Reply #26: cell phone design engineer here...

[batcave911]

i have been a desgn engineer for Sprint PCS, Verizon and some other companies for years now.
Let me try to address a few points here...

First, i am glad someone took the time to do all of this, i worked with Kee Dewdney on putting together something similar years ago, but a lot of it is lost from my hard drive now.

a lot of old technical discussions can be found here...
http://physics911.ca/org/modules/xfsection/article.php?articleid=1
http://physics911.ca/org/modules/xfsection/article.php?articleid=2

a few points...
the Commission points out: “All calls placed on airphones were from the rear of the aircraft.”

I didnt know that. Is there anything we can do to confirm this?
I would like to take it at face value, but 1/2 of what the commission said is BS IMHO.

I am not sure if there are/were any airphones in the front of the cabin?
As far as some of the technical stuff, most phones today (and in 2001) are CDMA, not GSM, though some are GSM, i dont know what percent may have been what in that area at that time.

I DID look into customer complaints of the western Penn area for summer of 2001, and the service was VERY POOR !
i lost the URL, but there were quite a lot of complaints.
I think it was verizon, it was a message board for one of the providers in that area.

The thing that amazes me the MOST is the 1 call that state police (911 dispatcher) took in Illinois.
http://physics911.ca/org/modules/weblog/details.php?blog_id=65


http://imageshack.us>




this makes NO SENSE !
If the call was made in Pa by a cell phone, then it would have been routed through the local switch. then to the LOCAL police.

IMHO, we caught them with their pants down, and no underwear.

- this call was a total fabrication.
- OR, there was a plane in trouble in chicago,
- OR, there was an excersice where someone was told to call 911

i seriously doubt B or C.
i think this call was Bull...



OK, that out the way, more on tehcnical stuff...
When i design a cell site, i DOWNTILT the antennas.
this makes the signal go to the immediate area you want it.
now, in rural areas, sometimes there is an OMNI antenna that runs 360degrees, then you dont downtilt, you let it blow as far as possible.
the reason you usually dont do this, is you dont want signals intermixing, you want them to stop where the other takes over.
when you are in a plane thousands of feet up, there are TONS of signals, this isnt good at all.
the phone doesnt know which site to handoff to.
if a signal comes in thats not in the handoff list, the call drops.
(thats IF you can make a call at that height.)

SPEED.
speed DOES make a difference.
i changed one antenna in alabama to work for cars on the freeway, cos they were going too fast.
i did the drive test, if you drove too fast there, the call would drop.
that was going 60-70mph.
think of going 450mph 35-40,000ft in the air ?

The antennas have a "roll-off", so going straight up doesnt work.
the signal is virtually nill.
in a plane, you would not be working on the antennas directly below you, cos they would have less signal, antennas miles from you would be more in the line of sight.
this scenario makes the handoff list useless.
almost all calls would drop IMHO.

most cell phones work at 1.8GHZ, and only a few still at 850Mhz
the higher you go, the more line of sight.
this is pretty far up there, so the planes skin DOES make a BIG difference.
which means you would have to get signal through the windows...
meaning even less signal from sites below you...
and even MORE handoff problems !

thats IF you ever establish a call at that height.
IMHO, its 1 in 1000 to get a stable 10 second call
at say 30,000ft and up.

other info...
cell phones now are ususally LESS than .6watts.
there are no more 3 watt transmitters, and never were 3 watt handhelds. (FCC rules)
The base stations power has more to do with the type antenna is used, than what the power is tweaked too.
most cell phones top out at .4 watts now.
cell phones are reverse link limited, meaning the call depends more on the reciever of the phone, than the transmitter.


cell phones battery.
the battery has NO effect on the power of the cell phone.
big myth here.
there is a power regulator, either it works, or it dont.
kinda like being 1/2 pregnent, no such thing.

more...
http://analysis.batcave.net/cell_phones.html


hope that helps,
Brad
http://911index.batcave.net