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Any tricks for long wire aerials?

Discussion in 'Radio and Communications' started by jasp3r, Jan 16, 2011.

  1. jasp3r

    jasp3r New Member

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    I have a long wire aerial for Crystal Sets, and some shortwave, it doesn't perform to well so I was wondering if there are any hints for optimum performance

    Jasper
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    The length required depends on the frequencies you're trying to get. It's not just a question of the 'longer the better'.
     
  3. jasp3r

    jasp3r New Member

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    That makes a difference, I am guessing there is a formula?
     
  4. dave

    Dave New Member

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  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I would suggest getting hold of a copy of either the RSGB Manual, or the ARRL Manual, these are the 'bible' for radio hams, old editions are fine.
     
  6. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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  7. JimB

    JimB Super Moderator Most Helpful Member

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    How long is "long" ?
    A long-wire antenna is generally several wavelengths long at the required frequency.
    The term "long-wire" is often used to describe a wire of random length which may not be long at the required frequency.

    Crystal sets are not exactly sensitive, or selective.
    Fun to work with? yes!
    But not noted for good performance.
    What are you using to receive shortwave? Are you sure that it is working correctly?

    Define "doesn't perform well".
    As well as the antenna, you also need an earth (ground) connection to make the most of the signal from the antenna.
    A good earth connection allows more current to flow in the antenna-earth circuit thus putting more signal into the receiver.

    Hints for best performance?

    Make the wire as long and as high as possible.
    Keep it clear of any other wires (especially power wires!).
    Make a good earth connection.
    Use an antenna matching unit.

    The impedance of the antenna varies depending on the frequency.
    An end fed wire which is a quarter wavelength long will have a low impedance.
    An end fed wire which is a half wavelength long will have a high impedance.
    Depending on the input impedance of the receiver the signal from the antenna may be severely attenuated by the impedance mis-match.
    An antenna matching unit is useful to sort out this problem.

    JimB
     
    Last edited: Jan 16, 2011
  8. 4pyros

    4pyros Well-Known Member Most Helpful Member

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    Pour water on the ground rod. Old army trick. Andy
     
  9. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Even better, pee on it...
     
  10. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Thats what we used to do.! just be sure to pee on the ground and not directly onto the rod when the ground is dry...:eek:
     
  11. .W4GNS

    .W4GNS New Member

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    A tuner will help out, especially if you working over a broad freq range. You can buy one, or better yet homebrew a tuner. Google and you will find lots of info. Just make sure you DO NOT get a autotuner, which will require that you transmit a carrier, for it to tune. When it comes to antenna's, bigger IS better. :D
    Also if you're using some type of twin lead line from the radio to the antenna, it must be keep away from metal and ground (at least 2 feet) coax is not sensitive to either.

     
    Last edited: Jan 18, 2011
  12. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I feel this moving towards electric fences! :p
     
  13. 4pyros

    4pyros Well-Known Member Most Helpful Member

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    Said but true, you need a good ground for an electric fence as well.
     
  14. bryan1

    bryan1 Well-Known Member

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    How Long is a Chinaman and Willi Makeit is his American cousin................
     
  15. TIPS

    TIPS New Member

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    How long is "Long" Twice as long as half its length. Ha. Tips
     
    Last edited: Nov 30, 2011
  16. mvs sarma

    mvs sarma Well-Known Member

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    Try active antennas in the HF range up to 30MHz.
    for example active mini patch by DL4YHF (homebrew)
    wellbrook AL1350 etc
     
  17. unclejed613

    unclejed613 Well-Known Member

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    another "trick" used in the early days of radio was a modification of the basic crystal set. add a 1.5V battery through very high resistance to the diode junction to just barely get it to it's conduction threshold. this increases the sensitivity of the detector.
     
    Last edited: Dec 15, 2011

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