Re: Low-elevation skymapping at 2.45 Ghz
The best way to do this is to mount the narrow-angle dish *and* video camera on the same mount, then use simple circuitry to superimpose white circle on the center of the image when signal exceeds some threshold (or vary the size with signal level.) The results could be startling. You could also use a stepper motor connected to the polar mount, and scan the sky (or the city under the hill) automagically. This could be interesting even in other bands. Could create some pretty pictures. :) Could it be possible to achieve the same without using a movable antenna? Eg, by an antenna array and comparing phases of the arriving signals?
Re: Low-elevation skymapping at 2.45 Ghz
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 0.25 glass will cost you 2-2.5 dB. At sufficiently good mechanical stabilization and gain, you will encounter perhaps The best way to do this is to mount the narrow-angle dish *and* video camera on the same mount, then use simple circuitry to superimpose white circle on the center of the image when signal exceeds some threshold (or vary the size with signal level.) The results could be startling. = end (of original message) Y-a*h*o-o (yes, they scan for this) spam follows: __ Do you Yahoo!? Take Yahoo! Mail with you! Get it on your mobile phone. http://mobile.yahoo.com/maildemo
Re: Low-elevation skymapping at 2.45 Ghz
At 12:52 PM 6/17/04 +0200, Thomas Shaddack wrote: Could it be possible to achieve the same without using a movable antenna? Eg, by an antenna array and comparing phases of the arriving signals? A phased array will work but few of us have the DSP or Ghz skills or $ to construct one. Whereas a scope drive is cheap and directional antenna are standard ARRL stuff.
Re: Low-elevation skymapping at 2.45 Ghz
At 10:40 PM 6/16/04 -0700, Morlock Elloi wrote: 0.25 glass will cost you 2-2.5 dB. Perhaps there are speciality glasses or polymer sheets which reduce that loss. At sufficiently good mechanical stabilization and gain, you will encounter perhaps The best way to do this is to mount the narrow-angle dish *and* video camera on the same mount, then use simple circuitry to superimpose white circle on the center of the image when signal exceeds some threshold (or vary the size with signal level.) The results could be startling. Nice idea; the radioastronomers do something like this (cross-band correlation) so they can see what their sources might correspond to.
RE: Low-elevation skymapping at 2.45 Ghz
Do optical mirrors still work in the microwave regime? I have no idea. -TD From: Major Variola (ret) [EMAIL PROTECTED] To: [EMAIL PROTECTED] [EMAIL PROTECTED] Subject: Low-elevation skymapping at 2.45 Ghz Date: Tue, 15 Jun 2004 15:09:26 -0700 Telescopes are sold for $200 which include programmable positioning devices (2 axes obvioiusly). I suppose its just a reduction drive and the usual electro-mech-control stuff but it implies a high degree of angular resolution for cheap. Has anyone: 1. ever used the refractor type telescope tube as-is as a super-long pringles directional 802.11 antenna? In fact the front optics may not interfere... 2. ever used the electronically controlled mount on a steady platform and a highly directional antenna (dishes included) to really see what the world really looks like at 2.mumble Ghz passive with an 802.11 decoder? I mean, radio astronomers do detailed sky surveys all the time. Why restrict yourself to the sky? (Yes, I realize our friends at Ft Meade have probably been using scanning-tunnelling-microscope type piezo-servo actuators to keep a steady gaze for some time..) _ Get fast, reliable Internet access with MSN 9 Dial-up now 3 months FREE! http://join.msn.click-url.com/go/onm00200361ave/direct/01/
Re: Low-elevation skymapping at 2.45 Ghz
On Wed, Jun 16, 2004 at 10:50:34AM -0400, Tyler Durden wrote: Do optical mirrors still work in the microwave regime? I have no idea. Aperture is tiny (and expensive, exponentially so). Visible wavelength vs. microwave is a complete overkill in terms of mirror precision (lambda/10..100). 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). If you're just going to scan the horizont, it's just one degree of freedom. 2 1/2 if you wiggle a little up and down. Easy enough to improvise for cheap, especially if you do it with a monster dish, which isn't at all like a truss of a lightweight giant scope. -- Eugen* Leitl a href=http://leitl.org;leitl/a __ ICBM: 48.07078, 11.61144http://www.leitl.org 8B29F6BE: 099D 78BA 2FD3 B014 B08A 7779 75B0 2443 8B29 F6BE http://moleculardevices.org http://nanomachines.net pgpXpKrKBuhKa.pgp Description: PGP signature
Re: Low-elevation skymapping at 2.45 Ghz
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.
