[ntp:questions] site with lots of GPS's and accessories

Chris Albertson albertson.chris at gmail.com
Tue Mar 20 23:07:18 UTC 2012


On Mon, Mar 19, 2012 at 3:06 PM, unruh <unruh at invalid.ca> wrote:

> On 2012-03-19, Chris Albertson <albertson.chris at gmail.com> wrote:
> > On Mon, Mar 19, 2012 at 10:25 AM, Alby VA <albyva at empire.org> wrote:
> >
> >> On Mar 19, 12:12 pm, unruh <un... at invalid.ca> wrote:
> >>
> >> > The actual PPS signal at the PPS pin has a rise time of about 10ns,
> and
> >> > the Sure has a normal sawtooth timing signal, so that would indicate a
> >> > few 10s of ns accuracy from the Sure, but the conversion to RS232
> washes
> >> > that out
> >
> >
> > Does the conversion to rs232 add uncertainty or simply a fixed delay.   I
> > can't believe the conversion is so noisy.  it can be done with a single
> > 2n2222 transistor or if you care about speed find a faster RF transistor
> > that works at UHF.
>
> Probably delays, but also noise. If the signal ramps up very slowly,
> then the slightest noise on the line will cause the transition to occur
> early or late ( and there is always noise.)
>

That's true, but the raise time is about 10 nanoseconds.  I'd think that
even with noise the transition would occur some time within the 10ns
raising edge.


Chris Albertson
Redondo Beach, California


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