Carl:
I have built quagis in the past and they worked fine, though usually a good
modern wood-boom Yagi design can do a bit better performance-wise at no more
cost.
I suspect you will find getting a dual-polarized quad driven element to work
properly to be fiendishly difficult.
You can't just use two cross-polarized loops, offset along the boom as in the
M2 satellite antennas, since they will couple strongly to each other, unlike
dipoles. Also, the quad reflector elements would couple to each other and to
both driven elements....what a mess !
K0OV claims to have done it (using a single driven element) at
http://www.homingin.com/dualfeed.html. But since he was interested in
receiving only, the SWR problems he encountered were not of too much concern.
I suspect the feed impedance of his antenna will depend quite strongly on the
length of the unused coax run and how it is terminated. In addition, he
probably should have put more ferrite beads on the coax runs at the top of the
mast to prevent currents from being coupled onto them in vertical polarization.
There's a discussion of this problem at
http://forums.qrz.com/archive/index.php/t-256862.html . Unfortunately, there's
nothing to distinguish between quoted text and replies so it is a bit hard to
follow.
There is a type of dual polarized element that looks a bit like a quad loop and
works well (see http://www.g6lvb.com/wimo_x.htm , for example). But this is
not a quad loop and would require re-optimization of all the quagi element
lengths and positions for correct operation.
73,
Steve VE3SMA
_______________________________________________
VHFcontesting mailing list
VHFcontesting@contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting
|