W3DZZ has input impedance close to 60 Ohms at 80 and 75 at 40,
, so, a 75-Ohms coaxial cable can be used for feeding of the antenna.
make antenna W3DZZ also in a vertical installation, where the
antenna has input impedance close to 30- 40 Ohms (in twice less
the dipole design), so a 50-Ohms coaxial cable can be used for
feeding of the antenna at all of the ranges. For a proper work
a vertical trap antenna must have several counterpoises for every
of operation ranges, especially for low amateur HF ranges 40-,
80- and 160-m.
trap design: Trap spool has 8.3-μH and contains
19 turns of silvered copper wire of diameter in 3-mm. Diameter
of winding is 50-mm. Length of winding is 80-mm. The trap should
be tuned to resonance to the frequency 7,05 (7.2 for USA) MHz.
It is possible use a GDO for the tuning. A capacitor at 3-pF is
bridged to trap capacitor when the trap is tuning to the resonance.
The capacitor is simulated a stray capacitance of the antenna
tuning: At first, with the help of a GDO tune trap
to 7,05 (7.2 for USA) MHz. Trap is tuned separately from antenna.
At second, get a minimum SWR on 40 meters by length A. At third,
get a minimum
on 80 meters by length B. At thus, you can get minimum SWR (well,
see in the above figures, the SWR is not so low!) also at 20,
15 and 10 meters.
band vertical one-trap antenna:
often use a shortened sample of the W3DZZ antenna intended for
40, 20, 15, and 10 meters. At radio amateurs literature there
are several description of the antenna, as at dipole as at vertical
installation. However, the first description, which I found off
for a vertical four band trap antenna, was made by K2GU in reference
5 shows the schematic of the antenna.
5 A four-band trap vertical antenna