ANTENTOP- 01- 2020 # 024

Antenna with Rotating Directional Pattern for the 80, 40, 20, 14 and 10 meter Band

Step by step you find tips how make the antenna.

Base design of the antenna is shown on Figure 1. The system consists of four sloper wire antennas. Each of the sloper antenna directed to the side of the horizon- South, North, West and East.

From each sloper antenna a feeding coaxial cable is going to special ATU, as it is shown on Figure 2. Each coaxial cable, going from sloper antenna to the ATU has electrical length of lambda/2 for the 80 meter band. The ATU is sitting on the table at radio shack and allows rotate the antenna directional pattern.

Figure 2

Sloper Antenna on the Mast

As you can see each sloper antenna is connected to the ATU through a length of the coaxial cable in lambda/2 for the 80 meter band. However, at the 40 meter band the cable has electrical length in lambda, at the 20 meter band the cable has electrical length in 2 x lambda, at the 10 meter band the cable has electrical length in 4 x lambda. Coaxial cable of such length carries the same antenna impedance from the connected antenna to the end. It allows use coaxial cable with 50 or 75-Ohm impedance. This length of the coaxial cable as well satisfactory works at the 15 meter band.

RA6AA used to coaxial cable with physical length 28 meter that has electrical length lambda/2 for the 80 meter band. So velocity factor for this coaxial cable was 0.66 that is match for coaxial cable with polyethylene dielectric. Coaxial cable with polyethylene dielectric was common in use in the USSR.

Velocity factor for the coaxial cable may be found from the datasheet so it is easy to find needed length of the coaxial cable used for the antenna design. If ham has a surplus coaxial cable with unknown velocity factor the factor may be easy to find in practical way.

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