And odd thought occured to me one day: why not use my computer as a
component in a homemade radar system? Something capable of tracking,
say, airplanes. Could be an interesting hobby. So, I'm looking for
instructions on what equipment (cheap as possible!) I'd need to do
this, how to set it up, and how to interface it with my PC.  Maybe I
could get some used military junk?
I did a brief google search but the only thing I came up with was:
http://www.geocities.com/capecanaveral/cockpit/7195/bistaticradar.html
and that's not really what I wanna do.
Yeah, I'm nuts. P.S.: I'll give a generous tip for the cheapest, most
interesting solution ;P

On the off (and unlikely) chance that you did build such a device,
just turning it on and "painting" aircraft in flight would cause the
authorites of many shapes and sizes to descend on your signal like
ravenous vultures. This is not paranoia - this is common sense. They
probably wouldn't bomb your house of course, but I can envision some
long drawn out discussion with you, your neighbors, and your family
and perhaps even an unusual interest in your bank account, phone bill,
employment history and even your sock drawer.

You can do what you want but in my friendly (and free) opinion, this
is a very creative, very interesting, but VERY, VERY bad idea.

There are already some internet sites that track aircraft for
entertainment purposes that you can visit. I'd rather do that than
have someone visit ME for tracking planes using a homemade system.
Know what I mean?

Regards;
tutuzdad-ga

Why not try radio Astromony

Excellent point tutuzdad,

You also have to consider that any device that transmits electrical or
radio waves is regulated by the FCC. Things like HAM radios and walkie
talkies operate on set bands allocated for that purpose.
For any kind of homemade radar with the power and ability to 'paint'
an aircraft in flight would require special equipment that you would
likely have to get a license or permit for.

Yes, given the political climate, a search warrant is likely to cause
me a bad day :)

Thanks, guys! nd yes, radio astronomy is quite cool. I'll have to
check that out.