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Cell phones (texting) and altitude


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#1 chrisk

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Posted 04 October 2013 - 03:57 PM

How high and fast can you go before text messages are unreliable?  My last two trips were at 16,000 and 17,000 ft.   I had zero cell phone reception at 17,000.   At 16,000, I was able to send a short text when I was directly over a larger town.    Both were around 165Kts, ground speed.

 

So, at what altitude does texting become reasonably reliable?



#2 Joe Zuffoletto

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Posted 04 October 2013 - 04:04 PM

On the ground!  :)

 

I've gotten lucky up high like that, but it's a crapshoot. One time I managed to place a voice call to customs from 16,000 feet over Guerrero Negro on the Baja Peninsula. I considered that to be a bona fide miracle.



#3 Shadrach

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Posted 04 October 2013 - 04:25 PM

As Joe says, it's a crap shoot. Odds seem to be better below 4000AGL.  I once talked to my wife all the way from the hold short @KCBE to 5500ft where I finally dropped the call. I was testing out the bluetooth on my new A20s. She'd no idea I was even in the plane until she asked when I was taking off and I replied that I was climbing through 3600ft at the moment.


Cheers!

Ross


#4 N601RX

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Posted 04 October 2013 - 04:39 PM

The antenna pattern for a cell tower is more outward than upward.  At a higher altitude you will be picking up one many miles away instead of the one under you. 

We have some commercial grade LTE Modems with a wifi interface at work. These have a external cell antenna and have a better radio in them than a standard cell phone.  I've been wanting to mount the antenna on the bottom of the plane and see how much better it works that just a ipad in the cockpit.



#5 1964-M20E

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Posted 04 October 2013 - 05:14 PM

I've had zero success with phone calls and very limited with texting at any altitude other than 0AGL. Of course the Bluetooth on my Light speed Sierra headset works well.  I used it once to get a flight plan filed at the last minute when DUATS for some reason did not accept my plan filed online.


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former 1964 M20E

#6 Piloto

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Posted 04 October 2013 - 05:16 PM

The shorter the text message is the better the chances of getting through. Unlike voice the text message is put on hold until a clear contact is established with a cell then is sent. If I only send my ETA to my waiting party it is a sure thing they will get it. 

 

José



#7 M20F

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Posted 04 October 2013 - 05:36 PM

I find geographic location matters the most, if I am over South Dakota as example I get great cell coverage up into the FL's versus being around a large city where I often don't get anything after a couple hundred feet.

My guess the number of towers than plays a big role as well.

#8 N4352H

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Posted 04 October 2013 - 06:08 PM

I have always been 100% disappointed when I try and then one in a hundred, I get a signal and actually keep it for a span of 5 minutes. At 155KTS...that's passing through a lot of cells or locked on to a distant cell continuously. Even above 6000.



#9 rbridges

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Posted 04 October 2013 - 07:08 PM

I find geographic location matters the most, if I am over South Dakota as example I get great cell coverage up into the FL's versus being around a large city where I often don't get anything after a couple hundred feet.
My guess the number of towers than plays a big role as well.


I would have guessed just the opposite.

#10 N601RX

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Posted 04 October 2013 - 07:20 PM

I think that goes along with what I posted earlier about the antenna pattern going outward and not upward.  At 17,000 you are not going to get the tower under you, you are going to get one many miles away. 

 

In the late 90's I used to fly around in my open ultralight with my cell phone.  I would occasionally get roaming charges on my bill from Georgia, which was about 80 miles away.



#11 Shadrach

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Posted 04 October 2013 - 09:31 PM

I would have guessed just the opposite.

 

Nope. Per my post earlier, KCBE (Cumberland Regional Airport, MD) is a small western MD town surrounded by mountains and rural farm land. I have better luck making calls over that sparsely populated area than I do say flying over Baltimore on my way to the beach. 


Cheers!

Ross


#12 Piloto

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Posted 04 October 2013 - 10:00 PM

I find geographic location matters the most, if I am over South Dakota as example I get great cell coverage up into the FL's versus being around a large city where I often don't get anything after a couple hundred feet.

