> (duh!) and am concerned about flashover. A latching relay would work best
> but I may have to fabricate something in the shop to accomplish this.
> Near as I can figure, there is no such thing as a HP latching relay (MSC,
> Newark, etc.).
You are begging for problems. The relay is at a voltage point, and
worse yet you have a vertical!
The voltage can be as much as twice the voltage on a dipole at the
end, assuming you have a good ground system. That means you
could have the equal of what a dipole would do with 6 kW applied
power!!
You can model this on EZnec by putting a second source at the
top just below the hat and setting that source to zero current. That
causes the source to appear as an infinite impedance, like an open
switch. A look at the source data will tell the voltage that would
appear across an open connection at that point in the antenna.
I did this quickly using a 2" diameter vertical, and there was about
3 kV RMS with 2 kW of applied power. That's over 4kV peak
voltage, that you'd have to handle in all kinds of weather. You're
talking HV vacuum latching relays, which use a very high pull-in
current. You have to be sure the path across any insulation, when
wet, would remain open.
The voltage would increase with a thinner vertical near the top, and
decrease with a thicker vertical near the top. A fat antenna near
ground tapering to a thin antenna at top would produce even more
voltage.
I'd switch a series inductance in at the base. There would be no
measurable decrease in efficiency, and switching would be easier!!
73, Tom W8JI
W8JI@contesting.com
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