[time-nuts] GPS Timing Source -- looking at buying

Hal Murray hmurray at megapathdsl.net
Fri Jul 9 01:26:53 UTC 2010


> I was just wondering if the following product: 
> http://www.triginstruments.co.nz/catalog/product_info.php?products_id=1302&os
> Csid=b80759ac903096c20d806ddeb3d71121

That's a Garming GPS-18 PC, the version that gets power from a cigarette 
lighter.  (What are they called now that lots of people don't smoke?)

> Would be good as a timing source for GPS -- does it have the necessary
> outputs and information out the serial interface to make a PC into a Stratum
> 0 timing device? 

What do you mean by "stratum 0"?  I'm assuming you mean for use with ntpd. 
The telephone industry has a different meaning.

There are two quirks in this area.

One is that the GPS-18 has been updated to the GPS-18x.  It's much more 
sensitive.

The other is to be sure to get a version with a PPS.  In particular, the USB 
version doesn't have it.

Lots of people use the GPS-18-LVC with ntpd.  Info here:
  http://support.ntp.org/bin/view/Support/ConfiguringGarminRefclocks

You have to provide power.  "Some assembly required.", but it's not a big 
deal if you know how to drive a soldering iron.

There are a couple of good links at the bottom of that URL above.


> Make a linux box into a master time source... It says I need windows XP and
> things, or is that just to configure and check connectivity.. 

Lots of people use the GPS-18-LVC without windows.


> EBU Timecode in LTC format (audio timecode) 

The NTP source code package includes a utility to make audio time codes.  
Look for tg2.c.  I don't know what EBU is, but that code might be a good 
place to start.





-- 
These are my opinions, not necessarily my employer's.  I hate spam.






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