Re: GPS tracking device allowed in commercial flights?

From: Alan Browne (alan.browne_at_FreeLunchVideotron.ca)
Date: 08/21/04 

Date: Sat, 21 Aug 2004 16:41:40 -0400

Meindert Sprang wrote:
> "Alan Browne" <alan.browne@FreeLunchVideotron.ca> wrote in message
> news:p7uUc.97900$sk2.2068110@wagner.videotron.net...
>
>>Oh please! Consult RTCA DO-160D. It outlines how equipment on
>>board must not only be resistant to interference, but how it also
>>must not interfere with other equipment. Only emissions within
>>its band and via the appropriate RF port is allowed.
>
>
> So, what does this tell you about possible interference of a cell phone?
> A cell phone is only supposed to emit signals within its band. A VHF is only
> supposed to receive signals in its band. For out of band signals, clear
> limits are set by this standard.
>
>
>>>Sorry, don't have that at hand. My job only deals with EN/IEC61000-6-1
>>>and -6-3 and the likes.
>>
>>Then you really have no place to make the comments you are
>>making.
>
>
> I think I do.
>
>
>>Commercial aviation requirements are very conservative
>>and tough.
>
>
> I know. It is my job to design electronics and to submit them to EMC tests.
> The standards I have to comply with are similar to RTCA DO-160D, they only
> differ in details and in minimum and maximum levels.
> So I know from personal experience how strong interference signals can be
> and I can make a fair prediction about EMC sensitivity of a device I have to
> design. And based on that experience, I stick to my statement that a cell
> phone is unable to disturb flight electronics that complies to almost the
> highest EMC standards in the industry.
>
>
>>>You can hardly compare a car radio with a professional VHF radio.
>>
>>That was in rebuttal to your previous statement (which you have
>>"conveniently" snipped out here) regarding an empirical test you
>>made (which is hardly applicable to airborne radios in the first
>>place).
>
>
> Well, I think a VHF radio, beit a ham radio or an aircraft radio, are of
> much better quality than a car stereo.
> So if a ham radio is already insensitive to cell phone signals, I am sure an
> aircraft VHF is.
>
>
>>Regardless, wiring errors can occur and remain in place aboard an
>>aircraft (Swisair 111 is an extreme example). Antennas provide
>>yet another means to get energy into places where it is not expected.
>
>
> Ok, another attempt to look at it logically: Two aircraft communicate on the
> same VHF band, but on different channels. While these signals ar in-band for
> the radios, they don't interfere with eachother. So it is extremely unlikely
> that an out-band signal from a cell phone would interfere with a VHF at all.
>
>
>>Again, see DO-160D and enjoy.
>
>
> Ok. And it specifies that equipment must be insensitive to radio signals up
> to a certain level. So the question is: can a cell phone meet or exceed that
> level? A cell phone has a fieldstrength of about 90V/m at four inches from
> its antenna, which drops very rapidly when you are moving away from the
> antenna. Peeking quickly into DO-160D, I see that equipment is tested
> against levels from 45 to 7000 V/m. Your turn.

And again you've missed two key points. In the reception band of
the piece of avionics, the system is allowed to trasnparent ...
it has to receive its own signal. This leaves it open to
harmonics from other equipment. Installation can allow signals
to be routed right through electrical connections, again the
harmonics apply. Most critical are any aircraft with FADEC'd
engines.

But, hey, don't listen to me, call the FAA or JAA.

Cheers,
Alan. 

-- 
-- rec.photo.equipment.35mm user resource:
-- http://www.aliasimages.com/rpe35mmur.htm
-- e-meil: there's no such thing as a FreeLunch.--

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