Does an AM/FM radio really cause interference on airplanes?

Discussion in 'Ask a Technical Professional' started by Sukhoi, Mar 20, 2003.

  1. Sukhoi

    Sukhoi Elite Member

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    Can they really cause interference?

    Assuming the Illini win tonight, they're going to be playing Saturday afternoon right when I'm flying home. I really don't want to miss the game, so I'm thinking of listening to it in the plane if it won't cause any problems. Thanks!
     
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  3. dejitaru

    dejitaru Banned

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    Yeah, but no. You have to disable the transmitting devices "just in case".
    You can reactivate your devices a while after takeoff.

    this isn't quite highly technical
     
  4. Sukhoi

    Sukhoi Elite Member

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    So I should be fine if I just turn it off during takeoff? I expect the game to be done by the time we land.

    Oh, not sure if this matters, but the plane I'll be on is one of the 30 seat Saab 340s.

    I know it's not really technical, but if I posted in OT some idiot would come in and tell me not to use it because that's what they always say in the safety procedure.
     
  5. dejitaru

    dejitaru Banned

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    If they tell you not to use the device, you shouldn't. They may permit its use later in the flight.
     
  6. RossGr

    RossGr Diamond Member

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    All AM radios produce what is called an Intermediate Frequency, at about 55Khz, this is used internally to extract the audio signal. If your radio is not well shielded you will be "broadcasting" at this frequency. I believe that this is what causes the interference which the airlines object to. Generally it only is critical during take of and landing. The real problem will be finding a consistent station broadcasting your game while you are flying cross country.
     
  7. Analog

    Analog Lifer

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    true. The PLL in FM does as well.
     
  8. Sukhoi

    Sukhoi Elite Member

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    Thanks, that's exactly what I was wondering about. I'll make sure not to use it during takeoff.

    Arrgh, just realized that I have an aisle seat...freakin' plane is only three seats wide and I get the one aisle seat. :|

    The Saab 340 only goes about that fast in MPH, so I should be in range of the local station for quite a while. Hopefully I'll be able to find the game on FM since I think that would make it to the interior of the plane better.
     
  9. Afro000Dude

    Afro000Dude Senior member

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    Is the same true for satellite radio? LIke, would the plane crash if I listen to XM? :)
     
  10. Mday

    Mday Lifer

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    no because it's a digital signal which does not rely on frequency change\modulation to change the station, iirc.
     
  11. Grant

    Grant Member

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    Not sure if it matters, since the Illini lost...
     
  12. Sukhoi

    Sukhoi Elite Member

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    No, I wanted to listen to the game today. Guess it didn't matter I only heard the first half before we tookoff. :|:(
     
  13. dejitaru

    dejitaru Banned

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    The signal is digital, but I would think that it still uses an analog carrier wave.

     
  14. sxr7171

    sxr7171 Diamond Member

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    True. I doubt that you'll be able to recieve the short wavelengths that satelite radio is broadcast on. Also, I believe that either XM or Sirius or both use land based repeaters to make sure you get the signal in all terrains/conditions.
     
  15. Menelaos

    Menelaos Senior member

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    yellowfiero

    You're statement about the PLL is not quite correct. The PLL is use for FM-demodulation. It synchronises on the 19 kHz CW to extract the 38 kHz carrier wave for the stereo info. The internal VCO follows the frequency modulated signal, resulting in the demodulated signal at the VCO input.

    The IM frequency RossGr was talking about (which btw is 455 kHz for AM and 10.7 MHz for FM) is used at the mixing stage to be able to switch between the different channels. Here the incoming signal is mixed with an locla oscillator signal. The frequency of the LO is such that the end result after mixing is exactly the IM frequency.

    It is possible to use a PLL for synthesizing the frequency of the LO, but then the interference wont be at the IM frequency.


    Greetz,

    Menel.
     
  16. dkozloski

    dkozloski Diamond Member

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    There has been a wealth of testing done under aircraft operating conditions that indicates there is a potential for interference even from pure digital equipment like a gameboy. The variables include the harmonic content and strength of the generated signal and your seat location in relation to antennae, among other things. You may be willing to disregard the dangers to yourself but you don't have the right to take chances with someone elses life such as a drunk driver might do. Granted, the chances of causing a crash are remote but they are real.
     
  17. thraxes

    thraxes Golden Member

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    EMI on a plane is no joking matter:

    Found a few reports in a Lufthansa Technical bulletin describing instances of EMI effects on aircrafts avionics: In one case a cheap CD-Walkman in business-class caused the Autopilot computer to display erratic course and speed settings on a 737. More spectacular was the effect of a WLAN enabled laptop (the WLAN module was even deactivated but obviously still pumping out RF signals) which made the autopilot throttle down the engines on a Airbus 340... thankfully this was while cruising and not at a critical flight stage like take-off or landing. Also common are GameBoys causing flight management computers to display an error message in the cockpit. On the other hand during a maintenance test flight, the engineers fired up a cell phone directly in the cockpit and placed a call without problems. They tried that even in the avionics bay, again without any effects on the plane.

    Nevertheless, there are a whole load of reports such as these so it is no joke when airlines say turn off the gadgets, especially in TO or LNDG, ignoring this can place you and all the other passengers and crew at unneccesary risk.

    Besides, I would think it would be pretty hard to receive a radio station while sitting in what effectively is a faraday-cage travelling at 700 - 900 KpH, or am I wrong at that?
     
  18. dkozloski

    dkozloski Diamond Member

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    Interestingly enough, the biggest objection to firing up a cell phone at altitude is not the danger to the aircraft but the fact that it screws up the cell phone network because it radiates a strong signal to so many cells at once that it ties up the processing system.
     
  19. sxr7171

    sxr7171 Diamond Member

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    I've heard that. In fact I've heard a rumor that people have crashed cell phone networks by using cell phones in aircraft. In fact I believe that it is a big issue in amateur/recreational aviation communities.