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40 meter dipole

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KC2USH, Jul 27, 2009.

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  1. KC2USH

    KC2USH Ham Member QRZ Page

    Im looking for plans for a 40 meter dipole the plans should include length of wire what kind of wire and what coax connecters are needed.
    Im new to this so i prolly have left something important out so please ask about anything i forgot.
    thanks 73s Evan KC2USH
     
  2. W4NA

    W4NA Ham Member QRZ Page

  3. KA4DPO

    KA4DPO Ham Member QRZ Page

    The simplest dipole would be made from 65 1/2 feet of #14 or #12 stranded or solid wire (it doesn't matter) and three insulators. One insulator on each end and one in the center. Connect the coax directly to the antenna and put a PL-259 connector on the other end to connect to the radio. Even though it's considered good practice you don't have to use a 1:1 Balun at the antenna. There are thousands of us who made such dipoles over the years and have worked a ton of DX on them with no Balun....

    There you have it, put it up as high as you can and check the SWR you may have to prune the antenna to get it where you want it and that depends a lot on how high you mount it. Higher is always better even if the SWR is better on a lower antenna. As long as the SWR is 1:5 to one or less your good to go, if it's higher that that then you need to trim the antenna a few inches at a time to bring it down. Be sure to trim the same amount off of each end so that both sides of the dipole are equal in length.

    You have just completed dipole antennas 101....:D
     
  4. WA9UAA

    WA9UAA Ham Member QRZ Page

    Evan,
    Be sure to weather seal the center insulator /coax so water can't get inside. A few layers of coax seal and tape should do the trick. I'd check for further suggestions on how, but keeping the weather OUT is important.
    73,
    Rob WA9UAA
     
  5. K7KBN

    K7KBN Ham Member QRZ Page

    Length of a dipole: 468 divided by the center frequency in MHz.

    (This should be part of Dipole Antennas 101). ;)
     
  6. K9STH

    K9STH Ham Member QRZ Page

    The approximate length in feet of an HF dipole made from 12 gauge to 14 gauge wire is 468/F where F is expressed in MHz. Using a smaller diameter wire will increase the length necessary to obtain resonance at any particular frequency.

    Also, how close to the ground, proximity of other objects, and so forth can definitely affect the length of wire needed for resonance. Therefore, general practice is to cut the wire longer than the formula dictates and then "prune" the wire until minimum reflected power/SWR is obtained at the desired frequency.

    Also, when "pruning" the wire it is best to use a frequency a little bit lower in frequency than the desired frequency. This is because you don't know when the resonant point has been achieved until the SWR starts going back up. Therefore, by using a frequency that is a little bit lower than the desired frequency when the SWR just starts to go back up the resonant point will usually be very close to the desired frequency.

    Glen, K9STH
     
  7. W9GB

    W9GB Ham Member QRZ Page

    At 7 MHz (40 meters) a standard horizontal dipole requires approximately 66 feet of wire (stranded 14 AWG), with Center and End (2) insulators, approaches 68 feet between rope supports.
    Obviously one must add several more feet to the total span for support.

    Parts list:

    14 AWG stranded wire. You can use normal stranded conduit wire with your choice of insulation colors
    Center insulator (Van Gorden or one with choke/current balun built in)
    2 End insulators (I like ceramic, but modern plastics are common)
    3/16" UV resistant rope

    Photos of an 80 and 40 meter dual band 1/2-wave dipole
    http://www.k0to.us/HAM/Dual Dipole/Dual Dipole.html

    w9gb
     
  8. AE5JU

    AE5JU Ham Member QRZ Page

    I think it was on the test.
     
  9. AE5JU

    AE5JU Ham Member QRZ Page

    Here's a great center section:

    [​IMG]

    By Jetstream. It comes in various colors, black, gray, blue, green, white.

    If you want to make a multi dipole, you can mount it on a piece of cheap kitchen plastic cutting board like this:

    [​IMG]

    Yes, 65 1/2' total, so half on each side. Make the ends about 1' too long, and double back on itself. Use cable clamps. Take some up, let some out to adjust SWR. I use parachute cord from the outer insulators to the tie off points. For me those are eyebolts on the top rail of a wood privacy fence.

    Wrap the Coax connector with "Coax Seal" or Scotch 130C butyl rubber tape to keep moisture out.

    Paul
    AE5JU
     
    Last edited: Aug 4, 2009
  10. KC2USH

    KC2USH Ham Member QRZ Page

    thank you to alll for the advice
     
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