Am 09.11.2011 um 19:03 schrieb Alexander Lehner:
>
>
> On Wed, 9 Nov 2011, RANJAN wrote:
>
>> Hi,
>>
>> Does any one know about the OpenMoko GPS chipset pin connection. After I
>> opened it I could find only one grey wire which appears to be the antenna.
>> Where are the Vcc,Gnd and Rx-Tx pins?
>
> I guess you mean this part:
> http://wiki.openmoko.org/wiki/Disassembling_Neo1973#Removing_PCB_from_case_frame
>
> The grey cable is a 2-wire coaxial cable. I once ripped it off and tried to
> re-solder it without success. It is too tiny to handle it with fingers.
Yes, they are very tiny. If someone is looking for a replacement,
you can cut this 10cm into two halves:
http://search.digikey.com/scripts/DkSearch/dksus.dll?KeyWords=hr5014-nd
>
> The actual antenna is (from my understanding) the big light-brown piece of
> plastic in the top of the phone, while the GPS chip is soldered on the board
> itself. I think this is so because there is also a second external GPS
> antenna connector on the side of the phone. Also, plenty of shielding metal
> next to the GPS antenna connector lets me assume, that there is some
> high-frequencey electronics working under ;)
>
> I guess it works similair to a TV satelite receiver (LNB) which is also
> powered and data-exchanged with a 2-line coax cable.
> No idead how they do this technically.
>
> Roughly, there is power and some commands to justify the satelite receiver to
> a certain frequency. But IMHO the actual logic to interpret GPS data is not
> inside 'that brown plastic piece'.
The brown "plastic" piece is the ceramic antenna patch.
Under the metal shield on the green PCB is just
a single transistor amplifier.
So it is a active antenna with pre-amplifier that is DC powered
through the line and sends back the amplified 1500 MHz GPS signals.
The real GPS receiver (with RX, TX etc.) and an
antenna switch (internal/external antenna) is on
the mainboard.
You can find the schematics here:
http://people.openmoko.org/joerg/schematics/GTA02/
Nikolaus
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