AM radio reception inside passenger planes?

On the way back, I spoke with a commercial pilot who was deadheading, on
this issue.
He said that it's not all that unusual to hear radio interference once they
have allowed the devices on, but when they are in cruise, they aren't
normally doing any urgent communications, so it isn't much of an issue. If
something comes up, then they will pass the word to shut down the PEDs.

On takeoff and landing though, the comms are much more rapid, and the
consequences of missing one transmission are much higher. They need to hear
all the comms, not just between themselves and the tower, but what the other
pilots are saying as well. Add to this, the fact that aircraft comms are
AM, which is inherently muddy, and it's easy to see why they take the extra
precautions.
 >> Stay informed about: AM radio reception inside passenger planes? 

"Dave VanHorn" wrote:
 > They need to hear
 > all the comms, not just between themselves and the tower, but what
 > the other pilots are saying as well. Add to this, the fact that
aircraft
 > comms are AM, which is inherently muddy, and it's easy to see why
 > they take the extra precautions.
 >

The design of newer comms doesn't help either. If they have automatic
squelch, set to break at say 1uV RF in, then obviously it doesn't take
much interference to break squelch. Then, they also may have "audio
leveling" -- a great feature when commonly using headphones -- but the
effect there will be to take a few uV of noise and amplify the audio
component to the level you hear when ATC hits you with as much as 50W,
and it's heard constantly between transmissions, to be hopefully
silenced when ATC talks. But not necessarily the case in monitoring
comms of other aircraft, where especially general aviation,
less-than-properly-functional 7W units can be relatively weak.

Fred F.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: AM radio reception inside passenger planes? 

"Some Guy" wrote in message
> The point was that consideration is being made to allow cell phones to
> be used while the planes are in flight. That intentional radiating
> PED's are even being considered for in-flight use when so much hype
> and concern is being given to the weak radiation potential of some
> non-intentional radiators like am/fm radios.

Because, as has already been pointed out, of the
differences in emission characteristics (and specifically
the frequency ranges likely to be affected) of the two
classes of devices.

> BTW, what is the potential of the local oscillators of small hand-held
> LCD-screen TV's to overlap with aviation frequencies?

I believe they should be somewhat less than is the case
with an FM receiver, but they're still a bad idea for
the same reason. Note that the analysis of the likely
frequencies provided so far has dealt solely with the
first-order effects of the receiver's local oscillator; we
have NOT discussed harmonics or other unwanted
emissions.

The problem is most obvious with FM receivers because
the standard 1st LO frequency is 10.7 MHz, and the
top of the FM broadcast band is adjacent to the bottom
of the aviation band (108 MHz) - which means that
simply adding the LO frequency to standard FM
broadcast frequencies can take you instantly into overlap
with the bottom 10.7 MHz of the aviation band (and
unfortunately, that's where a lot of the radionavigation
systems within that band tend to be). But this does
not mean that receivers for other services would not
cause similar problems. VHF television covers
frequencies below and above both FM and
aviation (two bands, 54-88 MHz for channels 2
through 6, and 174 to 216 MHz for channels 7
through 13). It is certainly very possible that receivers
intended for these bands would emit in the aviation
band. Other adjacent services that may be of concern
include public-service and commerical communication
bands (i.e., police scanners) and the 2-meter amateur
band.

Bob M.
 >> Stay informed about: AM radio reception inside passenger planes? 

"Geoff Glave" wrote in message

  > > Any explanation for this?
 >
 > FM radio generally operates at longer range than AM radio,

Nonsense! AM radio stations can be heard for thousands of miles, FM for
'line of sight', which is usually less than a hundred miles.

 > 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.

Nonsense! The passenger is sitting in a Faraday Cage, a fuslage made of
alumninum. The FM wavelength is short enough to go thru the windows,
but mot the AM signals.


 > Cheers,
 > Geoff Glave
 > Vancouver, Canada
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: AM radio reception inside passenger planes? 

"Ian Jackson" wrote in
message


   > >> 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.
  > >
  > >Cheers,
  > >Geoff Glave
  > >Vancouver, Canada
  > >
  > >
 >
 > 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.
 > --

If you stretch a string on a globe from London to Florida, it will show
the 'great circle' route that's the shortest, and that should be your
plane's path, barring storme, hurricanes, etc. You'll see that it comes
really close to the eastern Canadian provinces.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: AM radio reception inside passenger planes? 

