"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