[MAMS] [Mw] Computer clock

Sun Aug 30 08:37:11 EDT 2015

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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