Simple Antennas for Amateur Radio Operators–static charges on HF Antennas, post #238


STATIC CHARGES ON HF ANTENNAS

During the past weeks, I’ve emphasized the importance of good grounds for your antenna system.  This means not only disconnecting your station from your antenna when you are done but also grounding your transmission line to an actual earth ground.  The transmission line carries current from the antenna to your transceiver, and this electron flow down the wire can cause a build up of static electricity or even worse, fry your rig and perhaps you, if a lightning strike occurs near your antenna.  By installing lightning surge/EMI protectors, you can add a margin of safety to your station, your home, and yourself.  I’ve seen what a lightning strike can do to my antennas.  It isn’t a pretty site.  Thankfully, all of my antennas, including my full-wavelength loops, had surge protection and were disconnected from the shack.  Protecting your station from a lightning strike is fairly simple.  The time you spend on protection will save you a big headache later.  So, let’s begin.

MATERIALS NEEDED:

A fully assembled and erected antenna.  My last static protection project involved my recently completed 20 meter vertical dipole.  The dipole was attached to a 33-foot MFJ fiberglass mast.

Transmission cable.  In this case, I had some RG-6 fitted with UHF (SO-239) connectors in the shack.   Also, you could use 50-ohm cable such as RG-58, RG-8, or RG-8X.  The nominal 75-ohm impedance of the RG-6 didn’t present any problems to my antenna matching unit.

Antenna discharge unit.  There are several types of units available.  Checking the Fall/Winter 2012 AES Catalog, I found a couple of suitable units from Alpha Delta Communications, Inc. (p.75).  You could choose the surge protected antenna insulator kit (complete with center connector, replacement arc-plug, and end insulators) or the lightning surge/EMI Protector with  N or UHF connectors, arc-plug cartridge, and choice of power ratings from 200 watts to 2,000 watts.  I used the lightning surge/EMI system because that was what I had in the shack.  Depending on your needs, the price for this discharge unit runs from $49.99 to $74.99.  This is cheap insurance when you consider the price of rigs these days.

Ground wire.  I had some AWG #10 auto wire in the “junque box” for this purpose.

Ground rod, 6 to 8 feet long.  Check your nearest hardware or electrical supply house for this.

Ground rod clamp.

Hammer to pound the ground rod into the ground.

PROCEDURE:

Details will vary, depending on your requirements.  In my situation, I connected the RG-6 coax (with UHF connector) from the antenna to the discharge unit.  Then I connected the RG-6 coax (with UHF connector) from the antenna matching unit to the other end of the discharge unit.  The discharge unit was placed near where the shack coax ran through a window panel to the outside.

I crimped the ground wire to the terminal provided with the antenna discharge unit.  I found a pair of pliers suitable for the task.

Once the ground wire was attached to the discharge unit, I drove the ground rod into the ground with a hammer as close to the shack window as I could.  I left enough room for the clamp.

With 3-inches of the ground rod exposed, I attached the #10 gauage auto wire to the ground rod with a clamp using a screwdriver to tighten the clamp.  The ground wire was approximately 10-feet long.

RESULTS:

Since installing the antenna discharge unit, I’ve noticed a significant drop in antenna noise and static.  Verticals are susceptible to noise, since most noise appears to be vertically polarized.  Even though the discharge unit is working well, I always disconnect the antenna transmission line and connect it directly to the ground rod when I’m done operating.  As an added precaution, I lower my vertical antennas to ground level at the end of the operating day.  I also disconnect the short piece of RG-6 coax from my antenna matching unit and all connecting patch cords.

You will find an antenna discharge unit particularly useful in flat top dipoles, where it may be difficult to lower the antenna to ground level.  For a horizontal dipole antenna, you may find Alpha Delta’s surge protected antenna isolator kit a worthwhile addition to your antenna farm.  At last report, the unit costs $29.99.

It really doesn’t cost much to add more protection to your antenna system.

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Until next time,

Aloha es 73 de Russ, KH6JRM–BK29jx15–along the beautiful Hamakua Coast of Hawaii Island.

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