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

unruh unruh at invalid.ca
Mon Mar 19 22:06:59 UTC 2012

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.)

> I guess I could measure a or simulate a level converter but my guess is
> that it adds only a few nano seconds of noise.   Fixed delays don't matter

Fixed unknown delays matter. And they will depend on temperature, on
aging of capacitors, on aging of transistors, on power supply voltages, etc. 

> Chris Albertson
> Redondo Beach, California

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