[time-nuts] Reference oscillator accuracy

[Don Latham]

The ground wave path of WWVB varies due to a very small changes in the
index of refraction (temperature and absolute humidity) over the path. It
is not much, but is measurable.
Don

paul swed
> I use GPS and LORAN. Always nice to have a backup
> With LORAN being shut down, have resurrected the ole wwvb rcvr and built
> an
> amplified loop ant.
> Can work but it takes about 3-5 hours to get to 1X10^11 accuracy. Still
> observing various strange ness shuch as diurnal shift ...
> Odd wwvb works at least for me most stable in the day. I seem to remember
> night was supposed to be better.
> The signal is much stronger at night.
> So I guess its a play but sure not as easy as gud ole LORAN C has been.
>
> On Fri, Nov 13, 2009 at 12:48 PM, Brian Kirby
> <kilodelta4foxmike at gmail.com>wrote:
>
>> You will need a receiver to compare your references to.  It appears that
>> LORAN will be shut off, so that leaves two services available, either
>> WWV 60
>> Khz or GPS.  I do not use WWV any more, I can tell you about GPS.
>>
>> To compare against GPS you will need a timing receiver, there are
>> several
>> available.  A lot of us got Motorola Oncore VPs, UTs, or M12+, The
>> Rockwell
>> Jupiter is one and there are several more.  They provide a 1 PPS signal
>> that
>> is locked to the on board standards on the GPS satellite.  You put this
>> signal in one input of a time interval counter.  You use a 1 PPS divider
>> on
>> your local reference and put its signal in the other input of the time
>> interval counter.   You can record continuous or take daily 24 hour
>> readings
>> and derive your drift rates.
>>
>> GPS corrections are published at NIST;
>> http://tf.nist.gov/service/gpstrace.htm
>>
>> You can also compare against a GPS disciplined oscillator.  In the long
>> term it should be dead on, you will have to have it characterized for
>> the
>> short term.  The HP Z3801A was on the surplus market several years back,
>> its
>> probably one of the best.  The Trimble Thunderbolts were available to
>> the
>> group a while back.
>> Brian KD4FM
>>
>>
>> Glenn Little WB4UIV wrote:
>>
>>> While I was in the US Navy we had two Cesium standards for the
>>> navigation
>>> center on SSBN submarines.
>>> While in port, we would track LORAN C and compute the drift rate of the
>>> two cesium standards.
>>> Is there a service, that has drift rates published, that I can compare
>>> my
>>> standards to, so that I can determine the standard drift rate.
>>> I do not remember the drift rates that we determined on the submarine,
>>> that was a few years ago, but, I seem to remember that the rate was in
>>> the
>>> low nanoseconds.
>>> If a rubidium standard drifts in one direction (does it?) a drift rate
>>> could be calculated and, after a comparison to a known standard, with
>>> known
>>> drift rate, a very accurate standard could be had for the lab.
>>>
>>> What would I expect the drift rate, or jitter, to be in a FRK class
>>> rubidium oscillator?
>>>
>>> Is the drift rate constant enough that a drift rate could be applied to
>>> a
>>> rubidium oscillator to determine it's real frequency at any given time.
>>>
>>> We calibrated the submarine Cesium standards every three months.
>>> We had to know the drift rate of our standard as well as the drift rate
>>> of
>>> the standard in each of the LORAN stations to be able to do the type of
>>> LORAN navigation that we did.
>>>
>>> I would like to be able to verify that my PTB-100 rubidium oscillator
>>> is
>>> on frequency.
>>>
>>> If I compare two rubidium oscillators, what would I expect the relative
>>> drift rate to be?
>>>
>>> Thanks
>>> 73
>>> Glenn
>>> WB4UIV
>>>
>>>
>>>
>>>
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-- 
Dr. Don Latham AJ7LL
Six Mile Systems LLP
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POB 134
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