mobile phones

Eric Greenwell wrote:
Marc Ramsey wrote:
jeplane wrote:
However, you should not forget that the use of cell phones aboard
airborne aircrafts is banned by the FCC in 47 C.F.R. ? 22.925:
(Oct 1, 2006 revision) states "Cellular telephones installed in or
carried aboard airplanes, balloons or any other type of aircraft must
not be operated while such aircraft are airborne. When any aircraft
leaves the ground, all cellular telephones on board that aircraft must
be turned off."

47 CFR 22.295 applies only to "cellular telephones" (i.e. the old analog
things that operated in the 800 MHz band) licensed under Part 22. Most
of us now carry PCS (personal communications services) phones licensed
under Part 24, and as far as I can tell, the FCC has no regulations
against their use in flight...

My cursory Google search backs up Marc's comments (not that I doubted
him - I was just curious about the details). So, unless someone can find
contrary documents, this may be the end of one of our favorite perennial
threads. May "Cell phone use in gliders" rest in peace.

It would make sense (not that we necessarily expect the FAA to make
sense). My understanding is that the major problem with cell phones on GA
craft was simply that the old-style cell networks couldn't handle them. An
active cell phone in the air would be within range of a bunch of different
towers which caused confusion in the network, since it was built on the
assumption that the ground would limit your line of sight so that you
would only be in range of two or three towers at a time.

Modern networks don't have this problem so this reason goes away. Of
course there's still the issue of interference with avionics and such
which is why they're still banned on airliners, although as I noted in a
previous post, it seems that this ban isn't all that effective. For most
GA pilots the interference thing isn't too important, since even if you
did need them and even if they did start going wonky, you can always just
turn off the phone.

--
Michael Ash
Rogue Amoeba Software

Peter wrote:
What is the maximum altitude (about) when the mobile phone becomes useless?

I made a call while thermaling at 16,000 in Parowan a few years ago.

Jeremy

On Mar 4, 8:58 pm, "Mike the Strike" wrote:


Both text messages and some 911 calls will go through with much weaker
signals than needed to complete a regular call.


Mike


Why?
Is this a technical fact or just a wishfull speculation?

rk

snip Is this a technical fact or just a wishfull speculation? /
snip

It is a technical fact.

Both user equipment (your handheld mobile) and radio base stations
(what they talk to) have signal thresholds for "quality of service"
that must be met for normal calls (what you're paying for) to go
through. These thresholds are MUCH lower for text and emergency calls
for obvious reasons: text messages have no real-time requirements (and
much lower bandwidth requirements), and emergency calls are, well,
emergency calls; who cares about quality of service if it's an
emergency.

Additionally, normal calls are expected to use low uplink (transmit)
power levels on average, but they still require a lot more than text
messages. With modern mobile systems, power usage is EVERYTHING. If an
emergency call is placed (the system is 911-aware), this power
requirement is relaxed or ignored, in addition to the downlink
(incoming) signal-to-noise ratio thresholds.

-ted/2NO (former 3GPP Ericsson programmer)

p.s. the 3GPP specification can be browsed he http://www.3gpp.org/specs/specs.htm.

While most of the USA doesn't yet use 3GPP, the power usage designs
are prevalent in other, earlier technologies.

Michael Ash wrote:

My understanding is that the major problem with cell phones on GA
craft was simply that the old-style cell networks couldn't handle them. An
active cell phone in the air would be within range of a bunch of different
towers which caused confusion in the network, since it was built on the
assumption that the ground would limit your line of sight so that you
would only be in range of two or three towers at a time.


There are also interference issues with AIRCRAFT SYSTEMS.

At an FAA DER Seminar a couple of years ago, they pointed out that
some "phones" would transmit spurrious signals off their frequency
that could couple with antenna cables (shielded or not), and interfere
with aircraft navigation systems (mainly VOR). It's not as simple as
many think (and I'm an aero guy, not an electron guy, so I won't
pretend to really understand).

I was on a test flight where we determined that our telemetry
transmitter COMPLETELY wiped out the reception of our $25,000.00
Ashtech GPS receiver.

Older phones (and older aircraft equipment) tend to wander off of
their original specifications. While most gliders don't rely on VOR,
but rather GPS for navigation (some of us use windows, charts and
eyeballs), the interference from "phones" may not be as much an issue
-- but we've shown that it can be.

The FAA guy indicated that a particular Samsung phone (now off the
market, I'm told) could completely trash com and nav functions on an
airlner type "ship." Autopilots have been affected, too. "Hardening"
transport (airline) aircraft systems (for new models) is a serious
consideration in this modern world of emitters, but always needs to be
balanced against cost, weight and performance. Also, putting small
"pico" cells (a small cell "tower") ONBOARD the aircraft seems to
help: the closer tower causes the phone to shift into a lower power
consumption mode (i.e., lower transmit power, which translates into
less interference).

Caution is advised. It would be a shame if your 1000k log was trashed
when you called Mom to tell her you finally did it...

-Pete
#309

"309" wrote in
oups.com:
There are also interference issues with AIRCRAFT SYSTEMS.

Most definitely. The only question is "how serious".

At an FAA DER Seminar a couple of years ago, they pointed out that
some "phones" would transmit spurrious signals off their frequency
that could couple with antenna cables (shielded or not), and interfere
with aircraft navigation systems (mainly VOR). It's not as simple as
many think (and I'm an aero guy, not an electron guy, so I won't
pretend to really understand).

The root cause is that most of the objects in the world don't
behave like a nice simple ohmic resistor where V=IR. In practice
I=f(V), where function f can typically be exponential, but can
be virtually any function.

