Revised 14 June 2003
7
ATTACHING THE BOOM TO ELEMENT MOUNTING PLATES
It is now necessary to provide adequate support of nearly the entire length of the boom,
because you will be adding significant and uneven weight to the boom in the next steps.
This can be accomplished with a long table or 3 sawhorses (one for the center plate to
control rotation). The boom ends should protrude about 2 ft. beyond the ends of each
support. This same support setup can be used for final assembly.
Notice that at one edge of the plate, there is a single 3/16” hole, which can be used to
orient the plate for installation. When facing the boom,
which is now inverted for
assembly
, and looking from the rear end toward the front end, that small hole and the
edge that it is nearest, will be outboard, that is, nearer to you and the end of the boom,
and the hole will be 3 inches to the left of the centerline of the boom. The imaginary
centerline (in line with the boom) can also be identified by the two 1/4” diameter holes
that lie along it. The foregoing is also true for the front end of the boom, where you will
be looking from the front toward the rear.
Attach the aluminum rear element mounting plate to the boom as follows:
1. With the plate oriented as outlined above, install the U-bolts that attach the plate to
the boom. These U-bolts will be installed through their saddle pieces, and then up
through the element mounting plate, where each of the threaded legs of each U-bolt
will receive a 3/8” split-ring lock washer, then a flanged 3/8” nut. Leave the nuts at
the end of the threads at this time.
2. When all four U-bolts have been installed, turn the plate over, slide it onto the boom,
with the saddles resting on the plate, while you lift and manipulate each U-bolt to get
it over the end of the boom.
3. Once the boom tube is through the U-bolts and saddles, rotate the plate around the
boom tube so that the plate is again above the boom, align the plate’s two 1/4”
diameter holes with those in the boom, and install the two 4.5” long, 1/4” bolts, with
each bolt going first through the boom, then through the plate, where it receives a flat
washer, then an elastic stop nut. This will put the nuts down and out of the sun when
the beam is in use. Do not fully tighten the nuts at this time.
4. Now that you have gained experience using the lighter aluminum rear plate, install the
heavier stainless steel plate for the front element.
Note:
The weight difference of the mounting plates exactly offsets the difference
in weight between the front and rear element. This produces an antenna
that is weight-balanced at the center of the boom. This means that the
mast attach point will also be at the center, for a wind-balanced boom, and
that the antenna is torque-balanced as well. All this makes life much, much
easier on the rotation system.
5. Mutually level the element mounting plates. This is most easily done with 2 people
and two levels. The primary reason for having the elements mutually exactly level is
appearance.
