If you are a ham radio enthusiast and you have limited space where you live, a base-loaded vertical antenna may be an efficient option. The base-loaded antenna's unique design can match the performance of a larger antenna, and provides a space-saving solution. The base or coil-load provides inductance to the antenna, allowing the vertical element to be shorter. When an electrical balance is reached between the coil and the vertical element, the radio system will become optimised for maximum transmission power.
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Things you need
- Aluminium tube, 1/2-inch diameter, 80-inches long
- Electrical wire, 14 gauge, 63-feet long
- Coaxial cable with connectors, 50-ohm, 10 feet
- PVC pipe, 5 1/2 inch outside diameter, 1-foot long
- PVC cap, 5 1/2 inch diameter
- PVC glue
- Three machine screws with nuts and washers, 1/4-inch diameter, 1-inch long
- Wire-stripping tool
- Sand paper
- Utility knife
- Wire with alligator clips at both ends
- Soldering iron and solder
- Power drill and various bits
- Electrical tape
- Small piece of twine
Cut the electrical wire into one 50-foot length, and two 6 1/2-foot lengths.
Drill two 1/8-inch holes in the PVC tube, 1 inch from the end. Thread the 50-foot length of electrical wire through the holes, leaving 1 foot of excess. Wrap the remaining wire 34 times tightly around the tube, twisting the wire into a loop every five turns. The loops should stick out from the side of the tube. Place short pieces of electrical tape occasionally across the turns to hold the wire and loops in place.
Drill two 1/8-inch holes in the PVC tube, after the 34th turn. Thread the remaining wire through the holes to lock the wire in place. Snip the wire short at this end. This will be the bottom of the PVC tube.
Sand the plastic insulation from the wire loops on the PVC tube. These will be the wire taps used to tune the antenna.
Drill a 1/4-inch hole, 1/4 inch from each end of the aluminium tube.
Drill a 1/2-inch hole through the centre of the PVC cap. Insert an end of the aluminium tube through the hole in the top of the cap. Insert a machine screw through the hole in the end of the aluminium tube, and fasten it with a nut and washer. This will keep the tube from sliding back through the PVC cap.
Drill a 1/4-inch hole through the aluminium tube above the PVC cap. Fasten a screw through this hole, and tighten the nut and washer loosely.
Fit the cap on the top end of the PVC tube closest to the 1-foot length of electrical wire.
Strip 1/2 inch of insulation from the end of the electrical wire. Twist the wire around the screw above the PVC cap. Tighten the nut, securing the wire to the aluminium tube.
Insert the remaining screw through the hole in the free end of the aluminium tube. Tie a loop of twine around the screw, and tighten the screw to the tube with the nut and washer. Hang the antenna from this twine.
Cut a connector from one end of the coaxial cable. Remove 1 inch of insulation from this end. Pull the braided sheath back over the cable housing, exposing the insulated copper wire. Remove 1/4 inch of insulation from the copper wire.
Strip 1/2 inch of insulation from one end of each 6 1/2-inch length of electrical wire. Solder these ends to the coaxial braided sheath. These will be the ground radials for the antenna.
Connect the coaxial copper wire to a wire loop on the PVC tube using the alligator clips.
Spread the ground radials out from the bottom of the antenna. Connect the free end of the coaxial cable to the external antenna jack on your radio receiver. Tune the antenna by clipping different loops on the PVC tube.
Tips and warnings
- Ground your radio to a cold water pipe for improved performance.
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