Low-elevation skymapping at 2.45 Ghz

[Major Variola (ret)]

At 06:03 PM 6/16/04 +0200, Eugen Leitl wrote:
>Aperture is tiny (and expensive, exponentially so). Visible wavelength
vs.
>microwave is a
>complete overkill in terms of mirror precision (lambda/10..100).

Exactly.  I wasn't suggesting using the optical reflector (front surface
Al over glass)
but rather merely the tube.

>Depending on angular resolution you might want to check
>out a small parabolic sat dish (less wind load on the mount -- which
better be
>not
>azimuthal -- use a stepper-driven equatorial platform).

Herr Elloi often points out that a dish can be made of wire mesh instead

of solid for the wavelengths of concern.  This is useful if you're
outside
dealing with wind, or your motor-drive platform expects a load of a
certain
mass.

However, it should be known that fiberglass (eg van) panels are
transparent
to uwaves AFAIK and that a van with soft tires is a 0th-order
vibration isolation mount.  Amateur holographers use heavy granite
and low inflation inner tubes as optical benches too.   However vans
do rock in the wind and I don't believe the cheap telescope drives can
compensate.  Now if you had 2 802.11 scopes coupled, one pointed
at a bright "guide star", then you could do some cool stabilization.

At sufficiently good mechanical stabilization and gain, you will
encounter perhaps
amplifier electronic noise effects, other transmitters, or reflection
(ghosting) which then become the lower bound.

While not being a HAM, I'm also aware that there are extremely
directional
antennae fixed-frequency wire & pole antennae which are not dish shaped,
but may have less energy-collecting area than a dish.

I believe that a horn shaped input may also be useful for coupling the
impedence
of freespace aether to your circuits.  Think trumpet.   Perhaps this
matters only
for transmission; though transmission and reception tend to be equal.  A
microwave horn can be a truncated pyramid, etc.

Merely ideas for America's cryptoscout youth looking to earn another
badge
from the RF group.