Re: [chrony-users] Accurately measuring clock drift

[Rob Janssen <chrony-users@xxxxxxxxx>]

I don't care what the length of the pulse is, but I do need the input solution on the PC
to support the very short pulses (not configurable) output by older GPSDOs.
Most solutions, including the one proposed by Miroslav, do not directly support that.
So you need extra circuitry.  The circuitry itself is simple, but it is always a drag to
package, power and connect it.  A dedicated board with a BNC that inputs the pulse
directly would be nice to have.
I presume the driving end is properly implemented in the GPSDO, and input termination
is easy.

Rob

On 6/22/23 09:32, Bill Unruh wrote:
> 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 |____ unruh@xxxxxxxxxxxxxx
> 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


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