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[aprssig] Aircraft EMC, was Balloons, Ham Radio and APRS in UK

Fred Atkinson, WB4AEJ fred at wb4aej.com
Wed Apr 26 11:35:32 UTC 2006


Dave,

    I understand what you are saying.

    But is it really going to make any difference when it is hanging from a
weather balloon?  That is what started this thread.

    Regards,




Fred, WB4AEJ
----- Original Message -----
From: "Dave Baxter" <dave at emv.co.uk>
To: "TAPR APRS Mailing List" <aprssig at lists.tapr.org>
Sent: Wednesday, April 26, 2006 4:59 AM
Subject: [aprssig] Aircraft EMC, was Balloons, Ham Radio and APRS in UK


Oh how wrong that statement is!

> The FAA has been made aware that interference issues on aircraft
probably don't exist,

They "may" not exist with current phone/pda/laptop technology, as far as
most critical systems are concerned (flight controls, navigation,
engines on civil airliners etc.  Light aircraft are totally different of
course.)  But from tests done here in the UK, that our company were
involve with (we provided much of the equipment to do the tests, on a
real aircraft, typical of the fleet used by most airlines, not a test
setup) there are some serious problems with QRM getting into of all
things, the flight deck pilot intercom, at apparently quite "loud"
levels.  Just about all the wiring on a 'plane, eventually ends up going
back to the avionics bay, under the pilots feet we were told.

These tests were done not that long ago at Gatwick airport here in the
UK, on the ground it has to be said, but with proper EMC test procedures
in place, at the frequencies and power levels representative of most of
the mobile networks in use today, and one or two of the proposed
systems.  RF was launched from various places within the passenger area,
and field strengths recorded elsewhere, and other systems were also
monitored in real time.

It was quite surprising how much field could be produced by relatively
low power levels, after all, there is not that much RF Absorber in a
'plane, other than the "ugly bags of mostly water" sitting all over the
place!  And they only do a reasonable job of damping down 2.45GHz or
thereabouts.

In any case, if you were taking off, or more likely trying to land in
bad conditions (it happens!) would you want the pilot to suddenly have a
burst of cell phone QRM in his ears, at an "interesting" moment.

Considering that most of the world wide civil aircraft fleet has the
majority of it's wiring unscreened, (to keep weight down) and a lot of
it runs along just above you head when you are in your seat, so until
they have all exceeded their airframe hours and been taken out of
service, or been modified (some are going that route as an experiment)
common sense is not to have any passenger induced RF in the things, at
all...

On a personal note, I am amazed whenever I fly these days, that some
people (usually arrogant business types who should know better) just
"have" to call their office/wife/mistress, even before the wheels have
hit the ground on occasions, after there has been an explicit
instruction (not a request) to turn off all electronic devices prior to
landing, not that a phone should have been "On" in any case.  There are
even people who do not know how to turn off a phone, and think that just
locking the keypad is enough...  Yes, I know some PDA's and the like
have a "Flight Mode", but again, how many non technical owners actually
know what, how and why that is there?...

If in doubt, remove the battery, that'll do it!

They may not be as serious as some would make out, depending on your
point of view, but there are some EMC issues of note, with some
passenger aircraft systems and cell phones being used inside the
passenger cabin.

Sorry this went on a bit.....

73.

Dave G0WBX.
www.wmv.co.uk


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