[MAMS] [Mw] Computer clock

Sun Aug 30 10:58:18 EDT 2015

Fundamentally one can synchronize the local frequency standard to WWVB 
with a very long time constant control loop, like a day or by GPS which 
is the modern technique, then divide that standard to 32768 Hz and drive 
the computer clock with that. Then use the signal rise edges from WWVB 
to set the clock time. One could build a stand alone clock that does 
that with local high speed coupling to the computer like ethernet or 
USB. Best if the clock is the only data on that link. One can only 
eliminate the latency absolutely by having a really good frequency 
reference and taking it to Fort Collins for setting and clock 
synchronization and then taking it back home while its running and not 
drifting more than a part per 10^-12 per week. That is how the world 
time and frequency references have been synchronized. Much 
synchronization today is using the traveling clocks of the GPS.

The digital communications applications need timing tolerance because 
even with perfectly synchronized computers, the radio propagation paths, 
especially via the moon are not without variable delay.

73, Jerry, K0CQ

On 8/30/2015 7:37 AM, TexasRF at aol.com wrote:
> Is there no computer hardware add on that will keep the correct time
> directly without all these latency issues?
>
> I have spent some google time looking for such but nothing was found. Seems
>   like a really fundamental solution; what am I missing here?
>
> We can get our radios on frequency within 1 Hz at 10 GHz and have to
> tolerate 1 second or more errors in the computer?
>
> Seems something is wrong with this picture!
>
> 73,
> Gerald K5GW
>
>
>
> In a message dated 8/29/2015 9:31:50 P.M. Central Daylight Time,
> tomw at wa1mba.org writes:
>
> Most  amateur DX digital modes can syncronize with an error of one second
> (or  more) and still maximize the benefits that the mode offers.
>
> Time on the  cell networks is GPS based, and until recently there were
> two times being  reported. One was GPS time and one was actual time. They
> are different by  about 15 seconds (there have been that many leap
> seconds since the birds  were launched). There are very few phone
> applications which show seconds.  I talked one of the developers into
> putting a adjustment parameter into  the application to take care of the
> 15 second error. He did. In the past  two or three years Verizon switched
> to "corrected GPS" and so I changed my  app to about +1 second to get it
> dead on. I don't know what other carriers  do.
>
> Differences in TV delays come from a variety of sources, but most  of it
> is the encoders (at the source), recoders (at any processing in the
> broadcast network) and decoders (your TV). There is a lot of processing
> needed to encode and decode HDTV signals, and less expensive processors
> and more sophisticated algorithms may introduce more delay than  others.
>
> Of course 10 MHz and other WWV signals are only off by the  radio
> distance you are from the transmitter, and you cannot estimate the  time
> delay better than a few to a hundred milliseconds because of the  unknown
> path length for ionospheric bounces. WWVH does not get reflected  off the
> ionosphere, so you can calculate its 60 KHz distance (and delay)  very
> accurately and get time to better than a millisecond. So called  "Atomic
> clocks" and "Atomic watches" have a WWVH receiver in them. They  usually
> sample time at 1 or 2 in the morning when noise levels are lowest.  Even
> cheap timepieces like these can be quite accurate in the  morning.
>
> If you have an accurate GPS receiver, and it is doing the  correction,
> you should be able to get accuracy to better than 100  nanoseconds. Of
> course most HPS receivers do not have a data output port  to talk to your
> computer, and if they did, there would be a delay in that  communication
> that would have to be calibrated out.
>
> Network  (Internet) based time can be off all the time. The reason is
> that packet  delivery delay is random (within some boundaries).
> Technically, one  Ethernet packet could take infinite time to arrive, so
> there really is no  upper limit, but there are timeouts which will give
> up eventually. Good  software measures the ping (network response time)
> to and from the source  and compensates for it. The ping time is
> constantly changing. Only when  the network is in really bad shape do the
> pings exceed 1 second. Good  clock will keep time and re-ping when the
> source clock and local clock  vary by some threshold.  Typical clocks
> will just keep local time and  check the source on boot or once per hour,
> and that is good enough to keep  well within one second of accuracy. For
> fun you can ask your computer to  ping any network address and it will
> report the ping time. My windows  clock synchronizes every 7 days but not
> when booted. Mine has not  syncronized in 5.5 days and is off by 7
> seconds. I forced it to update and  it got to within 0.5 seconds. Crummy
> clock!
>
>
> Tom  WA1MBA
>
> On 8/29/2015 6:20 PM, Henry Hallam wrote:
>> If in doubt,  you can check http://www.time.gov/ which uses a browser
>> applet to  display the time from the official USNO time servers.  It
>> should  be good to about 1 second.  If that's not enough for you,
>> please  sign up to the time-nuts mailing list
>>   http://leapsecond.com/time-nuts.htm and be prepared to go down a
>>   rabbit hole... :)
>>
>> Henry
>>
>> On Sat, Aug 29, 2015  at 2:16 PM, Dave Sublette<k4to at arrl.net>  wrote:
>>> Sorry if  this seems off topic, but it does relate to the timing of
> sequences  ….
>>>
>>> I use a Mac Mini Computer.  The system clock  is synchronized
> automatically using
>>>
>>> time.apple.com<http://time.apple.com/>.
>>>
>>> If I look at the time  on my cell phone and compare the two, the
> computer is almost one minute faster  than the cell phone.  I thought cell phones
> were accurate.  Which is  correct?  Or…. how do I fix which ever one is
> wrong?
>>>
>>> Thanks,
>>>
>>> Dave,  K4TO
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