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Not sure of the post that started this, but I needed a good antenna
mount for my pickup and got tired of drilling holes, etc. into the top of the
cab and knew that lip mount antennas on the hood do not work because of
reflections from the car. I also do not like mag mounts. I took the suggestion
of a local ham and put a "headache rack" on the truck. I did not know what that
was, but to the uninitiated, it is mounted behind the cab to protect the window
from objects coming from the bed thru the rear window when you load stuff back
there. It also is useful for tying down long loads (like crappie pole antennas!)
to it. But the best use for it is the mounting of two or more antennas to it
made easy by the vertical posts most racks have on either side of the bed just
behind the cab. Mine has square vertical tubes, where at their top
most point, I made a simple aluminum angle piece to mount a 2 meter and a 220
MHz NMO antenna mounts. They are up and above the cab having good radiation
views. The antennas do stick up above the cab the height of the
antenna, but they work great. I routed the cables into the cab at the back
lower edge of the doors (thru some rubber grommeted holes in the front of the
bed), since I do not have a bunch of traffic in and out of them, it is no
problem. The truck is a F-250.
Roger W5RD
----- Original Message -----
Sent: Thursday, April 20, 2006 3:20
PM
Subject: RE: [Repeater-Builder] Anetenna
Help
Somebody, maybe Larsen
or Antenna Specialists, used to make a "stiffener" for use with NMO
mounts. It was basically an oversized brass fender washer with a 3/4"
hole in the center. It was thick enough that it stiffened the body near
the mount, but flexible enough that it would take the shape of the concave
contour of the roof when you tightened down the NMO. I haven't seen them
advertised in a while, not sure if they're still made.
I had a Diamond
dual-bander act as a can-opener to the roof of one of my previous trucks
(Chevy Tahoe). It got snagged on a low-hanging ice-laden branch on the
way up to a tower site. The roof gave up before the antenna did. I
guess that says something about Diamond mobile antennas...?
--- Jeff
Just about any 5/8 wave antenna mounted on top of a Ford pickup truck.
The roof metal is so thin that frequent flexing from antenna sway, wind
resistance, low tree branch contact can cause metal fatigue on the cab
roof. The antenna NMO mount was installed directly above the cab
interior light. Nice install but the metal finally cracked about 1/2
inch circumference further out from the outer edge of the NMO
mount. The singing problem was resolved by wrapping thin fishing line around
the full antenna length at about 1 turn per 1 1/2 inches for its full
length. The thinner the whip antenna the higher the audio
frequency. Observe automobile antennas and you will see many factory
manufactured AM/FM antennas wrapped as mentioned above. Go out and wiggle
your mobile antenna. Look at the automobile metal near the base. Watch it
flex. The longer the antenna the more flexing. I solved the problem by
relocating the antenna using a homemade bracket mounted between the front
fender and hood near corner of windshield.
Gary K2UQ
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