[Gta04-owner] Modem's GPS

Dr. H. Nikolaus Schaller hns at goldelico.com
Tue Nov 6 12:46:55 CET 2012


Am 05.11.2012 um 18:25 schrieb Christoph Mair:

> On Mon, Nov 5, 2012 at 6:15 PM, Denis 'GNUtoo' Carikli
> <GNUtoo at no-log.org> wrote:
>> Hi,
>> 
>> I found on the net how to activate the Option Modem's GPS:
>> http://www.option.com/en/support/faq/article/getting-gps-information
>> http://developer.att.com/devices/OPTION_GPS_AT_Command_Reference.pdf
>> 
>> The goal was to verify if the Modem's GPS can get a fix or not without
>> the antenna.
>> If it can't it's better because that way the Network
>> can't use RRLP and has to use a less precise estimation of where I am.
>> 
>> I didn't test if it can get the fix or not yet.
>> 
>> Simple howto:
>> On one ssh terminal do:
>> picocom -b 115200 /dev/ttyHS_GPS_Control
>> ATE //for the echo
>> AT_OGPS=2 //for enabling the GPS for more than 1 fix.
>> 
>> on another ssh terminal do:
>> picocom -b 115200 /dev/ttyHS_GPS
>> 
>> And you get NMEA.
> 
> 
> I tried once and it didn't get a fix even with some piece of wire
> soldered to the pin. You probably have to attach some kind of antenna

> and a matching pre-amplifier with filters to get something meaningful.

It usually needs 20-25 dB SNR to get a fix. Such preamplifiers (LNA)
typically have 20 dB amplification. And that makes the difference.

> It works (as expected) if you add a coax-cable and connect it to the
> GPS-Switch chip so that you can use the real GPS antenna.

It may be possible to optionally connect this Modem's GPS receiver
to the antenna switch on the GTA04A5 board. But we can't know if
and how good it works before it is done, because this trace is going
unsihelded across the whole board (crossing the SD card slot which
is operated at 25 MHz and 63*25 MHz is 1575 MHz...). So it is planned
to be an option needing to solder a 0 Ohm resistor to make the connection.

Nikolaus



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