Shortening 27MHz antenna for RC-Tx sender

Discussion in 'Wireless & RF Design' started by parmaja, Jul 15, 2016.

  1. parmaja

    Thread Starter Active Member

    Jul 2, 2008
    37
    0
    I have RC remote sender (tx) 27Mhz for Rc Car, lost its antenna, after I searched on internet I got it should be 1/4 of wave, finally told me it is meant it is 2.7 meter.

    If that right, Now 2.7 meter very long to add it to rc sender, how can i shorten it.

    Can I wind it around plastic string?

    I cant buy new one, it is not exists in our stores.

    rc-tx.jpg
     
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,951
    387
    It almost certainly didn't have a 2.7m antenna in the first place. Try it with various lengths of wire and check the range.
     
  3. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    27 MHz is the frequency for Citizens Band radio in the US. There are lots of CB antennas that have been shortened by electrical means. Search for CB antennas on ebay or in your marketplace.
     
  4. DickCappels

    Moderator

    Aug 21, 2008
    2,656
    632
    Just a little background to AlbertHall's post: Most hand-held devices that operate at HF and VHF frequencies such as your transmitter include circuitry to allow the physical antenna to appear electrically longer than it actually is.

    The transmitter was designed probably designed to use an antenna about 1 meter long. Any length other than that for which the transmitter was designed would result in reduced performance.
     
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  5. crutschow

    Expert

    Mar 14, 2008
    13,022
    3,236
    Typically an inductance is added in series with the antenna to allow it to resonant at the frequency of interest with a length shorter than a quarter wavelength. This can often be see as a loading coil at the base of a whip antenna.
    Some electrically short antennas (rubber ducky types, below) consist of a short hex-wound coil of wire that distributes the desired inductance along the entire antenna length.

    [​IMG]
     
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  6. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,951
    387
    I have seen and I own 27MHz transmitters and receivers for model control. The transmitter commonly has a standard telescopic aerial, perhaps 60cm long and the receiver has a simple length of wire, perhaps 30cm or less. Now these circuits may include some matching components inside (not my specialist area), but the aerial itself is just a conductor which is a lot less than 1/4 wavelength.
     
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