[time-nuts] Trimble Thunderbolt 1pps

[paul swed]

OK I can add something here.
Yes the spec is correct. But modern receiver chips actually can work with
single side signals. You have to look at the specs of the chip to see what
they will do.
Granted noise immunity is much lower but for most of us in the 10' run
distance its good enough. I operate this way on lots of things.

Seriously sleazy way to get +/- swings as long as the data flows somewhat
all of the time like GPS. Put the unipolar signal through a 1-10UF cap.
Smaller is better to a point.
Did I really suggest that. Will never admit it.
Regards
Paul.
WB8TSL


On Mon, Jan 27, 2014 at 9:08 AM, Attila Kinali <attila at kinali.ch> wrote:

> On Sun, 05 Jan 2014 13:35:43 -0800
> Hal Murray <hmurray at megapathdsl.net> wrote:
>
> >
> > attila at kinali.ch said:
> > > Also keep in mind that RS-232 relies on the voltage going negative to
> encode
> > > a "1". I.e. getting 0V is not enough and might only work by chance
> with some
> > > RS-232 receivers.
> >
> > I think there are 2 parts to this discussion.  What do the specs say, and
> > what actually happens in the real world?
> >
> > I think the specs say that -3 to +3 is no mans land.  A valid signal
> must be
> > over +3 or under -3.
>
> IIRC that's right. But i haven't had a look at the standard for a very
> long time.
>
>
> > In practice, the receiver chip only has one power supply.  It would take
> > extra work to make the switching threshold below ground.
>
> That's not correct. Standard transceiver chips (like the MAX232 family)
> have an integrated charge pump to get a negative power supply.
>
> I have never done exact measurements, but my experience is that going
> a bit (0.5V?) below GND and slightly more above GND is enough to get
> a proper 1/0 detection. Of course, if you rely on that you get a very
> poor noise performance.
>
>
>
>                         Attila Kinali
>
> --
> The trouble with you, Shev, is you don't say anything until you've saved
> up a whole truckload of damned heavy brick arguments and then you dump
> them all out and never look at the bleeding body mangled beneath the heap
>                 -- Tirin, The Dispossessed, U. Le Guin
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