Yesterday I was able to confirm that the installation of the Golden Delicious NavBoard V3 very seriously degrades the performance of GPS when using the built-in GPS antenna. Getting a 3D fix is taking over 20 minutes on average using the built-in GPS antenna. When using an external GPS antenna, the issue goes away and an unaided GPS cold start can be achieved in about 41 to 44 seconds.

I suspect that the use of unshielded cabling between the GTA02 is a likely cause. Being in the Avionics business, I am familiar with the use of shielded twisted pair wiring, but generally in large 22AWG (will have to figure out where to source very thin STP cabling). The wires we use to perform this mod is solid core, probably 30 AWG. In avionics, when it is desired to keep a signal from radiating outside a cable (such as Headphone/Microphone wiring), then the shield of only a single side of the cable is terminated to a good grounding point. When instead it is desired that the signal inside a cable be protected from EMI/RFI from the "outside", then the shields on both sides of the cable will be terminated to ground.

I theorize that only the SCL/SDA would need to be shielded (together in a shielded twisted pair cable ?), Power and Ground may not need to be shielded.

This issue seems very similar to the SD Card access/GPS issue of the earlier GTA02s, so I also wonder if a capacitor fix should be looked at in this case as well.


Openmoko community mailing list

Reply via email to