[ExI] Written for another list

[Keith Henson]

On Mon, Aug 6, 2012 at 5:00 AM,  Adrian Tymes <atymes at gmail.com> wrote:

> From: Adrian Tymes <atymes at gmail.com>

(snip, concede, can't argue if you think power in space is worthless.)

>>> or assume more ohms.
>>
>> Now, that you can't do.  The impedance of an antenna is fixed by physics.
>
> Of any given antenna, yes, but you can change the antenna.
> The impedance is best matched to the impedance of the line
> carrying signal to/from the antenna.  V = IR, we have a minimum
> V, and R is a function of materials.  So use better conductors =
> less R = more I for the line, and then configure the antenna to
> match the line's I.

It's not a function of the materials.  Analysis counts the conductors
as without resistance.  What's causing the voltage/current
relationship is the impedance of free space.

http://en.wikipedia.org/wiki/Dipole_antenna#Half-wave_antenna

I don't know if you are old enough to remember thin net.  That was
coaxial cable that required a terminating resistor on each end.  For a
given cable geometry it required a specific resistor of a limited
range.

> Materials science might not quite be advancing at Moore's Law's
> pace, but it is getting better.
>
> For instance - and standing outside the general thrust of "how
> do we do this at first" - what about tapping part of the power
> for cryogenics, enough to make the antenna from
> "high-temperature" (but still sub-room-temperature)
> superconductors?  What would 0 resistance enable?

You can make better resonate cavities with superconductors, but you
can't change the impedance of free space one iota.  Sorry, it's built
into the universe we live in.

snip

>> How does a maser reduce divergence over a phased array?
>
> Smaller beam waist = smaller footprint.

The divergence of a beam of electromagnet energy is theta = 1.22
lamda/diameter.  http://en.wikipedia.org/wiki/Airy_disk

"the angle at which the first minimum occurs (which is sometimes
described as the radius of the Airy disk) depends only on wavelength
and aperture size"

How does a maser affect this?

snip

> That didn't answer my question.  Are you just trying to make
> a theoretical case, or is this something you want to actually
> make happen?  People can and do spend huge amounts of
> time into just making theoretical cases, so that you have put
> much time into it could support either answer.
>
> If you're just making the case, do you just want to argue that
> it is physically and technically possible given an infinite budget,
> or do you want to make the case that it is economically
> feasible too?  In the latter case, you can not ignore startup
> costs and making a plan for how to bootstrap up to having
> multi-GW microwave powersats.  Yes, it's fine to have that as
> a goal, but to make the case, you have to show how we can
> get there, and "assume a huge investment before the specific
> organization putting the sats up has shown it can put lesser
> powersats up with a lesser budget" is as much of a nonstarter
> as "assume gravity stops for an hour".

Read the document I sent and see if that answers your questions.  I
would love to start this on my pocket change or even a few million.
If you have a way to modify the concept to reduce the cost, please do.

snip

Keith