[gta02-core] Modem schematic / RF help needed

Rask Ingemann Lambertsen ccc94453 at vip.cybercity.dk
Sat Sep 12 16:09:54 CEST 2009

On Sun, Sep 06, 2009 at 03:47:31AM +0100, Dave Ball wrote:
> I've had a first stab at schematics for the Telit modem.  Comments, 
> feedback, abuse all welcome :-)

   The GE865 Hardware User Guide recommends that the antenna trace be
shielded on all sides by ground traces (page 26). Looking at "3.1.1 BGA
Balls Layout", I think we should tie GPIO_07 to ground, thereby completing
the shield of ground balls around the antenna ball. Admittedly, doing so is
in conflict with the statement on page 9: "If not used, almost all pins
should be left disconnected." (listing some exceptions, which doesn't
include GPIO_07.)

   GPIO_04/TX_DISAB can be used to disable the transmitter (11.4). A
possible use for it would be to detect surrounding cells for use with the
cellhunter/openbmap database without spending battery power or privacy on
transmitting your own position[1]. This signal needs no fancy level
translation, I think, just a simple voltage divider. We have GPB5 available
and no special function to use it for, I think.

   What are the chances I could persuade you to move the MODEM_SERVICE and
MODEM_SLEEP signals from GPJ2/GPJ3 (cpu.sch) to GPC8/GPC9 (lcm.sch) instead?
Just two signals less on the camera interface.
[1] After which you send a clear text HTTP request to a map tile server for
retrieval of the map tiles of the area you're in. :-( But we'll get there

Rask Ingemann Lambertsen
Danish law requires addresses in e-mail to be logged and stored for a year

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