Building and raising a simple dipole antenna for ham radio

What’s a dipole antenna? Two wires with a connector in the middle, strung between two poles.

But it can be more than that.

Through learning how to raise a simple dipole antenna, this project teaches basic antenna and power safety, allows them to use those knots they’ve learned, and at the intermediate and advanced levels, learn and apply some of the physics of radio.

Most ham operators will have the few basic bits and pieces required. If your group doesn’t have a ham operator, local ham clubs often have members who will be happy to come out and help.

What it looks like:

Until we get our own pictures up, there’s a basic dipole antenna diagram on this site.

Objectives:

Basic (Cubs, Scouts)
  • Apply basic Scout knots (taut-line hitch, bowline, clove hitch + two half hitches)
  • Learn about antenna safety
    • It can cook your meat-sack face
    • Keep it away from places where people are (like not right next to your tent or building)
    • Raise it high enough so it can’t be reached by people on the ground
  • Learn about microwaves and radio
    • Microwave ovens are radio waves – at a particular frequency (microwave frequency) , and concentrated in a small space (your microwave oven)
  • Have antenna wire, insulators, centre balun already connected
  • Explain the importance of the insulators
Intermediate (Scouts, Venturers)
  • Calculate required wire length for antenna (more info at bottom of this document)
  • Learn about how radio frequency relates to antenna length
    • Basic speed-of-light calculations
  • Teach them how to splice up the antenna wire to the centre balun and end insulators
  • Explain how orientation of the antenna will affect communication
  • Give them a compass and request correct orientation of the antenna
  • More challenging knots (trucker’s hitch, etc.)
Advanced (Some Scouts, Venturers, Rovers)
  • Compare a hand-held radio’s reception with the built-in antenna against reception with the full dipole
  • Add soldering of the antenna wire splices
  • Provide a target destination, compass and  azimuthal map for them to determine how to orient the antenna
  • Challenge separate groups to see who’s fastest – raising the poles or climbing two trees instead. Now switch the task between the groups, and compare their combined time.

Competition or challenge criteria:

  •   Accuracy (length of antenna wire once installed
  •   Speed
  •   Quality of splice (maybe a pull/strength test?)
  •   Installation direction (i.e. exact north-south orientation)
  •   Proper use of all knots

Recommended equipment:

  • Any type of non-metal poles, at least 10 feet in length. Make it higher for a bigger challenge. Army surplus stores sell 4-foot fibreglass segments – we found ours at Princess Auto. Make it 20 feet if you’re going to use a high-power transmitter
  • Rope and tent pegs to tie up the poles
  • End and centre insulators to connect the wires to the poles.
  • Compass for orientation of the antenna
  • Simple wire – lamp cord is fine (18 gauge), but don’t go any smaller (higher gauge number) than that as it has to support the tension to hold the two poles up. Remember: lower gauge number (16, 14, 12)  = thicker wire.

If you’re going to hook up a radio… then you need someone who’s licensed to do that and has the equipment.

Antenna wire length

We recommend a half-wave dipole for the 15 Mhz metre band. Translated into English:

  • The speed of light if 300,000,000 metres per second
  • 15 MHz mean 15,000,000 waves per second
  • So each wave will be… 20 metres. (300,000,000 metres/second divided by 15,000,000 waves)
  • A full wave antenna would be 20 metres. A half wave antenna will be half that – 10 metres.
  • The dipole splits the antenna into two lengths, so each side will be 10 metres – but you need to allow extra for tying the wire to the end and centre insulators
  • So… two 11 meter lengths, leaving you a half-meter on each end to loop back and wrap around.

 

 

 

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