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Thread: Magnetic loop antenna using heliax

  1. #1

    Default Magnetic loop antenna using heliax

    I wish to make a magnetic loop antenna with 1/2 heliax and it occurred to me that because the outer conductor is corrugated, this will be longer to rf. Does anyone know how much this lengthening effect is with this coax? I have studied the data sheets and combed the internet with no definitive answer.

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    Super Moderator 5B4AJB's Avatar
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    It won't matter, the tuning capacitor will handle the tiny mismatch...

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    Quote Originally Posted by 5B4AJB View Post
    It won't matter, the tuning capacitor will handle the tiny mismatch...
    In my case I would like to know how long the heliax is to rf. For one it will be for single band use and I don't think I require a tuning capacitor of any great value, so I can use a simple wide spaced one, home made. Secondly, I would like for the coupling loop to be around the 1/5th of the main loop. I've got a feeling that the heliax needs to be cut a fair bit shorter, I mean when you look at the corrugations closely, the outside length must be far greater than straight pipe. I am surprised that there is no mention of this anywhere with quite a few builds using heliax and the like, but I suppose most of these are multi band and they are utilising larger tuning caps. I want to keep mine as simple as possible for single band which may also help with the efficiency.
    Jeremy.

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    Super Moderator 5B4AJB's Avatar
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    Quote Originally Posted by arcone View Post
    coupling loop to be around the 1/5th of the main loop
    That's pretty much your only constraint - I've made a few of these antenna and they all worked great (to a degree).

    They're performance is similar to a dipole but with far less noise. Bear in mind, if you put 100W into it your capacitor should be rated for about 10kV so mount it out of reach of children & animals.

    Performance at ground level is pretty good, although I used a 1.5m diameter one just sitting on the carpet on the first floor (worked all continents).

    Anyway, try to find a nice big variable capacitor and make up a remote tuning device with lots of gear reduction...

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