[time-nuts] Symmetricom X72

Heathkid heathkid at heathkid.com
Sun Jul 25 12:19:22 EDT 2010


Steve,

Thank you for your reply.

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.

The counter I mentioned (it's a DFD4 - modified with the tcxo as the "a" 
option wasn't available at the time) is not going to be my primary counter. 
It's just something I had laying around that I use when I'm working with QRP 
and QRPp rigs that don't have *any* frequency readout.  I've built a *lot* 
of tiny transceivers that are either xtal based or use a PTO (you have to 
learn to love the sound of the chirp but once people learn what it is I'm 
transmitting with they don't mind as much), or some other form of VFO.  So, 
a digital readout is quite helpful and necessary, especially with the PTO 
where the tuning takes place by screwing a 6-32 brass screw in and out of a 
coil.  That said, I did build it up as a "bench counter" and not a digital 
display.  It still does what I need it to do (for the ham radios) but there 
were some mods that were done if you look at the site 
(http://www.aade.com/DFD4A/dfd4a.htm).  The one I built is actually pictured 
there.  I know it's not very accurate, precise, or even all that stable. 
But... once I get a known frequency reference and accurately calibrate it... 
it'll be better.  Most likely right now it's off around 7 Hz but I usually 
operate on 40m so at 7.040 MHz +/- a few Hz isn't going to matter much (try 
adjusting a screw with a knob on the end of it to change the oscillator 1 Hz 
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).

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.

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".

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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>>
>>
>> --
>> 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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