Igor Grigorov, RK3ZK

A combined three-band antenna

Three band antenna fundamentals: At a lack of the place for installation of a separate vertical antenna for each of three upper HF ranges it is possible to use a combined three-band antenna that works at the ranges itself. Figure 1 shows schematic of a combined three-band antenna.

Figure 1 A combined three-band antenna

The antenna consists of from three quarter-wave verticals that are resonated for each of working ranges. The verticals are connected in the bottom together. Two quarter-wave counterpoises should be use for each operation range of the antenna A coaxial cable with 50-Ohm characteristic impedance will do well for the antenna. A coaxial cable with 75-Ohm characteristic impedance also would be work with the antenna, but a SWR in the coax will be higher compare to 50-Ohm coaxial cable. Table 1 shows the combination of ranges where a mutual influence of vibrators against each other is minimum.

Design of the Antenna: Three various designs of the three- range antenna are shown below. Figure 2 shows a simple design suitable for 6 - to 15-M. The three vibrators are placed on a small distance from

each other. The distances between the vibrators are fixed with the help of small plastic insulators. The design has very strong mutual influence for every vibrator against each other.

Figure 2 Simple design of a three ranges antenna

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