[time-nuts] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.

Tom Miller tmiller11147 at verizon.net
Mon Sep 15 15:04:23 EDT 2014

So does adding ~80 pF per meter or 8 nF for 100 meters (RG58) to your output 
have any effect on the risetime? Because that is what it will see with an 
open cable.

I am sure you can make a case for some condition(s) where an unterminated 
cable will still work. But it is not something we have been shown necessary 
to make precise measurements (something this group strives for).


----- Original Message ----- 
From: "Mike S" <mikes at flatsurface.com>
To: <time-nuts at febo.com>
Sent: Monday, September 15, 2014 10:29 AM
Subject: Re: [time-nuts] Correcting jitter on the 1 

> On 9/15/2014 10:01 AM, Tom Miller wrote:
>> Fast risetime pulses _are_ RF and need to be treated as such.
> You say that as if simply saying it provides an explanation, or even a 
> reason. Exactly what ill effect on a triggered measurement is there if one 
> does not terminate a PPS signal properly? Does/can termination increase 
> the slew rate or make the speed of propagation more consistent, which 
> might make the measurement more accurate?
> Like Tom said, what comes after the leading edge of a PPS signal (which is 
> the measurement trigger) seems irrelevant.
> A simple though experiment. If I take a high impedance measurement at a 
> tap 1M from the source, and the cable ends another 100M away, how can the 
> termination or lack thereof at that end effect my measurement of a single 
> event? It's over 700 ns round trip away? If I repeat that event 1/sec, is 
> it any different? I can see where there would be a difference when I get 
> close to a 700 ns cycle time, and likely before because of "ringing." But 
> for a 1 second cycle? Someone will have to provide more than a dismissive 
> "just because" to convince me.
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