Bad Gps HDOP compared with an Samsung Tab S

Hi all.

I have constantly bad HDOP on my JMT HJ 450, with GPS from JMT. I have compared the GPS values with my Samsung Tab S and when Tab S repports HDOP as 0.9 I only get 2.13 from the copter.
After 10 - 15 minutes I get better values and after 30 minutes will the copter repport 1,69 as the best value.
I have tested the values on different positions an every time repports Tab S better values than my copter.
Bad GPS receiver or ???

Regards //YB