AM radio reception inside passenger planes?

Reception of radiosignals inside a Faradaycage is limited to frequencies that are smaller then the holes in the cage. "Geoff Glave" schreef in bericht news:HxHud.9448$eb3.8331@clgrps13...

"see"

Not at all; however, there IS obviously a connection between various flight control functions (such as, say, the autopilot) and the information given by the avionics (esp. "nav" radios using ground-based sources such as VORs, etc.). It's not going to "send any plane into a tail spin", but it can certainly cause some problems.

You DO realize that these are on very different frequencies, and that the emissions of an FM superheterodyne radio are very likely to fall right in the aviation band, don't you? Hint: if you have to go look up "superheterodyne" to understand this question, I have serious doubts regarding your qualifications to comment on it.

No. It's not the TOTAL area of the "apperatures" [sic] that is important, it's the size of the individual openings. If this were not so, then a conductive mesh could never be effective as a shield.

No. "Ground potential" has absolutely nothing to do with it. Hint: what do you think is the RF environment within a perfectly conducting sealed enclosure, with respect to outside sources, even if that enclosure is completely isolated from any other surface or conductor?

Bob M. (KC0EW)

A pitot tube is a tube which protrudes from the aircraft body into the path of the air through which the aircraft is flying. They are used for such things as determining airspeed (which is the speed of the aircraft through the air, not over the ground), and in some meteorological conditions are prone to becoming clogged with ice. Hence, "pitot heat" is just that - the switch in question controls a heater (most often, electric) built into the pitot tube, which keeps in clear of ice. Losing pitot pressure due to having the damn thing plugged up is generally considered a Bad Thing, and unfortunate events have been known to follow such an occurence.

Bob M.

There have been numerous postings in various scanner, shortwave and ham groups by people who have been ordered to turn off their radio and other PEDs. More than one person has been ordered off, or met by the authorities on landing and at least one passenger who refused to turn off a cellphone ended up with some jail time after landing in the U.K. - it was pretty widely reported a year or so ago.

Dave

The I presume you specified AM because the LO operates outside aviation frequencies (now that LORAN A is gone), unlike the LO in an FM broadcast receiver which covers the VHF localizer and VOR frequencies very nicely.

Dave

I can't provide technical details of the operation because I don't know them; but I am familiar with a number of totally RF screened environments where use of electronic devices are tightly controlled. However, internal relays are used to permit operation of cell phones - which I always understood were specific models which had been certified for such use.

Dave

The point was not how the planes are being equipped to handle in-flight cell-phone use.

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.

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

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.

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.

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.

aircraft

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.

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

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.

it's

can "see"

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.

just

minute.

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.

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.

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!

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

You're even dumber than I had thought. Look up Faraday Shield. Here, try this:

"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message news: snipped-for-privacy@corp.supernews.com...

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

"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message news: snipped-for-privacy@corp.supernews.com...

He's not dumber than "I" thought!

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).

"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