AM radio reception inside passenger planes?

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?

Reply to
Some Guy
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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.

Cheers, Geoff Glave Vancouver, Canada

Reply to
Geoff Glave

In message , Geoff Glave writes

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! Ian.

Reply to
Ian Jackson

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 windows.

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...

Nick

Reply to
nick smith

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:

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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.

--
RF Gotta Go SomeWhere



"nick smith"  wrote in message 
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Reply to
Ether Hopper

In message , Ether Hopper writes

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. Ian.

Reply to
Ian Jackson

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, Dave

Reply to
Dave Bushong

And you do want the Avionics to work properly don't you ???

--
RF Gotta Go SomeWhere



"Ether Hopper"  wrote in message 
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Reply to
Ether Hopper

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?

Ed wb6wsn

Reply to
Ed Price

Part 91 GENERAL OPERATING AND FLIGHT RULES 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 other 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:

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--
RF Gotta Go SomeWhere



"Ed Price"  wrote in message 
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Reply to
Ether Hopper

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.

73's Richard Clark, KB7QHC
Reply to
Richard Clark

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?

Reply to
Some Guy

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 directionality).

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.

73's Richard Clark, KB7QHC
Reply to
Richard Clark

Too bad it's not that simple. But if you're really into this kind of argument, do a groups.google.com 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

Reply to
Roy Lewallen

Well you have been referred to the FAA Regs and the Airline policies and ignored them.

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Section 91.21

-------------------------------------------- So here is another URL we hope you read about GPS

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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? Answer: 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..

READ THE LAST SENTENCE AGAIN

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

--
RF Gotta Go SomeWhere



"Some Guy"  wrote in message news:41BB8C6A.FD42C1E7@guy.com...
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Reply to
Ether Hopper

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

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as

FRS

80
Reply to
CW

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.

Ed wb6wsn

Reply to
Ed Price

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.

Reply to
Dave VanHorn

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.

Reply to
Dave VanHorn

to

commercial

about

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.

Reply to
Charles Newman

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