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How to Build a 15M 20M Inverted V Antenna

Amateur radio antennas, like all antennas, need to be in resonance with their transmitted frequency. In addition to working well on its fundamental frequency, an antenna will also function on even harmonics of the fundamental frequency for which it was designed. The relationship between the 20-meter (14 MHz) band and the 15-meter (21 MHz) band is only 2/3 of a harmonic and is difficult to tune properly. A 40-meter (7 MHz) antenna, however, is resonant on both 20 meters and 15 meters as the second and third harmonics of 7 MHz respectively. Build an inverted V antenna designed for 7 MHz to achieve resonance and low SWR on the 15 meter and 20 meter bands.

Things You'll Need

2 34-foot lengths of No. 12 insulated stranded copper wire
3 ceramic or plastic insulators
Wire stripper/cutter/crimper tool
300 ohm twin-lead television wire
Soldering iron and solder
Silicone caulk
2 plastic zip ties
Nylon rope
Balanced line trans-match antenna tuner

Instructions

- 1
  Design a 40-meter (7 MHz) antenna by doing the math first. Apply the formula for a half-wave dipole: L (ft.) = 468/F (MHz) as follows: 468/7 = 66.85 feet Subtract 5 percent (3.34 feet) for the inverted V configuration for a total inverted V length of 63.5 feet or 31.75 feet on each side of the center insulator. Cut two 34-foot lengths of No. 12 insulated stranded copper wire for the two sides of the antenna.
- 2
  Attach the two 34-foot lengths of No. 12 insulated stranded copper wire to the center insulator using 14 inches of overlap to double loop and twist the two wires securely to the insulator. Strip off 1 inch of insulation and leave a few inches of wire free on each side for attaching the transmission line. Similarly attach an end insulator to each end of the antenna using 14 inches of overlap to secure the connection. The total antenna length between the end insulators should be 63.5 feet.
- 3
  Separate and strip the insulation 2 inches on each side of each end of the 300-ohm television wire transmission line. Use soldering iron and solder to securely attach the 2 conductors of one end of the transmission line to each side of the antenna across the center insulator. Wrap the 300-ohm twin lead wire once around the center insulator and strap it securely in place with the two plastic zip ties. Apply silicone caulk to cover the open soldered wires and to protect them from rain, snow and ice.
- 4
  Use a nylon rope suspended through a tree top, antenna mast or antenna tower to pull the center insulator as high as possible up into the air. Use additional nylon ropes to secure the ends of the antenna so that the two end insulators are about 20 feet above the ground surface giving the entire antenna an inverted V configuration. The major radiation pattern will be broadside to the antenna; so orient the antenna to give it the greatest directionality in the direction of your choice.
- 5
  Attach the two conductors at the radio-end of the 300-ohm twin-lead balanced transmission line to the two balanced line terminals on the back of the balanced line trans-match antenna tuner. Transmit a low power signal on a clear frequency near 7 MHz and rotate the three tuner dials to achieve the lowest SWR possible according to the tuner̵7;s twin meters. Record your tuner settings for future reference. Repeat this process for 14 MHz and 21 MHz. You may find that you have resonance on all three bands without the tuner, but you will need to use the tuner to tune throughout the entire bandwidths of your frequency allocations.

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