L-o-n-g article here (with pictures, graphs, etc.):
I believe the NASA study alluded-to in the article is this one:
.........
So when the terrorists eventually figure out that taking a doctored phone/DVD player/Laptop on board a flight (something designed to blast out interference at the press of a button) is a potentially effective way of bring down an airplane, then perhaps all that stuff at the airports scanning for explosives will be effectively obsolete?
As the article says, people won't accept a total ban on electronic devices so how are the authorities going to stop anything like this?
-- Regards, David.
David Clayton Melbourne, Victoria, Australia. Knowledge is a measure of how many answers you have, intelligence is a measure of how many questions you have.
A slightly less quick and more accurate summary:
"Yet our research has found that these items can interrupt the normal operation of key cockpit instruments, especially Global Positioning System (GPS) receivers, which are increasingly vital to safe landings."
It just won't happen. First, most of the instrument approaches made by airliners today are Instrument Landing System (ILS) approaches, which are ground-based and have nothing to do with GPS.
Second, where GPS is used the integrity and alerting modes would provide a warning in no uncertain terms to not rely on the GPS as the primary source for navigation.
Finally, the RF from a cell phone is highly unlikely to affect the GPS receivers, which are isolated from the cabin. The incidents referred to in the report were extremely isolated and the cause and effect were never determined with certainty. As I recall, the most likely suspect was a laptop in use by a passenger seated directly over the electronics compartment in an aircraft where the electonics compartment extended back past the flight deck to the first class cabin.
Last year while a friend was driving with me, he got a call on his AT&T phone, right after he answered it my TomTom GPS went nuts. I'm not sure if it was the phone as there were major power transmission lines crosssing the highway, so it could have been those, but in the past I never noticed it. He was on the phone just a short time so the next time he is with me I'll have him make a call and see what happens, my phone is Sprint and I have never had problems like that at all.
His phone was very close to your antenna and receiver.
That proximity can't happen on an airliner.
On Sat, 01 May 2010 15:18:04 -0700 Steven wrote: [snip]
AT&T uses GSM, which in turn employs TDMA transmissions. These switch your phone's transmitter on and off about 1000 times per second when the handset is communicating with a base station (yes, even when you aren't using it, the handset periodically checks in). The result is that a 1 kHz square wave is emitted. This can be induced into nearby unshielded electronics and heard as an audio buzzing sound. This often happens when a TDMA phone is next to a speakerphone, amplified computer speaker, etc. This emission is very low level, so the phone needs to be very close to the audio device.
Sprint and Verizon phones don't use TDMA transmissions, so they don't cause this buzzing.
I know about the types of technology that the companies use, I'm a COEI Installer and though I work mostly on wire line switches I have in the past and sooner or later will again work on Cell switches.
Right after the problem happened I contacted TomTom support and they told me about the same thing, but that the GPS is made so as not to get interference from other devices. I have since updated to a newer unit and have yet to have a problem, as I said next time I get a chance to test it I will. I have been on the same highway with the transmission lines and did not have a problem, the GPS I have now is set for real time updates so it is getting updated from traffic and weather services as well as other TomTom GPS units.
Technical nit:
" [...] " 1. ... General R/F pollution. Any system that switches its R/F " transmitter on and off rapidly (GSM does it 217 times a second, TDMA " does it 50 times) will scatter EMI throughout the adjacent radio " spectrum. " [...]
The above is from the comp.dcom.telecom archives, 11-March-1994. A copy of it was emailed to me last year during the "GSM Interference" thread and I posted that to the group. I also placed a copy on my web site so it'd be easier to find. :-) That copy can be found here:
I'm not talking about normal electronic items and their incidental effects, I'm talking about items that pass inspection for normal but actually are devices designed to interfere with the self-same critical systems that planes in flight rely on.
The bare fact is that you are currently allowed to take RF sources onto flights on the assumption that they are what they appear to be, where in fact they may well not be. One doesn't have to look back too far to see the chemical equivalent to this paradigm and the threat it posed.
-- Regards, David.
David Clayton Melbourne, Victoria, Australia. Knowledge is a measure of how many answers you have, intelligence is a measure of how many questions you have.
The basic GSM TMDA frame rate[1] is ~217 Hz, not 1000 Hz. A "full-rate" voice call is allocated only one slot per frame, so the duty cycle of the R.F. transmitter is only 1/8; a "half-rate" call [common with recent handsets with better codecs] uses only one slot every other frame, so it will appear to sound at ~108 Hz, rather than at 217 Hz. In either case, this makes the interference sound very rough -- more a "burp" (like a chain gun) than a "whistle".
Other than that, most of what you say is correct. All it takes is just a bit of nonlinearity in nearby electronics to demodulate the R.F. and produce the 217 Hz (or 108 Hz) buzz.
-Rob
[1] 8 slots of 577 us or 4.615 ms per frame, thus 216.7 frame/s.----- Rob Warnock
627 26th Avenue San Mateo, CA 94403 (650)572-2607
I get that from my iPhone with two devices in my house. It seems I have to be within about 3 feet of them to get it to happen.
Ross' paper is very well-known and is a good starting point. However, since
2001, GPS system front ends have improved substantially, while on the other side of the coin the current cellphone technologies cause more severe interference issues because of their waveforms.--scott
I got a chance to see if there was any kind of interference on my GPS from a GSM phone. A friend made and received calls on it as well as just leaving it on, no real interference as what had happened with my old TOMTOM, there was a little buzzing, but I don't think it was the phone. We linked the Blue Tooth devices; the cell phone and the GPS, no problems.
The date on the Spectrum article is March 2006!
Has anything happened since?
Mike
Just back from Poland, with two GSM phones always at the ready, in an apartment with a cheap clock radio, and some observations:
Know how you pronounce the Polish musician Paderewski? -- pa de REF (etc.)? Every time one of our phones was being sent an SMS (and lots of times between) that cheap clock radio spewed out a buzzy "REF, pa de REF, pa de REF, ... ". Perhaps a dozen iterations, before coming to a halt. 217 Hz buzz? Quite possibly. And about two "pa de REF"s per second.
Cheers, -- tlvp
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