> In my experience the rotary switch is a weak point in tuners, supposed to
> handle 2-3 KW.
The only requirement is that the RF switches have to exceed the
absolute breakdown voltage of the capacitors by a reliable safety
margin. That's true for all the RF switches in the tuner.
Some tuners used inductor switches that improperly placed the
highest voltage point of the switch (the lowest inductance
positions) next to grounded screws. Others placed a HV contact right
next to a LV contact.
HOW the contacts are laid out and wired are just as important as the
physical size of the switch, unless you want to waste money on
Properly designed and wired, there is no reason to waste money on a
drastic-overkill switch. The capacitors will limit the voltage
nicely, and automatically serve as "spark gaps" to protect the
more fragile and easily damaged switch contacts.
If the tuner and also if you (when you set the knobs) use enough
capacitance, the maximum voltage is greatly reduced. The leading
cause of arcs is not using enough capacitance in a T network, rather
than component voltage rating.. assuming there are no design
The very same tuner that will handle 1500 watts when properly
adjusted (using maximum C that allows matching the load) can fail
with a hundred watts or less if improperly adjusted (using maximum L
and miniumum C)!
73, Tom W8JI
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Administrative requests: towertalk-REQUEST@contesting.com