RadioBanter - View Single Post - No antennae radiate all the power fed to them!

rickman · November 2nd 14, 06:31 AM posted to rec.radio.amateur.antenna

On 11/2/2014 1:24 AM, wrote:
rickman wrote:
On 11/1/2014 7:59 PM, wrote:
rickman wrote:
On 11/1/2014 5:31 PM, wrote:
rickman wrote:
On 11/1/2014 1:03 PM, wrote:
gareth wrote:
Ignoring, for the moment, travelling wave antenna, and restricting
discussion to standing wave antennae ...

An antenna is an antenna.

Deep thoughts...

A wave is launched, and radiates SOME of the power, and suffers
both I2R losses and dielectric and permeability losses associated
with creating and collapsing the near field.

Nope, voltage is applied to an antenna causing currents to be created
which in turn cause an electromagnetic field to be created.

As antennas are made of real materials they have a resistance and the
current through that resistance leads to losses.

I thought there were *real* materials with no resistance. Isn't that
what a superconductor is?

Well, to be pendatic, there are no real materials with zero resistance
that can be used to build antennas.

Why can't you build an antenna with a superconductor?

As all the current existing superconductors require a bunch of supporting
equipment to keep them cold, they can't be used for antennas.

Really? What is the problem? There are super conductors at liquid
nitrogen temperatures and you can have that sitting in a flask on your
desk. Why couldn't that cool an antenna? Once you remove the I*R
losses, you don't even have to worry about the radiated power heating
the N2.

If one were realy determined to do it, one could build the antenna
in a non-metalic container of some sort and keep the container filled
with LN2.

I think you are confusing need with practicality. There is nothing to
stop you from making a superconducting antenna. There just isn't a need
for it unless you live in Gareth's world. Hmmm... wasn't that a movie?
Gareth's World?

It is not need versus practicality, it is practicality period.

If room temperature superconductors are ever invented...

However, those are like a cure for the common cold, practical fusion
power, and peace in the Middle East, all just around the corner for
the past half century or so.

I've never heard anyone say either a cure for the common cold or fusion
was "around" the corner. I've never heard anyone say at all that peace
is expected in the middle east.

You must not be very old then...

No, I'm not, I'm much less than a century old.

And I'm the better part of one and heard all of those many times now.

I forgot to add true artificial intelligence to the list.

I believe there are rather cold temperatures in space. A
superconducting antenna could be used there with *no* supporting
"apparatus".

You mean other than the shade screen?

You do understand two big problems with space stuff is how to get rid of
any generated heat and Solar heating?

Is there a lot of solar heating near Jupiter? I didn't realize...

Not a lot but the point is cooling options in space are limited and
you said nothing about where in space.

lol. No, cooling in space is very easy. Heat radiates quite well.
That's why they can power the electronics with RTGs so well.

In any case, why?

I^2R losses only become significant in very small antennas and there is
all the space you could ask for in space to build an antenna.

You snipped the part of my post that addressed your questions. It would
be better if you read posts before trimming them.

I snipped nothing when I responded.

You are right, it is all there.

--

Rick