Hearing ATC transmissions as interference on IFE channel

[Lord Bracken]

I flew HKG-SIN last week on a SQ A380 (9V-SKF I think it was).

Sat in 12A, the second row window seat in the forward upper deck Business cabin.

Fired up the IFE over lunch to watch a movie. Was surprised to be able to hear ATC transmissions as interference when there was no noise in the movie (i.e. at the beginning when the credits began to roll). I knew it was live and not a recording as I very clearly heard "Singapore Eight Six One" (my flight) talking to control.

Can any of the professionals comment?

[radeng]

Classic case of EMC - Electro Magnetic Compatability. Some non-linearity somewhere (could be a dirty connector) or a lack of or failure of cable screening allows the radiated signal from the aircraft transmitter to be detected. Many audio amplifiers will detect radio, either because of a large radio signal exceeding the capability of the amplifier or by bad design, or sometimes both. Happens with telephone exchanges too - a PABX about three mile from the Brookman's Park BBC station always had Radio 4 in the background, and it probably wasn't the only one to suffer. Telephones are bad, too. Way back in the mid 1980s, they put new electret microphones in telephones at Manchester airport: they detected all the air traffic signals, and had to be replaced with the old carbon microphones!

Unfortunately, even these days, designers rarely pay enough attention to EMC considerations at the design stage, and then it costs a lot more to sort them out when design is almost finished.

[Lord Bracken]

Thanks for the explanation - very interesting.

[PAXboy]

The PABX problem was enormous. I worked in telecommunications for 25+ years and long horizontal cable runs had to be avoided in order to prevent them becoming an aerial. Local taxi companies were the usual problem, as their signal was so much closer and stronger than general radio signals.

Over time, the insulation can wear down which can make cables more susceptible as receivers. Or a new item can be installed in the building/aircraft which creates a perfect attenna where none existed before.

You will all know of times (probably not on aircraft) when the human body acts as an aerial. Using an AM or FM radio on the fringe of reception spread, you get a better signal if you hold the aerial with your hand.

[radeng]

PAXboy

>You will all know of times (probably not on aircraft) when the human body acts as an aerial.<

When you do tests on a medical implant, such as a pacemaker with radio telemetry in it, you find that as you place the implant deeper and deeper, the polarisation of the signals emitted becomes that of the body. I did some work on this a few years ago: with the implant transmitter outside the body, the receiving aerial needed to be vertical. As the implant was placed deeper and deeper inside this anaesthetised pig, so the receiving antenna got a better signal when horizontal.

We did this work at a special veterinary place in the wilds of Sweden, with naturally, a lot of paperwork to get the government authorisation. But radio engineering, contrary to what you might think, is not always an occupation for the squeamish!

[PAXboy]

Most interesting radeng and also, Yuk! :yuk:

[radeng]

In REALLY bad taste.......

because of the drugs used for the anaesthetic, you couldn't barbeque the pig afterwards.

[PAXboy]

I am disturbed only that the thought she even have crossed someone's mind!!! Surely, after their dedicated service to humans, they can be cremated in piece and not cremated with BBQ sauce!!!

[radeng]

Actually, the corpses are buried, although in the middle of the Swedish winter, that means using a JCB.