[SEDXC] Working the JA's
Joe Subich, W4TV
w4tv at subich.com
Tue Sep 12 10:00:49 EDT 2006
> Avoid putting ANY yagi or antenna at multiples of .5 wavelength. The
> lobe creased straight up is enormous. Try at .625, .875, 1.125 for
Multiples of 1/2 wave are fine, they provide a null straight up.
You want to avoid ODD multiples of 1/4 wave (e.g., 1/4, 3/4, 5/4,
etc.) they have very strong vertical lobes.
This is one of the reasons that a 2 el 40 at 75 - 80 feet is often
better than one at 100 - 110 feet. Although the primary lobe is
lower at the greater height, more power is going into the "useless
lobe" and the high angle lobe also receives much more noise/QRM.
> Another factor is the take off angle by itself. If you consider it
> takes X number of reflections from the Ionsphere to reach your
> desired location, you need to put as much power as you can into
> a lobe which will give you a minimum of bounces.
An excellent tool for looking at take off angles is HFTA by Dean
Straw. It is included with the current ARRL Antenna Book.
... Joe, W4TV
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