[TowerTalk] Feeding half wave vertical (was Unique Inv L...Help!)

[Rick Karlquist]

Donald Chester wrote:
>
>
> Jerry, K4SAV wrote:
>
> "The problem with end feeding a half wave wire on 160 (in this case
> configured as an L) is that most people who operate 160 soon discover
> that you need an amplifier.  That translates into big voltages at the
> feedpoint.  In this case the feedpoint of the antenna at 1.87 MHz is
> about 7000 ohms.  At 1500 watts that is 4600 volts peak.  So you need a
> large vacuum variable.  You also need a sizable coil. You also need a
> lot of margin to handle high humidity conditions.   All wires inside the
> matching network have to be well insulated to prevent arc-over during
> high humidity.  A little condensation is a major problem.
>

I operated a horizontal 130 foot wire that was end fed on 80 meters for a
number of years.  It had a 120 pF fixed vacuum capacitor and a 6 inch coil
with taps going to a rotary switch controlled by a rotary solenoid.
The rotary switch was of the type suitable for a kW linear.  Each
tap covered 100 kHz with very low SWR.  The tuning network was mounted
in an aluminum box at the top of the tower.  The measured impedance
was about 3000 ohms.  The system worked perfectly from the get go and
never arc'ed over, etc.

Rick N6RK