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AM radio reception inside passenger planes?

Discussion in 'Electronic Equipment' started by Some Guy, Dec 11, 2004.

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  1. Some Guy

    Some Guy Guest

    I have no trouble receiving FM radio broadcasts on a small am/fm radio
    I sometimes listen to while onboard commercial jet airliners (flying
    at cruise altitude), but I never seem to be able to pick up AM radio
    stations. It's just static across the AM band.

    Any explanation for this?
  2. Geoff Glave

    Geoff Glave Guest

    Any explanation for this?

    FM radio generally operates at longer range than AM radio, however it's
    limited to line-of-sight. However, when you're 40,000 feet up you can "see"
    a lot of transmitters hence the FM signals.

    Geoff Glave
    Vancouver, Canada
  3. Ian Jackson

    Ian Jackson Guest

    The window holes are much too small to let the much longer wavelengths
    of the 'AM' signals through. The body of the plane is a very effective
    screen. The 'FM' signals can squeeze in, but it helps if you have a
    window seat. I've also listened to SW in the middle of the Atlantic.

    Flying from the UK to Florida, on the other side of the Atlantic the
    first FM stations you hear are usually speaking French (from Quebec)
    It's quite alarming!
  4. nick smith

    nick smith Guest

    I reckon you just answered the wrong question !!

    The reason A.M. radio can not be received in a plane is that it is a Faraday
    cage to the (lower frequency) A.M
    frequencies, whereas the VHF frequencies can just about get through the

    There may be a bit of frequency / range issue as well but top band and 80 mtrs
    gets across the pond so
    I don't think this is the issue here...

  5. Ether Hopper

    Ether Hopper Guest

    No one has mentioned that in many cases you need the pilot's permission to
    operate a radio or other electronic device for that matter on a commercial
    airliner. That includes AM/FM radios.

    Radio emissions may screw up the plane's avionics.

    See URL:

    It sez:
    "The FAA does not allow inflight use of walkie-talkies, radio controlled
    toys, AM/FM radios, portable telephones, or portable television sets, all of
    which may affect aircraft radio and navigation equipment"

    Also cruise ships may deny use of two way (FRS) or ham radios -- always
    check with the communications officer.

    For Hams always check with the person in charge on any commercial
    transportation, busses, taxi's, ships planes etc.

    Yeah yeah I know you did it without getting permission, but read the URL as
    to what airlines have published.

    And I know from personal experience that some cruise lines do not allow FRS
    or ham radios transmissions.
  6. Ian Jackson

    Ian Jackson Guest

    Virgin included the use of radio receivers in their 'permitted list'
    about 3 years ago. However, I do wonder about the use of the FM
    broadcast band because the LO (tuned freq + 10.7MHz) can land up right
    on top of something important in the ATC band.
  7. Dave Bushong

    Dave Bushong Guest

    Yes, there is. The AM cops have figured you out, since what you are
    doing is illegal on commercial airliners. The FM cops are a little
    slower, but they will pull the plug on you also, eventually.

    Seriously, though, you are inside a metal cigar tube you call an
    airplane, and you are being shielded by the body of the aircraft.
    Although windows (portholes, not Gates), and the metal itself, don't
    block out signals completely, you will see an effect from this (look up
    "Faraday Cage" on google). AM broadcast is a very long wavelength
    (hundreds of meters long) whereas FM broadcast is a smaller wavelength
    (around 3 meters). If you were trying to throw a bunch of marbles
    through an upstairs window, you would probably be able to do it. But if
    you were trying to throw a bunch of beachballs through an upstairs
    window, it wouldn't be as easy, right?

    The aperture is the important issue. Although the airplane is not a
    completely shielded RF-proof "screen room", it acts somewhat like one.
    That is why avionics antennas are on the outside of the plane, not
    inside. That is also why there is a teeny mesh grid in the door of your
    microwave oven - they have to be that small to block the microwaves.

    Using my example before: if you are throwing beachballs (AM broadcast),
    or marbles (FM broadcast) or a handful of sand (microwaves), how small
    would you want the window to be in order to block it?

    OK, getting back to my first paragraph, if you are ever on a plane with
    me, please let me know, so I can take the next flight. The local
    oscillator of FM receivers is often on the same frequency as the VOR
    stations that airplanes use to naviagate with, and can cause
    interference. There are failsafe solutions that the pilot has, to deal
    with loss of VOR coverage, but I don't want to depend on them because
    you are listening to gangster rap at 32,000 feet. Get an iPod or something.

    All the best,
  8. Ether Hopper

    Ether Hopper Guest

    And you do want the Avionics to work properly don't you ???
  9. Ed Price

    Ed Price Guest

    Exactly the concern. LO's are used for superhet receivers, and fancier
    receivers are more computer than analog RF. So now, you have a clock
    oscillator, with it's harmonics, as another RF source. And don't tell me
    these emissions are negligible. Receiver (and other electronics
    manufacturers) sweat blood to reduce those emissions so that they can meet
    FCC Part 15 (among other) requirements (modest radiation limits at 3 meters
    distance from the test specimen).

