[time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation

[John C. Westmoreland, P.E.]

Hello Everyone,

While we're on the subject - not to get too far off on a tangent - I have
been doing 'web-research' on this - but can someone recommend a great site
or reference for the specifications of the GPS signaling sent down by a GPS
satellite?  For instance, I learned that PPS for a military satellite and a
civilian satellite are not the same thing.  PPS meaning Precise Positioning
Service.

Thanks and 73's,
John
AJ6BC (Ham call sign)


On Mon, Sep 16, 2013 at 2:51 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> On Sep 16, 2013, at 9:48 AM, Jim Lux <jimlux at earthlink.net> wrote:
>
> > On 9/16/13 6:03 AM, David J Taylor wrote:
> >
> >>
> >> I am thinking about exact time measurement - getting your PPS edge
> >> exactly on the nanosecond.  People can add in the length of the cable as
> >> an offset, so they must also need to enter any delay through any
> >> filters, mustn't they?
> >>
> >> Agreed that for position alone it doesn't matter as much.  It's the
> >> antenna's approximate position which will be measured.
> >>
> >> Your points about dispersion in the filter, and temperature coefficient
> >> of delay are good ones.
> >>
> >
> >
> > It's trying to get nice flat group delay in the filter that causes all
> the issues with Light Squared.  *small*, *inexpensive* brickwall bandpass
> filters tend not to have nice delay properties, or at least ones that are
> temperature stable.  Spectrum regulators know this, of course, and assign
> adjacent services accordingly.
> >
> >
> > If you're only worrying at the few nanosecond level, you probably don't
> have to take into account continental drift (periodic resurveys of location
> to account for several cm/year?) and solid earth tides (on the order of
> 30-50 cm).  And, really, for a lot of applications, you're interested in
> relative timing, so the solid earth tide shift of 1-2 ns every day isn't a
> big deal.
>
> Well maybe it is….
>
> If
>
> 1) Your antenna is ~ 2 ns out of position
> 2) you have a small number of sats
> 3) Everything else is doing very well
>
> Then as you take sat's in and out of the mix, you will could get 2 ns more
> "pop" than you would have otherwise.
>
> Bob
>
> >
> >
> >
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