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  1. #1
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    Turn long wire into antenna

    I'm facing an interesting situation with an existing wire which I want to (ab)use as a dipole antenna for 433Mhz.

    My idea is to cut the (long >10m) wire and first bring both ends(different unknown lenghts) into resonance with T1 and T2 and secondly use a balun B to feed a 50Ohm coax.

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    Can you share your thoughts how to approach this and which tuning(T1, T2) and balun(B) ciruits to use?

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    Re: Turn long wire into antenna

    You can do this dipole antenna. The total length of a half-wavelength dipole at 433MHz will be 35cm (Lamda=70cm and Lamda/2=35cm).
    You have to put two isloators at each end of the dipole.
    Also, if you use a 50 ohms coax cable to feed the dipole, you need a balun.
    Here are some balun examples:
    http://dg7ybn.de/Symmetrising/Symmetrising.htm

    I would go for the one named: "Classic half-wave loop Balun for Folded Dipoles", even in the picture is shown a folded dipole.


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    Re: Turn long wire into antenna

    thank you so much for your quick response on my request vfone.
    Perhaps I had to mention but the challenge is that the length of the existing wires cannot be changed.
    So I must tune both (long) dipole-ends somehow and (and after the tuning) connect it to the balun you suggest.



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    Re: Turn long wire into antenna

    What radiation pattern do you expect for your long wire antenna? I guess nothing similar to a regular dipole. Rather a narrow conical beam in the wire directions with many side lobes. Probably not well predictable.


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    Re: Turn long wire into antenna

    there no specific requirement for radiation-pattern or gain/performance.
    My objective is to get this existing long wire resonating on 433Mhz, get it balanced to 50Ohm and see if I can use it as an antenna.
    I have VNA available to measure.



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    Re: Turn long wire into antenna

    Quote Originally Posted by rrrRbert View Post
    the length of the existing wires cannot be changed.
    The length of the existing wire will not be changed.
    The only thing that you have to do is to INSERT inside of the existing wire, the 35cm length dipole.
    The dipole will be done from a piece of wire of 35cm which is cut from the existing wire.
    Finally, the total length of the existing wire will be the same (could ignore the isolators dimensions).


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    Re: Turn long wire into antenna

    Thanks for the suggested solutions! but the challenge is not to modify the existing wires, insert isolators or insert a wire into the existing wire.
    The objective is to make a single (=1) cut in the existing wire and bring the two existing lengths in resonance to 433Mhz and use it as a sort of dipole antenna.
    There are no specific requirements on radiation pattern. I just want to see what I can achieve with existing wire/situation.
    Yes, it's a strange request, because normally you start from scratch. This is a how can we make use of it.



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    Re: Turn long wire into antenna

    Quote Originally Posted by vfone View Post
    You can do this dipole antenna. The total length of a half-wavelength dipole at 433MHz will be 35cm (Lamda=70cm and Lamda/2=35cm).
    You have to put two isloators at each end of the dipole.
    Also, if you use a 50 ohms coax cable to feed the dipole, you need a balun.
    Here are some balun examples:
    http://dg7ybn.de/Symmetrising/Symmetrising.htm

    I would go for the one named: "Classic half-wave loop Balun for Folded Dipoles", even in the picture is shown a folded dipole.
    yes, the suggested balun looks good. thanks for guiding!



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    Re: Turn long wire into antenna

    Quote Originally Posted by rrrRbert View Post
    there no specific requirement for radiation-pattern or gain/performance.
    My objective is to get this existing long wire resonating on 433Mhz, get it balanced to 50Ohm and see if I can use it as an antenna.
    I have VNA available to measure.
    You can insert capacitors in series with the wires to change their electrical length. You'll take a hit on the radiation performance but you can make your electrical length target.


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