Paul,
Never happen unless the isotropic antenna is
made with red wire...
'Doc

Paul@Rasdoc wrote:

I was implying iostropic in 3 dimensions....
Now for a paradox.....
If RX==TX as for as antenna gain
And 100W is 100W.... then isotropic had dBi =0 be the laws of
conservation of energy.....
No suppose we have an antenna that captures all of the energy passing
though a 1M square.......
Now make that a 10M square.....
Clearly a 10M "Fishing net" can capture more than a 1M net, but
Then RXgain != TXgain
So what gives where is this wrong?

The only application that I have seen in which this was true
was the so-called Rectenna - an array of low-gain dipoles,
each of which had a diode detector at its feedpoint terminals.
The direct-current diode outputs were summed to produce the
"signal" which was more-or-less proportional to the area of
the array. But the array itself had very low directivity -
pretty much that of a single dipole element - making it
unnecessary to beam-steer it.

This was proposed as the Earthside end of a space-based power
satellite system that would convert sunlight in geosynchronous
orbit to microwave energy and beam it down to the rectenna. There
it would be "detected" to DC which would then be converted to
60-Hertz HV sine waves for injection into the power grid.

The thing that makes this work was, of course, the non-linear,
non-coherent rectification process at each array element. And
it only works for DC. If a higher-bandwidth modulation is
imposed on the RF energy, a point is reached due to travel-time
delay where the detected signal at one end of the array is out
of phase with that detected at the opposite end. If synchronous
detection is attempted, the highly undesireable array directivity
is immediately restored - much to the chagrin of the system designers.


--
Jim Bromley, K7JEB k7jeb(at)arrl(dot)net
Glendale, Arizona

wrote in message
...
Is it possible to build an omnidirectional receiving antenna with
gain?
TV transmitting antennas are generally omnidirectional, and have gain. They
do this by concentrating all energy along the horizon. In fact, some work so
well that they put up a secondary antenna at 100ft or so to take care of
people who live close by.

If you want to talk about practicality, it would be easy to build one at 2
meters. Forget about it on 160m.

Tam/WB2TT

Is it possible to build an omnidirectional receiving antenna with
gain?

Yes. Assuming isotropic and assuming that negative values of gain are
permitted :)

--Wayne

"K7JEB" skrev i meddelandet
...

Paul@Rasdoc wrote:

I was implying iostropic in 3 dimensions....
Now for a paradox.....
If RX==TX as for as antenna gain
And 100W is 100W.... then isotropic had dBi =0 be the laws of
conservation of energy.....
No suppose we have an antenna that captures all of the energy passing
though a 1M square.......
Now make that a 10M square.....
Clearly a 10M "Fishing net" can capture more than a 1M net, but
Then RXgain != TXgain
So what gives where is this wrong?

The only application that I have seen in which this was true
was the so-called Rectenna - an array of low-gain dipoles,
each of which had a diode detector at its feedpoint terminals.
The direct-current diode outputs were summed to produce the
"signal" which was more-or-less proportional to the area of
the array. But the array itself had very low directivity -
pretty much that of a single dipole element - making it
unnecessary to beam-steer it.

This was proposed as the Earthside end of a space-based power
satellite system that would convert sunlight in geosynchronous
orbit to microwave energy and beam it down to the rectenna. There
it would be "detected" to DC which would then be converted to
60-Hertz HV sine waves for injection into the power grid.

The thing that makes this work was, of course, the non-linear,
non-coherent rectification process at each array element. And
it only works for DC. If a higher-bandwidth modulation is
imposed on the RF energy, a point is reached due to travel-time
delay where the detected signal at one end of the array is out
of phase with that detected at the opposite end. If synchronous
detection is attempted, the highly undesireable array directivity
is immediately restored - much to the chagrin of the system designers.


--
Jim Bromley, K7JEB k7jeb(at)arrl(dot)net
Glendale, Arizona


Thats in the right direction. The original question was about energy (DC)
and this is the answer. Modulated energy is another issue, not applicable
for the original question.
--
/ME (first time, checking my signature)