Airplane radio reception

Rules

Pardon my skepticism here, but the people who make rules also told us cell phones would cause interference. I always suspected the major interference from cell phones was with the airlines' ability to force passengers to use their own "Airfones" and charge $2.00 a minute. Now they apparently have decided maybe cell phones are OK.

It also seems like there are two issues here. (1) Does a device emit some kind of signal? It seems all consumer electronics devices do. (My laptop creates AM radio interference so it must send a signal, but they allow my laptop on a plane.) (2) Does the signal interfere with the Avionics? You did not speak to that one and it's not clear from your post (moderator mode off) whether you are also an Avionics engineer. I know a few radio engineers. I knew some Avionics guys in the Air Force and it seemed like a very different breed of cat.

Like the rest of us, I have had lots of experience with "dumb rules" from the government. Maybe the no-radios-on-airplanes is not one of them, but please forgive us for being doubtful.

> > i personally think it's a dumb rule. i mean how much
> output
> > could a walkman actually generate? yes, i know it's the
> > rule and we have to obey it, but an airplane is a big
> place,
> > and i'd guess that your receiver would have to be pretty
> > close to the antenna in order to cause any intereference.
>
> > at that proximity you'd have to be outside (in the 'gone
> > with the wind' smoking section).
>
> I can produce credentials as a broadcast engineer. Can you?
>
>
> If not, then it doesn't matter whether or not you think it's
> a "dumb rule". Those of us who know about the subject know
> better.
>
> And if you are not an engineer, your "guess" is meaningless.
>
>
> {moderator mode on}
>
> Did I, or did I not, say this thread was NOT to become a
> war?
>
> {moderator mode off}
>

Re: Rules

>
> It also seems like there are two issues here. (1) Does a
> device emit some kind of signal? It seems all consumer
> electronics devices do. (My laptop creates AM radio
> interference so it must send a signal, but they allow my
> laptop on a plane.) (2) Does the signal interfere with the
> Avionics?

The avionics band is immediately above the FM band. The FM IF creates a signal 0.7 MHz above the fundamental. Thus, anyone tuned to an FM signal above 100 MHz is creating an IF offset signal at avionics frequencies. The fact that MobileTrak can easily detect FM IF offsets at over 100 feet shows the range of these avionics band signals.

Re: FM radios also transmitters

> If
> this would work for FM, would it also work for AM? TV?

It would and it did back in the 1960's when some ratings outfit
was experimenting with using the generated frequencies to do
their work. A friend invested and lost his shirt. I'm working
from memory, here, but I vaguely recall the problem was that
people drive too close together; the generated frequencies
stomp all over each other, sum, subtract, multiply and perhaps
even divide. In short it proved unreliable and impractical
and ultimately, like the stock in the company, worthless.<P ID="signature">______________

Due to continuing underwhelming popular demand...</P>

Re: Rules

> Pardon my skepticism here, but the people who make rules
> also told us cell phones would cause interference. I always
> suspected the major interference from cell phones was with
> the airlines' ability to force passengers to use their own
> "Airfones" and charge $2.00 a minute. Now they apparently
> have decided maybe cell phones are OK.

Those pay phones have been disappearing from my flights I've
used in recent months. I've heard it claimed they were a
useful tool for would-be terrorists but also that the airlines
were embarrassed by some of the calls made on them (and cell
phones) from on board planes that were going down, letting
entire families hear daddy die. Proving once again: The
family that flies together, dies together.

> It also seems like there are two issues here. (1) Does a
> device emit some kind of signal? It seems all consumer
> electronics devices do. (My laptop creates AM radio
> interference so it must send a signal, but they allow my
> laptop on a plane.)

Computers generate a lot of electronic crap but it does not
fall anywhere near navigitational/communications channels
used in aircraft. But...come the day the airlines are set
up to rent you a computer to use in flight they might make
wonderful new discoveries....

> (2) Does the signal interfere with the
> Avionics? You did not speak to that one and it's not clear
> from your post (moderator mode off) whether you are also an
> Avionics engineer. I know a few radio engineers. I knew
> some Avionics guys in the Air Force and it seemed like a
> very different breed of cat.

AM, and even moreso, FM, receivers generate signals that do
fall within avionics frequencies. Yes, VHF aircraft stuff
starts (VOR/TACAN/DME) right above FM broadcast and
communications starts just above the navigational gear. Then
there are UHF navigational and communications and navigation
facilities as well. From personal experience (I used to fly
privately and used my old First 'Phone license to do some
avionics installations and repairs back in the 60's), I have
had AM/FM receivers used by passengers in light aircraft cause
problems with older model Nav/Comm receivers. It was also
possible to use some of the older "coffee grinder" tunables
to pick up harmonics from broadcasters. Those aircraft radios
are AM but do an amazing, though poor-sounding, job with FM,
especially when you're much rather that they do not.

Never had trouble with cell phones and aircraft radios but
cell phones hadn't been invented when I quit flying...or,
rather, when the FAA discovered I really should no longer
have been. I have had trouble involving cell phones/sites
and ham radio but that's a side issue.

> Like the rest of us, I have had lots of experience with
> "dumb rules" from the government. Maybe the
> no-radios-on-airplanes is not one of them, but please
> forgive us for being doubtful.

> > > i personally think it's a dumb rule. i mean how much
> > output
> > > could a walkman actually generate?

