Re: "the jammers revenge on mobile prattlers" in the Times

Graeme Wall

In message <>
Alasdair <.uk> wrote:

> On Fri, 7 Dec 2007 19:51:22 -0000, "Trust No One®"
> <> wrote:
>
> > I notice with horror that they are
> >looking at introducing the use of mobile phones on aircraft - Sheesh!
>
> If this does happen, I imagine the phones will be special ones
> supplied by the airline and calls will cost an arm and a leg.

They've existed for some years now, and yes they do cost an arm and a leg.

>
> The argument for prohibiting the use of mobiles in aircraft has always
> been that the radio transmissions could affect the electronics of the
> aircraft and could be dangerous. Are they now saying that we have
> been conned all along and mobiles are quite safe if used in flight.
>

The ones fitted are properly screened.

--
Graeme Wall
This address is not read, substitute trains for rail.
Transport Miscellany at <http://www.greywall.demon.co.uk/rail/index.html>

tony sayer

In article <>, Alasdair
<.uk> scribeth thus
>On Fri, 7 Dec 2007 19:51:22 -0000, "Trust No One®"
><> wrote:
>
>> I notice with horror that they are
>>looking at introducing the use of mobile phones on aircraft - Sheesh!
>
>If this does happen, I imagine the phones will be special ones
>supplied by the airline and calls will cost an arm and a leg.
>
>The argument for prohibiting the use of mobiles in aircraft has always
>been that the radio transmissions could affect the electronics of the
>aircraft and could be dangerous. Are they now saying that we have
>been conned all along and mobiles are quite safe if used in flight.
>

No give them their due the aircraft environment is a very sensitive one
and is very safety conscious. If there was the slightest risk then they
should not be allowed but its taken some time to get that far.

--
Tony Sayer

tony sayer

In article <fjdbd6$6vl$1@stable.tornevall.net>, John Williamson
<johnwilliamson@btinternet.com> scribeth thus
>Christopher A.Lee wrote:
>
>>> The argument for prohibiting the use of mobiles in aircraft has always
>>> been that the radio transmissions could affect the electronics of the
>>> aircraft and could be dangerous. Are they now saying that we have
>>> been conned all along and mobiles are quite safe if used in flight.
>
>The plan involves a very low powered base station actually inside the
>aircraft, linked to a satellite channel to allow calls while in flight.
>There will, naturally, be a premium rate charged for calls. This will be
>turned on when the plane is at cruising height, & turned off when landing.
>
>The problem has been that cellphones don't work inside aircraft without
>cranking the transmit power up all the way, which can potentially
>interfere with the signals used for glidepath control while landing, as
>well as GPS signals, especially when you have a couple of hundred phones
>all shouting as loud as they can to find a cell to use. They also stop
>working on flights over water once you get more than a few miles from
>land. Another problem is that they can't lock onto the channel if
>they're moving at more than about 300 mph relative to the base station
>due to the doppler effect.

Not quite true.. If your sideways on to a BST the relative speed will be
much less...

However you will also interfere with a lot of base stations using the
same channel..
>
>The proposed system means that the transmit power on the phones will be
>minimal & under the control of the aircrew. They could also potentially
>transmit a "System not working" signal to stop phones from transmitting
>at dangerous points of the flight.
>
Or if it gets too noisy)
--
Tony Sayer

Woody

"Graeme Wall" <.uk> wrote in message
news:.uk...
> In message <>
> Alasdair <.uk> wrote:
>
>> On Fri, 7 Dec 2007 19:51:22 -0000, "Trust No One®"
>> <> wrote:
>>
>> > I notice with horror that they are
>> >looking at introducing the use of mobile phones on aircraft -
>> >Sheesh!
>>
>> If this does happen, I imagine the phones will be special ones
>> supplied by the airline and calls will cost an arm and a leg.
>
> They've existed for some years now, and yes they do cost an arm and a
> leg.
>
>>
>> The argument for prohibiting the use of mobiles in aircraft has
>> always
>> been that the radio transmissions could affect the electronics of the
>> aircraft and could be dangerous. Are they now saying that we have
>> been conned all along and mobiles are quite safe if used in flight.
>>
>
> The ones fitted are properly screened.


I assume you mean the aircraft (electronics) has proper screening? Why
screen a mobile - it is designed to radiate?

Having said that I read recently that mp3 players generate many times
more RFI than either a mobile phone or a laptop, although I don't own a
mp3 player so I can't test the validity.


--
Woody

harrogate three at ntlworld dot com

John Williamson

tony sayer wrote:

<Cellphones travelling fast>

Another problem is that they can't lock onto the channel if
>> they're moving at more than about 300 mph relative to the base station
>> due to the doppler effect.
>
> Not quite true.. If your sideways on to a BST the relative speed will be
> much less...
>
As I said "relative speed" ;-)

I maybe should have said "with a radial velocity relative to the
transceiving antenna", which would be more accurate.

Another slight problem would be that the radiation from the base station
antennae is very reduced once you get out of the horizontal plane
relative to the antenna. There's quite a high gain on the designs
normally used, giving a much tighter vertical pattern than a standard
dipole.

> However you will also interfere with a lot of base stations using the
> same channel..

Modern cellphones use channel sharing anyway. IIRC. Either CDMA or TDMA,
though I can't remember which is used where. The overall network design
should be tolerant of such errors, though. Things like not re-using the
same channel set within a biggish group of cells, for instance.

