At which frequencies drones operate?
We saw in the second post of Sobre DRONES (2 – Curiosidades: “como funcionam?”) (https://www.sobredrones.com/post/sobre-drones-2-curiosidades-como-funcionam), that “the radio waves generated by the control, at specific and predetermined frequencies, are received by the aircraft's electronic circuits and command the rotors in a way to give them direction and power”.
Let's talk a little more about this...
The drone systems are composed of the remote flight control (GCS – Ground Control System) and the drone itself, with all the internal systems and external loads that the drone can carry on board. The communication link that joins the two subsystems (control and the drone) is also part of this system and has fundamental importance, since it’s through that all information is transmitted between the control and the drone.
A remote control can be a manual type or a system with a control application, installed on a cell phone, tablet, laptop or computer. There we’ll command what’ll be executed by the drone.
All of this information is transmitted via a communication link. Through the command and control link (C²) action commands are transmitted to the drone, which alter its operation, such as: changes in speed, direction of flight and altitude. It can also be used to command external drone loads and optical sensors.
Through the telemetry link, the drone's status warnings and notifications, such as its position, speed, altitude, remaining battery charge and images from its optical sensors, are sent from the drone to the remote control, when available. Most of the drones we're talking about have their video camera, don't they?
Figure 1 - Communication link between the Remote Control and the Drone
These communication links are operated on specific frequencies, designated within the electromagnetic spectrum. These are radio frequencies (RF), intended only for drones and which are managed by ANATEL - Agência Nacional de Telecomunicações (National Telecommunications Agency). That is why ANATEL participates in the Certification and Homologation of drones that are operated in Brazil, as it’s the one that verifies if the RF channels used by the drone are within the expected range.
Figure 2 - Electromagnetic Spectrum (symbolic chart)
Most of them operate in the same frequency bands or radio bands as Wi-Fi compatible devices (2.4 GHz and 5.8 GHz) to control the drone and transmit telemetry information from the drone to the remote control operator. Some more advanced equipment can be equipped with modems that transmit and receive data in the frequencies of 433 MHz or 915 MHz.
These are the most common transmission bands for drones available on the market, but any other part of the radio spectrum could theoretically be used in a custom system...
Figure 3 - Manual Remote Control (Eachine E520S model)
Counter-Unmanned Aircraft Systems Technology Guide - September 2019. Available in: <https://www.dhs.gov/sites/default/files/publications/c-uas-tech-guide_final_28feb2020.pdf> Accessed on: 28 May 2020.
Rio de Janeiro, May 28, 2020.