christofire wrote:

... and when you get back, let's see some proof that all this wacky
'new-age' theory is of any practical use to mankind.

I'd be willing to bet, say, 100 UK pounds that Professor Unwin can't create
an antenna in hardware that radiates isotropically, that is, over a whole
sphere within, let's say +/-1 dB with respect to any chosen (but constant)
polarisation. Anyone wish to up the ante?

Chris

I'd be glad to, but there's no way to prove it. Measurement accuracy and
repeatability just aren't that good, especially if you're trying to do a
full 3D measurement. The closest I've seen to a 3D measurement system
actually measured just one hemisphere. It was at what used to be NRAD
(Naval Research and Development center) and before that NOSC in San
Diego, consisting of a large (100 foot diameter if I recall correctly)
rotating circular platform with a semicircular arch overhead. By
rotating the platform and moving the detector along the arch, a full
hemispherical measurement could be made. The models were physical scale
models of Navy ships having appropriately scaled antennas. Even then,
though, engineers there told me that when the measured results differed
from NEC computer model results, they tended to believe the computer
results. It's extremely difficult to make highly, or even moderately,
accurate field strength measurements.

A while back I designed an antenna for a consulting job which was simply
a two-sloping-radial ground plane made with fairly wide traces on a
low-loss PC board. George Brown, the inventor of the ground plane
antenna, had observed an omnidirectional pattern in the horizontal plane
with only two radials, but the marketing department at RCA insisted on
adding two more to make it look symmetrical before selling them. Hence
the ubiquitous 4-radial design. (The pattern of the 4 radial version is
more circular above and below the horizontal plane, but not by a whole
lot.) Anyway, I was concerned that maybe the PCB or the relatively wide,
flat conductors might have a detrimental impact on the pattern
circularity, so I took it to a local lab that has a high quality
anechoic chamber and ran the pattern. When the plot was finished, the
lab technician muttered "Holy $/!%", hit the print button, grabbed a
camera, and ran into the chamber to take a picture of the antenna. Then
he went around to the other folks at the lab with the picture and plot.
Seems that it was circular within about a dB, better than their $10k
reference antenna. The prototype, by the way, was made with adhesive
copper tape and an X-Acto knife and looked as crude as it was. I can't
claim that the pattern was really better than their reference antenna
because small differences in positioning of the feedline (even though
decoupled), the antenna, and anything else in the chamber can easily
cause a couple of dB of pattern deviation.

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
christofire wrote:

... and when you get back, let's see some proof that all this wacky
'new-age' theory is of any practical use to mankind.

I'd be willing to bet, say, 100 UK pounds that Professor Unwin can't
create an antenna in hardware that radiates isotropically, that is, over
a whole sphere within, let's say +/-1 dB with respect to any chosen (but
constant) polarisation. Anyone wish to up the ante?

Chris

I'd be glad to, but there's no way to prove it. Measurement accuracy and
repeatability just aren't that good, especially if you're trying to do a
full 3D measurement. The closest I've seen to a 3D measurement system
actually measured just one hemisphere. It was at what used to be NRAD
(Naval Research and Development center) and before that NOSC in San Diego,
consisting of a large (100 foot diameter if I recall correctly) rotating
circular platform with a semicircular arch overhead. By rotating the
platform and moving the detector along the arch, a full hemispherical
measurement could be made. The models were physical scale models of Navy
ships having appropriately scaled antennas. Even then, though, engineers
there told me that when the measured results differed from NEC computer
model results, they tended to believe the computer results. It's extremely
difficult to make highly, or even moderately, accurate field strength
measurements.

A while back I designed an antenna for a consulting job which was simply a
two-sloping-radial ground plane made with fairly wide traces on a low-loss
PC board. George Brown, the inventor of the ground plane antenna, had
observed an omnidirectional pattern in the horizontal plane with only two
radials, but the marketing department at RCA insisted on adding two more
to make it look symmetrical before selling them. Hence the ubiquitous
4-radial design. (The pattern of the 4 radial version is more circular
above and below the horizontal plane, but not by a whole lot.) Anyway, I
was concerned that maybe the PCB or the relatively wide, flat conductors
might have a detrimental impact on the pattern circularity, so I took it
to a local lab that has a high quality anechoic chamber and ran the
pattern. When the plot was finished, the lab technician muttered "Holy
$/!%", hit the print button, grabbed a camera, and ran into the chamber to
take a picture of the antenna. Then he went around to the other folks at
the lab with the picture and plot. Seems that it was circular within about
a dB, better than their $10k reference antenna. The prototype, by the way,
was made with adhesive copper tape and an X-Acto knife and looked as crude
as it was. I can't claim that the pattern was really better than their
reference antenna because small differences in positioning of the feedline
(even though decoupled), the antenna, and anything else in the chamber can
easily cause a couple of dB of pattern deviation.

