[time-nuts] new member with questions NTP, PRS, GPS, ocxo

[Chris Albertson]

On Fri, Aug 17, 2012 at 6:12 PM, Frank Hughes <hp_ciscovss at yahoo.com> wrote:

> So what I am trying to come up with now for home/shack is:
> - An NTP server for our LAN
> - A very high quality 10Mhz source to distribute to all the HP and Agilent equipment here.

Here is what I would do again,...

1) first get the NTP server running but use pool servers from the
Internet as the reference clocks.  Get this working well before you
attempt to set up a GPS.   But when you choose a computer make sure
that it has an RS-232 serial port.  Accuracy is more then an order of
magnitude better then a USB hookup.   It fack USB is so poor you can't
take full advantage of GPS.   I use an Intel Atom board.  I got the
one that uses a pasive heat sink and it only burns a very few watts.
This matters becaue it runs 24x7.  A big PC can cost $40 a month to
run.  The best OS to use  is either BSD or Linux.  These have order of
magnitude better performance than others for this purpose

2) Find a place for a GPS antenna.  It should be able to see to the
horizon all 360 degrees.  Well if you live in the USA some blockage to
the North is OK.  Put it on a short mast and as a ham you know about
lightening and grounding and so on..  Don't skimp on that.   3/4 iron
plumbing pipe with a pipe flange on top makes a perfect mast and you
can run the cable down the pipe.   Getting a good view of the entire
sky helps a lot.   Although it can work even just looking out a
window.    The 75 ohm double sheiled cable TV coax works well and is
cheap.

3) Buy a Trimble Thunderbolt GPS from eBay.  These are the best and
easy to use and cost maybe $125.  They produce a very good 10MHz
output from an internal OCXO.  They also have a one pulse per second
output and of course serial rs-232

4) Finally connect Thunderbolt's PPS and serial data to the computer
and edit the NTP config file to add the GPS.  Keep the Internet pool
servers.

Chris Albertson
Redondo Beach, California