[ntp:questions] ntp server specs

David J Taylor david-taylor at blueyonder.co.uk.invalid
Wed Jun 15 05:30:16 UTC 2011

"C BlacK" <rblak at non.net> wrote in message 
news:G6KdnapTj_XCfWrQnZ2dnUVZ_oKdnZ2d at supernews.com...
> For our discussion, lets say there are many machine but the distance is 
> not going to me more that 100ft.

Then some top-of-the head sums might be:

100 machines - RS-232 input resistance, guess, 4K, all 100 in parallel 40 

Voltage needed, +/- 5V, so let's guess on a 50-ohm driver source.  Hence 
the drive voltage needs to be a little above +/- 10V, say 12V (still 
within RS-232 levels).

Strawman suggestion, based slightly on thin-wire Ethernet: find a driver 
which will supply (nearly) +/-12V into an open circuit, with a 50-ohm 
source impedance (i.e. it supplies +/-6V into a 50-ohm load).  Drive that 
signal into a piece of 50-ohm cable, with T-pieces used to tap off the PPS 
signal as required.  Terminate the far end of the 50-ohm cable with the 
resistance required to approximately halve the open-circuit voltage of the 
source, thus providing an approximately correct termination to reduce any 
reflections.  Take a look at the waveform to ensure that it's reasonably 

Doubtless others will come up with improvements on this scheme!


More information about the questions mailing list