Roy Lewallen, W7EL


Interesting stuff. I think one can get a good idea what's going on by
measuring in the cardinal planes and some 45 degree cuts. It would soon
become apparent whether the antenna warrants closer inspection.

I recall seeing what you describe at NRAA and NOSC also at ASWE in
Funtington, near Portsmouth GB. There they also had an aluminium 'sea' and
copper scale models of most of the British fleet for checking the ELF to HF
patterns (scaled conductivities). For the case in hand, though, there's no
requirement for a ground plane (viz. 'spherical' in the title) so the
resulting hardware antenna could be oriented in a number of different ways
and rotated about a single axis for measurement. I've had experience of
doing this with a Lindenblad array, and measuring axial ratio at the same
time. I've also been aware of someone else's model, made using flexible PCB
material formed into a cylinder, which outperformed the brass-tube-and-rod
one we were working on!

Feed-line radiation can easily be overcome by using a small oscillator and
battery: tiny, stable ones are available nowadays. I'd be convinced if the
protagonist managed a truly isotropic pattern at just one frequency.

Chris

On Fri, 11 Sep 2009 23:32:39 +0100, "christofire"
wrote:

I'd be convinced if the
protagonist managed a truly isotropic pattern at just one frequency.

Hi Chris,

Half-Isotropic (if you allow for total field - you didn't specify and
any protoplasm could game that loose specification) at:
http://www.qsl.net/kb7qhc/antenna/In...-1%20Field.gif

The design has been kicking around for 10+ years now at that link, and
not even original when I posted it.

As for gaming the lack of polarization spec, I might simply offer that
it doesn't matter - if you use an isotropic detecting antenna to
measure the field of this antenna model in the link. For that
isotropic detecting antenna, I would offer a golf-ball lump of coal
and a thermistor.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
news
On Fri, 11 Sep 2009 23:32:39 +0100, "christofire"
wrote:

I'd be convinced if the
protagonist managed a truly isotropic pattern at just one frequency.

Hi Chris,

Half-Isotropic (if you allow for total field - you didn't specify and
any protoplasm could game that loose specification) at:
http://www.qsl.net/kb7qhc/antenna/In...-1%20Field.gif

The design has been kicking around for 10+ years now at that link, and
not even original when I posted it.

As for gaming the lack of polarization spec, I might simply offer that
it doesn't matter - if you use an isotropic detecting antenna to
measure the field of this antenna model in the link. For that
isotropic detecting antenna, I would offer a golf-ball lump of coal
and a thermistor.

73's
Richard Clark, KB7QHC


Well the title of the thread is 'Spherical radiation pattern' and I
interpret that as meaning a far-field pattern that is uniform (within the 2
dB margin I offered) in respect of the transverse electric, or transverse
magnetic, field strength, or the resulting power-flux density, over a whole
sphere.

I'm not sure what you mean by 'total field' in respect of a far-field
pattern - all induction components should be insignificant including any
'cross-field' longitudinal ones. Also, my wager is in respect of a hardware
antenna being built, not an NEC model.

Regarding your lump of coal and a thermistor - how would you connect the
thermistor? Surely that would impose some kind of polarisation however it
was done ...?

Chris

"christofire" wrote in message
...

"Richard Clark" wrote in message
news
On Fri, 11 Sep 2009 23:32:39 +0100, "christofire"
wrote:

I'd be convinced if the
protagonist managed a truly isotropic pattern at just one frequency.

Hi Chris,

Half-Isotropic (if you allow for total field - you didn't specify and
any protoplasm could game that loose specification) at:
http://www.qsl.net/kb7qhc/antenna/In...-1%20Field.gif

The design has been kicking around for 10+ years now at that link, and
not even original when I posted it.

