Message Order

[Jonathan Hutchins]

On Thursday 20 November 2003 01:39 pm, Zscoundrel wrote:

> If I REALLY needed a hyper-accurate time hack, I would build a little
> adapter to monitor the BCD (binary coded decimal) sub carrier
> transmitted with the WWIV short wave broadcasts.  It would decode the
> BCD signal, compute the miniscule time delays cause by the RF travel
> time from Fort Collins to my location, compare it to an internal time
> clock, and then update the  PC via USB or serial port.

That's what one of my references recommends - you just feed an audio signal to 
a simple pulse detector.  They did not adjust for the lightspeed propagation 
delay.  This was one of the methods used to measure the accuracy of NTP, 
which they found was sufficient to keep a system that was self-adjusting 
within 100ms.  They also found, however, that there was significant potential 
for a single NTP reading to be off by 300ms or more.  Add that up over three 
links and you've got most of a second of error on a level 3 server.

Again, this is only relevant if you have systems with independent time 
references that need a precise common time, or if you're doing something that 
needs a very accurate real time.