[Elecraft] Antenna grounding idea

[Don Wilhelm]

Rick and all,

It used to be common practice back in the 'old' days when we made our own
vertical antennas - to put an RF choke across the feed end of the vertical
to bleed off static charges.  A 44 uH inductor at 160 meters has about 500
ohms reactance and anything bigger will work FB.  Wind 12 to 15 turns of
wire (I suggest #20 wire) on a FT114-43 toroid core - connect one side to
the antenna and the other side to ground.

This is not lightning protection!!!  - it is only to bleed off static
charges that can lead to pops and clicks in your receiver.  A 4:1 balun will
also do the same function - but a 1:1 current balun will not.  You could use
a similar inductor at the feedpoint of a dipole or use it at the shack end
of the feedline.  If you are using a multiband antenna, figure the impedance
of the antenna system at the point you want to place the RF choke - and size
the RF choke so it has about 10 times the impedance of the antenna system at
that point - otherwise the RF choke may be too small and swallow up part of
your precious watts.

73,
Don Wilhelm  - Wake Forest, NC   W3FPR home page: http://www.qsl.net/w3fpr/
  QRP-L # 485   K2  SN 0020   mailto: w3fpr@arrl.net


----- Original Message -----
> From an old Air Force safety film, I remembered that the electric
potential
> in clouds is followed by an equal, but opposite, charge along the ground
> beneath the cloud (ground is not a perfect conductor so local potential
> differences can exist). Clouds would pass over my R7 vertical and an
> opposite charge on the ground increased the potential difference between
the
> driven element and ground (the ground potential changed but the insulated
> driven element remained at its original potential (probably zero volts)).
> When the voltage got to be too much, a spark would occur! I tried loading
> the arrestor with a 1k resistor to bleed off electric potential.
Apparently
> the resistance could not conduct the charge away fast enough.
>
> Later, I switched to a ladder line-fed dipole and experienced the same
> phenomenon.
>
> Finally, I bought a 4:1 balun and placed it outside the house and grounded
> the center tap on the antenna side (ladder line to ant). I ran coax into
the
> house (abt 10 ft) and to the K2 (now with a KAT2).  No more static
> discharges! Both dipole elements are at DC ground, so no charge buildup
can
> occur.  I hope this idea helps someone!
>