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A Five Bands Vertical Trap Antenna

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ANTENTOP- 01- 2004, # 005

A Five Bands Vertical Trap Antenna



M. Chirkov, UL7GCC


The 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 spool.


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 to 0.75l at 20-m.


Do not forget, verticals like counterpoises, so use several 1/4l counterpoises for each bands.



M. Chirkov, UL7GCC: Multi range vertical // Radio #12, 1991, p. 21.



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