[bjdecker]

Looking at the attached pictures of the GTN 650xi, is it possible to determine which configuration is "better?" Is there more/different information available to assist with this analysis in the diagnostic mode of the GTN?

The equipment: GTN 650xi, GA 35 WAAS antenna.
Location: N30°40.72', W097°40.49', 800'MSL
Time: 18:45Z - 19:20Z, June 11, 2024

 

[AZSteve053]

Did you know you can capture screen prints of the GTN by holding the bottom right small knob in & tapping the Home button ? *.bmp files will be saved on SDcard in the "print" sub directory (from memory, could be a different name). Very useful for saving config & other things like this pics'. I convert .bmp's to PDF's & combine - add notes etc to key my brain later.

I'm not quite sure what you're asking - I see the plane is parked, Sat constellation is moving, as Sat constellation moves some Sats go up, some down, some will set (or go below horizon - can't see)... all of this will change the instantaneous qualitative GPS solution presented.

 

[bjdecker]

Thanks @AZSteve053 - good tip.

Between each pic, I was making a subtle change to the interconnect between the Antenna and the GTN. Looking for some way to determine the relative benefit (or not) of each change - unfortunately I can’t see absolute signal strength of the SBAS/WAAS, just the GPS vehicles — and they’re moving, so that complicates things…

 

[AZSteve053]

Well - As you've identified... your chasing a moving target - literally. We had special test sets we used to look at the GPS downlinks for "tuning" and troubleshooting link closure and performance issues, I'm real sure the GTNxi has none of that. If you're really into the weeds - you'll need a spectrum analyzer, calibrated signal source for the L1 freq, possibly a time domain reflectometer - all to do a performance analysis of your hopefully RG400 coax assembly. This is all way overkill to just use the GTNxi, but you may have a inner need... Most if not all GPS antenna do not have a purely circular reception pattern due to internal construction, then when mounted any deviation from true horizontal changes the pattern geometrically too (and the plane in flight is doing all of this). My 1st blush from your pic's (all) - you have plenty of link margin for a solid 3D solution - and plenty of Sats - So I would presume you should have no GPS performance problems. PM me if you want to talk more in depth at some point.