Antenna problem, can I fix this?

[greenman]

Before factory reset, I finally decided to check the signal status. It says it's at -103 dBm (yes, minus) and 5 asu. Is that especially low?

You are looking for bigger the better.
Remembering that dBm is negative, around -60 is said to be optimum.
With 5 signal bars and H+ I'm on -89 dBm at moment and 12 asu.