[time-nuts] Another "atomic" clock question

GandalfG8 at aol.com GandalfG8 at aol.com
Sun Mar 2 06:45:49 EST 2014


In a message dated 02/03/2014 02:07:05 GMT Standard Time,  
bob91343 at yahoo.com writes:

All this  is very interesting.  However, my interest is frequency.  In 
other  words, I want to know that my standard oscillators are as close to 
desired  frequency as possible, and how close that turns out to  be.
-------------------------
 
Hi Bob
 
Without wanting to get bogged down in questions of how long is a piece  of 
string and close is close etc etc, I do think your best starting point would 
 be a GPS frequency standard.
 
Nothing is ever perfect, but without reliable access to alternatives, such  
as Loran or WWVB and its equivalents, a GPSDO is still just about the only  
option available at anywhere near a sensible price that is likely to do  
what you're asking.
 
It shouldn't mean either that buying one automatically excludes the  option 
of eventually building your own, or otherwise getting more  deeply involved.
Once started on the slippery slope there's more than  enough opportunity 
for experimentation with well proven designs and  concepts aready out there to 
provide endless fun,  and/or frustration:-)
After that there's no telling where you might end up:-)
 
It is true, as has been stated, that the Trimble Thunderbolt isn't  quite 
the economic entry point it once was, but that doesn't mean there  aren't 
viable alternatives.
One good example is the Trimble Nortel NTGS50AA, as can be found  in Ebay 
buy it now 291054324150 and often for a bit less in  auctions from the same 
seller.  
These might be getting a bit long in the  tooth, there has been some 
experience of oscillator's having aged  to outside the unit's EFC range, although 
they generally do work "out of the  box", even though there isn't one:-), 
but the seller is helpful and should  it prove necessary the oscillator can be 
changed with a bit of care.
 
As a bonus, Lady Heather, she of Thunderbolt  whipping fame, can also knock 
these into shape, and there's plenty  of existing users here with 
experience of them.
 
There is then, of course, the consideration of  how you compare your 
oscillators with the standard, do you have or do you invest  in an appropriate 
frequency counter?, do you have or do you invest in a suitable  'scope plus the 
necessary time to monitor the drift?, and so on and so  fifth.
 
What was that about the length of a piece of  string?:-)
 
Regards
 
Nigel
GM8PZR
 
----------------------------





Yes, the Internet gives me time of day as close as I  care to know.  I have 
an 'atomic' clock from LaCrosse that resets itself  nightly, although it's 
fussy about where in the house I put it.  If I put  it where I'd like, it 
won't receive WWVB, so I put it across the room.  I  called the company 
inquiring about augmenting the internal antenna but they  were of no help.


While watching the clock and listening to WWV, it  seems the clock is a 
fraction of a second behind.  Even that doesn't  matter, but calibrating the 
counter time base is another kind of  thing.

I am trying to understand how this is done.  Should I ever  get a rubidium 
standard, I'd want to check its calibration, and that's not a  trivial 
exercise.

Bob




On Saturday, March 1, 2014  4:56 PM, Paul Alfille <paul.alfille at gmail.com> 
wrote:

There are  WWVB clocks with serial output. Arcron made one that I added
linux ntp  support for some years  back.
http://www.atomictimeclock.com/radsynarcron.htm

http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver27.html

As  I recall, it was under $100, quite nicely styled, and is sitting here on
my  desk. (Reception on the East Coast can be spotty, so I've switched  to
standard internet net time source).






On Mon,  Feb 24, 2014 at 7:44 AM, Bob Camp <lists at rtty.us> wrote:

>  Hi
>
> Ok, so 0.1 second at the sync point is indeed a reasonable  estimate. If
> that's all you need to deal with (you correct out the  crystal offset one
> way or the other) then:
>
> At 1 day  you have 11.5 ppm accuracy. Roughly a 100 Hz beat note with WWV
> at 10  MHz.
>
> At 10 days you have 1.15 ppm. Roughly a 1 Hz beat note at  10 MHz.
>
> At 100 days you have 0.115 ppm. That would be about a  10 second period
> beat note.
>
> None of that is to say  that a beat note is all there is to getting
> accuracy off of WWV or  that the two approaches deliver the same net
> accuracy. Yes I've done  the 10 second beat thing, it can be done with 
care
> and a good stable  WWV signal.
>
> Bob
>
> On Feb 23, 2014, at 5:21 PM,  Tom Van Baak <tvb at LeapSecond.com> wrote:
>
> >> Now  that you have brought up this subject, do you know of any way to
> use  these LaCrosse clocks to calibrate frequency standards?
> >
>  > I suggest using a direct electric (1.5 VDC high-Z) or indirect  
magnetic
> (high gain) pickup on the coil to get the +/- pulse per  second. Compare
> this time with your local frequency standard and over  several days you
> should get accuracy better than 10 ms per day (1e-7).  Here's an example 
of
> a raw phase plot:
> >  http://leapsecond.com/pages/Junghans/
> >
> > /tvb
>  >
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