[ntp:questions] Thunderbolt at NTP ref clock.

Mark C. Stephens marks at non-stop.com.au
Fri Aug 2 01:01:07 UTC 2013

You can control the thunderbolt PPS width with Lady Heather software:

Or build the TAPR fat PPS Pulse stretcher section on breadboard, not so complicated, just use the 1/2 of 74HC121 and a 74AC04 (or MAX232) to drive the serial port (or LPT port - less jitter) make sure any unused inputs are on the other 1/2 are tied to ground or pulled up to VCC.
The circuit for the 74AC04 can be lifted from the output section of the TAPR PPS distribution amp (TADD-3).
Or, you can use Just use the FATPPS circuit in its entirety - I built 3-in-1 custom PPS stretchers on one breadboard and it took me 1-2 hours.

Please drop me an email if you need me to express this in a circuit.


-----Original Message-----
From: questions-bounces+marks=non-stop.com.au at lists.ntp.org [mailto:questions-bounces+marks=non-stop.com.au at lists.ntp.org] On Behalf Of DaveB
Sent: Friday, 2 August 2013 5:11 AM
To: questions at lists.ntp.org
Subject: Re: [ntp:questions] Thunderbolt at NTP ref clock.

In article <ktcujr$vpc$1 at dont-email.me>, david- taylor at blueyonder.co.uk.invalid says...
> On 31/07/2013 20:36, DaveB wrote:
> []
> > The server is using 5 'net based servers at this time (my original 
> > GPS RX died) and is only just stable enough for what I'm doing.  
> > Sometimes due to asymetric ping times, it "wanders a bit" for an hour or three.
> []
> > Oh...  Though the time server is FreeBSD based, other boxes in my 
> > empire are a mixture of Windows and Linux, various versions types 
> > and requirements.
> >
> > Cheers All.
> >
> > Dave. (G0WBX/G8KBV)
> Dave,
> A small GPS with PPS I can recommend to you is this one:
>    http://www.adafruit.com/products/746
> At least here, on the top floor of a two-storey house in Scotland, it 
> gets enough signal to lock consistently.  Not too expensive, and 
> available from a UK stockist.
> http://proto-pic.co.uk/ultimate-gps-breakout-66-channel-w-10-hz-update
> s-mtk3339-chipset/
> A few hundred microseconds should be enough for your pulse, although 
> GPSs tend to use either 100 ms or 200 ms by default.  Easier to see on 
> a non-storage 'scope as well!  I'm pondering on making a driver and 
> having a terminated line running around the shack here (at pseudo 
> RS-232
> levels) for feeding PPS into all my PCs which have COM ports to get 
> the best time synchronisation.  AT the moment, those PCs which aren't
> stratum-1 have the poll interval set to 32 seconds to the local
> stratum-1 servers.
> I'm sure you know about the information on my site for FreeBSD, 
> Windows and Linux, but others may not:
>   http://www.satsignal.eu/ntp/index.html

Yes, well aware of your wonderful resource pages.  And thanks for the link to the adafruit site, I'd forgotten about them.

I now have a new-old-stock GPS-16 (with unmolested full length lead and original connector) should I need, but I may end up using that for similar needs in a mobile setting, hence my interest in using the TB to drive the shack NTP box.

Took a look at the TB's PPS signal last night, & yes, 20ns duration, and though it can be turned -ve (as in 0 to -5V) or off, the width can't be changed.

Too many toys, so little time. :)



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