PS Magazine - TB 43-PS-561
PS, The Preventative Maintenance Monthly
ISSUE 561
AUGUST 1999
Dear Half-Mast,
What’s the story on whip antennas?
Do they always have to be tied down
when the vehicle is moving?
And, if so, is there a minimum height
to which you tie down an antenna? I’ve
seen them as low as eye level and so
high they looked like they weren’t tied
down at all.
Do we leave them tied down when the
vehicle is not moving?
Finally, is a tip cap mandatory?
SPC K. W.
Vehicular Antennas . . .
Wrap
1
/
2
-in pressure tape, NSN 7510-00-582-4771, six times around the whip
two inches from the top.
Push the tip cap down over the tape. Starting just below the bottom of the cap,
wrap the top antenna element and the cap with the
1
/
2
-in tape. Cover it completely.
Finish up by covering the cap with
3
/
4
-in electrical tape, NSN 5970-00-419-4291.
Dear Specialist K. W.,
Whether your vehicle is packing a SINCGARS or AN/VRC-12-series radio, you
need to tie down the whip antenna when you’re on the move. Antennas left standing
tall can smack into an overhead bridge or tree limb and shatter. Even worse, they
could strike a power line.
Tie down the antenna at a 45–60
o
angle to the ground. That’s low enough to
avoid collisions with most overhead obstacles, but not so low that you risk cracking
the antenna sections or the base.
Attach the antenna clip midway between the tip and the base.
Get a tiedown kit for your AS-3900 antenna with NSN 4020-01-341-8795. NSN
4020-00-908-6416 brings a tiedown kit for the AS-1729 antenna.
If your vehicle has more than one antenna, tie them down alongside the vehicle.
Never cross them. If you do, the transmitting antenna will feed its signal to the one
it’s touching. You’ll get interference and maybe even damage to your radio’s circuits.
When your vehicle is parked for any length of time, like overnight, you should
take the antenna out of the clip and let it stand straight up.
That relieves tension on the base spring. A base spring kept under tension all the
time will weaken.
Also, an upright antenna keeps the base spring coils close together, which helps
keep out moisture and dirt. A tied-down antenna has its spring coils spread open
making it easier for dirt and moisture to get inside and damage the base and the
RF cable.
Finally, a tip cap should always be used. The risk of injury is too great without
one. Here’s how to make sure the tip cap, NSN 5820-00-437-2353, stays on tight.
The pressure-sensitive tape holds the two shells of the cap together, cushions
the cap impact and holds it firmly on the top element. The electrical tape protects
against sunlight and moisture.
Replace the tape when it becomes badly scuffed or worn out.
this
antenna
is
too
high
...
...and
this one's
too low
.
this
one is
just
right
.
just
don't
leave
it
tied down
all night
!
PS 561
49
AUG 99
PS 561
48
AUG 99
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