It seems that this subject comes up once or twice every decade. I have never used anything but a metal cross boom since I joined AMSAT in 1974. Later there were some tests run by Kent Britain, WA5VJB. His measurements resulted in the following recommendations:

1. Mount the antenna with the tips of the elements as far from the support boom as possible. Instead of mounting them in a + form, mount them as an X in relation to the cross boom.

2. Saw off any excess cross boom so that it doesn't extend past the antenna boom.

3. Avoid mounting the boom 1/2 or 1 wavelength from the driven elements. (I would modify that to multiples of 1/2 wavelength)

4. Run the coax out the metal boom and down the antenna boom. Keep the turning radius of the coax small but not to the extent of damage to the coax.

I have never detected any bad effects of this arrangement and had stumbled into this configuration years before Kent published his findings in the 1993 AMSAT Symposuim Proceedings. I did it to avoid having the coax from hanging off the rear of the antennas and dragging on the roof of my house and changing fore/aft balance with ice loads. Incidentally, I think I recall that Jim, G3RUH was also using this method. If anyone wants a photo of the antenna setup and contacts me directly I will send it to him.

Roy -- W0SL AMSAT 410