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[aprssig] Appalachian Trail APRS trip report

Mark Saurman vo1one at gmail.com
Wed Mar 8 18:16:01 UTC 2006


On 3/8/06, Andre PE1RDW <aprs at pe1rdw.demon.nl> wrote:
> Stephen H. Smith schreef:
>
> > scott at opentrac.org wrote:
> >>
> >>>6) Cell phones didnt (though we were getting full
> >>>   scale signal readings (maybe we were hitting too
> >>>   many cells?
> >>
> >>My experience (usually on a boat off the California coast) seems to be that the cell towers are easily heard by the phone way out there, but not vice versa.
> >
> > Typical -- (Relatively) high-power base station talkout v.s.
> > flea-powered battery-limited talkback from mobile (hand-held cellphone).
> >
> > [ I'm forever trying to convince my girl friend that I can't hear her
> > cell phone decently, even though she hears me clearly from the
> > wireline side,  when she calls on it from inside the house. ]
>
> The GSM system like it used in europe is better matched, it also alows
> the tower to controll the mobile´s output power (most of the time the
> handheld will be in the 10mW range)
> If you can recieve the tower then the tower can recieve you, no exception.

Not necessarily.  If you are greater than 35km away from a GSM cell
site, you can have a strong signal from them, but you will not be able
to obtain a time slot.  Aircell (if they're even still around) was a
cellular phone service available for aviation used AMPS because it
wasn't dependant on having time dependant slots to operate and could
be used effectively for a couple hundred km's depending on altitude,
etc.  CDMA is also limited, I think the figure is 57km.  Still another
issue at high altitude is cell sites on the same frequency interfering
with each other.  With digital, it's all or nothing.  With AMPS, a
white noise laden interfered with signal is still usable, your call
has a better chance of getting through and you can adjust your
position for better reception.

73,
Mark VO1ONE




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