[amsat-bb] Microwave link demos (and strange things)
bruninga at usna.edu
Tue Sep 25 10:05:53 PDT 2007
Strange things happen...
Was giving a satellite lab where we put two tiny "labsats"
(spysats) with 2.4 GHz cameras about 1/4 and 3/4 miles away and
then use a dipole with and without an 18" dish to show gain and
the difference in path loss.
See the set-up in the right hand photo at the top of this page:
My technician placed the cameras out at 7 AM before class (both
are across bodies of water, so the access distance is much
greater than the line of sight path). I was giving the demo
for the first group of Midshipmen and while looking at the image
from the one camera, we noticed it moving and then saw a face.
Looked out across the water (on the point of land right behind
the dish in the photo) and saw a truck load of mexicans closely
inspecting the camera. We were sure a full scale security alert
would follow, because the string of "D" cell batteries inside a
PVC pipe strapped to a dead tree sure looks like a pipe bomb.
Then we noticed something even worse. The truck they were in
was carrying a NEW tree!
Fortunately, as everyone who works on a government facility
knows, the diggers and the fillers are never the same crew.
They tossed the new tree off the truck and drove away. SO my
technician madly raced over to move the camera, while I madly
scurried inside to call the local security to put out any brush
Fortunately, we got the camera moved to a nearby light pole
before the fillers got there and replaced the tree. Second lab
period began, new tree in place as if nothing had happened. No
security drill either..
The academy does things like that. Complete flower beds
replaced overnight so that there are no dead flowers and there
is always something in bloom. Oh, and no wonder all the trees
are in good health... If it ain't, then it is replaced!
I was sure I was going to be spending the day chasing a
landscaping crew to the nearby landfill to retrieve my camera
and other goodies...
Anyway, these little $75 cameras at 2.4 GHz are a great way to
bring microwaves and small dishes into the classroom. Just be
careful where you put them. Oh, and plan on seeing LOTS of
intereference from LANS.
For clear links, choose some of the $75 wireless cameras on 1.2
GHz which don't compete with LANS. But I think the FCC has cut
off the supply of these coming in from China...
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