HF Mobile Installation Tips

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 screws.)

(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 information.2


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.

 

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