[ntp:questions] Atomic Signal Transmitter/Repeater???

mitch at niftyegg.com mitch at niftyegg.com
Tue Sep 30 01:48:30 UTC 2014


On Monday, June 13, 2011 8:17:54 AM UTC-7, Chris Albertson wrote:
......
> 
> My purpose for getting WWWV is to compare it with GPS time and I hope
> maybe learn something about the atmosphere.  Any different in the two
> times must be because of the path delay.

Partly solved problem:
There are interesting ways to discover time delay data.
All you need do is keep the GPS receiver fixed in space.
Any apparent motion over time belongs to atmospheric changes.
The apparent wandering of multiple GPS receivers might give 
additional information.

GPS time is accurate and precise---
Research differential GPS.
   "http://en.wikipedia.org/wiki/Differential_GPS"
GPS assisted surveying has proven to have astounding
quality and many Automobile GPS devices have a parallel
receiver to collect current data and apply it.

Back of the envelope GPS reacts to picosecond time signals
to generate a default accuracy of 15-meter nominal accuracy 
and when augmented to about 10 cm in case of the best implementations.

The back of my envelope demands no wire longer than 15 meters
and if I am serious 10 cm (about 1.x nano seconds).  All logic and
amplifier delays insert additional errors and even when understood
must be stable over time and temperature. 

Inside a single GPS receiver clock deltas can be measured in picoseconds
even if the absolute time is +/- 100ns... 

Look hard at individual GPS receivers because many can lock on numerous signals:
"receiver that tracks both GPS and GLONASS satellites simultaneously. When using them together, the receiver has the ability to lock onto 24 more satellites than using GPS alone".   If you can extract the raw data
you can look for differential transit time data from all 24 paths. i.e.
does the local location appear to move as each satellite is added to or
removed from the computation.

Small systems like the Raspberry Pi now have GPS add on devices inspect the device driver code to see how much you can dig out of the hardware.  An old
Android phone likely has GPS hardware and Android is mostly open source.



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