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conehead

Cell phones causing RF interference

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I’m not seeing the connection of blanking screens and on-board cell phone use. Has to be a coincidence and not a result of cell phone use.

I’ve noticed on some of the newer aircraft such as the 787 once the doors are closed, it is difficult to get a cell phone signal. Our cell phones operate on the FM band which is the same as ILS transmitters but that shouldn’t cause any interference with a signal generated from the ground and all the cables connected to the aircraft antennas are shielded. 

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I think I have posted this before.

Some years back I was involved in the final fitting of an interior of a custom Global Express interior complete with all of the "office in the sky"  technology.  This included working with the engineering company to ensure that the installed equipment would not interfere with any of the flight systems of the aircraft.

Part of that certification was analyzing the frequencies and power emitted by all of the electronic added.  When looking at the spectrum analyzer and seeing that the equipment was emitting frequencies all over the map, the engineer I was with asked me if I wanted to see something interesting.  (for this test our phoned had to be turned off).  He left the machine running and asked me to turn on my phone.  When I did EVERY frequency on that analyzer lit up.  That phone put out at least something on almost every frequency including ones that could cause interference with navigation.  

Now that being said, this was measured right next to the analyzer.  The power measurements were low but they were present.  This is why they always said POSSIBILITY of interference.  if you were right next to the ILS antenna you could likely cause an issue but thats wont happen in flight.

Also as BD mentioned above, once you are locked in the cabin you are essentially inside a faraday cage and it is difficult to get a good signal.  It is ok when you are close to a tower but get in the air and the signal fades very fast.

So yes there is a potential for interference however unlikely.

 

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On 7/19/2019 at 7:54 AM, blues deville said:

I’m not seeing the connection of blanking screens and on-board cell phone use. Has to be a coincidence and not a result of cell phone use.

I’ve noticed on some of the newer aircraft such as the 787 once the doors are closed, it is difficult to get a cell phone signal. Our cell phones operate on the FM band which is the same as ILS transmitters but that shouldn’t cause any interference with a signal generated from the ground and all the cables connected to the aircraft antennas are shielded. 

The issue was with CRT (not LCD) screens and Wi-Fi frequencies (not cell).  The screen-blanking effect could be reliably replicated under certain conditions and thus the flight deck ban on Wi-Fi until all CRTs had been replaced with LCDs.

The cellular frequencies don't interfere with any of the screen types--although I can hear the interference in my Bose A20 headset when they ring.  I can also hear the sweep of the SSR in YWG and YOW. 

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Cell phones (and almost all electronics) emit signals on many frequencies other than their primary operating frequency.  They are not sheilded well at all

 

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