On 8/9/2011 10:40 PM, Alan wrote:
In Eric writes:

As I recall from the description of the antenna, it is a variant of a
j-pole, where the first 1/4 wavelength of the length is actually a quarter
wave impedance transformer in the bottom tube.

As such, it does not need a ground plane or ground at the base to function
as an antenna.

HOWEVER, it does need a ground connection at the base of the antenna tube
to prevent static charge buildup and coupling down to the radio.


You are describing operating a radio connected to the wire coming down from
a lightning rod, where the point concentrates electric field at the top.
Even without lightning, air blowing past it can pick up a static charge
capable of startling a person. (There is also precipitation static in
rain...)

The base of the antenna should be clamped to the metal body of the vehicle,
preferably a solid point (not the sheet aluminum body of a motor home). Be
sure to have a good connection.

Our motorhome, like most motorhomes, does not have a metal skin body;
instead, the body is a metal framework encased in "sandwich" panels
composed of fiberglass/plywood/foam core/plywood. It would be possible
to find the closest metal rib and run a wire to it; however, I'm
wondering if the same effect could be achieved just by plugging the
radio into the 12 V power socket, rather than powering it just from it's
battery (thus, no connection to the motorhome frame).

While at it, a provision to tip it down flat to not stick up above the
vehicle when lightning is possibly in the area.

We can already do this, but we'd like a solution that let's her use the
radio and extended antenna when I'm flying, especially when I'm flying
to a distant airport and she's bringing the motorhome and trailer.

Aside from making a mess of your radio, and probably your motor home,
people are killed by lightning.

We want to eliminate this possibility, of course! It does seem possible,
as I've never heard of anyone getting shocked like she did. This makes
me suspect it is something specific we are doing and can easily correct.

Interference

We discovered the some new fluorescent lights in the basement ("troffer"
style) cause a lot of static on the A6 when it's used with the external
whip antenna on top of the house. With the lights off, the squelch can
be set to 2; with the lights on, it must be set to 14 or 15 avoid the
static.

The radio is normally plugged into an Icom CP-20 Cigarette lighter
cable, which is plugged into a 12 volt output/120 VAC input bench style
power supply; however, the static and squelch settings are the same when
it's use on it's battery only.

Grounds matter here, too. Be sure the frame of the fixture is well grounded
to the green wire of the circuit. Some modern fixtures won't work at all without
it, so they are leaking something out there.

I'll check the grounding.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)