Theoretically,
1. Wouldn't these meta antennae act like the high rise building built
between you and your favorite repeater. Absorbing/blocking "your"
signal down range from the source transmitter?
2. Wouldn't all that RF building up inside the room act like the
story we have all heard about "the cat came in from outdoors wet, so I
tossed him into the microwave!"?
Years ago when a building was being built near the phone company
building where I worked, the microwave signals would fade for no
apparent reason. As the building, a block away, started to appear above
the nearer buildings, we saw the crane used to raise material for the
construction rising up in height, also. It turns out the crane cab was
at the 250 height of our tower antenna. Whenever the cab swung into
position to put it's load on the new building, we lost signals to/from
our next relay tower, a major route node.
Using a bit of hype, we told the crane operator that he would become
sterile if he kept getting in the beam between towers. They moved the
crane to another location. Both parties were happy.
Jim WA4IVM
ps: 23 mile path length, 2 degree beam width, 1/2 watt ERP.
On 11/8/2013 11:35 AM, Simone wrote:
Bob,
I agree with you on the fact that RF energy harvesting is not practical for
high powers, but I think we should re-locate these devices into their
context: rectantennas and similar devices are designed to power extremely
low power devices, in places where there is no access to sun light.
Think for example to tyre pressure monitoring sensors: some types of
devices harvest power from the transponder used to communicate with them.
Still we are far from energy harvesting houses, where walls and tiles are
made of antennas that sucks all the incident RF power... in any case, as
you pointed out, even in the case such a scenario would work, people living
inside would have no radio and no cellphone working!
73
Simone - IU1AFY/F4VPY
2013/11/8 Robert Bruninga <[email protected]>
A fellow came to me convinced that capturing RF energy from cell phones,
and radio and TV waves was free energy. He couldn’t wait to invest in
these pocket sized antennas that have achieved the same 37% energy
reception efficiencies as do the most expensive solar cells:.
http://www.sciencedaily.com/releases/2013/11/131107154818.htm
I told him to not believe everthing he hears and you Amsat radio guys
might get a kick out of my response:
--------------------------------------
Thanks for sending me this interesting example of hype gone ridiculous. I
was glad to receive it.
The problem is apples and oranges. Yes, they got ”37% efficiency, similar
to the most expensive solar cells”, but the difference is that solar energy
imparts about 100 watts of energy per square foot on a solar panel –
remember, ONE HUNDRED WATTS/sqft.
The amount of energy from a Cell tower onto a small antenna 1 mile away
from the cell tower (typical) is only 0.000000000004 Watts. So there is
about a one hundred trillionth of the practicality.
Or another way to look at it. If you could hold their RF energy collecting
antenna 1 inch from the cell phone tower (not one mile), to get more power,
then the most power he could get would be only 3 watts. Still nothing
close to what the sun provides. Plus, he would be absorbing all the power
from the cell phone tower making it useless, plus the energy is not free.
SO to get the same power as a palm sized solar panel, his RF capture
antenna would have to be ONE INCH away from THIRTY cell phone towers.
And, to generate that same 100 watts worth of RF energy, it takes about
300 watts of electrical power. (1 inch away)
All to deliver about 1 Watt of power compared to the Sun which is free.
Thanks. A great lesson in hype!
Bob Bruninga, WB4APR
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_______________________________________________
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Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
_______________________________________________
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Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
