[VHFcontesting] QUAGI'S

[Steve Kavanagh]

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