Adapting 2.4GHz antenna for 100MHz

Discussion in 'Wireless & RF Design' started by KJ6EAD, Feb 3, 2012.

  1. KJ6EAD

    Thread Starter Senior Member

    Apr 30, 2011
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    I have a flexible antenna that I picked up at a surplus store. It has no brand markings but appears to be made by Laird. It has a mini UHF connector with a 90° hinge joint. Physically, it's about 6.5" long though I have no idea what it's electrical length is (it may have a built-in loading coil).

    My guess is that it's a 2.4GHz WiFi antenna.

    What would be the best way to make it useable on 100MHz (FM broadcast band)?

    If no one gives me a better suggestion, I'll just start experimenting with some base loading coils.
     
  2. K7GUH

    Member

    Jan 28, 2011
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    A dipole cut for the center of the FM broadcast band would be just over 57 inches long. Loading the GHz antenna down to that length would be possible in theory, but I wouldn't hold my breath for a successful outcome.

    If you need an antenna for FM broadcast, it's easy enough to construct one out of old TV antenna hardware. Element length and spacing info is available on the net and/or from publications on VHF antenna construction.
     
  3. #12

    Expert

    Nov 30, 2010
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    The American FM broadcast band (88 MHz. to 108 MHz.) is between channels 6 and 7 of a TV tuner. That's why TV equipment works in the FM band. Be careful about the fact that some TV antennas have an optional modification to reject the FM radio band. It is usually accomplished by snapping off certain segments of certain rods on the TV antenna.
     
  4. KJ6EAD

    Thread Starter Senior Member

    Apr 30, 2011
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    I expected it would be lossy so I may have to counter with amplification but I need the compactness. I may look at some VHF ducks later but I want to see what I can get out of this antenna first.
     
  5. KJ6EAD

    Thread Starter Senior Member

    Apr 30, 2011
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    I like the idea of using the VHF portion of a TV Yagi for experimentation and I may attempt to come up with a compact Yagi later as well but the ≈40" span of even a 3 element FM Yagi is far too large for my nefarious purposes.
     
  6. K7GUH

    Member

    Jan 28, 2011
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    Lossy doesn't half cover it, OM. You may (emphasis to be noted) get it to work, but to get it working satisfactorily, whatever your nefarious purposes, may be far, far more trouble than it's worth.
     
  7. K7GUH

    Member

    Jan 28, 2011
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    Lossy doesn't half cover it, OM. You may (emphasis to be noted) be able to get it working, but getting it to work satisfactorily may be far, far more trouble than it's worth.
     
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