My guess the number of towers than plays a big role as well.

What you were experiencing is the mutual interference level. As you fly into high density areas where there are a large number of cell towers your cell phone gets overwhelmed by the mutual interference among them. This makes getting a clear channel almost impossible. As you go lower in altitude your cell phone receive less number of stations thus less mutual inteference. On remote locations there is less number of cell tower thus less mutual interference. You see the same effect when trying to watch TV in-flight. The interference problem is related to the limited number of channels available per cell tower. The problem does not show on the ground because the line of sight limits the interference from other cells using the same channel. The mutual interference would be the same if all ATC coms were on the same frequency. You would have a hard time understanding them. And that is with planes just imagine with millions in a city using their cell phones.

 

To bore you more Glonass satellites (Russian SAT NAV) have similar problem with their frequency channel allocation. So satellites on the same channel frequency are located at antipodal points on the same orbit. This way the Earth keeps you from receiving both satellites on the same channel. But as you go higher in orbit you have a chance of momentary mutual interference.  

 

José 



#13 N201MKTurbo

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Posted 04 October 2013 - 10:33 PM

I have found texting to be the most reliable means of communications while flying. Sometimes it will take an hour or so for it to go through, but eventually it goes and it happens with no effort on my part.

 

I had my vacuum pump fail on my last trip to Oregon. It was VFR so I flew home on the standby. The little electric motor ran for six hours straight without a complaint!

 

I texted my wife while aloft and told her what to get and where to get it. There was a new pump waiting for me at the hanger when I landed. I fixed it that night and we left on vacation the next morning.

 

That never would have happened without texting.



#14 ottorecker

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Posted 05 October 2013 - 01:00 AM

Google Doppler Shift and implications on mobile phone coverage while airborne.....SMS?....yeah......perhaps....phone convo?.....marginal at best...

 

Not to open up old wounds, but I have often wondered how passengers used their mobile phones successfully on the ill fated 9/11 aircraft ......and I am not a conspiracy advocate.

 

....



#15 DrBill

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Posted 05 October 2013 - 01:43 AM

Most cell phone antennas are VERY directional and are set with a down beam of at LEAST 5 degrees from a 200-300 ft tower.  Each cell is usually dividen into 6 subcells. I find that analog cell access is decent up to about 2000 AGL. Over that it gets spotty.  Each cell is about 3 mi in diameter MAX so at 120MPH, You are switching towers every 1.5 mins, given 3 cells in that tower (from say East to North to West), you're switching cells every 30 seconds. Lots' of opportunity for a dropped call.

i did my PhD thesis on Survivability of Wireless (cellphone) networks. Google heybruck thesis. .It was fun times...

BILL

 

Oh.. regarding the 9/11 calls, they used the AIRPHONES in the aircraft not their personal cellphones as the media would like you to believe.



#16 Piloto

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Posted 05 October 2013 - 01:48 AM

Google Doppler Shift and implications on mobile phone coverage while airborne.....SMS?....yeah......perhaps....phone convo?.....marginal at best...

 

Not to open up old wounds, but I have often wondered how passengers used their mobile phones successfully on the ill fated 9/11 aircraft ......and I am not a conspiracy advocate.

 

....

Not to claim knowledge on the 911 event. It is conceivable to establish cell phone contact with airborne directional antennas that only see one sector of the area. This would reduce the mutual interference problem. On a large aircraft a person sitting next to a window would provide the same effect as a directional antenna. In fact parabolic directional antennas are used on different ground links that are on the same frequency. 

 

The radio altimeter on large aircraft use dual directional antennas to reduce interference from the transmitter to the receiver. This way the receiver sees only the ground return.

 

José



#17 ottorecker

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Posted 05 October 2013 - 03:08 AM

Thanks Dr. Bill.....I should have known better to trust the media.......

