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Fibre optic cable for antennas?

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Discussion in 'General Electronics Discussion' started by ubercool, Dec 19, 2012.

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  1. Dec 19, 2012 #1
    ubercool

    ubercool

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    Can we use fire optic cable for connecting antennas to communication equipment? Why do we use only coaxial cable for connecting an antenna to a transceiver whereas fibre optic is used only in data communication?
     
  2. Dec 19, 2012 #2
    davenn

    davenn Moderator

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    not directly, need lots of additional equipment

    look at the answer I gave you in the other forum

    Dave
     
  3. Dec 19, 2012 #3
    Jotto

    Jotto

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    Two words, triple beat. Hope your also designing the system for side lobe suppression.

    Coaxial is used because it doesn't allow leakage of the transmitted signal, if it wasn't shielded, there would be stray RF all over. The antenna is tuned to the specific frequency range of the device transmitting. Fiber is used in data because its light pulses, it can't be used properly for a transmission line.
     
    Last edited: Dec 19, 2012
  4. Dec 19, 2012 #4
    davenn

    davenn Moderator

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    Even the best coax cables leak a bit of signal

    ummm..... optical fible is used for transmission lines, often VERY long ones up and down countries and across oceans
    you do know you can send data via radio dont you? ;)

    they transmit light rather than an electrical current
    they are just a different style of transmission line :)

    Dave
     
  5. Dec 19, 2012 #5
    Jotto

    Jotto

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    I have never seen fiber optics used in a antenna system used for transmitting and receiving, I would like to see that.

    Of course there is always leakage, but there is also a acceptable amount. Which is one of the problems with cable.
     
  6. Dec 19, 2012 #6
    davenn

    davenn Moderator

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    in the other forum, that I wont post to on here, I explained to the OP how such a system would be used and why it would not normally be practical

    unless there were exceptional circumstances like very high voltage fields as often is the case in power generating stations where fibre is used to get through those high interference and electric potential areas then there is just normal RF transceive gear interfaced on each end of the fibre link

    A fellow RF tech here in my city has just been describing a system he's been installing over the last couple of weeks in a building for cellphone access ....

    RF being transceived on the rooftop needs to be reradiated in the basement areas 15 levels down. Coax runs were going to be much too lossy at the freq's involved so he used RF to fibre interface gear at the antenna end and fibre back to RF at the basement end so thatthe RF could be reradiated around several basement carpark levels

    Dave
     
  7. Dec 20, 2012 #7
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I think a major difference is that you can transmit a lot more power through coax than fibre...

    (Also fibre operates at frequencies around 10^14Hz to 10^15Hz which is many orders of magnitude higher than most (all?) coax)

    If you were transferring an RF signal via coax, it would be the signal that was modulating another carrier.
     
  8. Dec 20, 2012 #8
    Jotto

    Jotto

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    I would guess that they are taking a analog signal and converting it to a low voltage digital signal. Then returning it to the analog signal again?

    Thanks for the information, I was very curious about this.

    I can't see fiber being able to handle any type of RF signal because of its material. The reason I felt this way was because fiberglass or glass for that matter is mostly used as a non conductive material.
     
  9. Dec 20, 2012 #9
    davenn

    davenn Moderator

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    well it can be analog or digital doesnt matter :) ... in the example I gave in the last post
    about the cellular signal, then its digital


    Thats true, and pretty obvious, but I dont think the OP realised that
    the way his question was worded in both forums indicated that he expected just to
    screw the fibre under the antenna terminals ??? maybe??

    Dave
     
  10. Dec 24, 2012 #10
    ubercool

    ubercool

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    Nov 6, 2012
    yeah you are right I cant screw it directly cx they are two different frequencies...I would have to use a fibre optic transmitter and a fibre optic receiver at both ends. The original signal is a voice signal which is being modulated on a RF frequency so going through another modulation to convert it into light seems pointless


     
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