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Thread: Can I use a 40 meter dipole on 20 and 15 meters?

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  1. #1
    W6IRE Guest

    Default Can I use a 40 meter dipole on 20 and 15 meters?

    I'm looking at the Force 12 "Sigma 40" 40 meter vertical diplole...

    Presumably, this antenna is a half wavelength at 40 meters, so with an antenna tuner (or not) would I be able to use it on 20 meters? Also, since 15 meters is a third harmonic, could I use this antenna on 15 meters?

    Also, could I listen (not transmit) to 75 meters?

    Many thanks in advance!

    73...............Richard

  2. #2

    Default

    IRE:

    The antenna should work fine on 15 meters as a 3/2 wave antenna. However, on 20 meters or 10 meters the antenna is going to present a very high impedance to a coaxial cable feedline. You might be able to use an antenna tuner to "match" your transmitter to whatever impedance the feedline presents at the transmitter end. However, the line losses in the coaxial cable will definitely be considerably higher than when operated on 40 or 15 meters.

    As for receiving on 80 meters, it should work fairly well. But, to transmit using the antenna you will definitely need to use an antenna tuner and the performance may be anything from OK to really dismal. You just will have to try to load the antenna with your tuner/transmitter arrangement and see what happens.

    Glen, K9STH

  3. #3

    Default

    I've tried a horizontal wire 40m dipole. I could tune it with a tuner, but it was worse than dismal on 80m and 20m. Very good on 15m, and great on 40m (or it wouldn't be a 40m dipole). It was also pretty good with a tuner on 30m and fair on 17m. Not bad for a single wire antenna. The math should be the same with a vertical dipole.

    Edit: Since this vertical dipole is only 24 feet tall, I'm not so sure how it will perform on other bands (or even 40m). That is shortened.

    Edit #2: $749.00?!
    Last edited by WW3QB; 04-29-2009 at 12:11 AM. Reason: Price shock

  4. #4
    W6IRE Guest

    Default

    Thanks guys! Yeah, that price is a bit high, reviews at eHam say guys are paying about $488

    Thanks again, guys!

  5. #5
    Join Date
    Apr 2001
    Location
    Southern Wisconsin, EN52
    Posts
    6,207

    Default

    people are paying nearly $500 for a 40 meter vertical dipole ?????
    I have a pair of phased 40 meter verticals, with 60 radials, and a 'perfect' matching system the whole shebang must have cost me about $300 including some nice aluminum and heavy duty mounting system.
    "Clear intent is the best predictor of experience"

  6. #6
    Join Date
    May 2007
    Location
    Etna PA
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    2,860

    Default

    Yikes, Thats a lotta $$$ !

    You can homebrew a 40M vertical for WAY less $$$

    That sigma40 will work "OK" anywhere above 40M- The issue will be a high VSWR causing extra loss in the coax. The antenna is already "short" on 40M,but not too bad, 80 and 160 will be a exercise in frustration.


    Rege
    Now my mistakes travel at the speed of light!:cool:

  7. #7
    Join Date
    Jul 2001
    Location
    New Castle County, Delaware
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    7,292

    Default

    Quote Originally Posted by WA9CWX View Post
    people are paying nearly $500 for a 40 meter vertical dipole ?????
    Funny, sad, and amazing..... all at the same time.

    P. T. Barnum reigns supreme!

    For 1/10th of the cost, an ARRL Antenna Book (and some of your time) is a wise investment.
    Last edited by KJ3N; 04-29-2009 at 01:50 PM.

  8. #8
    Join Date
    Feb 2002
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    Default

    Quote Originally Posted by W6IRE View Post
    Thanks guys! Yeah, that price is a bit high, reviews at eHam say guys are paying about $488

    Thanks again, guys!
    Unless you just like weird antennas, you can get a Butternut HF6V for a little less money and it's only 26 feet tall (2 feet higher than the Sigma). It will work 80 through 6 meters and my experience with that particular antenna has been very good. The only difference is you will need to put down a reasonable number of radials to make it work well. The best part is you won't need a tuner.
    I'm sorry you don't have the experience or understanding to realize that others possess a skill set that you seem to dismiss as fantastical.

  9. #9
    Join Date
    Jul 2001
    Posts
    21,474

    Default

    The best part is that it doesn't cost $500 ! ! ! Does it ?

  10. #10

    Default

    Quote Originally Posted by K9STH View Post
    The antenna should work fine on 15 meters as a 3/2 wave antenna.
    Why is a 3/2WL vertical dipole on 15m a bad idea? Because the take-off-angle is high and most of the RF is lost in space. At the low of the sunspot cycle, 15m needs all the help it can get from low-angle radiation. For a vertical center-fed dipole, the length needs to be 1.25WL (or less).
    73, Cecil, www.w5dxp.com
    Can CO2 emissions save us from the coming ice age?

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