Monday, November 1, 2010

I’d like to try microwave operating from home, but I can’t put up antennas outdoors...

Q I’d like to try microwave operating from home, but I can’t put up antennas outdoors. Is it possible to at least receive microwave signals with an attic antenna? Will the signals make it through a standard shingled roof? I’m thinking specifically of receiving satellite microwave downlinks. Bob Bruninga, WB4APR, answered this question with an interesting experiment:

A “Since I have a Direct-TV 1-meter dish on a tripod that I
use for demonstrations, I decided to check its performance through various materials. The unit has a bargraph signalstrength meter for use during alignment. The meter scale goes from 0 to 100. Here are the results:

Outdoors in the clear: 92
1/4-inch plywood covering: 80
7/16-inch plywood covering: 77
3/4-inch plywood: 60
3/4-inch Masonite: 70
3/4-inch stack of paper: 60
1.5 inches of plywood: 43

(Note that the signal drops out completely at 35.)
“I have no idea if the scale is at all linear or logarithmic, and my arm was too short to both hold the wood and see the monitor well. So, your mileage may vary.

“With digital the picture is always perfect. You don’t lose any quality until it drops out completely. Of course, most of this margin is needed in case of rain. But it looks to me like it should be possible to receive microwave downlinks through a simple 3/4-inch roof and shingles, as long as rain, ice or snow are not involved.”

From QST February 2001