oops, sorry for the misfire.

For $99 I would take the risk to damage it... Or find someone with x-ray gear and have a peak inside. Or take it with you on your next plane flight and grab a photo of the TSA monitor as you pass through.

That's a good question. It all depends on what you're using it for. If you're a mm survey kind of guy then mix that antenna with half a dozen name-brand antennae that you already own and trust. See how it stacks up in real-time or post-processing benchmarks. I'm a fan of measurement more than specs, so collect as much data as you can and share with us.

If you're a time-nut it's more complicated. It's possible you don't have anywhere near the kind of equipment that can detect sub-10 ns sort of bias or wander or noise. And then there are issues of orientation, elevation, linearity, thermal stability, etc. If it's not in the NGS database be suspicious. Ref:

https://www.febo.com/pipermail/time-nuts/2018-January/108519.html

/tvb

There's a picture of the guts in the ebay description...it's a dual
patch antenna!
the patches seem to be trimmed to get a pattern.

On 2018-02-05 20:33, John Green wrote:

--
Dr. Don Latham
PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304

Moin,

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

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.

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

Hi

One gotcha (if the data sheets are correct) is going to be the supply voltage.
We normally stay away from 12V antennas because TBolt’s put out 5V. In the
case of a survey antenna, 12V is what most of the gear puts out. I don’t know
of any L1 / L2 gear that puts out 5 rather than 12V ….

Bob

On Tue, 6 Feb 2018 08:54:23 -0500
Bob kb8tq kb8tq@n1k.org wrote:

Well, that's at least a very easy modification. Just open up the connection
between the bias-T and the LNA and insert some LM1117 or better an TPS7A45xx.

			Attila Kinali

--
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

On 6 February 2018 at 03:33, John Green wpxs472@gmail.com wrote:

I used to work in the antenna industry selling 'professional' antennas -
not aimed at the amateur radio market. Many specifications are invented to
be better than a competitor. The competitors do it too, so it is not just
one company. If you sell antennas with valid specifications, it would be
next to impossible to sell them, as competitors will have higher
specifications.

Another RF engineer, who I don't know from working with antennas, said to
me that antennas are a still a charlatan's paradise.

With antennas, probably more than any other device, I would believe the
specifications if I could verify them. Unfortunately, for that sort of
antenna, I don't know how to verify them.

If nothing else, I would ask the seller for a copy of the test reports that
back up the specifications.

I got a couple of WiFi antennas free from eBay, after proving the gain
specifications were vastly exaggerated. Depending on the phase of the moon,
the numbers that came up in last months lottery, eBay policy changes with
reguard to who pays the return shipping fee on items that are not as
described. If you can show its the seller, then in many cases they will not
wish to pay the return cost.

Dr David Kirkby Ph.D C.Eng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3
6DT, United Kingdom
Registered in England and Wales as company number 08914892
http://www.kirkbymicrowave.co.uk/
Tel 01621'680100 / +44 1621-680100 <01621%20680100>