Tuesday, June 17, 2014

VHF/UHF Ground Plane antennas for under $20

The entire antenna consists of a panel mount SO-239, some stiff wire (like aluminum welding wire, brazing rod, 12 GA bare copper wire, electric fence wire, etc) or thin brass tubing, some solder, and four 4-40 3/8" long screws, washers, and nuts

Cut the wires to length in accordance with the chart provided for the band you want. You will end up with 5 pieces of wire, 4 the same length (radials) and one slightly longer (driven element). Use a good high wattage soldering iron to tin one end of the driven element

HINT:Cut your radials extra long, mount them on the SO-239, mark the point to start the bend, remove the radials, make the 45deg bend, remount them, then measure and trim to length. When tuning for lowest SWR, remember that the angle of the radials affects the value, so feel free to adjust them anywhere between 30 and 45 deg for best reading. Also, if tubing is used, one end of each radial can be soldered to a ring terminal or hammered flat and drilled

There are several ways to attach the radials:

  • Bend the wire through the corner hole and solder in place — Requires a lot of heat, no longer removable for transport but better electrical connection
  • Use a pair of needle nose pliers to fashion one end into a tight loop just big enough for the 4-40 screws to get through — Takes a little work, can loosen over time [use split washers for extra tension], but no soldering
  • Solder (or crimp) ring terminals on one end — clean, professional looking, but may break over time with repeat bending
Notice that the length of the radials is measured from the 45 deg bend to the tip, so which ever way you choose, allow for this extra length in your calculations.

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