    The fact that apertures in the fuselage allow FM frequencies INTO the
    aircraft, letting you pick them up with the miserably small FM antenna in
    your receiver, also means that LO leakage from your receiver can get OUT of
    those same apertures.

    You now have the effect of having a small radiation source immediately
    outside the fuselage, just feet or so from the Avionics antennas. What are
    the coupling effects? What frequency will your LO land on? Do you feel
    lucky, punk?

    So, in all honesty, YOU can't really say how dangerous operation of an FM
    receiver will be; but you KNOW that it's potentially harmful.

    The advice to ask the PIC (pilot in command) to make allowance for you is
    just plain dumb. The guy is an aircraft driver, not an expert in RF
    propagation. He has overall responsibility for getting you to your
    destination while avoiding legal exposure to himself and the airline. You
    are asking him to allow a potentially dangerous device to be operated just
    for your convenience and entertainment. Switch roles for just a minute.
    Would YOU allow that? Now switch back. If your PIC would allow it, what else
    would he be willing to allow or overlook?

    While I will admit that aircraft disasters are rarely caused by a single
    factor, it's just plain dumb to add risks that you don't need to take. I
    want pilots who are conservative, who do a thorough pre-flight walk-around
    even when it's raining, and who will enforce rational rules on
    self-centered, ignorant passengers. Can't you put your electronic life on
    hold for a few hours? Whatever happened to reading a book, or just looking
    out the window?

  10. Ether Hopper

    Ether Hopper Guest

    Subpart A--General

    FAA Regulations Sec. 91.21

    Portable electronic devices.

    (a) Except as provided in paragraph (b) of this section, no person may
    operate, nor may any operator or pilot in command of an aircraft allow the
    operation of, any portable electronic device on any of the following
    U.S.-registered civil aircraft:
    (1) Aircraft operated by a holder of an air carrier operating certificate or
    an operating certificate; or
    (2) Any other aircraft while it is operated under IFR.
    (b) Paragraph (a) of this section does not apply to--
    (1) Portable voice recorders;
    (2) Hearing aids;
    (3) Heart pacemakers;
    (4) Electric shavers; or
    (5) Any other portable electronic device that the operator of the aircraft
    has determined will not cause interference with the navigation or
    communication system of the aircraft on which it is to be used.
    (c) In the case of an aircraft operated by a holder of an air carrier
    operating certificate or an operating certificate, the determination
    required by paragraph (b)(5) of this section shall be made by that operator
    of the aircraft on which the particular device is to be used. In the case of
    aircraft, the determination may be made by the pilot in command or other
    operator of the aircraft.

    Seems to me the pilot ought to know.

    Again I direct you to URL:
  11. Hi Ed,

    This would make sense (to switch roles) if the administration hadn't
    trumped that call. Reports recently indicate that the FAA may soon
    allow anyone, anytime, to make cell phone calls while in flight.

    Anything goes for a price. The FDA has proven that it is no longer
    the watchdog of medicine, and the FCC is the gateway for spectrum
    bargains and marketplace sweeps.

    With these acronyms, one may well wonder what the "F" stands for.

    Richard Clark, KB7QHC
  12. Some Guy

    Some Guy Guest

    What a load of horse shit.

    You guys are acting as if the engines and flight control surfaces of
    an aircraft are intimately tied to the plane's radio receiver, and the
    slightest odd or out-of-place signal that it receives is enough to
    send any plane into a tail spin.

    All this while the air travel industry is considering allowing
    passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT
    by adding cell-phone relay stations to the planes and allowing any
    such calls to be completed via satellite. So I guess the feeble
    radiation by my FM radio (powered by 2 AAA batteries) is enough to
    cause a plane to dive into the ocean, but the guy next to me putting
    out 3 watts of near-microwave energy is totally safe.

    What about my hand-held GPS unit? Any chance me using it (during all
    phases of a flight, which I do routinely) will result in a one-way
    ticket to kingdom come?

    Getting back to the original question (poor to non-existant AM
    reception), I understand the idea of aperature and long wavelenths of
    AM radio and the size of airplane windows - but what about the effect
    of ALL the windows on a plane? Don't they create a much larger
    effective apperature when you consider all of them? And since the
    plane isin't grounded, isin't the exterior shell of a plane
    essentially transparent to all RF (ie it's just a re-radiator) because
    it's not at ground potential?
  13. This becomes a matter of the distance between them and the phase
    separation at any wavelength. What you describe is a common technique
    for coupling power between waveguides (in what are called directional
    couplers). However, this is not the same thing as accumulating and
    enlarging an opening because such couplers will add energy in one
    direction, and subtract it in the other (which makes for their
    Ground does not always mean "at one with the dirt and rocks." At one
    time it did, when cowboys put up talking wires, and indians pulled
    them down. Ground has since come to mean "common" (which when you
    think of it, brings us back to dirt, metaphorically). Common means
    that everything is at the same potential. If there is no potential
    difference, then there is no way to measure a voltage based signal.
    In other words, it's a massive short circuit, and the only way to
    sense a signal is to inductively couple to the short circuit current.

