Re: Accurately measuring clock drift

Why do you care what the lengthof th epulse is? The time is the in the
transition not in the length of the pulse. To reduce that error you wnat to
make sure that you use Impedence matching in cable connecting the gps receiver
to the computer.That aloso means that you power supply needs to handle
relatively high currents, since the cable impedance tends to be low ( 50 ohm,
300 ohom, the forver would require a pulse current of .1Amp).

But that assumes you do not want the pusle rise smeared out from its few
nanosecond rise time  at the gps receiver.

William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
UBC, Vancouver,BC _|_ Program in Cosmology |____ [email protected]
Canada V6T 1Z1 ____|____ and Gravity ______|_    theory.physics.ubc.ca/

On Wed, 21 Jun 2023, Rob Janssen wrote:

> [CAUTION: Non-UBC Email]
>
> Miroslav,
>
> Are you aware of any affordable PCIe card that supports PPS input on a generic PC server?
>
> Ideally would be like this:
>
> - TTL input of a PPS signal with minimal pulse length all the way down to 100ns
> - some hardware time stamping method
> - supported interface to chrony
> - maybe even a serial port in addition
>
> That would be ideal to interface an external GPSDO to a Linux server with best accuracy,
> like for simulcasting.  We could use a couple of these in our network...  it would work better
> than the RS232 DCD input that we use now, avoid the need for a "pulse stretcher" as is
> now required with some types of GPSDO, and custom cables to feed the signal in the RS232
> port that is already used for many purposes.
>
> It seems like something that could be easily designed, but of course any low-volume PCIe
> card tends to be quite expensive...  and cards from the well known manufacturers in this
> field are way outside our budget.
>
> Rob
>
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