How To Build a 1/2 Wave Dipole:

  Determine your center operating frequency, and using the following formula, calculate your wire length in feet:

formula

  For example, if I wanted to build a 20 meter dipole for a center frequency of 14.300 MHz, I would divide 468 by 14.300 and get the result of 32.72 feet.  Multiply that by the velocity factor of the wire used, for the overall total length.  If I am using 12 AWG stranded copper wire with the jacket on (I never use bare) then I would multiply my length by .975 for an overall total length of 31.9 feet.  If you multiply the .9 by 12, that will give you your length in inches. So 30 feet, 10 and 3/4" is very close.

  If I take 31.9 and divide that by 2, I get 15.95 feet, which is one leg of my 20 meter dipole.  So cut two wires 17 feet long and wrap the wires thru the center insulator and the end insulators.  Leave a little stub hanging at the ends so we can tune the antenna once it's built.

  There are countless ways to make the feed point of your dipole.  Some people use plexi-glass, some use PVC T-fittings, some use a piece of thin PVC Pipe, there are feed points for sale at most ham shops.  We called them "Cobra Heads" in the military.  Alpha-Delta makes a great dipole "kit" called the Delta-C that includes two end insulators and the feed point head with a replaceable lightning arrestor built in.

bad example   good insulator

  Whatever you decide to use is of little consequence as long as you provide a means to keep water from getting into the end of your feed line.

  The left picture above shows the feed-line soldered to the wires on an insulator.  This design is not the correct method, the coax should be looped over the insulator so as to remove the strain from the solder joints.

  The right picture above shows a good example of an end-insulator.  Note, you can leave some wire hang down from the insulator, creating "tuning stubs" to help match your antenna.


The above formulas and the lengths given in the charts below can also be hung as an "Inverted Vee" configuration.


Dipoles are not omni-directional, in other words, looking down on a dipole, the signal radiates perpendicular to the antenna itself, not in all directions like a vertical antenna does.  Therefore, if you hang a dipole with the end insulators oriented to the East and West, the antenna will primarily transmit and receive to the North and South.  The picture below is looking directly down at a transmitting dipole.


 

Amateur Band Dipole  Overall Lengths

160 meters - 260 ft.

80 meters - 126 ft.

60 meters - 87 ft.

40 meters - 66 ft.

30 meters - 46 ft

20 meters - 33 ft.

17 meters - 26 ft.

15 meters - 22 ft.

12 meters - 19 ft.

10 meters - 16.5 ft.

 

Shortwave Broadcast Band Dipole Overall Lengths

120 meters -195 ft.

90 meters -142 ft.

75 meters -120 ft.

60 meters - 98 ft.

49 meters - 79 ft.

41 meters - 63 ft.

31 meters - 51 ft.

25 meters - 40 ft.

22 meters - 34 ft.

19 meters - 30 ft.

16 meters - 27 ft.

15 meters - 25 ft.

13 meters - 22 ft.

 
 
 
 
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