With all the different types of installations possible, there
are many unique problems that can occur. We have compiled
some additional notes on specified areas.
(1) GROUNDING ANTENNA: Obtaining a good ground is very
important to any HF mobile installation. No matter where your
antenna is mounted, it is highly recommended your run a heavy
copper strap or braid (1 to 3) between body and
frame of your vehicle. (NOTE: Copper wire is not sufficient!)
If you have ignition noise problems, it is also recommended
to ground the end of your tail pipe to the frame.1
(2) OPTIMUM MOUNTING LOCATION: You should always mount
your antenna as high on your vehicle and as far away horizontally
from other metal objects as possible. The center of your roof
is the best location; however, this is not always practical
or possible for most HF antenna installations. The next best
location is in the center of the driver's side of the trunk
(side mounted on driver side to avoid low hanging curbside
branches or objects). The DIAMOND K400C and K600M series mounts
work well with the MV3A.
The front or rear bumper is another possible mounting location;
however, due to high ground loss, this should be last choice.
If you must use a bumper mount, it is recommended to use a
base extension to raise bottom of antenna to equal height
of top of trunk. Grounding of this extension will become important.
(3) TRUNK LID MOUNTING: Probably the best mounting
location for most vehicles. Usually, adding one or two copper
straps from the hinge area to car body will improve grounding
(and thereby antenna tuning). It is necessary that at least
two of the four sockethead screws on mount penetrate paint
to metal for proper grounding. (A little clear nail polish
or other acrylic paint may be used to seal around mounting
(4) COAX: If you use an antenna mount other than DIAMOND
ANTENNA models K400C or K600M, it is very important to use
a quality 52 ohm coax (RG8U, RG58U, RG213, Teflon Coax, etc.
with at least 95% shield and stranded center conductor). Do
not use foam coax or coaxes with solid center conductors.
Foam coax can deform in heat and absorb moisture, solid center
conductor coaxes have less flexibility and may become brittle
and break in mobile applications.
(5) EMI: Electromagnetic Interference is the single
greatest concern for HF mobile applications. Route your cable
as far from the vehicles ECM (Engine Control Module) and vehicle's
electrical systems as possible. Sometimes a ferrite choke
may be required on coax near mount. There are many books on
the subject of interference, refer to endnotes for additional
1 J. Seybold, HF Mobile Installation Tips, December
1995 QST, pg. 58-60.
2 ARRL, Radio Frequency Interference Tips: How to find
it and fix it., The book is available from your favorite
amateur radio dealer or ARRL headquarters.