[time-nuts] Another "atomic" clock question

[Bob Camp]

Hi

If all you need is frequency to 0.1 ppm, then a zero beat with WWV under good conditions will take care of your needs. If you need 0.1 ppb then it’s going to be harder to do. I’m assuming you are already into the “harder” category and WWV does not do what you are after.

Like it or not time and frequency are joined at the hip. If you have trouble with one, it will show up in the other. 

If you want a “pure” frequency reference, you really only have one option - get a cesium beam standard and plan to replace the tube every so often. Even if you have one, there are still tweaks you would need to do to be *sure* it’s right.  That’s mostly hard in the bank account department. You’ll spend more on the Cs than on a car. 

The only practical / cheap way to get accurate frequency in your basement is by doing a time comparison. There are lots of sources of accurate time out there. Setting up for a time comparison is really no more difficult than setting up for a good frequency comparison. Both take some care and some time. There’s no free lunch. 

These days, GPS is probably the best way to get the job done. There are $100 (ish) boxes on the auction sites that will do it all for you. 

Bob

On Mar 1, 2014, at 9:04 PM, Bob Albert <bob91343 at yahoo.com> wrote:

> 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.
> 
> 
> 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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