Hi Uwe

I cant resist... Brrrr COLD! I visited Toronto early this year and
havent gotten over the throat irritation yet! It was about 33C when I
left Sydney and -25C when I got to Toronto!

Well then I can now see the use of employing the narrowest band design
possible, assuming you only want the Canadian station. Personally I
wouldnt want to limit its bandwidth because I *might* one day want to
use it for another distant station.

Is it worthwhile doing an analysis of those stations that might
interfere? Like if the interfering source is at 90 degrees heading from
the station you want, anything that starts as a dipole element will
help. If its directly behind you may want to adjust for best front to
back, even to the point of tuning the reflector with some C. This BTW is
much easier on a quad reflector than a yagi. (ie make a "Qagi")

My theoru isnt good on this, but I can see you want a design that has
got low sidelobes and good front to back. Yagis can be optimised for all
manner of things so one design you see may work great for f/b but bad in
sidelobes. Is a phased array better? (ie mount your boom at right angles
to the station and use 2 element designs) How does a quad or helix
compare? Does choosing circular polarisation help? This is actually a
more difficult problem than first thought.

My path would be not to think too much, but put up a helix and see how
it performs. I use to have one on 2M for satellite work that I also used
for terrestrial TV and FM. (Very wide band) I was however in a zero
interference area. Given though that I guess you want to go with a yagi
design, my thought is to build it to the Canadian station frequency with
a tuned refelector and also see what happens. When you have built it
plot the pattern at various frequencies. Have a look at Mr Cebiks web
page on OWA yagi's. (http://www.cebik.com/2mowa1.html) He often shows
radiation patterns and lots of other data. Well worth a look.

Apologies for the length!

Cheers Bob VK2YQA





Uwe wrote:
Bob, the reason to want the high gain is as follows.

I live in Maine south of the Canadian border, close but not quite close
enough to receive Canadian FM stations. I can receive one station faintly
using a Radio Shack BC band antenna and wanted to expand on that with a
better antenna and possibly a change in IF filters in the tuner I use.

And I thought that a very high gain antenna with its narrow pattern would
also aide in adjacent channel rejection. I realize that it could be a
problem covering the entire BC band and I am not set on any particular
design, I first wanted to see what people here had to say.

Regards Uwe
KB1JOW