[time-nuts] OOPS on my wwv legal post

Bob kb8tq kb8tq at n1k.org
Thu Aug 30 09:53:45 EDT 2018


Hi

If you are talking about HF or VLF propagation, indeed the whole issue of what you 
trace to is relatively minor. In the case of GPS, it can indeed matter. The precision 
you can achieve is much greater with a satellite based system.

This difference is also at the heart of the way a number of modern systems use GPS
for time. They do very tight synchronization based on GPS. Doing the same level of
sync based on a HF radio signal just isn’t going to happen. Doing it off of a VLF signal 
that has traveled a thousand miles is also a non-starter. It’s not that VLF or HF is a 
bad thing. It’s just that the systems have been designed to take advantage of the 
precision that GPS (and the other systems) offer. 

Yes, I spent a lot of years locking things to Loran-C and getting the data from USNO
to correct for this and that. It was fun back in the day. It also was a lot of “hands on” 
work to get right. I’ve done the same process with WWVB, but Loran was always 
able to produce better results. Would it be fun to be 20 years old again? In some ways
sure it would. You would have to cherry pick a bit between the fun and the not so fun 
parts though ….

Bob



> On Aug 30, 2018, at 5:31 AM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> Since propagation issues quickly degrade both frequency stability and time
> accuracy, I see little point in worrying about the difference between UTC
> and UTC(NIST).
> 
> Of greater interest should be the meaningfulness of time transfer obtained
> with
> NIST's TMAS service.  It is apparently referred to UTC(NIST).   See:
> 
> 
> https://www.nist.gov/programs-projects/time-measurement-and-analysis-service-tmas
> 
> It's an interesting service; it has been in use at the Arecibo Observatory
> since soon
> after its inception (~5 years ago IIRC) to provide information relevant to
> decisions
> for  tweaking the observatory's H-maser's frequency.  TMAS revolves around
> "Common
> View GPS measurements".   A major down side (for most time-nuts, anyway) is
> the cost
> of the service, which is presently  in the neighborhood of $10k per year.
> 
> I have made inquiry regarding whether or not TMAS is also on the chopping
> block;
> nothing heard back so far.
> 
> Dana
> 
> 
> Dana
> 
> 
> 
> 
> On Thu, Aug 30, 2018 at 2:05 AM John Marvin <jm-tnut at themarvins.org> wrote:
> 
>> I was under the mistaken impression that WWV/WWVB had some type of
>> direct line to NIST in Boulder. However, when I toured the facility in
>> Fort Collins earlier this year, I learned otherwise.  The signals and
>> carriers are derived/synced from "ordinary" HP (possibly some more
>> recent Symmetricom's) cesium beam atomic clocks.  I wish I remembered
>> the details, but I asked how they synced them with NIST. I believe the
>> answer was that at one time they had some type of connection to Boulder,
>> but now just use a GPS based solution.
>> 
>> The WWV and WWVB stations in Fort Collins are old, and run on a fairly
>> tight budget, with a very small (but dedicated) staff. They are not on
>> the cutting edge of timekeeping technology.  I'm not trying to imply
>> that WWV/WWVB is "inaccurate", but there is nothing special there. Many
>> of the participants on this list, if they were determined, could put out
>> a signal every bit as accurate as WWV or WWVB, they just wouldn't be
>> able to do it at the power levels (especially WWVB) that WWV and WWVB
>> signals are transmitted at. The antenna's and transmitter's are some of
>> the most impressive parts of the WWV / WWVB facilities.
>> 
>> Regards,
>> 
>> John
>> 
>> P.S. I was also impressed with their backup generator, although I now
>> can't remember if that only provided power for the WWVB station, or for
>> both WWVB and WWV (they are separate facilities, although in easy
>> walking distance of each other on the same property).
>> 
>> 
>> On 8/29/2018 7:24 PM, Steve Allen wrote:
>>> On Wed 2018-08-29T19:49:59-0400 Bob kb8tq hath writ:
>>>> A few more details about “traceability”. USNO is by statute the
>> official source of time for the US.
>>> I suggest reading Matsakis, Levine, and Lombardi from this year's PTTI
>> meeting.
>>> USNO and NIST are both legal sources for the US.
>>> The USNO site currently has a broken SSL cert, but the paper is also here
>>> 
>> https://www.researchgate.net/publication/323600621_Metrological_and_legal_traceability_of_time_signals
>>> 
>>> --
>>> Steve Allen                    <sla at ucolick.org>              WGS-84
>> (GPS)
>>> UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat
>> +36.99855
>>> 1156 High Street               Voice: +1 831 459 3046         Lng
>> -122.06015
>>> Santa Cruz, CA 95064           http://www.ucolick.org/~sla/   Hgt +250 m
>>> 
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>> 
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