cellphones???

John Galban wrote:
The old analog 800 Mhz phones (the ones the FCC prohibits in the air)
used to work just fine at cruising altitudes. The downside was that
you lit up every cell within your line of site and ****ed off the phone
company.

....and the dozens of other cell phone users on the ground that had their
call drop because of you.

The newer digital services (operating on frequencies not prohibited
by the FCC for air use)

Urban myth. The table of allocation in Part 1 does not authorize the
frequencies allocated to PCS to be used for air to ground service,
period. These tables are controlling regardless of what your
interpretation of Part 22 may be.

don't seem to work once you get a few thousand
feet AGL. I was talking to a Sprint engineer about it and he told me
that the antenna patterns on the newer cell services are angled
downward in most places, which degrades the signal received in the
aircraft.


True; the down tilts are used to mitigate against inter-cell interference.

Others should not have their calls dropped no more than if a person is
calling from top of a hill or in a good position seeing different
towers. A cell phone "dialogs" with every tower in sight and ties up
only ONE channel on each. Which means you use more total channels than
necessary, possibly denying new call service (but not necessarily) to
others in bussy times. If all cell phones in use were doing the same
thing there would be very limited number of chanels open for new phone
calls.

Doug Carter wrote:

...and the dozens of other cell phone users on the ground that had
their
call drop because of you.....

abripl wrote:

Others should not have their calls dropped no more than if a person is
calling from top of a hill or in a good position seeing different
towers. A cell phone "dialogs" with every tower in sight and ties up
only ONE channel on each.

Not so. The system designer will ensure that every cell within line of sight of
hills or other high spots is using a different set of frequencies. It is only
when the caller is in line of sight of cells relatively far away (usually 40 to
60 miles) that the call will cause conflicts.

George Patterson
I prefer Heaven for climate but Hell for company.

George Patterson wrote:

abripl wrote:

Others should not have their calls dropped no more than if a person is
calling from top of a hill or in a good position seeing different
towers. A cell phone "dialogs" with every tower in sight and ties up
only ONE channel on each.


Not so. The system designer will ensure that every cell within line of sight of
hills or other high spots is using a different set of frequencies. It is only
when the caller is in line of sight of cells relatively far away (usually 40 to
60 miles) that the call will cause conflicts.

There are algorithms built into the cell selection and re-selection
process that mitigate against interference but if the base station
receiver can't decode the uplink channel from the mobile then you have a
problem.

To achieve a usable BER (Bit Error Rate) and acceptable frame loss to
set up and maintain calls, all cellular and PCS networks, whether they
are CDMA, GSM, TDMA, etc. are designed to a specific C/I+N ratio
(Carrier to Interference plus Noise) rather than S/N (Signal to Noise).

No operator has as much spectrum as they would like and the principal
goal is to lay out the system for maximum frequency "reuse."

Over the years this has led to reduction of base station antenna heights
(few antennas are more than 100' high in an urban system) and down
tilt antennas.

Thus, any given channel may be "reused" 10-100 times in a given city.

The system design presumes the mobile units to be no higher than the
building heights. Any co-channel energy that the unintended base
station receiver hears from aircraft will reduce the C/I+N ratio and may
lead to dropped calls in that cell.

Perhaps more simply,regardless of protocol, if you can't hear your
messages over the interference it does not matter how strong the signal
is, you can't decode it.