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.