On 5/22/2011 8:26 PM, Jeff Liebermann wrote:
On Sun, 22 May 2011 17:55:16 -0500, John
wrote:

* Try moving your existing antenna. Even a small movement may cure the
problem as you may have cancelling reflections at times. There is almost
always a "sweet spot" somewhere in the vicinity.

I beg to differ. I have about 30 years experience in dealing with
propogation through a dense redwood forest (Ben Lomond CA). The trees
in my area are about 120ft high. While moving the antenna around may
temporarily improve the signal quality by reducing frequency selective
fading, multipath, reflections, and just plain bad luck, they do not
tend to remain improved. Trees grow and move around. What works well
now, will probably not work well tomorrow.

You may be right, Jeff. But he may not have 120ft redwoods around and,
after all, this is a temporary fix until his yagi comes in.

I gave up on fixed antenna mounts for my rooftop verticals. (Well, I
have one mounted on a tripod, but that was before I realized what was
happening). Most of my verticals are mounted on 2x12 planks, held
down to the roof with sand bags, concrete blocks, and buckets full of
water. Every few months, I move the antennas around to see if I can
improve the signals to specific repeaters.

Good for you! Pat yourself on the back.

* Try tilting your antenna to 45 degrees and see if that helps. It might
improve reception due to the random polarization of the incoming signal
caused by the trees.

I beg to differ again. Tree trunks are mostly water and do an
impressive job of simulating a slot type polarization filter at 2m and
440Mhz frequencies. Leaves and branches will pass RF fairly well, but
not tree trunks. I've played with both polarizations, circular
polarization:
http://802.11junk.com/jeffl/circular-polarization/
and some diversity reception. Empirically, signals are about 6dB
stronger going through the trees vertically polarized, than
horizontal. The effect continues up to at least 2.4GHz. Above that,
at 5.7GHz, the signals seem to be going through the holes between the
leaves.

I must admit that I haven't actually tried 45 degrees on 2m or 440Mhz,
but I don't think it will help much. Still, it's an easy thing to
try.

You spent more words debunking the suggestion than admitting that you
don't really know whether it could help or not. Good move. And, by the
way, I have experience to the contrary at both 144 and 444 MHz. It all
depends on the location of the source and the receiver. At 2 meters,
some rotation of the antenna can sometimes be helpful. Note that we are
not concerned with GHz.

John