[time-nuts] Choke-Ring Antennas for GPSDO use?

[Bruce Griffiths]

Michael Baker wrote:
> Hello, All--
>
> Over the past couple of years I have seen several references
> indicating that the reason all GPS units intended for
> precision survey applications use a choke-ring antenna is
> that a properly designed GPS choke ring antenna will cut
> multi-path reception down very significantly.  Other
> references I have seen indicate that using a choke-ring
> antenna results in a moderate improvement in GPSDO performance.
>
> Can any list members comment on this?  If a choke-ring
> antenna does improve GPSDO performance, what degree of
> improvement can be expected?  Enough to be worthwhile?
> Would switching to a properly designed choke-ring
> antenna on my Trimble Thunderbolt GPSDO be worthwhile?
> My house is surrounded by large trees and my roof-top
> GPS antenna does not have a foliage free view of the
> sky until about 40-degrees above the horizon.  I have
> set a horizon elevation mask of 30 degrees in my T-bolt
> software but have wondered if multipath through the
> remaining tree-tops may still be a slight problem.
>
> Only very rarely do used GPS choke-ring antennas show
> up on eBay and they typically ask around $600 to $800.
>
> My good friend Bob Johnson, WB4JZM, tracked down some
> references to GPS choke-ring antennas which he sent
> to me (Thanks, Bob!!) and I have taken the liberty of
> appending some of his post below:
> -----------------------
>
>
>
> Mike Baker
> WA4HFR
> Gainesville, Florida
>   
Mike

There are other antenna designs that have similar performance to a choke
ring antenna:
Novatel Pinwheel antenna:
http://www.novatel.com/Documents/Papers/gps_pinwheel_ant.pdf

http://www.novatel.com/products/gps_701_702GG.htm

Trimble microcentred antenna:
http://www.trimble.com/microcenterant.html

Designing a choke ring for 2 or 3 frequency operation is a bit of a
compromise and the performance isnt as good as that of a single
frequency choke ring.
With the enhancement of the GPS system multifrequency operation will
become more important.

Pinwheel antennas and ground planes with dissipative boundaries can more
readily  achieve good multi frequency performance.

Bruce