redburgundy

Can you be a little more specific about this?
Are you saying that two 850 MHz devices will create intermod products at 1100 MHz?

IFE Wizard

Let me explain why I believe that my statement is accurate.

There are many factors to the problem of mobile phone interference with aircraft systems.

Under normal circumstances, it is recognised that one mobile phone, operating correctly and within its specified limits poses little threat to any aircraft avionic equipment, itself operating correctly and within its specified limits.

However, even with a single phone that is malfunctioning, for whatever reason (ie has been subject to abuse, eg dropped), it can exceed its specified outputs, which in turn COULD affect other equipment.

Similarly if the equipment on the aircraft and its associated wiring has been compromised in any way, it COULD raise the risk of allowing spurious signals to enter and cause problems.

The actual position of the offending mobile within the aircraft cabin is also critical. Certain seats, ie window seats in close proximity to any external aircraft antenna, seats located over the electronics bay (typically located under the floor at the back of first class on a 747) are two such “hotspots” (my word).

Signals within this sealed metal tube (yes, I know the windows and doors can “leak” signals) can “bounce” (my word) around the cabin.

Finally, it has been shown in testing that when a GSM phone is transmitting in close proximity to a transmitting AMPS phone, intermodulation occurs. This results in unwanted frequency components that can affect the DMS system on the aircraft.

Now, if you have a full complement of passengers (typically 400) all using their mobiles;

1) The chances of a faulty mobile on-board is increased,
2) The absolute certainty that passengers will be located in “hotspots” on the aircraft.
3) There will be a cumulative effect of the signals “bouncing around” the cabin.
4) There will be a very high probability that there will be a mix of GSM and AMPS phones in close proximity thereby causing intermodulation.

I am sure that this answer will not satisfy everybody on this forum so I suggest that if you really need to see results from tests, scientifically carried out you can checkout the following site http://ntrs.nasa.gov/search.jsp

Once on the home page enter Doc ID 20030107608. This 198 page document should answer all you outstanding questions.

IFE Wizard

I will try and reply to your question.

In testing (see link in my previous message) it was noted that when telephones of different systems i.e. GSM and CDMA were in close proximity and transmitting at the same time a “third-order intermodulation” product was observed in the DME band and “fourth order” in the GPS band, with the un-wanted frequency components as high as aprox -15dBm. This signal would only exist with two or more phones transmitting at the same time.

Note:- Intermodulation products are unwanted frequency components resulting from the interaction of two or more spectral components passing through a device with non-linear behaviour. The unwanted components are related to the fundamental components by sums and differences of the fundamentals and various harmonics.

Well…..you asked.

Is this specific enough???

videomaker

I wasn't looking for generic NASA or any Wikipedia (reliable source--not) links, just the study that you say proves everyone turning on a cell phone on a 747 "can and will" cause interference to the aircraft's navigation. Can you provide that, or not?

redburgundy

No. I wanted to know what specific frequencies were involved. Third order intermod occurs at the frequency 2xf1-f2. If f1 and f2 are close in frequency, then third order intermod occurs in the same band as f1 and f2. I didn't see how two cellphone signals could cause third order intermod in the 960-1215 MHz band. But after looking at the report you cited, I see that they had one phone set up for the US frequency band at 824 MHz and the other set up for the European band at 901.9 MHz. The report says that such an intermod occurance is very unlikely because in any location only one band or the other is used, not both. But I wonder how quad-band phones work when they are out of range of any cellular network and they search for a network. Maybe this kind of intermod could occur then.

IFE Wizard

Please....If I take the time to respond to your messages then please do me the courtesy of reading what I have written.

When I wrote the following:-

"Mobile phones, as an example, transmit a signal which increases in power until it finds a (ground) station. Flying at 35,000 feet this will almost certainly mean that the mobile phone is transmitting at max output. Now consider (as the FAA authorities have to) if all passengers on a 747 use their phone together, the radio interference can and will cause problems for the aircrafts vital systems."

there is nothing here that states or even hints at this statement being the result of any study.

I hardly believe that the NASA report can be classed as generic. It is very specific and very detailed.

As for Wikipedia, while I agree this is not the definitive source of all knowledge it is independent and covers a range of references from scientific to very basic TV journalistic reporting.

videomaker

OK, so your conclusion of "can and will" cause interference was your opinion only, not the result of any scientific study. That's what I've been asking you to clarify.

IFE Wizard

Again, I must reiterate, If you took time to read and understand the messages I have posted here you would have seen that in my message #12 on this link I categorically stated:

"I am not posting on this forum to educate or to force my opinions on others. I have just stated my humble, honest opinion."

So what part of that statement did you have problems understanding?

videomaker

And you said there were no references to a study? This is what you said in post 9.

So now we know, it's your opinion. Thanks for the clarification.