[time-nuts] Anyone have experience with this antenna?

Attila Kinali attila at kinali.ch
Tue Feb 6 06:48:34 EST 2018


On Mon, 5 Feb 2018 21:33:59 -0600
John Green <wpxs472 at gmail.com> wrote:

> https://www.ebay.com/itm/High-Precision-L1-L2-GNSS-GPS-GLONASS-BeiDou-RTK-CORS-survey-antenna/162718512935?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649
> Listed on eBay as a L1/L2 antenna with decent specs. They seem to indicate
> it is as good as a choke ring antenna. I suspect it is just a patch in a
> fancy package. 

It actually is. The fourth picture in the ebay listing shows that it's
a dual, stacked patch antenna with a 4 point (0°, 90°, 180°, 270°)
excitation using fiberglass as substrate. I am not sure I would trust
the +/-2mm phase center error, but it's probably quite decent.
But advertising it as "high precision" or even "chocke ring antenna
functionality without out the size or weight" is an outright lie. 
For one, they are too cheap to use nylon screws instead of
metal screws in the antenna, which will lead to distortions in the
radiation pattern. For another the fiberglass/epoxy substrate is going
to change its dielectric constant with humidity, which will inevitably
lead to changes in its resonance and radiation pattern. Third, the
choke ring is to minimize influence of reflections close to or below
the antenna horizon. This antenna does not have anything that comes even
close to provide this feature.

Judging from the meager information on the ebay lsting, it's most likely
a Shenzen Beitan 7151[1] or a 7201[2] ("data"sheets attached).

BTW: You can get the 7151 for 75USD and free sheeping on aliexpress.

> That is what the Leica and Trimble survey grade antennas I
> have contain anyway. I bought one but haven't had the chance to do any
> testing. I couldn't figure out how to get to the insides to take a peek
> without damaging it. My antenna testing abilities are pretty feeble.
> Mostly, I will just compare it to the Leica and Trimble to see how many
> satellites it sees and look at position wander of the uBlox. Is there any
> simple way to judge the quality of a GPS antenna?

If you have a known-good reference antenna and two receivers that can
record the carrier phase data of the two antennas, then it's relatively
easy to compare them (although there is quite a bit of math involved
and you probably eed to write the software yourself, as i am not aware
of any publicly, for hobbyists available software package).

			Attila Kinali

[1] http://www.sz-beitian.com/ProductsDetail?product_id=53
[2] http://www.sz-beitian.com/ProductsDetail?product_id=52

It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson
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