[time-nuts] Trimble Thunderbolt 1pps

Björn bg at lysator.liu.se
Sat Jan 4 15:45:01 EST 2014

The RIPE ntp system does a little bit of this.



<div>-------- Originalmeddelande --------</div><div>Från: Brian Lloyd <brian at lloyd.com> </div><div>Datum:2014-01-04  19:26  (GMT+01:00) </div><div>Till: Discussion of precise time and frequency measurement <time-nuts at febo.com> </div><div>Rubrik: Re: [time-nuts] Trimble Thunderbolt 1pps </div><div>
</div>On Sat, Jan 4, 2014 at 12:05 PM, Hal Murray <hmurray at megapathdsl.net> wrote:

> albertson.chris at gmail.com said:
> > Where those using the cat-5 wire as a twisted pair?  If sothat's
> "cheating"
> Yes.  I was thinking that 4 pairs would be Rx, Tx, PPS, and power.  If I
> need
> Ethernet, I'll pull another Cat-5.

Pulse quality of single-ended RS232 over unbalanced twisted pair is going
to be pretty bad beyond a few feet. If you want to transport the 1pps over
twisted pair there are a couple of options:

   1. A BALUN. There are lots of 75ohm-to-CAT5 BALUNs out there
   specifically for transporting NTSC video over CAT-5. At the far end use
   another BALUN before running into a TTL-to-RS232 line driver. There should
   be sufficient drive without too much extra hardware. (Terminate into 75
   ohms tho'.)
   2. Use an RS-422 driver. This will accept the TTL-level 1pps in and
   produce a nice differential output to drive the twisted pair. You can find
   serial cards that have RS-422 line receivers that will plug directly into
   the PC.
   3. Simply use coax that is properly terminated at the far end to drive a
   TTL-to-RS232 line driver right at the computer's RS-232 input.

All three of these should result in an acceptable 1pps with jitter levels
lower than the timing resolution of the NTP server you are running on the
target machine.

Brian Lloyd, WB6RQN/J79BPL
706 Flightline Drive
Spring Branch, TX 78070
brian at lloyd.com
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