with electrical length in λ/2 (having physical length bit
less then λ/2) has input impedance less them 75 Ohms and
maybe, close to 60- 50-Ohms, see Figure
3B. So, for feeding a dipole trap antenna a 50-Ohms
coaxial cable can be used with a high efficiency.
dipole trap antenna is very easy for tuning and has high efficiency,
however, radio amateurs very seldom make as a vertical as dipole
trap antenna having a
of traps more than one. The reason is that the antenna sections
should be electrically insulated from each other. It is hard enough
to do a mechanical strength design of such antenna in radio amateur
conditions. Radio amateurs usually prefer a W3DZZ antenna. The
antenna has only one trap, and, as it seems by many hams, works
at several amateur ranges. What is a W3DZZ?
W3DZZ: In1955 C. L. Buchanan, W3DZZ, developed a multirange
dipole antenna with only one trap, see reference . Recently
the antenna is known as "antenna W3DZZ." Figure
4 shows schematic of the antenna W3DZZ.
W3DZZ works in several amateurs range with low SWR in its feeder.
Proper choosing data of the trap turns the trap or to lengthening
inductor at low range (ranges) or to shortening capacitor at high
range (ranges), or to only a trap at a proper range. For the antenna
shown at Figure 4, trap LC
is the trap for 40