[time-nuts] GPS Antennas

[John C. Westmoreland, P.E.]

To the OP, Dan,

Just curious - do you use something like this:
https://endruntechnologies.com/products/antennas-accessories/lightning-arrestor


Good luck with the new antenna.

73's,
John
AJ6BC


On Sat, Sep 7, 2019 at 3:17 AM Björn <bg at lysator.liu.se> wrote:

> https://www.ngs.noaa.gov/ANTCAL/#
>
> Look at say an old Ashtech ASH700936D_M which you can find calibrations
> for both SCIS and “Snow” radomes and without radome for the same antenna.
>
> I have seen more recent radomes that are hemisphere-shaped. However these
> are more prone to be favored bird view points.
>
> Radomes, like the Aeroantenna SPKE with a plastic “spike” to discourage
> birds are less ideal for super high accuracy applications due to its non
> uniform signal delay impact.
>
> See also clear acrylic domes OSOD/OSOS
>
> http://www.euref.eu/symposia/2015Leipzig/p-02-01-Ohlsson.pdf
>
> https://kb.unavco.org/kb/article/unavco-resources-radomes-520.html
>
> /Björn
>
> Sent from my iPhone
>
> > On 7 Sep 2019, at 02:54, Bob kb8tq <kb8tq at n1k.org> wrote:
> >
> > Hi
> >
> > Based on the papers I have seen, there is no “magic” shape that can be
> ignored.
> > Part of the issue is that the cover is going to be in the near field of
> the antenna.
> > As noted in another post, the impact is more complex than a simple
> delay. ( consider
> > that signals bounce off the cover material …. ).
> >
> > Also consider that if I’m going to 3D print the device, I have a limited
> number of
> > materials available. Teflon isn’t going to run through a 3D printer.
> Unless you paint
> > the gizmo it will not be water tight so humidity will get into the act
> as well.
> >
> > =====
> >
> > A “good” GPS antenna should have roughly the same phase center
> regardless of
> > the angle to the sat it’s receiving. Indeed GPS antennas in general get
> this right.
> > There is a modest variation with angle, but it’s not all that great.
> Units of mm are not
> > uncommon. It will be greater on a multi band design. The impact of your
> cover also
> > will be greater on a multi band device. All the various delay /. loss /
> reflection parameters
> > are frequency dependent…..
> >
> > Bob
> >
> >> On Sep 6, 2019, at 5:57 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> >>
> >>
> >> kb8tq at n1k.org said:
> >>> The gotcha with putting anything on top of a GPS antenna is that it
> impacts
> >>> the phase  shift from the sat’s. How important that is gets quickly
> into just
> >>> how picky you happen to be.
> >>
> >> How picky do I have to be before that is significant?  How geeky would
> I have
> >> to be to measure it?
> >>
> >> Would a hemispherical cover provide equal delays at all elevations?  I
> think
> >> the solidly mounted USGS fault/volcano monitoring setups have a round
> top.
> >> https://www.usgs.gov/media/images/gps-tracks-ground-deformation
> >>
> >> Do any antenna manufacturers advertise uniform phase delay?
> >> Do any software vendors advertise that their software works better with
> >> specific antennas?
> >>
> >>
> >>
> >> --
> >> These are my opinions.  I hate spam.
> >>
> >>
> >>
> >>
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