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How to Stack a Yagi Antenna

The typical VHF or UHF Yagi is designed to be a cost-effective way for the radio amateur to achieve 7 to 10 db (decibels) of gain in a favored direction, to the exclusion of other directions. The amateur who desires more gain than that must deal with doubling the boom length for every 2.5 to 3 additional db. Such long-boom Yagis are expensive because of their specialty nature. But there is another way to gain 2.5 db: stack a pair of the shorter Yagis.

Things You'll Need

RG-59/U or similar 75-ohm coaxial cable, about 10 feet
Tape measure
Cable cutter
Utility knife
Soldering iron and solder
4 PL-259 coax connectors
4 UG-176/U reducing adapters
Antenna mast
UHF T adapter
UV-resistant wire ties
SO-239 to SO-239 adapter
Coax seal

Instructions

- 1
  Calculate an electrical quarter-wavelength for the desired band. Use the standard formula of 234 divided by frequency in megahertz, and multiply that by the velocity factor of the coax. For example, use 146 MHz for the FM portion of 2 meters and 0.66 for the velocity factor of RG-59/U; thus 234 divided by 146 is 1.603. Multiply that by 0.66 for a total of 1.058. The answer is in feet, so multiply by 12 to arrive at 12.70 inches.
- 2
  Cut two sections of coax to the calculated length from Step 1. Solder a PL-259 with UG-176/U adapter onto each end of the two sections. If you don't know how to do this, the ARRL Handbook (see Resources) contains instructions.
- 3
  Mount one Yagi to the top of the mast. Connect one of the sections of coax to the Yagi. Connect the T adapter to the other end of the coax.
- 4
  Connect the other section of coax to the second Yagi, and to the other end of the T adapter. Stretch the coax along the mast and secure it with wire ties. Mount the second Yagi to the mast, so that it points in the same direction as the top Yagi.
- 5
  Connect the feed line from your radio to the input of the T adapter. You will need the SO-239 to SO-239 adapter to do this.
- 6
  Dress the feed line down the mast and secure it with wire ties. Apply coax seal to all connections.

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