Hi the reason for using a ubec to power the rx was that in the beginning (in the german forum this tip is still given) of hott support, most people recommend to not power the rx directly from the aq.
Max: i didn't put an additionally ground wire from rx to aq because im afraid of building a ground loop, the ubec i use have internally connected the input and output ground pins. To assure signal quality i use a shielded cable (like chschmied do:
viewtopic.php?f=26&t=2327&p=13018&hilit=shield#p13018) for the signal from rx to aq and connect the shield only to the ground of the rx side.
I will do like suggested and power the rx directly via a motorport, so there is one part less that can fail.
have a nice weekend Michael