GTA02: NavBoard V3 causing GPS interference
hrabosh136 at gmail.com
Thu Feb 7 21:01:32 CET 2013
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.
> 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
> >> 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
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