    This takes us to the second killer courtesy of physics. High
    frequency current travels on the surface of smallest, positive radius.
    AM frequency qualifies here in spades, even though it is
    conventionally called not HF but MF (even VLF qualifies as High
    Frequency in this context). The aircraft frame thus presents both
    curvature and radius such that the current confines itself to the
    outside of the shell with an inclination for the narrow wings and tail
    section, rather than the elongated body.

    You might be tempted to inductively tap into this frame current, but
    then you are on the negative, inside radius of the current carrier
    (makes the tube interior self-shielding). Whatever current is
    flowing, is on the outside of the skin, not the inside - that is,
    until we consider skin depth and penetration. But then it appears
    that experience described here suggests that not much of that frame
    current penetrates inside.

    Richard Clark, KB7QHC
  14. Roy Lewallen

    Roy Lewallen Guest

    Too bad it's not that simple. But if you're really into this kind of
    argument, do a search of the sci.geo.satellite-nav
    newsgroup. There you'll find endless argument, speculation, and
    rationalization ranging from well informed to completely clueless.
    There's surely more than ample ruminating there to satisfy anyone,
    regardless of your orientation or clue level; it's surely not necessary
    to do it all over again here.
    A bit larger, yes. But the attenuation inside is still very high, since
    the windows are extremely small and spaced very close, in terms of
    wavelength. Sort of like the screen of a screen room.
    No, being at "ground potential" plays no part in shielding. Currents and
    fields on the outside aren't magically allowed to violate basic laws of
    physics and migrate through a good conductor just because a shield isn't
    at "ground potential". For that matter, a box that is at "ground
    potential" at the bottom is nowhere near that potential a quarter
    wavelength up the side. No shield over a small fraction of a wavelength
    on a side could work if "ground potential" were a requirement. Yet
    room-sized shielded enclosures are routinely used into the microwave
    region. Try your own experiment. Turn your portable radio on, turn up
    the volume, put it into a sealed can, set it on a stool, and see how
    much you hear.

    Roy Lewallen, W7EL
  15. Ether Hopper

    Ether Hopper Guest

    Well you have been referred to the FAA Regs and the Airline policies and
    ignored them.
    Section 91.21
    So here is another URL we hope you read about GPS

    Just a snip:
    There are documented cases of AM/FM radios causing interference with Avionic
    systems and as a result, AM/FM radio receivers are generally prohibited.

    You will be happy to learn of this quote;
    "By design, (or happy accident), the "spurs" generated by a GPS generally
    fall outside the communications frequencies used by Aircraft and so have not
    been a problem even though a few "spurs" exist.
    But SOME airlines do not permit the use of GPS receivers. Why is that if
    they are "safe"?"

    You will be unhappy with the answers. Hope you go to the URL for the answers

    Here is one:
    If a GPS is safe, why can't I use it on an airplane anyway, even if the
    pilot says NO?
    This would be a) unwise, b) illegal and c) dangerous. Never presume that
    you have more authority than the Captain of a ship! He is responsible for
    the lives of his passengers and likely has knowledge and experience about
    his aircraft and/or equipment and/or this particular flight that no one else
    has.. The use of a GPS by a passenger is NOT worth a confrontation and a
    possible visitation from the police or FBI when you land..


    Be safe, obey the law, stop guessing -- get educated and read these URL's
  16. CW

    CW Guest

    So, you contend that he cannot hear AM (MW) transmissions because the pilot
    didn't give his permission?
  17. Ed Price

    Ed Price Guest

    Yes, you are a wholesale distributor. Further, you are a loud-mouthed,
    egocentric nitwit with a knowledge of physics equivalent to a smart gerbil.
    You should be allowed on an aircraft only as freight.

  18. Dave VanHorn

    Dave VanHorn Guest

    Given that the aircraft voice comms are just above the FM BCB, and the
    typical first IF is 10.7 MHz, it's not too hard to imagine the LO sitting
    right on the tower comm frequency.
    You may only radiate a microwatt, but you're much closer to that antenna on
    the aircraft than the tower is. Inverse square law makes it very easy for
    you to win that contest.

    This is a pointless argument though. It's a health and safety issue, and
    you either follow the airline's rules, or I hope they boot you off the plane
    (optionally, landing first for your convenience) It is just that simple.
  19. Dave VanHorn

    Dave VanHorn Guest

    (5) Any other portable electronic device that the operator of the aircraft
    So in the case of an airline (air carrier) the airline makes the
    determination to allow, NOT the pilot.
    In a private plane, the pilot can decide to allow.
  20. Virgin is a British Airline, so they can permit the operation of radios
    once the plane leaves US airspace. Once the plane leaves US
    airspace, it is no longer subject to FAA regulations.
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