Your Tower May Be in the Crosshairs
Our broadcast towers often
are built in remote places, and autumn brings a special kind of
vandal to such sites, one who is armed and thinks your tower, tower
light and coax line are fair game.
Fig. 1: A
bullet pierced a leg of a tower; the damage was noticed by a tower
rigger performing a quarterly inspection.
Shooting damage can be a
nuisance or it can be catastrophic. Such incidents also pose a threat
to an engineer.
“No Hunting” signs
are respected by responsible hunters, and you should use them. But
what about after damage has occurred? Unless a bullet pierced your
transmission line or antenna and caused an immediate, dramatic leak
in air pressure (or worse), you may not even know your facility has
That’s why a quarterly,
even yearly, inspection by a rigger is so important. Yes, it’s
expensive. Treat it like insurance: What problems will the rigger
find that could have escalated into a terrible disaster?
Fig. 1 gives us an
example. This “guy with a rifle” (I won’t honor him with the
title of hunter) had amazing aim. But pity the tower rigger whose
line is clamped to the tower and who snapped the photo. This kind of
damage is scary!
In addition to the hole
through the tower leg, your tower inspector can find coax nicks or
holes, broken support straps or hangers, and cracked or broken tower
light lenses. As this engineer did, make sure the climber brings
along a camera. Documentation of this sort opens the door for a great
discussion with your GM (not to mention giving you great visuals to
share with fellow engineers in a future Workbench column —
anonymity is assured).
The tower climber may also
find things that need attention, such as rusted line clamps. It’s
easy to see from the pictures that this tower needs some help. But
help costs money, and as long as the station is on the air, such
problems may be set aside by upper management.
Pictures also serve to
protect you, the engineer, against false claims that you’re “not
doing your job.” In today’s climate of lawsuits, take the time to
type up the findings, submit them to the GM or owner, and keep a
Your tower inspection
should not only include the tower but the guys and anchor points.
Visit the anchor points, walking the site with the rigger, asking for
his professional opinion of things that could be improved or
upgraded. With many stations preparing budgets this time of year, a
new coat of paint on the tower may trump new sales computers!
* * *
Paul Sagi, an engineer in
Malaysia and longtime Workbench
contributor, wonders how many
engineers are still using Ampex open-reel tape machines. In today’s
digital age, my guess is not many. However, I have visited stations
where the production room holds at least one vintage reel-to-reel,
just in case.
has some experience repairing these machines, and offers a tip to
readers. Remember the venerable Ampex 600B reel-to-reel? Great
machines, but after years of use, the clutches sometimes seize up.
The cause is the clutch-bearing grease hardening.
used eddy current clutches in these machines; the service manual
warns that the machines need special jigs/fixtures, and can’t be
repaired in the field. At issue is a 1/10,000-to-1/20,000-inch
dismantled the clutches anyway, including the bearing dust covers,
used solvent to remove the old grease from the bearings, added fresh
lithium grease and reassembled. Sure enough, there was no clearance.
The rotors were frozen.
he thought about the problem, Paul realized the magnetic field inside
the clutch would be symmetric and centered. The small gap inside the
clutch would present an intense field, and thus the field would exert
a strong force on the rotor to self-center it.
procedure is to assemble the clutch but leave the screws a bit loose,
so the clutch parts have a little freedom to move. Then apply the
usual 110 VDC supply to the clutch coil, which will align the clutch.
You may prod the sections a bit with your fingers, in case you have
the screws a little too tight. Now, confirm
rotation, and gradually tighten the screws, all the time confirming
free rotation. Remove the voltage source, and confirm free rotation;
and you’re done.
jigs or fixtures; and the process does not take long. You can figure
five minutes alignment per clutch.
odd that the engineers at Ampex never thought of using the magnetic
field of the clutch coil to self-align the clutch.
Alleo has a fun website for engineers who like to experiment and
build circuits. You’ll find a variety of power supplies and motor
controllers at www.bangkoktoshop.com.
to Workbench. You’ll help your fellow engineers, and qualify for
SBE recertification credit. Send Workbench tips to
firstname.lastname@example.org. Fax to (603) 472-4944.
John Bisset has spent 44 years in the broadcasting industry and is
still learning. He handles West Coast sales for the Telos Alliance.
He is SBE Certified and is a past recipient of the SBE’s Educator
of the Year Award.