But i have one more question. Ist it possible somehow to view/increase the gain of the RTL Blog V4 Stick in the rbfeeder?
The dump1090-rb is based on source code of dump1090-fa, which is open-source and available at
https://github.com/flightaware/dump1090 . Although dump1090-rb is clone of dump1090-fa, its config file /etc/default/dump1090-rb is not provided, systemd service file is not provided, and map folder /usr/share/skyaware" is not provided. As a result user cannot directly control it's config, and there is no map like skyaware map of dump1090-fa.
Also the systemd service file for dump1090-rb is not provided, and it is not configured to start automatically on boot/reboot. Instead, it gets start command from rbfeeder if network_mode is set to false.
Like startup parameter "network_mode=false",, the rbfeeder must have other parameters to pass-on to dump1090-rb to control it's gain.
Unfortunately RB24 developers have kept this setting "undeclared", although there is no logic and advantage in depriving users from this facility and keeping the gain setting parameter a secret.
This leaves the users only one option: Quit using dump1090-rb, and install open-source dump1090-fa or dump1090-mutaility whose all settings are declare and can very easily be changed by editing their config fie "/etc/default/dump1090-fa" OR "/etc/default/dump1090-mutability". These two decoders have additional advantage of providing local map in user's Browser in his PC/Laptop/Phone at "IP-OF-PI/skyaware/" OR "IP-OF-PI/dump1090/gmap.html".