[time-nuts] ground plane for cheap helix antennas?

[Attila Kinali]

On Thu, 23 Jul 2015 17:38:00 +0000
Alan Ambrose <alan.ambrose at anagram.net> wrote:

> Hi, is there any benefit in adding a ground plane to these simple
> timing antennas? e.g. GPS-TMG-26N
> 
> http://www.antenna.com/apg_products.cgi?id_num=11740
> 
> In which case, how big? And I'm imagining immediately underneath the
> antenna? This ublox note suggests probably not?

That highly depends on the inner structure of the antenna.
There are two helical antenna designs, one that works with an
anular ground ring/ground plane and one that works without.

In the former case, the antenna will benefit from a ground plane
and you should use an as large as possible. In the latter case,
a ground plane will not really help, respectively might actually
decrease performance. What you want in that case is backplane of
absorbtive material that minimizes reflections.
(which is not the same as choke ring, btw, but a choke ring can
substitute for absorbtive material, if used correctly)
 
> http://www.u-blox.com/images/downloads/Product_Docs/GPS_Antennas_ApplicationNote%28GPS-X-08014%29.pdf
> 
> The 58503A sitting on this atm gets '4.3us/initial 24 hours' prediction
> although I have seen it around 2.2us. Also max ~110 'SS'.
> 
> Also is it helpful to increase the elevation mask?

Depends on your situation, ie on the antenna position and its surrounding.
Generally speaking, you do want satellites as low on the horizon as
possible, because they give you the most accurate x/y position solution.
But at the same time, the lower a satellite is, the more multipath you
will get. Hence this becomes a tradeoff that is defined mostly by the
multipath generating structures around your antenna and their position.

				Attila Kinali

-- 
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Metastability is the little-death that brings total obliteration.
I will face my metastability. 
I will permit it to pass over me and through me. 
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