[ntp:hackers] u-blox reference clock driver

[Gary E. Miller]

Yo Udo!

On Wed, 15 Aug 2018 15:12:04 +0200
Udo van den Heuvel via devel <devel at ntpsec.org> wrote:

> Question: So what antenna would we need?
> 
> One that covers multi GNSS, i.e.: GPS, Glonass, Galileo, Beidou, etc,
> etc.

Much easier said than done.  Technically GPS L1 and GALILEO E1 use the
same frequency:

    1.575.42MHz

GPS L1 bandwitdh is 15.345 MHz.  GALILEO E1 is 12 MHz.  So a GPS should
work fine w GPS.  Right?

GALILEO uses a suppressed carrier.  Most of the GPS signal is
close to the carrier.

To improve their performance some GPS antennas actually have a badnwidth
closer to 2 MHz and thus filter out GALILEO.

BeiDou B1 is down at 1.561 GHz.  So that needs a GPS antenna of large
bandwidth.

Only way to tell is to try an antenna.  I have many seemingly identical
GPS antennas that perform very differently.  "High end" often means
narrow bandwidth and you do not want that.

Here is a list of the bands used:

http://www.rfwireless-world.com/Terminology/GPS-Frequency-Band-and-GNSS-Frequency-Band.html

And a nice graph:

https://www.labsat.co.uk/index.php/en/applications/labsat-frequency-guide

GLONASS is spread around.  In thhe region of 1.600 up to 1602 GHz.

I have good luck with cheap GPS+GLONASS antennas for
GPS+GALILEO+GLOASS+BeiDou.

I you are lucky to have an L2, L3 or L5 GPS receiver, pretty rare, then
a wideband 1.150GHz to 1.61 Ghz will get you everything.  An expensive
L1/L2 antenna will not get GLONASS.

u-blox has an app note:

https://www.u-blox.com/sites/default/files/products/documents/GPS-Antenna_AppNote_%28GPS-X-08014%29.pdf

In Section 5.1.1 they recommend a 50mmm to 70mm square ground plane
under a patch antenna.  They do not recommend anything larger then
100mm (4").

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin
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