Topband: Switching in Extra Antenna Length

[i4jmy@iol.it]

Personally I do not find practical and reliable to install a switch at 
a voltage point.
At the edge of a quarterwave vertical there are tens thousand or even 
hundred thousands volts.
An interesting and symple approach than a realy or a classic trap is to 
create an 80m quarter wave stub along the horizontal wire.
To do this is enough to arrange a part (or the whole) of the horizontal 
wire as a ladder line, open at the vertical end shorted quarterwave 
away.
This solution is relatively lightweight and automatically switches off 
the horizontal wire when the antenna is used on 80m, doesn't require 
weather proof or switching, hardly arcs or has losses.
The bad side of the horse is a slight increase in weight.
On 80m the antenna will work as the horizontal part does not exist with 
only a small reduction in BW, anyway less than with a good trap that 
has an higher Q.
For matching purposes on 160, since the antenna will be anyway slightly 
inductive (i.e. 30 +j100) it's enough a series capacitor at the base, 
capacitor that can be switched (shorted) easily by a common and cheap 
relay.
Lenghtening the horizontal wire beyond the point where the ladder is 
shorted is possible to further rise the resistive part of the complex 
impedance to 50 Ohms, but I would be careful not to move up too much 
the current point from base. 
 
73,
Mauri I4JMY