Topband: Choke Construction Info Needed

[Guy Olinger K2AV]

>
> >I need to construct a heavy-duty choke to be installed from the feed point
> > of my 160 meter vertical to ground, for static drain and for lightning
> > protection. How large does the wire, form, and inductance need to be?
>
> Phil,
>

One method of dealing with this problem, particularly if one is using an
FCP, where the IMPEDANCE is higher at the feedpoint than a resonant feed,
is to go to ground with a 5 meg 10 watt resistor in parallel with a lawn
mower non-resistance spark plug, gap set to 25 thousandths.  The former
keeps static drained, the latter gives a path for serious induced voltage.

If you get a direct strike, everything at the bottom of the wire is toast,
and #12 copper for the vertical is most likely evaporated.  I can't think
of anything doable that make survivability anything better than a pure
fluke.  Lightning around here turned the top 75 feet of a 120 foot tulip
tree literally into toothpicks scattered over a 125 foot radius, welded
conductors in buried cable 25 feet away.  So you design for static and
induced current/voltage.

Feeding the base of a 160 vertical wire over radials with an ISOLATION
transformer (not a balun) will give you the DC ground without letting in
all the common mode current from the coax to the antenna. Wound after the
fashion of the isolation transformer for an FCP, it will also keep an
induced strike off the coax to the shack.

73, Guy.