On Sun, 22 May 2011 11:04:10 -0700, 'Captain' Kirk DeHaan
wrote:
I'm living in a wooded area and am trying to hit our club repeater
reliably.
I live in a dense mostly redwood forest. Signals vary from full
quieting to not copyable. We also have two co-channel repeaters
sharing the frequency, that also vary radically in strength. I can
often point my 5 element 2m beam in a totally insane direction, and
improve the signal.
I go from keying the repeater with no intelligible signal to not being
able to hit it. Today I actually have an S meter reading due to the
clouds. I am currently using a J-pole and will put up a Yagi soon but
wonder if NVIS would work on 2m? I have only seen references to it
being applied in HF.
I just love technical posting with no numbers. It would be helpful if
you would offer a clue as to the distance you're trying to cover, what
manner of impervious to RF dirt is along the line of sight, antenna at
the repeater, power levels, etc. For extra credit, if you disclose
these plus your exact location, the repeater's exact location, and I
will contrive a Radio-Mobile path profile from you to the repeater.
That should give you a clue as to what challenges you are facing.
http://www.cplus.org/rmw/english1.html
It will look something like this:
http://802.11junk.com/jeffl/coverage/RST/RST-KCRA.jpg
As for a seat-of-the-pants guess as to a solution, I don't like J-pole
antennas. Actually, the antenna is fine, but the way most people
build, tune, and position them, is what I find disgusting. The lack
of any commercially manufactured J-pole antennas (other than the
American Legion J-poles) should offer a clue. Plenty of plans:
http://www.google.com/search?q=j-pole+antenna&hl=en&prmd=ivns&tbm=isch
but nothing from a commercial antenna manufactory.
In my never humble opinion, if you can barely talk to the repeater
with a J-pole, then a yagi will offer a substantial improvement. The
problem is how much gain is going to be needed to make it reliable. My
guess(tm) is that the J-pole has a gain of about 2.5dBi (opinions vary
on the gain), and that you'll need about 5dB more gain to get a decent
link. That means you'll need a yagi with about 7.5dBi of gain. That
can be done with a 5 element 2m yagi. Obviously, more gain is better
as is more altitude.
Good luck.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558