your DFD1 to match that. At least you should
>>> be in a better position than you are now.
>>> 
>>> As you built the DFD1 yourself, you should have the schematic and may
>>> be able to engineer in a connection for an external reference. There
>>> is plenty of people here who would be happy to advise you on a
>>> suitable interface if you can attach the part of the circuit where the
>>> TCXO is located. If you do get a T'Both, you would be able to use it
>>> as a reference or, perhaps, build in one of the FEI-5660s as an
>>> internal reference. The limiting factor though is how good is the
>>> circuit used in the DFD1 which will limit it's stability and accuracy.
>>> There are many factors, including input circuit, voltage regulation,
>>> counter stage design, level detection, etc. which have a major impact
>>> here. What I'm getting at is that to write-off a bunch of FEI-5660s
>>> after checking them with such a device as this, is a very poor
>>> decision.
>>> 
>>> Maybe you could look at a better counter on fleeBay before you make
>>> further assumptions.
>>> 
>>> 73,
>>> Steve
>>> 
>>> On 26/07/2010, Steve Rooke <sar10538 at gmail.com> wrote:
>>>> 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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>>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
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>>>>>>> 
>>>>>>> 
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>>>>>> 
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>>>>> 
>>>>> 
>>>>> _______________________________________________
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>>>> 
>>>> 
>>>> --
>>>> Steve Rooke - ZL3TUV & G8KVD
>>>> The only reason for time is so that everything doesn't happen at once.
>>>> - Einstein
>>>> 
>>> 
>>> 
>>> --
>>> Steve Rooke - ZL3TUV & G8KVD
>>> The only reason for time is so that everything doesn't happen at once.
>>> - Einstein
>>> 
>>> _______________________________________________
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>> 
>> 
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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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