Reason for GPS problems found!

Yaroslav Halchenko at
Tue Jul 15 17:39:00 CEST 2008

well -- one of the reasons to suspect EMC is that GPS internal antenna
connector (being not far from external antenna connector as well) is
barely not touching (or may be actually it does) the cradle for
SD+SIM: look here

so it is in a very proximity to SD card which is not shielded in any way
seems to me. Also few external resistors or capacitors are nearby SD
cradle, thus not too far from GPS antenna socket, thus not too far from
GPS internal antenna itself.

Are the schematics / boarding scheme (not sure on english term) released
'open source' as well? or just CAD files?

I don't have an actual unit yet, so I am basing only from visual
inspection and I am not sure how GPS antenna itself is positioned in
respect to SD but can't be too far (unfortunately)

On Tue, 15 Jul 2008, Torfinn Ingolfsen wrote:

> Hello,

> On Tue, Jul 15, 2008 at 12:42 PM, thomasg <thomas at> wrote:
> > We'll do more tests later, but for now we surely know what's causing the
> > problem (and it seems to be a EMC problem).

> Why does people seem to think it's an EMC problem? Ill hazard a guess
> here (and I haven't even seen the schematics for the device); it is
> probably a voltage or current problem. When the SD card is in, it
> draws power, causing the voltage to something in the GSM circuit (for
> example, the antenna selctor circuit) to change. Or current.

> > Testresults from other people appreciated.

> Well, I am currently inside (it's raining), but on the SS screen of
> openmoko-agpsui I now have 13 (yes, thirteen) blue bars, most of them
> above 150 dBm. Before (with the SD card in) I never even had one blue
> bar on the ss screen.

> Great work discovering this.
Yaroslav Halchenko
Research Assistant, Psychology Department, Rutgers-Newark
Student  Ph.D. @ CS Dept. NJIT
Office: (973) 353-5440x263 | FWD: 82823 | Fax: (973) 353-1171
        101 Warren Str, Smith Hall, Rm 4-105, Newark NJ 07102

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