Topband: How to detune a wire Inverted L? How to 'detune'electrical fence

[Tom W8JI]

> Q1) Would a simple relay disconnecting the vertical wire at the TX antenna
> feedpoint be good for detuning TX antenna? (I am using a piece of wire
> attached to 18m Spidermast for the vertical section) and another piece of
> horizontal on the top.
>
> Q2) Are there any practical solutions for detuning TX antenna by using 
> some
> circuitry at the shack end instead?
>
> Q3) What in practice could be done about the impact of the electrical
> fence? (other then moving RX antenna as far away as possible/ and
> considering using a shielded coax loop / or Waller Flag to 'null' the 
> fence
> out?)
>
>

Assuming it is a 1/4 wave L, anything that electrically opens the base of 
the antenna at the feedpoint with maximum possible impedance detunes the L.

Depending on any networks or transmission lines between the detuning switch 
and the element, the optimum termination at the switch might be almost 
anything. It is quite possible to detune the antenna from the shack, 
although it will generally require a certain value of inductance or 
capacitance to be switched in. I detune my 200 ft tower, fed through an L 
network, about 50 feet from the element and L network with a short.

Tom