"markvictor" wrote in
oups.com:

And the fact that your aluminum mast is gonded ...why challenge the
working parameters of your tuner? It also prevents those tingles you
refer to when someone(yes, perhaps foolishly) comes in contact with
that backstay or mast while TXing... And I'm sure you realize that
despite what anyones opinion of it might be, that plastic AT-130 is the
most common tuner in the fleet these days...and works well enough with
an INSULATED backstay and efficient counterpoise....
regards
markvictor




You obviously don't work around RF. This isn't AC power. At some
frequency, when something resonates, your shroud and your handrail could
be several hundred volts DIFFERENCE, which is the only way to get zapped.
There is NO GROUND in an RF system. 1/4 wavelength back from some
reference point, say the engine block at sea potential, there exists a
virtual open circuit at that RF frequency....a point of no current and
high voltage to that engine block. Divide 246 by the frequency in
megahertz to find how many feet that is. Every 1/4 wavelength, the
opposite condition repeats itself over and over. If your backstay is
64' long with an insulator at the top that always makes that point the
high impedance point (an open), where voltage is high and current is
zero, on 7 Mhz, the feedpoint at the tuner is very low impedance, indeed.
Current in the wire is high, voltage is very low at the tuner output.
The backstay is 1/4 wavelength long. On 14 Mhz, the backstay is two 1/4
waves long. The high voltage, low current at the insulator repeats
itself and the voltage on the tuner output is very high...high impedance.
The low impedance point on 14 Mhz is in the middle of the backstay,
again, 1/4 wavelength back from the insulator at the top.

If things are bonded with very short bonds together, there won't be a
potential difference between points, say the shroud and handrail of a
sailboat. But, if the shroud has a bond from the chainplate down into
the bilge back to the engine block "ground" and the handrail is bonded
back by the engine room, a significant part of a wavelength DIFFERENCE
exists between the two lengths of grounding bond. ANY conductor is an
ANTENNA, even the bonding straps, handrail, shroud. If the chainplate,
at some frequency, was 1/4 wavelength to the engine and the handrail and
its bonding system were 1/2 wavelength (or some DIFFERENT LENGTH), at the
point where the shroud comes over the handrail, there could be a
CONSIDERABLE difference in RF voltage right between them as you're
leaning over the rail touching the shroud.

However, at 150 watts on the yachtsman's little Icom, you won't feel
much. Raise that up to 1500 watts on my ham radio station and it will
light your fire, induced from that totally isolated backstay antenna...by
RF induction crossing these other conductors aboard. Raise it to 5-50KW
a broadcaster runs on AM and those kinds of potentials are MOST
impressive, indeed...(c;