[BC] cell phone hash

[Kirk Harnack]

Mark Humphrey wrote:
> I had always thought the bigger problem with using cell phones while
> in flight was that they could hit too many cell sites simultaneously,
> causing interference or erratic operation.  That's why I'm surprised
> there is talk of relaxing the current restrictions .

Mark, you're right.  I'm not sure if cell phone are likely to interfere 
with properly-working avionics, but a single cell phone will, indeed, 
illuminate many cell sites.

I had heard that cell phone use on airlines would be through a mini site 
installed in the aircraft.  That might keep all the phones at their 
lowest power setting.  That cell site would then relay the multiple 
conversations to more specialized terrestrial sites.

> 
> One of my transmitter sites is on the top floor of the tallest
> building in Philadelphia and my phone (T-Mobile GSM) has major
> problems up there, at a mere 850 feet AGL.

Same experiences for me in NYC and in Chicago on the Sears tower. And I 
wonder if that's due to illuminating too many sites *or* if it's because 
cell site antennas are mostly downward pointed, leaving less or little 
signal at higher elevations.

> 
> Of course, the big problem with FM broadcast receivers is leakage
> from the local oscillator, which would operate as high as 118.6 (when
> tuned to 107.9) and possibly interfere with navaids.
> 
> Here's an interesting paper I just found while searching for more on
> this subject: http://www.bluecoat.org/reports/Helfrick_96_PED.pdf
> 
> Mark

Kirk Harnack