classical W3DZZ antenna
in vertical installation designed by UL7GCC and shown at the Reference 1 is well known in Russia. Figure 1
shows the antenna. Diameter of sections A and B is 40- 50-mm.
How is it work?
40-m band: The trap LC
cut out the upper section B from the antenna. So only section
A works as a radiator, and the section A has length in 10.1 meters,
i.e. has electrical length in 1/4l. Vertical
radiator having with the length of 1/4l
has a quarter- wave resonance and works in very effectively way.
At the band the circuit LC works as a trap.
80-m band: On the 80-m band the antenna has summary physical length
of this two sections A+B a little less
than 1/4l. A + B = 16.47 meters, less then 20 meters OF quarter wave
length for the 80-m band. A short vertical radiator has a capacity
part in its input impedance.
But the circuit
LC at the 80-m range has an inductance part in its impedance.
The inductance part compensates capacity part of the electrically
short vertical, and the antenna has a low SWR at the 80-m range
too. In other words, the inductor of the LC works as a usual lengthening
10-, 15- and 20-m Bands: Visa
versa, at the 10-,
15-, and 20-m the LC has a capacity part at its impedance that
goes the electrical length of the antenna to 1.75l
at 10-m, to 1.25l at 15-m and
not forget, verticals like counterpoises, so use several 1/4l
counterpoises for each bands.
Chirkov, UL7GCC: Multi range vertical // Radio #12,
1991, p. 21.