Neoprene rubber drops GPS multipath signals to zero
My TW4722 GNSS active antenna is on a 100 mm stainless ground-plane,
placed on 2" of wood on a window sill behind two panes of glass, between
metal blinds and the glass, almost touching the glass. Feeds a NEO-M8T.
Late yesterday I placed old neoprene rubber mouse pads, rubber side
outwards, up the metal blinds between the blinds and the antenna.
All signal levels dropped, many around 3 to 5 dBs, a few as much as 15
dBs. Seemed to equally affect LOS and multipath signals.
After running the night with that to see the affect, I stripped the
neoprene rubber off another mouse pad and placed the resulting neoprene
rubber pad under the antenna's 100 mm stainless circular ground-plane
(left resting on the pad), with the front of the pad folded upwards
extending an arbitrary 2" up the glass window pane. Pad is 8.75" wide.
Multipath signals reflecting from the bank of buildings opposite the
window were as high as 24 dBs. After placing the neoprene rubber pad
under the ground-plane and up the glass, they dropped down to zero.
Zero.
0.0
(screen shot from LH attached)
(Skyview is somewhat less than azimuth ~60 degrees to ~240 degrees.
Everything outside of that is multipath.)
Mouse pads were the earlier thin bottom-textured pads of denser neoprene
rubber, not the later thick smooth air-foamed pads (which I've not tried).
Hope this info can help someone as much as it's helped me.
Michael
In message 589F4A79.3050800@rogers.com, MLewis writes:
Late yesterday I placed old neoprene rubber mouse pads, rubber side
outwards, up the metal blinds between the blinds and the antenna.
I can guarantee you that it is not the neoprene itself which does it.
It could be residual ZnO, used to catalyze polymerisation of the neoprene,
but more likely it is metal deliberately added to the neoprene to
change the RF impedance of the material.
Polymers with varying metal content offer a handy range of
electromagnetic impedances between "short" and "open"[1], and it
is used a fair bit in various niche markets.
See for instance the first document here;
http://www.eccosorb.com/resource-white-papers.htm
It is not inconceiveable that off-spec or scrap materials from
the production might end up as mousemats.
Here is an interesting article about other things you can do with
such materials:
https://archive.org/details/bstj27-1-58
Poul-Henning
[1] If you arrange for the imperance to ramp from open to short you
have a "stealth material".
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Interesting.
My guess wasn't a material made for RF but a carbon added to give a
decent black colour.
"It is not inconceiveable that off-spec or scrap materials from the
production might end up as mousemats." and "stealth material".
Very interesting.
At an airshow many years ago, these mouse pads were a promotional
give-away by the Department of National Defence in Canada...
I'm now seeing some multipath signals sneak through, usually in the
single digital strength but for brief moments as high as 15 dBs. Coming
from elevation 5 to 10 degrees, between azimuth 300 to 330 and also
azimuth 30 and 60. I'm suspecting the office tower at 135 that sticks up
above the bank of buildings. I'll have to add a 1" strip up to 3" high
in LOS to that building to see what that does.
The other multipath signals remain at 0.0.
Michael
On 11/02/2017 1:22 PM, Poul-Henning Kamp wrote:
I can guarantee you that it is not the neoprene itself which does it.
It could be residual ZnO, used to catalyze polymerisation of the
neoprene,
but more likely it is metal deliberately added to the neoprene to
change the RF impedance of the material.
...
[1] If you arrange for the imperance to ramp from open to short you
have a "stealth material".
Hi
For any microwave material, the good old “toss it in a microwave” test is a quick
and dirty one. If the material heats up, it’s lossy. Yes, there are other fairly exciting
things that can happen other than it warming a bit ….
Bob
On Feb 11, 2017, at 5:51 PM, MLewis mlewis000@rogers.com wrote:
Interesting.
My guess wasn't a material made for RF but a carbon added to give a decent black colour.
"It is not inconceiveable that off-spec or scrap materials from the production might end up as mousemats." and "stealth material".
Very interesting.
At an airshow many years ago, these mouse pads were a promotional give-away by the Department of National Defence in Canada...
I'm now seeing some multipath signals sneak through, usually in the single digital strength but for brief moments as high as 15 dBs. Coming from elevation 5 to 10 degrees, between azimuth 300 to 330 and also azimuth 30 and 60. I'm suspecting the office tower at 135 that sticks up above the bank of buildings. I'll have to add a 1" strip up to 3" high in LOS to that building to see what that does.
The other multipath signals remain at 0.0.
Michael
On 11/02/2017 1:22 PM, Poul-Henning Kamp wrote:
I can guarantee you that it is not the neoprene itself which does it.
It could be residual ZnO, used to catalyze polymerisation of the neoprene,
but more likely it is metal deliberately added to the neoprene to
change the RF impedance of the material.
...
[1] If you arrange for the imperance to ramp from open to short you
have a "stealth material".
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On 2/11/17 10:22 AM, Poul-Henning Kamp wrote:
In message 589F4A79.3050800@rogers.com, MLewis writes:
Late yesterday I placed old neoprene rubber mouse pads, rubber side
outwards, up the metal blinds between the blinds and the antenna.
I can guarantee you that it is not the neoprene itself which does it.
It could be residual ZnO, used to catalyze polymerisation of the neoprene,
but more likely it is metal deliberately added to the neoprene to
change the RF impedance of the material.
Or to make it heavy, so it lays on the table better. They could just
load it with sand or iron oxide or scrap whatever.
Polymers with varying metal content offer a handy range of
electromagnetic impedances between "short" and "open"[1], and it
is used a fair bit in various niche markets.
See for instance the first document here;
http://www.eccosorb.com/resource-white-papers.htm
It is not inconceiveable that off-spec or scrap materials from
the production might end up as mousemats.
I don't know if the production volume is high enough.. one never knows..
Eccosorb and related RF elastomers are sufficiently expensive that they
must do something with it.