Antenna Sharing

Discussion in 'Wireless & RF Design' started by richbrune, May 19, 2006.

  1. richbrune

    Thread Starter Senior Member

    Oct 28, 2005
    106
    0
    I have a friend who has an airplane, and in it is two receivers that are on at the same time. One is for communication of voice signals, and one is for navigation. They share an antenna via a splitter, similar to a television antenna splitter. He was told that it was legal and safe to run both of these receivers off the same antenna so he installed it as such.
    Both the receivers are FM, around 120 Mhz, and I'm pretty sure they're phase lock loop and Super Het and all.
    Another person told him that each receiver would only receive 1/2 of the total signal, thus sharing the antenna would cause each reciever to have a weak signal. This didn't sound right, and I was wondering if any one out there can explain.
     
  2. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    Yep, there is loss. Somewhere around 3.5 to 4 dB depending on the quality of the splitter.
    It's about the same loss you would get if you ran an extra 10 to 20 meters of RG58 coax to the antenna.
    Probably barely noticable on a receiver but if you were really worried about it and needed to hear those signals way down in the "mud", then installing a small RF amplifier before the splitter as close to the antenna as possible would eliminate both the Splitter AND coax losses.
     
  3. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    Oops, double post....
     
  4. richbrune

    Thread Starter Senior Member

    Oct 28, 2005
    106
    0
    So the loss is all attributed to the splitter, and nothing to do with the impedance of the amps?
     
  5. Gadget

    Distinguished Member

    Jan 10, 2006
    613
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    The purpose of a splitter is to divide the signal without altering the impedance while keeping the receivers reasonably well isolated from each other. The majority of the loss is due to the fact the signal is divided.
     
  6. n9xv

    Senior Member

    Jan 18, 2005
    329
    1
    A very important distinction here is -

    Are those just receivers or tranceivers. That is, the COMM unit would be a transceiver and the NAV unit would be a receiver. If thats the case, then its not a splitter you have there but a duplexer. Allowing the COMM radio to transmit & receive while simultaniously receiving VOR/LOCALIZER signals on the NAV receiver all using the same antenna. The loss in the duplexer should be on the order of 1.5-dB or so.

    Incidently, the modulation is AM and not FM for aviation.
     
  7. richbrune

    Thread Starter Senior Member

    Oct 28, 2005
    106
    0
    Thanks! ----RB
     
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