meters: Section A is tuned for operation on 20-meters
by its length. Trap LC turn off upper antenna parts behind the
trap from operation of the antenna when 10 meters range is used.
meters: By length of the Section B we tune the antenna
parts "Section 1 plus LC plus Section B" to resonance
and 10 meters: The trap serves as a shortening capacitor
at that ranges.
you can see input impedance, SWR and DD of the antenna W1LNQ.
The figures are obtained with the help of Free Antenna Simulation
Program MMANA (MININEC based). Section A has diameter
of 20 millimeters, section B has diameter of 10 millimeters. You
can see, that a SWR at 15 meters is too high. It is impossible
to find such length of the antenna and data for trap that the
antenna works at all of the ranges. So, an ATU and a good coax
is need for the antenna if you work at 15 meters. A 50-Ohm coaxial
cable can be used for feeding of the antenna at all of the ranges.