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.
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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