[ntp:questions] ntp server specs

Chris Albertson albertson.chris at gmail.com
Tue Jun 14 19:52:43 UTC 2011

>> <http://www.ptsyst.com/TT-10188-B.pdf>
> <http://www.tapr.org/kits_tadd-3.html>

The problem with both of those is that the Linux machines are all
going to want the PPS to be conected to the DTR pin of a serial port
and for that you need rs-232 levels with wides plus and minus volts.
TTL level or wose is not going to work.

So either your distribution amp needs to swinge from about +9V to -9V
or you will need a level converter at each Linux machine.

What to do depends on what other equipment you have.  Most electronics
(other then a computer) will want the 0 to 5V TTL level pulse or maybe
a 3 volt pulse.  With mixed equipment in a large lab you's want the
local level converters but if you know that every user of the PPS is
going to need rs-232 then build that into the amp.

For very long didtance runs you'd need the level converters because
you'd have to send the PPS as a differential signal maybe using rs442
drivers and receivers.

I use an RS232 level signal on Cat-5 network cable and it will go 100
feet with no problem.  Iuse the common  TTL->RS232 chip made by Max as
the "amplifier"   I found a source on ebaywho sells this chip and the
required capasitors built onto a DB9 connector for just a few bucks.

Chris Albertson
Redondo Beach, California

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