GTA02: NavBoard V3 causing GPS interference

[Pascal Gosselin]

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.

-Pascal
http://www.wi-flight.net/