>> The proposed system means that the transmit power on the phones will be
>> minimal & under the control of the aircrew. They could also potentially
>> transmit a "System not working" signal to stop phones from transmitting
>> at dangerous points of the flight.
>>
> Or if it gets too noisy)

That'll not be the crew deciding that. After all, each person yammering
is a revenue earner for the carrier :-)

--
Tciao for Now!

John.

John Williamson

Woody wrote:

>> The ones fitted are properly screened.
>
>
> I assume you mean the aircraft (electronics) has proper screening? Why
> screen a mobile - it is designed to radiate?
>
Aircraft electronics is *very* well shielded at the point of origin of
any potential interference, (Things like ferrite beads on all leads
passing through the casing, properly bonded joints where metal plates
join for access plates & so on)& any antennae are shielded from internal
interference by being on the outside of the metal fuselage, usually as
far away as possible from interference generation on the manufacturer's
fitted equipment.

To get the type approval for the phones currently used in aircraft cost
a fortune, & the test program for the new cellphone units is still in
progress with a budget of millions of pounds so far. Flight testing
using a 747 isn't cheap, & separate approval has to be given for every
individual aircraft design. The new airbus designs are going to be even
harder to certify, as they use a non-conducting fuselage material.

Non type-approved transmitters, transmitting variable frequencies at
varying power from random locations in & around the airframe are a
*very* hard to shield effectively from, & there are limits imposed by
weight considerations. It's easier & cheaper, not to mention a lot safer
just to ban them altogether. There are a number of recorded incidents of
aircraft having to miss a landing & go around, with all the risks & cost
that involves, due to somebody making a cellphone call while the plane
was on final approach.

> Having said that I read recently that mp3 players generate many times
> more RFI than either a mobile phone or a laptop, although I don't own a
> mp3 player so I can't test the validity.
>
It would depend enormously on the design. I've got one that's built in
what amounts to a faraday cage, with a metallic coating on the inside of
the case, I've got another with no shielding, just the plastic case.

Mobile phones & laptops are more expensive units, so I would think less
corners are cut during design & manufacture. MP3 players run their
processor more slowly, so the interference would occur starting lower in
the spectrum than mobile phones & laptops, with closer spacing of the
harmonics. On the other side of the problem is the fact that MP3 players
use the lowest possible power consumption processors available, while
mobiles & laptops use the circuits that give the best results with
reasonable power consumption, so there's more power being switched than
in an MP3 player.

There are tests which they're all supposed to pass regarding RFI
generation to get approval for sale in various territories, but how many
of the cheaper units are even tested, or would pass if they were is a
moot point. The approval mark is very easily reproduced for a casual
buyer/ non-suspicious customs officer, especially if there is a decent
quality forged certificate of compliance with the shipment.

I've not got the gear to check properly for myself, but I note that
neither of the MP3 players or the laptop I'm typing on interfere with
the FM receiver I'm listening to at the moment, but the GPRS datacard in
the laptop sometimes does, even when it's just changing cells.

Toss a coin, would you, please. ;-)

--
Tciao for Now!

John.

Neil Williams

On Sat, 8 Dec 2007 11:30:39 +0000, tony sayer <.uk>
wrote:

>No give them their due the aircraft environment is a very sensitive one
>and is very safety conscious. If there was the slightest risk then they
>should not be allowed but its taken some time to get that far.

Given that just about every flight these days has one or two mobiles
that their owner has forgotten to turn off (I've done it), and that we
haven't heard of any accident relating to one, I think you can be
reasonably sure they aren't a big risk.

Neil

--
Neil Williams
Put my first name before the at to reply.

Neil Williams

On Sat, 8 Dec 2007 11:30:39 +0000, tony sayer <.uk>
wrote:

>No give them their due the aircraft environment is a very sensitive one
>and is very safety conscious. If there was the slightest risk then they
>should not be allowed but its taken some time to get that far.

Given that just about every flight these days has one or two mobiles
that their owner has forgotten to turn off (I've done it), and that we
haven't heard of any accident relating to one, I think you can be
reasonably sure they aren't a big risk.

Neil

--
Neil Williams
Put my first name before the at to reply.

Ivor Jones

"Neil Williams" <.uk> wrote in
message news:
: : On Sat, 8 Dec 2007 11:30:39 +0000, tony sayer
: : <.uk> wrote:
: :
: : : No give them their due the aircraft environment is a
: : : very sensitive one and is very safety conscious. If
: : : there was the slightest risk then they should not be
: : : allowed but its taken some time to get that far.
: :
: : Given that just about every flight these days has one
: : or two mobiles that their owner has forgotten to turn
: : off (I've done it), and that we haven't heard of any
: : accident relating to one, I think you can be reasonably
: : sure they aren't a big risk.

How do you forget to turn it off once the flight crew have told you to do
so before takeoff..?

Ivor

Ivor Jones

"Neil Williams" <.uk> wrote in
message news:
: : On Sat, 8 Dec 2007 11:30:39 +0000, tony sayer
: : <.uk> wrote:
: :
: : : No give them their due the aircraft environment is a
: : : very sensitive one and is very safety conscious. If
: : : there was the slightest risk then they should not be
: : : allowed but its taken some time to get that far.
: :
: : Given that just about every flight these days has one
: : or two mobiles that their owner has forgotten to turn
: : off (I've done it), and that we haven't heard of any
: : accident relating to one, I think you can be reasonably
: : sure they aren't a big risk.

How do you forget to turn it off once the flight crew have told you to do
so before takeoff..?

Ivor