Remote Spectrum Monitoring Drone from RTL-SDR, RPi, 4G internet using OpenWebRX

Can be used as an improvised “virtual antenna tower” for example in emergency situations, ham radio activities or experimenting.
Possibly words cheapest aerial spectrum monitoring tool as of today.
You can see APRS and ham radio FM repeaters in the spectrum plot of the below video.

Our next goal is to put a transmitter there to have a full functional remote aerial transceiver application.

SW tool: OpenWebRX
SW integration: sdr.hu

HW integration: rfsparkling.com

Spectrum analyzer: RTL-SDR dongle
On board computer: Raspberry Pi 2
Wireless link: 4G mobile internet
Drone: DJI F450