[time-nuts] Re: GPS Elevation Mask Values.

[Dana Whitlow]

In fact, I believe that the satellite positions shown on screen plots are
those
calculated from almanac data.  My reasoning is that most GPS receivers
seem able to put up such plots first thing after turn-on, before ephemeris
data from even a single satellite is available.

IMO, if the almanac positions differ from ephemeris positions enough to
be resolvable on such plots, either the whole GPS system is in deep trouble,
or the receiver in question has not been turned on for a very long time.

Dana

On Mon, Nov 15, 2021 at 12:03 AM Keelan Lightfoot <keelanlightfoot at gmail.com>
wrote:

>
> Isn’t the position of the satellite in these plots calculated from
> ephemeris rather than based on observations? It seems to me that you’d need
> multiple  receivers in different locations on the ground to figure out the
> position of a satellite in the sky based on observations alone.
>
> - Keelan
>
> > On Nov 14, 2021, at 2:27 PM, Dan Kemppainen <dan at irtelemetrics.com>
> wrote:
> >
> > Hi,
> >
> > Still trying to sort out the cause of that 'finger' of signal.
> >
> > Hooked up two more different GPS modules. A ZED-F9P, and a Jackson Labs
> LTE-LITE eval board.
> >
> > The F9P sees the same finger in the north as the other Ublox GPS module.
> The Venus receiver in the LTE Lite does not report signal above the north
> pole. See attached images.
> >
> > The data for these images was all recorded concurrently. All three GPS
> Modules are attached to a splitter on the same antenna, with nearly the
> same length jumper cables running from the splitter to each module.
> >
> > Currently running the same test again with the Ublox Timing module, the
> LTE Lite, and an adifruit "Ultimate GPS Breakout board V3" (MediaTek
> MT3339).
> >
> > Dan
> >
> >
> >
> >> On 11/11/2021 3:30 AM, time-nuts-request at lists.febo.com wrote:
> >> Message: 1
> >> Date: Wed, 10 Nov 2021 09:54:09 -0500
> >> From: Dan Kemppainen<dan at irtelemetrics.com>
> >> Subject: [time-nuts] Re: GPS Elevation Mask Values.
> >> To:time-nuts at lists.febo.com
> >> Message-ID:<aa2e648c-79b5-f680-e573-53da374e5957 at irtelemetrics.com>
> >> Content-Type: text/plain; charset=utf-8; format=flowed
> >> Hi,
> >> So, that finger of signal appearing above the north pole shows up even
> >> after the GPS survey is done. Any ideas on how to figure out what's
> >> causing that?
> >> My first thought is to try look at it with a different model of GPS
> unit.
> >> Is it possible it could be a signal reflection in the cable or something
> >> weird going on in the feed???
> >> Another thought would be to log the GPS data, to sort out which birds
> >> the GPS thinks is up there. Comparing to where they actually are would
> >> help sort out what the signal might be bouncing off of.
> >> Dan
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