Jiří Pinkava píše v Čt 07. 02. 2013 v 18:18 +0100: > Dne 7.2.2013 18:00, Hrabosh napsal(a): > > A few comments inside: > > > > Pascal Gosselin píše v Čt 07. 02. 2013 v 08:36 -0500: > >> 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 > > We are usually trying to refrain from connecting shileding to ground on > > both sides as a prevention of grounding loop. > > > > > >> . > >> > >> 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. > > We have never twisted two differnet signals together. What about > > cross-talks? The only type of signal we are twisting together are for > > example positive and negative leg of RS422 bus. Or A429 (you may be > > familliar with). > Just ground betwen all data lines is common solution to this. > > Like > GND|DATA|GND|CLK|....|GND > > Emited radiation is equal of surface of closed loop betwen GND and > signal line. >
Yes, this is quite common for ribbon cables (like the one for connecting ATA100 hard drives for example). But shielded TWISTED PAIR was mentioned originally... > > > >> 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/ > >> > > > > Zbynek > > > > > >> > >> _______________________________________________ > >> Openmoko community mailing list > >> community@lists.openmoko.org > >> http://lists.openmoko.org/mailman/listinfo/community > > > > > > > > _______________________________________________ > > Openmoko community mailing list > > community@lists.openmoko.org > > http://lists.openmoko.org/mailman/listinfo/community > > > _______________________________________________ > Openmoko community mailing list > community@lists.openmoko.org > http://lists.openmoko.org/mailman/listinfo/community _______________________________________________ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community