 

With your knowledge about these things, isn't the doppler shift the primary reason mobile phone operation just doesn't work whilst flying?  I get the directional antenna issues, but I do you think that even if you point your mobile antenna the most optimal direction and position out of a a/c window it would not help significantly with your reception capability? The skeptic in me says......nope...

 

I have had zero success calling my wife 'at work' (in a big fast jet at altitude..and I have tried this in the mooney as well)........even when close to a big metro area right over the homestead........

 

...curious.....and would appreciate your insight....



#18 flyboy0681

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Posted 05 October 2013 - 03:57 PM

The shorter the text message is the better the chances of getting through. Unlike voice the text message is put on hold until a clear contact is established with a cell then is sent. If I only send my ETA to my waiting party it is a sure thing they will get it. 

 

José

 

The only sure thing would be a reply from your wife consisting of "José, be sure to stop at the supermarket on your way home and pickup a quart of milk, a dozen eggs, four ears of corn, a loaf of wheat and gallon of your favorite ice cream". 



#19 Piloto

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Posted 05 October 2013 - 05:49 PM

Although the FCC is concerned about an airborne cell phone disrupting the cell network the fact is that a cell phone will not attempt to login unless it has a clear signal from a cell. Due to the mutual interference generated by cells on the same channel the cell phone just remains quite until it finds a clear channel. Otherwise it will drain the battery very quickly.

On well designed receiver doppler shift of a few hertz is not a problem. In fact on the Iridium and GPS constellations were the satellites move at over 10 times the speed of sound doppler shift is not a problem.

 

 

Here is an excerpt from Wikipedia "Mobil phones on aircraft"

The U.S. Federal Communications Commission (FCC) currently prohibits the use of mobile phones aboard any aircraft in flight. The reason given is that cell phone systems depend on channel reuse and operating a phone at altitude may violate the fundamental assumptions that allow channel reuse to work.[30]

Cell phones are intentionally designed with a low power output. A tower is the center of a "cell" and due to attenuation with distance (inverse square law) cell phone transmissions at ground level can usually be received only weakly by towers in adjacent cells and not at all in cells farther away (non-adjacent cells). This allows the channel used by any given phone to be reused by other phones in non-adjacent cells. This principle allows tens or hundreds of thousands of people to use their phones at the same time in a given metropolitan area while using only a limited number of channels.

Channel reuse works because a cell phone on the ground will only have one "closest" tower that can possibly use a particular group of frequencies, CDMA codes, or time slots. The software that manages the system assumes that the signal from a phone on a particular tower can, on other towers, only be "heard" at greatly reduced signal strength. The frequency, code, or time slot used by the phone can therefore be reused by other phones on other towers.

If a cell phone is operated from an aircraft in flight above a city these assumptions are no longer valid because the towers of numerous different cells may be about equidistant from the phone. Several towers might well assume that the phone is under their control and the phone could be assigned a free channel by one tower but could also be heard on other towers using the same channel group. The channel might already be in use on those other towers and could cause interference with existing calls. Even if the software can cope with hearing the same phone on multiple non-adjacent towers the result at best is an overall decrease in system capacity.

An additional concern is the output power of the cellular handset. Because the towers might be miles below the aircraft the cell phone might have to transmit at its maximum power to be received. This would increase the risk of interference with electronic equipment on the aircraft.

 

José



#20 Martin H

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Posted 06 October 2013 - 06:30 PM

When I was back in the states, I flew frequently from Ft. Polk, LA to Tara Field, GA (south of Atlanta, next to the Motorspeedway).

 

Anytime I was higher than 3500'MSL it was a crap shoot.   Even over the swamps of LA and MISS, it was a huge maybe and battery drain on the cell phone.   I would usually type a text, put phone on the Glare Shield, and sometime during the flight, it would send and download any pending messages.

 

I have never experienced any cell phone reception for texting above 7000' and rarely any type of connectivity above 5500'.

 

This gets frustrating flying over Mid to Eastern Alabama trying to give an ETA but nothing registering until I am decending beyond the Chattahooche River.

 

Martin






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