Quality of altitude hold and quality of GPS lock

[HeliHenkie]

Hi all,

At the moment I'm still struggling to get a good quality altitude hold. It's driving me crazy.
How easy it was to setup my DJI Naza!. Maybe my expectations are to high?

After establishing there's nothing wrong with my pressure sensor the hunt for good alt/pos hold continues.
Now my focus is on the quality of the GPS lock.
Can someone explain the relation between the quality of the GPS lock and the quality of the altitude hold?
My findings are:
My AQ controller gives a 3D GPS fix within a minute.
The first few minutes alt/pos hold sucks. Now and then the blue light blinks.
After about 5-8 minutes the Hacc and Vacc values drop down to about 0.5 m. The blue led stays solid.
Only then my quadcopter seems to hold altitude. I assume this means SBAS fix.

Is it necessary for altitude hold to have SBAS fix?
What kind of accuracy in alt/pos hold can you expect with and without SBAS fix?

Best regards,

Jan Willem

[bn999]

If you're GPS LED is not rock solid, you should expect poor performance from any sort autonomy. The threshold for it to turn solid is actually quite a ways from where the best performance starts, which is a hAcc of < 1.0m. SBAS can get you down below 0.5, but is not required.

If you can't get your hAcc better than 1.0m within the first minute of power up, there is a problem with your GPS signal reception. Limited sky view, poor antenna choice, insufficient ground plane / shield, or interference from other electronics.

[HeliHenkie]

Hi Bill and other,

I checked a couple of files. hAcc is around 0.7 m in about 50 seconds, after about 5-8 minutes it drops to 0.35 m.
The values of vAcc are about twice as high.
So this means GPS fix is as can be expected?
This makes it even harder to understand why alt/pos hold doesn't work in the beginning but only the last few minutes of my flight.

Best regards,

Jan Willem