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Multiple Antennas Using One Feedline

Discussion in 'Amateur Radio Antennas' started by Riverman71, Jul 6, 2018.

  1. Riverman71

    Riverman71 Sr. Member

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    I have some questions concerning antennas like the fan dipole, cobweb or hex beam which consist of separate wire antennas for each band. For this discussion we'll say it covers 10, 12, 15, 17 and 20 meters.

    Since no manual switching between the individual antennas takes place, when the radio is set to say, 20 meters:



    1. Is it receiving signals from all five of the antennas? If so, is that a benefit or a hindrance?
    2. Does it transmit through all five at once as well? If so, is the amount of power going out on 20 meters only 1/5 of the total power transmitted?
     

  2. Dmans

    Dmans Well-Known Member

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    Riverman71,
    I would say that when transmitting or receiving on a certain Band, your output or input will travel the path of least resistance or the path of best resonance. A coat hangar can receive or transmit but how well?

    This may not be the most technologically advanced answer, but in my 40+ years in this hobby, is only my personal opinion.

    I would invite a more technical answer or correction so that I can learn as well.

    73's
    David
     
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Since maximum power transfer occurs when impedances are equal the antenna with the best match will radiate the most power. Same for receive. Just how much each antenna contributes depends entirely upon the individual impedances.
     
    Mudduckmobile likes this.
  4. Dmans

    Dmans Well-Known Member

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    Thanks CaptainK. That confirms my suspicions.

    73's
    David
     
  5. The DB

    The DB Sr. Member

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    Yes, an antenna is receiving signals across the spectrum even if it is a single band antenna. Radios have filtering to attenuate the frequencies you are not intending to receive to a level that they won't be a problem.

    The technically correct answer is yes, all wires will get some part of the transmitted signal, however, they don't all get the same amount of said signal.

    Think of it like driving from point a to point b. Most people will take the shortest, fastest route between said two points. However, other routes between these points also exist, and while most people will ignore these routes all together, some people will opt to take them instead of the shortest route. The longer the route is the fewer people will take said route.

    Its the same when it comes to the different bands of such a multi-band antenna. The wires that are tuned for the frequency that you are using are seen as the shortest route, while the other wires are all seen as being various long ways around. Because of this, while all wires get some part of the overall signal, 99% or more of it will make a beeline for the set of wires specifically meant to carry the frequency in question.


    The DB
     
    338_MtRushmore and Mudduckmobile like this.
  6. Riverman71

    Riverman71 Sr. Member

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    Thank you, guys. (y)
     
    #6 Riverman71, Jul 7, 2018
    Last edited: Jul 7, 2018

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