High HDOP(+2) and signals fraticide(interference)

Hi All ,
Second day of flying… got 2 flights in on IRIS but on 3rd attempt and subsequent attempts the HDOP was 2.1 pegged for the next hour no matter how many times I attempted while my iphone and samsung tablet were reporting hi accuracy fixes. now If I was launching in between buildings from an alleyway or though a hole in the treecover then I dont have an issue with the high hdop… but this was the middle of the berkeley marina and it was CAVU with zero clouds. as I have altered NOTHING on the internal config of the IRIS (its a brand new uncrashed machine) yet,couldnt update firmware as the hull mounted MicroUSB socket broke off in the first attempt to use same and 3dr is still in the middle of the warranty process for same I havent even mounted the included 2D tarot chassis yet so that would not be a interference source… what I have noticed and shudder about from my days with paparazzi is the fact that a LOT of signal cables are totally unshielded and are free to sit there and radiate garbage if same is leaking on to them. so I COULD put a coax touch probe from an SDR receiver inside the hull and see if ANY strong harmonics are around the frequency range of the L1 GPS signal(1575.42 MHz) OR I could simply wrap and twist most of the wiring in there, along with using this medium copper foil to fabricate a proper ground plane for this hull mounted GPS rcgroups.com/forums/showpost … stcount=40 ,

other choices are a folding mast for the GPS antenna affixed to the hull in some fashion and getting the GPS antenna external to the hull.

What have others discovered as a possible solution to High HDOP?

Other REALLY ANNOYING thing is it would NOT arm in stabilize mode(I found out later about resetting max HDOP to arm, but not convinced that is a good idea) which supposedly does NOT require the GPS, first thing I will be looking to debug once I can use the USB socket to flash new firmware, whats up with that? I thought the manual explicitly stated we could arm in the non GPS modes with out having a GPS fix?


I made and mounted an insulated copper ground plane behind the GPS , used plastic screws and rerouted RX antennas and while HDOP did NOT go down as far as I can tell very much I can now get a 3D lock and a flashing green led… and I can ARM inspite of high HDOP it would seem(I did wind up resetting the GPS HDOP arming setting(cant remember the name at present) to about 3.5 to allow arming for manual flying.

Off to find shielding braid effective at GPS L1 and L2 frequencies as I have an electronic background and this is starting to piss me off enough to reflash the ublox 6H for GLONASS instead, at least until my navspark dual play(GPS/GLONASS) chips get here…(indiegogo). I should probably take a look at the APM GPS code and see what changes if any are needed for GLONASS support.


ps I hope the US GPS system is not going to crap… no constellation satellites are due to be orbited this year or next(budget) so coverage WONT be getting better.

Hey HZL,
How come 3DR never answers your great questions?

Because there is no question in this posts and it’s no Iris-support issue.

There are legitimate questions in his post.
Also, that;s the second or third post of his that wash;t answered…
What gives here?

Sorry, I was unprecise. I can’t see technical support questions.

E.g. “What have others discovered as a possible solution to High HDOP?” is a classical community discussion question.
The rest of the post is mainly a description of his DIY-modification.

If the OP has a clear hardware support related question, I will happily move the thread back to the Hardware section - for the GPS module, not for the Iris.

Other REALLY ANNOYING thing is it would NOT arm in stabilize mode(

copter.ardupilot.com/wiki/flight … Dependency