"Doug Gavilanes" wrote in message
ink.net...
Greetings from So.Cal.

I'm at wits end, now having gone through 4 antenna mounts on my vehicle.
This is the situation: I have a Jeep Wrangler, on the rear of which I
have a trail rack (for cargo, and mounting Gerry cans). Over the last few
years, the trail rack has become my mobile antenna farm, hosting a Diamond
NR770 NMO dual band whip, a 1/2 wave Larsen base loaded NMO 220MHz whip, a
1/2 wave Larsen base loaded NMO 144MHz whip (for APRS), and a Larsen
VHF-UHF-800/900MHz NMO center loaded monitor antenna. For HF, I mounted a
K400 mount with 3/8" stud for a Lil' Tarheel II compact screwdriver (16"
body, plus 5' whip), on the left rear corner of the trail rack (about 6'
off of the ground). This location puts the antenna at a high point at the
rearmost location on my Jeep. Being a short wheelbase vehicle with a 3"
lift and 32" tires, the ride is inherently bouncy. The daily commute on
the I-405 in the South Bay of the L.A. basin injects speeds of 5 to 70MPH
during the commute. To date, I have cracked the base plate of the trunk
lip K400 mount around the front edge of the round protrusion where the
adjustable head of the mount supports the antenna. Twice, on separate new
K400 mounts. The K400 is too flimsy (the fact that it is being made in
China from metal not of the same original stainless grade as the original
article is a separate issue) to support the stiff antenna, which is
bounced and rocks front to back and side to side on every bump, dip, and
pothole. Complicating matters is that the mount is at the rearmost and
highest point on the rear of the vehicle, and the momentum of flexation is
greatest at this spot. However, it is the absolute best spot to mount the
antenna for performance and loading (perfectly flat on all bands 10
through 75M).

My Alinco DX-70T only delivers 100W, and when mobile in motion, doesn't
always have enough punch, so I enlisted an amp that would provide me with
about 200W PEP, the max. rating of the Tarheel II. The amp exceeded this
a few times, and after replacing the coil once, Tarheel informed me that a
new compact version was under development, with a max. rating of 500W PEP.
Armed with this knowledge, I installed an Ameritron ALS-500M with remote
and soon abandoned the K400 and smaller Tarheel II for the heavier duty
Tarheel "Stubby" (16" body with 5' whip) and a new Hustler stainless ball
mount. Worked great, but within two weeks, upon arriving at my office one
day, a co-worker asked me if my antenna had broken. When I went out to
check, the antenna had rotated down at a 45° angle into a big 6.5' curb
feeler mode into the left parking space next to me. I removed the
antenna, and found that the outer ball half had cracked at the 3/8" stud
that protrudes from it, causing the ball to loosen and slip. The candy
store was nice enough to replace the part under warranty, and that night I
was back on the air.

A couple of weeks later, I noticed (during my daily mount checks provoked
by the paranoia of losing a $350+ antenna on the freeway, and causing an
accident, to boot) that some "wiggle" had developed between the 3/8" stud
exiting the outer ball half, and the outer ball half itself. Enough
movement to make me fear that another 30 or 40 miles would be enough to
snap off the antenna cleanly from the replacement ball mount,
unexpectedly. I removed the antenna, and searched for a stronger mount.
I remember the old Motorola stainless ball mounts from the Broderick
Crawford 2150 days, and that they were nearly bullet-proof. I also
remembered that Antenna Specialists made them for Motorola (ASP-3, or
something like that). These are as rare as $3 bills nowadays, since A/S
abandoned making them. However, I collected an ancient Batwing ball mount
with a cracked gray phenolic base (too bad, as that's where the Moto
branding was) years ago at the swapmeet, so I tore my garage apart and
finally located the old gem. I retired the Hustler stainless hardware,
and installed the Moto / A/S stainless hardware into the black phenolic
Hustler baseplate. Perfect fit, and very tight mount (no slop at all).
About three and a half weeks have passed, and I have just discovered the
same "wiggle" that caused me to scrap the Hustler ball mount. Needless to
say, my screwdriver is again off the air.

Sorry for the preceding "diary" - but a good understanding of my dilemma
couldn't hurt. Now, does anyone out there know of a strong 3/8" stud
mount that will support my screwdriver (which probably weighs about 8 to
10 pounds, with a 16" body, 2" dia. coil, and 5' whip) now and forever?

I am able to bolt into the 1" square tubes of the trail rack - that's how
I affixed the fabricated steel mounting plate that I put on the side of
the rack to host the ball mount. The top and bottom tubes are about 4"
apart. Can anyone offer a practical solution? My HF capability is
important to me (ARES emergency comms and stuff, you know...). Thanks in
advance.

73 de Doug, N6XQY

Doug,

If I understand you correctly, you have changed over to a sort of full-sized
screwdriver? If so, I might suggest that you got to a slider mount that
slips into the end of a Drawtite or Reese hitch. It is shaped like a
reversed "F" with the center bar of the "F" facing to the outside of the
hitch. It seems you ARE suffering from vibration severe enough to cause the
kind of damage you are experiencing. *IF* you ARE using basically a
full-sized screwdriver, the advantage of this is you can secure the antenna
FULLY at the top of the now upside down "F" with a piece of Lexan
(non-conductive). It firmly prevents any "wiggle" and absorbs most of the
shock by taking most of the strain off the bottom of the antenna and spreads
the load across a wider area. Granted, it is better if you can have the
antenna up and away from ground losses, but my experiences have been that
the securely fastened, essentially bumper-mounted antenna works quite
well-and, of course, prevents the extreme shocks that a single-point mount
must absorb on its own.

I hope you find a solution and I hope that I might help in your search for
what has to be a very frustrating problem for you. I, too, am heavily
involved in emergency comms (CAP) and I have a 3" diameter antenna that has
been mounted on my Chevy S-10 for 2 years + with no problems. If you hit the
mount, it would probably destroy the antenna and mount.

73

Jerry

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