"Richard Clark" wrote in message


 > wrote:
 >
  > >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.
 >
 > 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

If you make your own TRF receiver, with no LO, it won't interfere with
anything. In fact, you can then put an AM detector in it, and also
listen to the aircraft chatter.

Another way is to listen to stations at or below 97.3 MHz, which would
keep the LO at 108 MHz or below.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: AM radio reception inside passenger planes? 

"Some Guy" wrote in message

 > 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.

No, the laws say that you can be arrested for breaking them, and one way
to break them is to use a FM radio while the aircraft is flying.

 > 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.

You don't know what you're talking about. With the attitudes of the air
marshals nowadays, making airliners turn around and go back to their
departure point just because a passenger is unruly, there is a high
probability that one of them is flying along on your flight, and if he
sees an earphone hanging out of your ear, you might be that unruly
passenger they arrest at the departure point. Especially with your
nasty attitude!

 > 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?

Geez, what a TWERP! You can't add two and two without jumping to
conclusions! A rational conversation with you is nearly impossible.

 > 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?

You're even dumber than I had thought. Look up Faraday Shield.
Here, try this: <a style='text-decoration: underline;' href="http://www.physlink.com/Education/AskExperts/ae176.cfm" target="_blank">http://www.physlink.com/Education/AskExperts/ae176.cfm</a>
You don't have to worry about a ground for it to work. Duh.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: AM radio reception inside passenger planes? 

"Watson A.Name - "Watt Sun, the Dark Remover"" wrote
in message
>
> "Richard Clark" wrote in message
>
>> On Sat, 11 Dec 2004 14:11:44 -0800, "Ed Price"
>> wrote:
>>
>> >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.
>>
>> 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
>
> If you make your own TRF receiver, with no LO, it won't interfere with
> anything. In fact, you can then put an AM detector in it, and also
> listen to the aircraft chatter.
>
> Another way is to listen to stations at or below 97.3 MHz, which would
> keep the LO at 108 MHz or below.
>
>
>

Like maybe putting the LO at about 80 MHz, so that the 3rd harmonic of the
LO drops into the UHF navcom band?

Ed
wb6wsn
 >> Stay informed about: AM radio reception inside passenger planes? 

Ed Price wrote:
>
> "Watson A.Name - "Watt Sun, the Dark Remover"" wrote
> in message
> >
> > "Richard Clark" wrote in message
> >
> >> On Sat, 11 Dec 2004 14:11:44 -0800, "Ed Price"
> >> wrote:
> >>
> >> >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.
> >>
> >> 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
> >
> > If you make your own TRF receiver, with no LO, it won't interfere with
> > anything. In fact, you can then put an AM detector in it, and also
> > listen to the aircraft chatter.
> >
> > Another way is to listen to stations at or below 97.3 MHz, which would
> > keep the LO at 108 MHz or below.
> >
> >
> >
>
> Like maybe putting the LO at about 80 MHz, so that the 3rd harmonic of the
> LO drops into the UHF navcom band?
>
> Ed
> wb6wsn

It is official; i just read in one of my electronigs mags i get that
the FAA indeed has ruled that airlines can allow use of computers over
the net when flying.
But it is up to each given airline to modify their own giudelines (as
they see fit).
 >> Stay informed about: AM radio reception inside passenger planes? 

