Thread: Antenna mount
View Single Post
Old 10-25-2016, 07:26 PM   #10
NN5I
Carl, nn5i
 
NN5I's Avatar
 
Join Date: Sep 2011
Location: Tallahassee, FL
Posts: 1,441
Default

It will probably be inefficient. Most antennas, and especially most small antennas, are.

That's not as bad as it seems, though. Suppose an antenna system radiates only 6.3% of the RF energy fed to it, and wastes the other 93.7%. That's a 12dB loss, which is only two S-units. If a perfect antenna would get you an S9 signal report, you'd still be S7. Big deal. And there are no perfect antennas anyway, though N5SU once got over 85% efficiency out of a very big array. That was a VOA station, I think he said, with a gas-pressurized coaxial feedline nearly a foot in diameter, and many radials extending hundreds of feet. He showed photos, and they were very impressive.

That's why big antennas for point-to-point communications (as opposed to broadcast) are usually directional. If you can double the energy going in the direction you want, at the expense of other directions, that's 3dB right there; and many directional arrays can do much better than that. I once had a six-element 20m beam that probably was 15dB better than any vertical. When I switched to a vertical (not a very good one, either), I thought my receiver was dead.
__________________
-- Carl
NN5I is offline   Reply With Quote