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[aprssig] Appalachian Trail APRS trip report

Brian Webster bwebster at wirelessmapping.com
Wed Mar 8 18:51:05 UTC 2006


In most these systems you also have diversity antennas, processor gain and
sometimes preamps on the receive side to help balance out the path
differences from the high power base transmitter and the lower power of the
phone.  While the power output levels would let one assume an asymmetrical
link, the end result is to have a balanced path. It has to be this way as
the phone call is full duplex. The overall power budget planning will get as
close to a symmetrical path as possible when done properly.



Thank You,
Brian N2KGC

-----Original Message-----
From: Wes Johnston [mailto:wes at kd4rdb.com]
Sent: Wednesday, March 08, 2006 1:16 PM
To: TAPR APRS Mailing List
Subject: Re: [aprssig] Appalachian Trail APRS trip report


TDMA2000 system used here allows the tower to alter the handset's power
up/down from 340mW in 1dB steps down to -80dB  under 340mW (what ever that
is).  The problem is what we call "windup" in the process control world...
once the handi reaches 340mW, it can't go any higher in power, but the base
keeps asking for more.  The base keeps jacking up it's power and the handi
is unable to comply.  You end up with an asymetric link.  Me thinks the
solution is to limit the base to 340mW like the handi.  Or to have the base
never go up on power unless it knows the handi has gone up.

Wes


----- Original Message -----
From: "Andre PE1RDW" <aprs at pe1rdw.demon.nl>
To: "TAPR APRS Mailing List" <aprssig at lists.tapr.org>
Sent: Wednesday, March 08, 2006 12:52 PM
Subject: Re: [aprssig] Appalachian Trail APRS trip report


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.
>>
>>Scott
>>
> 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.

73 de Andre PE1RDW

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