[time-nuts] Serial port splitter s/w

David McGaw n1hac at dartmouth.edu
Wed Feb 26 12:10:33 EST 2014

Serial outputs can usually drive several serial inputs if the cables are 
short (to avoid reflections).  You can wire it yourself, serial out from 
the TB to both LH and NTP, serial in from LH only.


On 2/26/14 11:51 AM, David J Taylor wrote:
> I'm running Meinberg NTP on the Windows 7 x64 machine to which my 
> Thunderbolt is attached.
> I'd like to be able to share the serial port between LH and NTP so 
> that I can run the machine as an NTP Stratum 1 server locked to the 
> TB, and also be able to use LH to check things.
> I looked around the with Google, and saw *numerous" serial port 
> splitters. Which is recommended?
> Also what's the best way how to configure NTP to lock the the TB on a 
> serial port?  Do I need to modify the TB to deliver the PPS down one 
> of the serial data lines or will NTP work well by parsing the NMEA 
> time messages?
> Many thanks
> David Partridge
> =====================================
> David,
> Can't comment on the COM port splitters.
> For best results with NTP you need a PPS signal on the RS-232 DCD 
> line. Using NMEA alone is often worse than just Internet sync. Look 
> for a white flash with my Serial Port LEDs program:
>  http://www.satsignal.eu/software/net.htm#SerialPortLEDs
> The pulse needs to be rather more than a few microseconds - 100-200 
> milliseconds is typically used.
> Cheers,
> David

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