15
INSTALLING THE MAST ON A WOOD ROOF FRAME
4. With an assistant place the base plate on the centerline at the
spot you plan to install it (see Figure 15).
5. Plumb the mast in two perpendicular directions (Figure 16).
If you successfully plumb the mast proceed to step 6. If you
cannot plumb the mast find another location to install the
antenna. Note: it is essential that the mast be plumb. If you
cannot make the mast plumb at this point, find another
installation site.
6. Mark the center of the base plate’s top center hole
7. Drill a hole on the center mark in the manner described
below. Note: to avoid drilling too deeply, wrap a piece of
masking tape around the drill bit shank at the appropirate
depth so that you can see when you should stop drilling.
Drill a 1/8-inch pilot hole 2 inches deep.
Going into the pilot hole, drill a 1/4-inch hole 4 inches deep.
Going into the 1/4-inch hole, drill a 3/8-inch hole to a depth
equal to the unthreaded portion of the 3/8-inch x 4-inch lag
screw.
8. Apply silicone sealant the thickness of a bead to the entire
back side of the base plate. Apply enough so that it will
press out around the edges when you install it on the post
(see Figure 18). Doing this will help prevent water from
seeping into the wood.
9. Install a 3/8-inch washer on a 3/8-inch x 4-inch lag screw.
Apply soap or some other lubricant to the screw.
10. Use a wrench (preferably a ratchet) to screw the lag screw
into the top center hole of the base plate (see Figure 11).
You may need to swing the mast out of the way temporarily.
Tighten the screw snugly so that the base plate can barely
move.
Note: Do not pound the lag screws into the post with a hammer or
mallet. Doing so may split the wood and render the post unusable.
11. Replumb the mast in two perpendicular directions as you
did in step 5. You may need to make adjustments to the mast
and/or the base plate. If you adjust the base plate, do not
move the center of the bottom center hole off the centerline
more than 1/16-inch.
12. Tighten the screw snugly so that the base plate cannot move.
13. Tighten the adjustment nuts.
14. Replumb the mast. (Tightening the nuts can move the mast
off plumb.) Note: the mast must be plumb before proceed-
ing.
15. Adjusting the drilling depth for the 3/8-inch by 2-inch lag
screws, repeat steps 6 and 7 to drill holes for the four corner
holes. See Figure 16. Note: You must mark the center of all
screw holes accurately so that you can plumb the mast. A
Stanley Jumbo Self Centering Nail Set or similar product
will produce the best results. A #6 washer can also be used
to guide your pencil as it marks the hole center.
Note: the base plate must not move when you drill the holes.
Figure 15
Figure 16
Corner holes
Corner holes
Top center hole
Bottom center hole
Centerline
Rafter or truss
Center hole lag
screws are 3/8 inches
by 4 inches
Corner lag screws
are 3/8 inches
by 2 inches
Mast
(top view)
Level
Mast
Plumb vial
Adjustment nut
(2 places)
Pivot bolt
Bubble must
be centered
between
marks
Carpenter's level
Bubble
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