Examples of non-linear objects: semiconductors, joints between
some metals, rusty bolts, mercury amalgam fillings, magnetic
components (e.g. transformers) and there are many others!

So what? Well, it turns out that this has two main consequences:
1 if there are two RF frequencies f1 and f2 impinging on the
non-linear object then the object will multiply the two
frequencies and radiate the results at harmonics of the
frequencies and of the sum and difference frequencies
(and harmonics of the sum and difference frequencies).
2 RF power can be rectified to produce a DC offset

The re-radiated frequencies due to (1) are unpredictable
in practice and splattered across band allocated to other
RF services. Example: warships can't use all their
RF equipment separately due to the rusty bolt problem.
HMS Sheffield was sunk by an Exocet because satellite
comms couldn't happen when the primary radar was on, and
that was the time at which the Exocet was launched.

(2) may or may mot be a problem. Typical electronic equipment
is able to cope with constant DC offsets associated with
constant RF power. But there are problems with varying RF power.

CDMA cellphones largely keep their tx power constant,
varying it slightly and occasionally when the transmission
path changes.

TDMA systems (e.g. GSM) have pulsed RF tx power at 217Hz
1/8 duty cycle and 8 times peak power. Put one of these
near to a phone or hifi or hearing aid and the results
are clearly audible. Such interference can completely
disrupt the operation of some equipment.

On Mar 7, 5:09 am, Tom Gardner wrote:
"309" wrote groups.com:

There are also interference issues with AIRCRAFT SYSTEMS.

Most definitely. The only question is "how serious".

At an FAA DER Seminar a couple of years ago, they pointed out that
some "phones" would transmit spurrious signals off their frequency
that could couple with antenna cables (shielded or not), and interfere
with aircraft navigation systems (mainly VOR). It's not as simple as
many think (and I'm an aero guy, not an electron guy, so I won't
pretend to really understand).

The root cause is that most of the objects in the world don't
behave like a nice simple ohmic resistor where V=IR. In practice
I=f(V), where function f can typically be exponential, but can
be virtually any function.

Examples of non-linear objects: semiconductors, joints between
some metals, rusty bolts, mercury amalgam fillings, magnetic
components (e.g. transformers) and there are many others!

So what? Well, it turns out that this has two main consequences:
1 if there are two RF frequencies f1 and f2 impinging on the
non-linear object then the object will multiply the two
frequencies and radiate the results at harmonics of the
frequencies and of the sum and difference frequencies
(and harmonics of the sum and difference frequencies).
2 RF power can be rectified to produce a DC offset

The re-radiated frequencies due to (1) are unpredictable
in practice and splattered across band allocated to other
RF services. Example: warships can't use all their
RF equipment separately due to the rusty bolt problem.
HMS Sheffield was sunk by an Exocet because satellite
comms couldn't happen when the primary radar was on, and
that was the time at which the Exocet was launched.

(2) may or may mot be a problem. Typical electronic equipment
is able to cope with constant DC offsets associated with
constant RF power. But there are problems with varying RF power.

CDMA cellphones largely keep their tx power constant,
varying it slightly and occasionally when the transmission
path changes.

TDMA systems (e.g. GSM) have pulsed RF tx power at 217Hz
1/8 duty cycle and 8 times peak power. Put one of these
near to a phone or hifi or hearing aid and the results
are clearly audible. Such interference can completely
disrupt the operation of some equipment.

is that the reason why when from time to time my Motorola GSM phone
pulses (not necessarily for a call) I can hear the pulse through my
computer, car radio etc? If so, that could be an issue for
instruments and radio in the aircraft if I understand this correctly.

Tuno wrote:
snip Is this a technical fact or just a wishfull speculation? /
snip

It is a technical fact.

Both user equipment (your handheld mobile) and radio base stations
(what they talk to) have signal thresholds for "quality of service"
that must be met for normal calls (what you're paying for) to go
through. These thresholds are MUCH lower for text and emergency calls
for obvious reasons: text messages have no real-time requirements (and
much lower bandwidth requirements), and emergency calls are, well,
emergency calls; who cares about quality of service if it's an
emergency.

This is quite similar to the ham radio operator voice vs morse code
situation. While the signal strengths of both types of signals from a
single transmitter will be identical, the *usable* signal strength for
code is much less. This is because if a signal is weak or if there is a
lot of background noise, it is is much easier to detect dots and dashes
than voice.

Tony V.
morse code, RIP :-)

"chipsoars" wrote in
ps.com:

On Mar 7, 5:09 am, Tom Gardner wrote:
TDMA systems (e.g. GSM) have pulsed RF tx power at 217Hz
1/8 duty cycle and 8 times peak power. Put one of these
near to a phone or hifi or hearing aid and the results
are clearly audible. Such interference can completely
disrupt the operation of some equipment.

is that the reason why when from time to time my Motorola GSM phone
pulses (not necessarily for a call) I can hear the pulse through my
computer, car radio etc? If so, that could be an issue for
instruments and radio in the aircraft if I understand this correctly.

I expect so. The GSM interference during call-setup is
"di-di-di, di-di-di, di-di-di, brrr..." duration ~2s.

There can and will be different interference at other
times, e.g. location update, SMS rx/tx, cell handover.

Whether it is a problem for instruments depends on the
amount of power coupled into the instrument (filtering,
orientation, range) and whether is is susceptable to
217Hz changes in DC offset.

How loud it sounds is a strong function of distance,
falling off at somewhere between r^4 and r^8; test
it with you phone and hifi