"Robert Baer" wrote in message



SNIP

>> >> > "Faraday shield" to some degree is a myth.
>> >> > I have seen radars inside quonset huts track a *bird* flying a few
>> >> > miles away (thru the metal wall)!
>> >>
>> >> You must have some strange buddies. Who in the world would set up a
>> >> radar
>> >> within a metal hut? And even if they did, who would think it's a good
>> >> idea
>> >> to stay inside with it if it were on?
>> >>
>> >> There's nothing mythical about the Faraday shield; it works really
>> >> well,
>> >> so
>> >> long as there are no discontinuities (apertures) and sufficient
>> >> thickness
>> >> and conductivity. Under real-world conditions, steel works pretty
>> >> good,
>> >> and
>> >> any thickness sufficient to support itself will yield great shielding
>> >> effectiveness. So the only real performance variable left is the holes
>> >> in
>> >> the conductive surface. How many, maximum dimension, proximity of
>> >> radiating
>> >> source to the shield, etc.
>> >>
>> >> While I would expect a Quonset hut to really mess up the accuracy of a
>> >> radar, it likely wouldn't be a good shield, as the floor isn't metal,
>> >> I
>> >> don't think the ends are metal, and the various skin panels are rather
>> >> poorly RF bonded.
>> >>
>> >> Ed
>> >> wb6wsn
>> >>
>> >
>> > I do not think your objections concerning the floor or the bonding of
>> > the panels are too relevant.
>> > The ends are metal and not relevant either.
>> > The radar was pointing right at the wall (no windows nearby); any
>> > presumed leakage via remote holes that you assumed might allow the
>> > transmitted signal to leak, but would then not be focused on the
>> > bird(s)
>> > and the path lengths would vary.
>> > But the reflected signal from the bird or birds would be rather weak
>> > and could not possibly be received via the same wild path(s) to a very
>> > directional antenna.
>> >
>> > My point is that a Farady shield is a good attenuator, but not
>> > "perfect" as ASSuMEd.
>> > And it sure is not "flat" in attenuation characteristic as a function
>> > of frequency.
>>
>> Those weren't objections, they were speculations on my part as to how you
>> boys could have been finessing the generally applicable laws of physics.
>>
>> But truly, the story stinks. So you and your army buddies are in this
>> metal
>> hut, with a fairly high-power radar, and somebody comes up with the
>> bright
>> idea to turn the thing on. Apparently no thought about RF personnel
>> hazards
>> and no concern about strong reflections cooking your detector. Did you
>> test
>> your M16's in a Quonset hut too?
>>
>> Next point. "The radar was pointing right at the wall..." Now tell me, in
>> a
>> semi-circular Quonset hut, how do you point anything "right at the wall"?
>> Maybe straight up?
>>
>> Now, a bird doesn't have a very big radar cross section, maybe only about
>> 0.01 square meters, so the return loss is really big. And to resolve a
>> single bird, I'm gonna guess that you had an X or K band radar. So let's
>> run
>> some numbers. Let's say you had a 100kW radar, with a 30 dBi antenna of 1
>> square meter aperture. At 1500 meters, your detector power would be about
>> 1
>> picowatt, or -60 dBm. Well hey, that's pretty decent, I'll bet you could
>> see
>> a bird at one mile.
>>
>> But that's assuming no loss at all due to the metal hut skin. Let's see
>> what
>> happens if we say that the metal hut walls give us only 40 dB of
>> shielding
>> (by absorption or reflection, it doesn't matter). That bites 80 dB out of
>> your path budget, putting your detector signal down to -140 dBm. I think
>> your story just ran out of luck.
>>
>> Now you can argue about the 40 dB shielding effectiveness of the metal
>> wall,
>> but I'll say that I was being very generous about that. At 10 GHz, I know
>> (How? Easy, I do it everyday. Just 3 days ago, I was keeping some 1.3 GHz
>> from radiating off of some cables, and it was common old Reynolds Wrap to
>> the rescue.), I can get >100 dB out of a sheet of aluminum foil. The SE
>> is
>> so damn high from the material that the only significant factor is when
>> the
>> energy finds a path around the shield.
>>
>> Don't try to argue that a Faraday cage leaks; you appear to be trying to
>> build a general case based on your experience of always having observed
>> leaky structures. Sure, I know that shielding varies with lots of
>> factors,
>> conductivity, permeability, thickness, frequency, angle of incidence,
>> distance from source, and then there's the problem of apertures. But your
>> hut, with plain old galvanized steel about 1/16" thick, would make a
>> great
>> shielded enclosure, as long as the joints didn't leak.
>>
>> BTW, I don't like using the term "Faraday cage". Despite all due respect
>> to
>> Mr. Faraday, calling it a shielded enclosure is a clearer description.
>>
>> Ed
>> wb6wsn
>
> I was not alluding to leakage; a more accurate term would be
> re-radiation.
> Take an ordinary transformer; it radiates a magnetic field, despite
> the fact that the core is a closed loop.
> In fact, one could get nasty and say the same thing about a toroid
> transformer.
> Now add a shorted copper turn around the outside of the ordinary
> transformer's core (i have seen this on many TV power transformers and
> others as well).
> What happens? That magnetic field induces a current in that shorted
> turn, making an opposing magnetic field - thereby reducing the net
> radiated magnetic field greatly - but not to zero.
> Now, instead of using that closely wrapped copper shoted turn, put
> that transformer inside that shielded room you love.


