Shortened 30m Dipole

Table of Contents

Why and what

This aricle describes the construction of a 9,50 m long dipole for the 30 m band (10.1 MHz to 10.15 MHz). It was designed to be mounted ca. 6m above ground inside an attic. The calculations were performed by OE1MEW with the help of this antenna calculator. To reduce the length of the ~15 m long dipole, a coil will be integrated into each side of the dipole.

The following diagram shows the dipole in theory:

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Bill of materials

  • 1 feed point connector with PL socket or a 1:1 balun
  • 2 isolators
  • 2x 1 m antenna wire
  • 2x ca. 4 m antenna wire
  • 2 short pieces of 16 mm installation tubes
  • several meters of 1.5 mm2 copper wire (e.g. out of NYM-J 3 x 1,5 cable)

Construction

Coils

Drill a hole into the 16 mm installation tube and stick a few centimeters of the 1.5 mm2 wire through it. Afterwards tightly wind the wire around it 37 times. After the 37th turn, drill a hole closely to the wire into the tube and stick the wire through it. It now should look like this:

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Repeat this step to build a second coil.

Assembly

Connect 1 m antenna wire to each side of the feed point connector (or the 1:1 balun). Now solder the ends of the antenna wires to one side of each coil. Use shrink tubing to make it water resistant. Solder the 4 m pieces of antenna wire to the other side of the coils. Both ends should then be terminated with isolatiors. A good start for tuning is a wire length of about 3,60 m between coil and isolator. Wrap around the remaining 40 cm for the tuning procedure.

The result should look like this:

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Result

The antenna ended up being 9,30 m long (including feed point, excluding isolators). The following photos show how nicely this antenna can be tuned:

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