Coax is a transmission line, it has both series inductance
and shunt capacitance and it has standing waves.
Ignoring that effect is the same thing that causes trap
calculators to have error.
One method I hav used to create capacitors for end fed 1/2 waves and
traps on 40 and below is to construct capacitors from brass hobby
tubing. By using two telescoping tubes of a foot or less I make a
tuneable capacitor. In general I have used plumbers teflon tape as a
dielectric wrapped as thick as desired on the inner tubing. The
resulting C is easy to calculate from an old physics text. I use these
presently in a traped 40/80 dipole with transmission line traps and at
the base of a 1/2 - 1/4 wave vertical with good results. I don't know
the voltage breakdown if the dielectric I have used but it works well
for by barefoot installation.
The only challenge is trying to get the guy at the hardware store to
tell be the dielectric constant of the plumbers tape.
brian, n6iz
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|