My shielded enclosure only asks that I respect it; I don't think it would
provide better SE even if I told it that I loved it.


> Results: great reduction, but not to zero.


Nothing ever goes to zero; I'll usually settle for "great" reductions.


> Increase the frequency to something one might consider RF.
> Now one has an RF transmitter inside that shielded room, inducing
> currents in the wall(s).
> Those currents create opposing fields, and greatly attenuate the
> signal outside the walls.


You're getting a little fuzzy here. The propagating wave induces surface
currents on the metal barrier. The currents "sink" into the metal,
decreasing to about 37% (1/e) in what's called a "skin depth". At 10 GHz, a
"skin depth" in steel is really thin. After even 10 skin depths, the current
is down to only about 1/100,000 of what was on the surface. And there's a
whole lot of more skin depths to go before the current is presented to the
far surface of the steel barrier. And only then does the surface current on
the far side of the barrier get to launch a propagating wave.

Note that the "opposing fields" you mentioned are on the INSIDE, the near
surface, of the barrier. The reflected field is 180 degrees out of phase
with the incident field, so, real close to the metal surface, the E-field
nulls. OTOH, that reflected wave now goes marching back at you, creating
lots of fun with out-of-phase energy pumped back into the original radiating
element. Everybody sees bad, bad VSWR. And, since you guys were inside a
metal hut, there's even more fun in store for you. Not all that energy goes
back into the originating antenna. A lot of it just keeps bouncing around
inside the hut, creating 3-D variations in power density. Think of yourself
as a potato, slowly cooking.

So, to keep this straight, the current that survives Ohmic losses to make it
to the far side of the barrier doesn't "greatly attenuate the signal outside
the walls". It actually creates the signal (the propagating wave) on the far
side of the barrier.

We can talk about aperture leakage and re-radiation from barrier impedance
discontinuities some other time.


> But they are not zero.
> BW, radar is usually pulsed, and in the megawatt to multi-megawatt
> region for the pulse.


Multi-megawatt? Hmm, 10 MW? OK, and maybe a duty cycle of 0.01%? Isn't that
1 kW average? I own a 250 kW X-band radar that will do up to 0.1% duty
cycle. I sure wouldn't sit in a metal box with that thing running! I
wouldn't even want to be in the boresight of the antenna within a few
hundred feet. I was trying to be charitable in assuming that nobody would be
so dumb as to fire up a multi-megawatt radar INSIDE a metal hut. Looks like
you guys proved me wrong!

Ed
wb6wsn


Ed
wb6wsn
 >> Stay informed about: AM radio reception inside passenger planes? 

FAR more likely that the antenna for the radar was outside the hut.
There may have been one slaved to it, inactive, inside the hut to
demonstrate what's going on upstairs.

There are plenty of good reasons why such a demo wouldn't work as described,
from killing the detector with strong reflections, to massive
re-re-reflections inside the building, to the fact that radar relies on a
"pencil" beam that wouldn't survive through those walls in any rational way,
and so on.
 >> Stay informed about: AM radio reception inside passenger planes? 

What's with all the recipe bullshit posts?

Who's posting these?

Ed Price wrote:
>
> oil.
> Add a little water, season, then add the carcass.
> Simmer for half an hour keeping the stock thick.
> Remove the carcass and add the vegetables slowly to the stock,
> so that it remains boiling the whole time.
> Cover the pot and simmer till vegetables are tender
> (2 hours approximately).
> Continue seasoning to taste.
> Before serving, add butter and pasta,
> serve piping with hot bread and butter.
 >> Stay informed about: AM radio reception inside passenger planes? 

"Julia Child" wrote in message

> What's with all the recipe bullshit posts?
>
> Who's posting these?
>
> Ed Price wrote:
>>

SNIP

No, I didn't write that. However, "Julia", rest assured that, by posting
your question, your address will soon be harvested for use by the Hipcrime
bot in the DOS attack. Don't reply, don't post about it, don't help the bot.

Ed
wb6wsn
 >> Stay informed about: AM radio reception inside passenger planes?