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USG BR-355-S4 GPS upgrade?


I have a SkyRadar-D which came with the br-355 but I'm not sure it is getting waas (the alt differs from my airplane's GPS by 50-100ft).
I recently ordered an s4 hoping for better accuracy.  Anybody know if the SkyRadar is compatible with the s4 and if I'll get better accuracy?  I'll post an update when I'm finished with my testing...

Thanks -- Bob

Okay, more info.  I verified that the br-355 reads 75-100ft higher than the two GPSes in my airplane.  According to WingXPro, about halfway through my second leg I got a WAAS signal (it is very rare to see the waas indicator).  The alt diff was the same though.
I received the S4 from amazon, and also a USB to PS cable.  I downloaded the SirfDemo pc program from the USGlobalSat forum.  I used the program to compare the two GPS receivers.  The S4 received more satellites and got a waas correction signal.  The altitude was also more accurate.  The s4 was sending some messages the surf demo program didn't like but otherwise all was good.

I then installed the s4 in my airplane (connected to my SkyRadar-d) on the ground I received only intermittent gps signals and it hand the same behavior in the air.  Boo Hoo Hoo.

Unfortunately, when I powered off and reattached the original GPS it also didn't work.  Switched back to the S4 and not even intermittent.  GPS totally dead now.  The SkyRadar still sends ads-b messages and also Levil attitude info, but no more GPS data.  Wah.  It's possible the SirfDemo program changed the baud rate of the BR-355 or something, so I will try to restore it when I get home.

As a side note I reverted to the iPad's internal GPS during the flight (position is more important than ads-b or attitude) and it was ~100' higher than the airplane GPS as well.

Any info on this would be much appreciated.  Maybe a firmware upgrade so the SkyRadar can talk to the S4...

Thanks -- Bob

Still more info ...  After ~52hours of power off time, I restarted the system and both GPS units are now working.  I think the internal super-capacitors died and the units returned to their default baud rate.
However, my problem remains: both units (and the iPad internal GPS) return altitude values which are 75-100ft higher than the GPS in my airplane.
I think this is not a GPS accuracy issue but rather a subtle math error of some kind.  Possibly one of my systems is not subtracting geoid height.  Frankly I suspect my airplane GPS may be at fault because after landing at ksql elevation 5', the airplane said -96', and the SkyRadar w/BR-355S4 said -9'.


Altitude information is most inaccurate information that comes out of GPS, i would not rely on it for serious air work. It can deviate +/-300 ft easily even with WAAS correction. It is not expensive aviation grade GPS where they do additional math and checks to come up with better altitude estimation. SkyRadar-D is compatible with br-344-s4 as long as you don't change default settings of the GPS receiver.

Thanks for reply.  I agree BR-355-S4 works as long as you don't change default settings.

Also I'm convinced BR-355 altitude is correct - the GPS altitude from my sophisticated airplane GPS is being displayed prior to geoid correction and is thus useless to a pilot.

The BR-355-S4 seems to be incrementally better than the the original BR-355.  It seems to have WAAS more often, and it is slightly more accurate.



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