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

rickman wrote in :

No, cooling in space is very easy. Heat radiates quite well.

True but to get the best of it you have to have high grade energy to radiate.
(High temperatures, short wavelengths). If you could efficiently convert low
grade warmth in large amounts, to a small source of incandescent light, you'd
improve it. I'm not sure if such a process is easy or practical. To be worth
doing, it would have to cost less energy to convert than the difference in
that emitted for the two temperatures. It would probably have to use storage
too, for long slow inputs, short strong bursts of output, which complicates
things.

The problem is that low temperature superconductors are way too cool to start
with, so the supporting equipment would be as awkward as that on Earth, and
likely more so.

Lostgallifreyan wrote in
:

True but to get the best of it you have to have high grade energy to
radiate. (High temperatures, short wavelengths). If you could
efficiently convert low grade warmth in large amounts, to a small source
of incandescent light, you'd improve it. I'm not sure if such a process
is easy or practical. To be worth doing, it would have to cost less
energy to convert than the difference in that emitted for the two
temperatures. It would probably have to use storage too, for long slow
inputs, short strong bursts of output, which complicates things.


Never mind what I wrote just now. Can't beat entropy.

On 2014-11-02 11:01:54 +0000, Lostgallifreyan said:

Lostgallifreyan wrote in
:

True but to get the best of it you have to have high grade energy to
radiate. (High temperatures, short wavelengths). If you could
efficiently convert low grade warmth in large amounts, to a small source
of incandescent light, you'd improve it. I'm not sure if such a process
is easy or practical. To be worth doing, it would have to cost less
energy to convert than the difference in that emitted for the two
temperatures. It would probably have to use storage too, for long slow
inputs, short strong bursts of output, which complicates things.


Never mind what I wrote just now. Can't beat entropy.

No, but you *can* use a heat pump to move it somewhere else.

--

Percy Picacity

Percy Picacity wrote in
:

Never mind what I wrote just now. Can't beat entropy.

No, but you *can* use a heat pump to move it somewhere else.


Yes, sort of what I was getting at, I'm just not sure what qualifies as
'worth it' For example, you could store some low grade heat converting to
electric charge in batteries. This could then power a hot high current heater
to radiate overcoming local ambient heat from solar energy in a space
installation. If you had enough shade that would be likely less useful, it
might be cheaper to set up large low-grade radiators instead. it seems to me
that all kinds of compromises with cost, size, ambient conditions, will rule
what actually gets done.

Given that laser diodes can radiate a lot of power now, and be small with
very low mass, and convert upwards of 30% electrical input to light, they
might become part of a compact space-based heatsink. I suspect that 30% will
not be nearly enough to be usful in most cases because there will be other,
greater losses (laser diodes are some of the most efficient transducers ever
made).