As for gaming the lack of polarization spec, I might simply offer that
it doesn't matter - if you use an isotropic detecting antenna to
measure the field of this antenna model in the link. For that
isotropic detecting antenna, I would offer a golf-ball lump of coal
and a thermistor.

73's
Richard Clark, KB7QHC


Well the title of the thread is 'Spherical radiation pattern' and I
interpret that as meaning a far-field pattern that is uniform (within the
2 dB margin I offered) in respect of the transverse electric, or
transverse magnetic, field strength, or the resulting power-flux density,
over a whole sphere.

I'm not sure what you mean by 'total field' in respect of a far-field
pattern - all induction components should be insignificant including any
'cross-field' longitudinal ones. Also, my wager is in respect of a
hardware antenna being built, not an NEC model.

Regarding your lump of coal and a thermistor - how would you connect the
thermistor? Surely that would impose some kind of polarisation however it
was done ...?

Chris


.... Oops, scratch that last bit - my mind must have been elsewhere! Of
course you'd just drill a hole in it.

Thinking about your lump of coal reminded me about the kinds of antenna used
in radiation hazard meters, often three short dipoles mounted mutually
perpendicularly, each with some kind of bolometer element at its centre. If
one didn't care about polarisation then perhaps a similar arrangement could
be used to transmit with a near-isotropic pattern, but that wouldn't be an
efficient solution for communication. No, the challenge for Art Unwin,
should he wish to put his money where his mouth (keyboard) is, is create and
demonstrate a hardware antenna that exhibits a spherical radiation pattern
in respect of a single polarisation. That would be useful.

What is the red line in the pattern to which you gave the link?

Chris

On Sat, 12 Sep 2009 12:45:28 +0100, "christofire"
wrote:


Well the title of the thread is 'Spherical radiation pattern' and I
interpret that as meaning a far-field pattern that is uniform (within the
2 dB margin I offered) in respect of the transverse electric, or
transverse magnetic, field strength, or the resulting power-flux density,
over a whole sphere.

Hi Chris,

Well, simply put this antenna with its mirror image elements into free
space and it accomplishes that quite easily.

What is the red line in the pattern to which you gave the link?

XYZ Axis.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sat, 12 Sep 2009 12:45:28 +0100, "christofire"
wrote:


Well the title of the thread is 'Spherical radiation pattern' and I
interpret that as meaning a far-field pattern that is uniform (within
the
2 dB margin I offered) in respect of the transverse electric, or
transverse magnetic, field strength, or the resulting power-flux
density,
over a whole sphere.

Hi Chris,

Well, simply put this antenna with its mirror image elements into free
space and it accomplishes that quite easily.


Have you ever built one and measured its radiation pattern?

Chris

Roy Lewallen wrote:


George Brown, the inventor of the ground plane
antenna, had observed an omnidirectional pattern in the horizontal plane
with only two radials, but the marketing department at RCA insisted on
adding two more to make it look symmetrical before selling them.

Side note, Roy. I take a lot of Morotcycle rides to the north central
part of PA, and being a remote area, that have a fair number of radio
systems to tell them of the shape of the power lines in eh area.

They use a ground plane antenna that consists of a spring mounted
vertical, and two horizontal radials. They are pretty homely.

- 73 de Mike N3LI -

Chtistofire wrote:
"I`d be willing to bet, say, 100 UK pounds that Professor Unwin can`t
create an antenna in hardware that radiates isotropically, that is over
the whole sphere within let`s say +/- 1 dB with respect to any chosen
(but constant) polarisation."

Many would bet just as Christofire.

An isotropic may fit Art`s definition of "equilibrium" but according to
Terman it is impossible. Terman`s footnite on page 871 of hid 1955 opus
says:

"An isotropic antenna produces waves that are of equal strength in all
directions. Although an isotropic radiator of coherent waves does not
exist because it cannot satisfy Maxwell`s equations, the properties of
such an imaginary antenna are easily visualized, and the concept of an
isotropic radiator is often found useful to the analysis of antenna
systems."

My money is on professor Terman.

Best regards, Richard Harrison, KB5WZI