ANTENTOP- 02- 2004, # 006

Multirange Trap Antennas

SWR at 15 meters W1LNQ Antenna

antenna 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.

A 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

number 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?

Figure 3 A shortening and full size dipole antenna

Antenna W3DZZ: In1955 C. L. Buchanan, W3DZZ, developed a multirange dipole antenna with only one trap, see reference [4]. Recently the antenna is known as "antenna W3DZZ." Figure 4 shows schematic of the antenna W3DZZ.

Antenna 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

http://www.antentop.org/

Page 50