Boom

Fig. I. Alternate methods for mounting the beam elements on ihe boom.

material is purchased new, choose rigid aluminum tubing 1" and %" in diameter (or similar relationships in size) so that the center sections can be made of the larger tubing with the smaller tubing inserted into the ends to form the adjustable sections. For a 4-eIemenE beam, you 11 need four lengths of the larger size, and three lengths of the smaller. This is assuming you get 12-13 foot lengths which are pretty well standard, he three lengths of smaller tubing can be cut into four foot pieces for the end sections, w.th a little left over, If cost is a prime factor, you can use old booms from defunct TV antennae as 1 did- scrounged a bunch of these from a local service shop, took off all the elements and assorted junk, and ended up with excellent material for the beam elements.

Without doubt, the best material for the boom is old reliable irrigation tubing. The 2" diameter stuff is fine, in a 20 foot length. This gives reasonably wide element spacing. As a matter of fact, a 5-element beam can be mounted on such a boom if you wish, but 1 happen to prefer the wider spacing. Steel TV masting is another common material which can be used for the boom, but it is quite a bit heavier and you may have to couple sections together to make up the re quired length.

Several methods can be used to mount the elements on the boom, as shown in Fig. I. In both cases, standard automobile mil filer clamps are used to fasten the element support plates to the boom. Make sure the clamps are given a couple of coats of rust-proofing first, By using the flat plates, the elements can be laid across the long di-

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