On Thu, Jun 4, 2009 at 9:58 AM, Robert Bruninga bruninga@usna.edu wrote:
I want... a dual band 144/440 antenna on my 85' tower. Can I get away with a fixed elevation of about 30 degrees and horizontal polarization?
Three facts say that 30 degrees is the wrong angle.
- The amount of time that LEO satellites are above 30 degrees
is less than 20% of all view times.
- You don’t need gain when satellites are above 30 degrees
because they are much closer and 6 to 10 dB STRONGER.
- You DO need gain at the horizon where they are 6 to 10 dB
WEAKER.
So putting the beam at 30 degrees is counterproductive to LEO satellite reception, you will be giving up 3 dB where you need it most!.
The answer is to elevate it to 15 degrees.
Once again, Bob's advice is very good. I followed it when I began satellite operations, and it was quite helpful. Some further notes:
1. This pertains to shorter, and therefore wider beamwidth, antennas only.Fortunately, these are quite acceptable to communicate with LEO satellites.
2. You needn't be too fussy about the exact angle. 30% is too high, but you'll probably not notice the difference between 12 and 17, for example.
3. With a tower that high, you must include low noise preamps at the top of the tower. The ones from Advanced Receiver Research and SSB USA are highly regarded on this list.With that much cable between you and the antenna, you will be better off with a simple 1/4wave vertical and a preamp than you would with these antennas and no preamp.