Hi Jim,
Enjoyed your info on the tram line experiences. As I watched this thread
the past few days, most of the fine points have been covered by others,
although this subject is best covered in a magazine article where photos and
drawings can tell a thousand words... but I did want to add one thing which
I haven't seen covered. N6ND and I together have trammed up perhaps 150
antennas for ourselves and others over the past 25 years, so we've had a few
knocks! As you suggested, one of the biggest problems is 'rolling' of the
boom, which causes the element tips to go 'high or 'low' relative to the
slope of the guy wires you are trying to avoid near the tower top. Another
is the tendency of the boom to wander in the horizontal plane, so that your
reflector (or last director) element tip may arrive at the mast area before
the boom-to-mast plate gets there ( this can be minimized by use of
lightweight tag lines controlled by ground people but is not always
satisfactory).
The fix for both problems is the following. Use a bridle to hang the boom
about three feet below the upside-down traveling pulley. Of course, the
boom should be normal to the direction of the tram wire, with the element
tips pointing at the target tower and elements parallel to the earth.
Adjust the bridle position carefully over the c.g. for best boom balance to
keep it level. At this point, most people tie their haul-line either to the
boom itself, or to the traveling pulley. Either method causes the problems!
The solution is to use a 'torque arm' on the lower end of the haul line.
The arm is made of a piece of angle iron, 1/8-inch by 1-inch by about 28
inches long. Drill one end to accept a shackle for the haul line. Drill the
other end to accept a single HD muffler clamp for the boom in use. With the
antenna hanging on the bridle a few feet off the ground, and the boom
balanced end-to-end, put the muffler clamp and torque arm onto the boom,
next to one or the other edge of the boom-to-mast plate, which keeps it near
the c.g. point.
The torque arm points at the target tower. You will find that you can set
the 'angle of attack' of the elements by swiveling the arm and tightening
the muffler clamp wherever you want it. In general, with a tram system you
want the leading tips of the elements to be perhaps 10-15 degrees above the
angle of the tram wire itself. This keeps them out of the upper guy wires
as the beam approaches the tower top, but not angled so high that they
collide with another beam which might already be up ten feet on the mast. In
most cases I have found that putting the torque arm in approximately the
same plane as the elements is about right (sometimes a bit below their plane
is best). KLM antennas in particular need the torque arm, because they are
so top-heavy and want to roll over, backward, without it. In any case, try a
few short test lifts part way up the tram and keep adjusting the torque arm
until you get the angle-of-attack right.
With a rigid torque arm at the base of the haul-line you will find that the
boom cannot roll over, nor will it wander in the horizontal plane even with
a bit of wind blowing. The rigid arm keeps the boom perpendicular to the
tram (and thus the elements remain parallel to the tram, which means they
won't try to cross over the tram and get hung up). These features make
taglines unnecessary, and one-man installations are possible. I hang a
come-along from a mast clamp about five feet above the target location.
When the upper end of the torque arm arrives at the mast, I reach out and
attach the come-along lower hook to the boom bridle and pick up the load.
Then the lower end of the tram can be slackened and removed, and walked in
toward the tower. Then the upper tram area is dismantled and the boom plate
fastened to the mast, positioned by the come-along.
BTW, if you do a few of these you should make a permanent wire rope bridle
which terminates on short angle-irons with a muffler clamp in each to fit
the boom. You can move the boom back and forth through the clamps to quickly
find your balance point and then tighten them. Nicopress a big thimble in
the middle for shackling, etc.
This has gotten a bit long but hope the torque arm description will be
useful to some of the gang who use tramming systems.... 73!
Glenn K6NA
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