hey both,
thanks for your feedback.
i already changed from USB power to an external power supply from the very beginning since i could not get GSM connection with just USB.
now what i understand from your suggestion is that the external power adapter might be to weak!?
i am currently using the following external power adapter:
- voltcraft; 1500 mA; 12 V/DC
so i will give it a try and switch over to another model with >1.6 Amps.
will let you know the result and keeping you posted...