It's not so much how much your walkman radiates; it's how
sensitive is the receiver in the aircraft? They're a lot
more sensistive than consumer stuff. Plus, where is the
antenna located? In many cases, about halfway back on
the roof of the fuselage. Right over your Row 27 aisle
seat, probably.

Here's one you can try at home without killing anyone or
hurting yourself:

Turn on an AM radio and tune it to a moderately strong, but not
close-by local, station. Set it on a table somewhere. Nice
to use some station above, say, 1200...maybe up to about 1500.
Leave it turned up pretty good (volume)

Take another radio, maybe your Walkman, and stand about 15-20
feet away. Turn it on (AM) and start moving the tuning up
slowly from the low end (530) with the volume turned 'way
down so you mostly hear the other radio. As you tune you'll
find at least one place where the other radio starts to
howl. Experiment. Once you get a good howl, tune up a little;
down a little. Note how you can change what's coming out of
the other radio by diddling the one in your hand. When you've
had enough of that, try running further up the dial and see
if you can make it happen again.....


Now, why might the rules change? Because aircraft radios and
getting better and better and antenna design is slowly improving.
The day may come when you can play with your AM, FM, TV, etc.
without doing any harm. For some aircraft that day may be here.
Want to bet your life on whether or not the aircraft you're on
today is the latest and greatest?


<P ID="signature">______________

Due to continuing underwhelming popular demand...</P>

Re: Rules

>
> Those pay phones have been disappearing from my flights I've
>
> used in recent months. I've heard it claimed they were a
> useful tool for would-be terrorists but also that the
> airlines
> were embarrassed by some of the calls made on them (and cell
>
> phones) from on board planes that were going down, letting
> entire families hear daddy die. Proving once again: The
> family that flies together, dies together.

There was no profit in the phones, and the equipment weiged so much as to increase fuel consumption. American removed them from all but some 67's and triple 7's about two years ago.

It had nothing to do with content. And, if I am correct, no payu flight phone was used on 9/11 because using them takes a credit card and a lot of dialing to get a call through.

I used to use the phones mostly to let people on the ground know my arrival time, and seldom saw anyone else using one. Once the novelty of calling from the air wore off, the iniitial charges for the first minute made the phones pretty unattractive to most flyers.

Re: FM radios also transmitters

> > If
> > this would work for FM, would it also work for AM? TV?
>
> It would and it did back in the 1960's when some ratings
> outfit
> was experimenting with using the generated frequencies to do
>
> their work. A friend invested and lost his shirt. I'm
> working
> from memory, here, but I vaguely recall the problem was that
>
> people drive too close together; the generated frequencies
> stomp all over each other, sum, subtract, multiply and
> perhaps
> even divide. In short it proved unreliable and impractical
> and ultimately, like the stock in the company, worthless.
>
Eldon (Pete)Barr used this method for AM in the 60's in small markets in the Pacific Northwest. It DID work then, but there were only a few stations in each market. Example: Tri-Cities, WA with 4 AM stations. Pete would park in a residential area and count the blips around each frequency. Also worked ok in Yakima, same deal.

Worked a helluva lot better than paying somebody $1.00 to pretend that they kept track of their radio listening for an entire week!

Re: FM radios also transmitters

"Worked a helluva lot better than paying somebody $1.00 to pretend that they kept track of their radio listening for an entire week!"

<big>What could possibly work better than that!?</big>

<center></center>
<P ID="signature">______________
Jerry

"Everyone is entitled to his own opinion, but not his own facts" - late Senator Daniel Patrick Moynihan</P>

From an avionics engineer

..and former broadcast engineer. My company installs and maintains airport navigation and communications gear. I spent 20 years in the broadcast engineering biz.

Here's why your radio can and sometimes does interfere with navigation signals.

The runway centerline signal is about 15 watts. The indication the pilot gets showing if he is lined up on the runway is based on the balance between two modulated audio signals 90 Hz and 150 Hz. They are only modulated at 20% each. ANY intermodulation interference can throw off that balance resulting in an erroneous cockpit indication. There are some tricks used in the transmitter to minimize this, but is is certainly possible.

If that hasn't convinced you, the VERTICAL guidance transmitter is based on the same principal, but typically outputs only 3 watts, with secondary signals at about 300 milliwatts. I turn off my stuff when flying and I'll become quite militant if another passenger refuses to do so.

PS My cell phone, when it in the car cradle, can produce hash on the AM band. Those things are really noisy RF wise.

<P ID="signature">______________
Never hold a cat and a dustbuster at the same time.</P>

>I never heard of an airline that permits radios on flights.
>
> I was on a plane where a guy refuesed to stop using his
> Blackberry... at the arrival gate, there were TSA agents and
> they arrested him. Some airlines would do the same for use
> of an FM radio. Best to ask, before the flight. Some
> airlines allow radios, but most specifically prohibit them.
>
<P ID="signature">______________
[email protected]</P>

> >I never heard of an airline that permits radios on flights.
>
> >
> > I was on a plane where a guy refuesed to stop using his
> > Blackberry... at the arrival gate, there were TSA agents
> and
> > they arrested him. Some airlines would do the same for use
>
> > of an FM radio. Best to ask, before the flight. Some
> > airlines allow radios, but most specifically prohibit
> them.

In another thread, a poster said US Air did allw radios. I have no way of verifying that, as I never fly US Air... maybe that is why!!!