[time-nuts] Symmetricom X72

Bob Camp lists at rtty.us
Mon Jul 26 12:34:03 EDT 2010


Hi

One gotcha on the conversions: 

How close did they set the DDS before they shipped it. A few seem to do a
less than perfect job of it.

Bob


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Steve Rooke
Sent: Monday, July 26, 2010 7:54 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Symmetricom X72

Yes, it's because of the various types that you need to verify exactly
what you have. A number of them are made to customer specifications
with undocumented option numbers but if you have anything like an
option 8 then you have the 1Hz to 20MHz version. Beware that to
program the thing you need to provide +5V as well as the +15V to run
it. Along with the output options, there are a slew of options on such
things as ageing and temperature stability. If you have one from a
telecom's cellular tower, it's likely to be of higher spec.

Steve

On 26/07/2010, Bob Camp <lists at rtty.us> wrote:
> 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...
>>>>>>>>>>
>>>>>>>>>> _______________________________________________
>>>>>>>>>> time-nuts mailing list -- time-nuts at febo.com
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>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> _______________________________________________
>>>>>>>>> time-nuts mailing list -- time-nuts at febo.com
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>>>>>>>>
>>>>>>>> _______________________________________________
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>>>>>>>
>>>>>>> _______________________________________________
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>>>>>>
>>>>>> _______________________________________________
>>>>>> time-nuts mailing list -- time-nuts at febo.com
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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
>>>>
>>>> _______________________________________________
>>>> time-nuts mailing list -- time-nuts at febo.com
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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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>
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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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