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Thread: Dipole dimensions

  1. #1
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    Dipole dimensions

    So I wanted to build another couple of dipoles.
    My itention is to use bycicle wire since it bends back into shape nicely,
    use epoxy to harden the feed point and wrap the elements with shrink wrap.

    I remember there was a poist (think by Alex) that said something like
    "for a dipole with center frequency of 433MHz (I wouldn't mind it being a couple MHz hiher actually so 435-437) when using average bike wire and sleeving it with shrinkwrap use an element length of xxx mm but I can't find that post or anything
    that is in some way definitive (in the form of I tried it, tested it, do this)

    Anyone got any ideas? Alex maybe?

  2. #2
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    I measured my VAS dipole (which is made using bicycle cable) and it's about 6.25" from the center feed to each end. They are pretty forgiving in terms of tuning so that should be fine.

    Here's what IBCrazy posted some time ago on RCGRoups for the length of one of the elements:

    Length in Inches (for 22AWG wire) = 2808/frequency in MHz

  3. #3
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    You can get a dipole to work very easily. But without equipment you won't get it spot on.

    I made dipoles for my frsky. They were 29mms long per leg for a nice tuning at 2450MHz. Nice tuning means less than 1% power reflected. As soon as you put them in some sort of sleeve the difference can be huge.

    the same dipole, for the active element I put it in pp tube to be always straight. For the ground portjon I used fuel line made out of silicon. That ahifted resonant f down to 2115MHz. It still works but no longer spot on.

    Either you try to avoid all the tubing or find someone with the equipment or accept the fact that tuning might be off.

    dio
    Latest Crafts: The Anti-Gravity-Machine, Carbonator, Guava 2m, Wunderwaffe I, Wunderwaffe II, Uberwaffe, Plankton v2, TBS discovery

  4. #4
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    I use 165mm per element myself I believe. Works pretty good. The true electrical wavelength is 173mm, but I have mine wrapped in plastic antenna tubing which has an influence, so the ideal length is a little lower.

    An easy way to determine it yourself without any sophisticated equipment is taking a transmitter and a receiver, putting your antenna with a longer length (say 180mm) on the transmitter and NO antenna on the receiver. Hook the receiver's RSSI to an OSD to read the RSSI value. Then get some distance in between the two until you see your RSSI drop on the screen.

    The next step is trimming 1mm off the antenna and checking the RSSI again. The length that gives the highest RSSI value is your ideal length
    Cheers, :)
    Sven
    [QUOTE=c5galaxy engineer;522178]Zee is wrong, Grasshopper is ALWAYS right![/QUOTE]

  5. #5
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    I build my dipoles out of Bicycle cable epoxy and heat shrink exactly as you describe. I cut my lengths oversize and after it is assembled and heat-shrinked, I use an antenna analyzer and trim them down to peak SWR at 435MHz, they pretty much always end up exactly the same length for me at 6 3/16" or 157mm per element.

    I think if you trim to that length you will be in great shape.

  6. #6
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    What would the lengths be for doing a dipole on 1.2G?

  7. #7
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    What Frequency? For 1.258Ghz to 1.280GHz which we use in the US, theoretically 56mm would be good.

  8. #8
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    Quote Originally Posted by JP1 View Post
    What Frequency? For 1.258Ghz to 1.280GHz which we use in the US, theoretically 56mm would be good.
    Perfect, thanks!

  9. #9
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    Wink Tuned Vee dipole for 1280mhz

    Works like a charm.
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  10. #10
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    An inverted vee won't increase range over a standard dipole. If it does then your dipole was bad

    Don't get me wrong, it's a great antenna, and arguably better because of the slightly better reception when flying back towards yourself
    Cheers, :)
    Sven
    [QUOTE=c5galaxy engineer;522178]Zee is wrong, Grasshopper is ALWAYS right![/QUOTE]

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