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53 lines
2.0 KiB
Markdown
53 lines
2.0 KiB
Markdown
---
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title: "Shortened 30m Dipole"
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date: 2020-02-02T15:00:00+02:00
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url: /30m-dipole/
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---
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# Why and what
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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](http://66pacific.com). To reduce the length of the ~15 m long dipole, a coil will be integrated into each side of the dipole.
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The following diagram shows the dipole in theory:
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![image][1]
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# Bill of materials
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* 1 feed point connector with PL socket or a 1:1 balun
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* 2 isolators
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* 2x 1 m antenna wire
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* 2x ca. 4 m antenna wire
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* 2 short pieces of 16 mm installation tubes
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* several meters of 1.5 mm2 copper wire (e.g. out of NYM-J 3 x 1,5 cable)
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# Construction
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## Coils
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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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![image][2]
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Repeat this step to build a second coil.
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## Assembly
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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.
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The result should look like this:
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![image][3]
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# Result
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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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![image][4]
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[1]: /img/30m_dipole_schematics.jpg
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[2]: /img/30m_dipole_coil.jpg
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[3]: /img/30m_dipole.jpg
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[4]: /img/30m_dipole_nanovna.jpg
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