Position 1 fail / GPS status page

[swamif16rv7]

Two issues that might be interrelated:
1. I get a Position 1 fail every flight during the duration of the flight. It seems I am still getting good GPS position. I have an HDX, SV-250-GPS (set as pos 1 in serial port 5), GTN 625 (set as GPS 1 in ARINC429. I get Position 1 fail within minutes after I turn on my avionics/GTN 625 (AFS quick build w/ACM).
a. I suspect it is a settings issue in the HDX but I have been unable to find a solution. Help?

2. I don't know if this is related, but in the system setup/GPS status page of the HDX, I see the SV-250-GPS status data including # of satellites and the status resolves to a 3d Diff even though the satellites are always yellow, not green. My antenna is on the glare shield. In addition, when I turn the GTN on, the HDX GPS status page goes blank and in the upper right corner of the page the source changes from Pos 1/SV-250-GPS to GPS 1/ GNS 430. I understand the GTN doesn't populate the HDX GPS status but I would like to be able to monitor the SV-250-GPS status during flight.
a. Why do the SV-250-GPS Satellites always show white/yellow and some never resolves to green status?
b. How can I have the SV-250-GPS HDX GPS status page always show the status of the SV-250-GPS and not go blank when I turn on the GTN?

 

[DBRV10]

They never turn green, so yellow is green if that helps.

Where is your GTN antenna? I suspect it may be faulty and killing off the SV-GPS or just too close to each other. Must be 2' or more apart.

 

[swamif16rv7]

Thanks for update on SV GPS satellite status color. Odd that the Dynon documentation shows white, yellow and green for stages of accuracy.

SV GPS antenna is on glare shield and GTN antenna is aft of canopy so over 6 feet apart.

 

[DBRV10]

Yeah.......I have never seen green, so maybe we are just the unlucky ones

There is still a chance that the GTN antenna is the problem. If you power up the GTN and the SV GPS crashes something is wrong there somewhere. You may have to borrow an antenna from someone to try. I have seen 2 or 3 faulty Garmin Antenna problems over the years so it does happen, even if not often.

 

[swamif16rv7]

So...is there an easy way to test your theory on the GTN antenna? Possibly... put a tin can over the antenna, turn the GTN on and see if the SV-GPS continues to populate the GPS status page and I don't get a POS 1 FAIL?

Thanks for your expertise.

 

[DBRV10]

Sad to say mate, find another expensive antenna. It could be poor crimped cables or something too...... Sorry to not have a simpler method.

 

[swamif16rv7]

Darn. I liked the the redneck idea. Too good to be true. I'll work on finding a local shop that might be able to assist with the troubleshooting.
Thanks again. Love Brisbane and the river cats!

 

[RV8JD]

They never turn green, so yellow is green if that helps.

Yeah.......I have never seen green, so maybe we are just the unlucky ones

These comments caused me to check my Sat reception. I have the SV-GPS-2020 GPS Receiver/Antenna under the cowl, on a tray attached to the firewall of my RV-8. Sat reception is good:

Is Sat reception/coverage worse in the Southern Hemisphere?

 

[swatson999]

No, that's why it's called "Global" . Seriously. Technically, the terrestrial service volume (surface to 3000 km) has 100% constellation coverage.

 

[DBRV10]

There ya go!

I wonder if it is the WAAS capable satellites that go green. Like I said I have never seen green bars on any Skyview installation (from memory), and the difference being is we do not have WAAS down here on the underside of the earth.

 

[RV8JD]

... and the difference being is we do not have WAAS down here on the underside of the earth.

Interesting. Didn't know that.

EDIT: Now that I looked it up, my memory is refreshed:

Wide Area Augmentation System - Wikipedia

en.wikipedia.org

"The Wide Area Augmentation System (WAAS) is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability.
...
WAAS uses a network of ground-based reference stations, in North America and Hawaii, to measure small variations in the GPS satellites' signals in the western hemisphere."

 

[DBRV10]

RV8JD,

You are clearly not flying an RV8..... so what is it? TAS 204, seems more like a rocket in MPH or a Lancair.

 

[RV8JD]

Honest, it is an RV-8 equipped with an IO-360-M1B swinging a 72" Hartzell CS BA prop, a Slick mag and an LSE Plasma III EI, and leaned to 100 Deg F ROP. Note that the speeds are in MPH and not KTS. The TAS value shown is about 5 MPH optimistic (based on GPS runs at 8,500'), so the TAS achieved is actually about 199 MPH TAS.

 

[DBRV10]

Ahhh......thats cheatin' ;-)

Static error can be dialled out, depending on the static port you used as to what will work, but if you want to get your altimeter and IAS/TAS correct, you can experiment with sticking fences in front of the port. Or a few other things.

I started out at -9 knots of error on our RV10. At one point I had plus 6.....smokin'