Can a drone be controlled without WiFi?

A friend of mine said that drones can only be controlled by WiFi connection. But I myself use an older radio remote control system. As a result, I started to read up on the different options for radio connectivity. What I found about communication systems and how they work you can find here.

Can a drone fly without WiFi connection? Yes, there are a variety of different radio links between the pilot and the drone. Conventional connections are Bluetooth, 2.4Ghz (z.B. WiFi), 27.12 MHz, 40.68 MHz and satellite link for military applications. Which system is most suitable depends on the application.

Many new drone pilots wonder how the radio connection to the drone works. Here is a compilation of various transmission systems.

How does the radio transmission between the drone and the controller work??

To control a drone, the radio remote control sends the desired signals to drone. Generally, this is a pulse-pause modulation (PPM) signal. The duration of the pauses between the pulses determines how strong the analog control signal is. On the control side, the four signals throttle, yaw, roll and pitch are transmitted. The receiver routes this signal to the flight controls. This calculates the corresponding signals for the individual controllers of the motors.

Your control movements on the remote control are transformed into electromagnetic waves by the transmitter and sent out. The receiver on the drone receives and translates this signal back to the PPM signal.

In general, the frequencies and strengths of radio signals are regulated by law. Different frequency bands are defined and some are reserved for specific purposes, such as for emergency services. Various frequency bands are open to the public for radio contact with the drone.

The most common frequency bands for wireless connections can be found in the international ISM band (industrial, scientific, and medical).

 

Frquency	Bandwidth	Medium frequency
6.765 – 6.975 MHz	0.03 MHz	6.78 MHz
13.553 – 13.567 MHz	0.014 MHz	13.56 MHz
26.957 – 27.283 MHz	0.326 MHz	27.18 MHz
40.66 – 40.7 MHz	0.04 MHz	40.68 MHz
433.05 – 434.79 MHz	1.74 MHz	433.92 MHz
902 – 928 MHz	26 MHz	915 MHz
2.4 – 2.5 GHz	100 MHz	2.45 GHz
5725 – 5875 MHz	150 MHz	5800 MHz
24 – 24.250 GHz	250 MHz	24.125 GHz
61 – 61.5 GHz	500 MHz	6.250 GHz
122 – 123 GHz	1000 MHz	122.5 GHz
244 – 246 GHz	2000 MHz	245 GHz

 

For each radio standard there is a transmission protocol, which regulates the data structure and monitors the transmission. Different transmission protocols are used for the individual radio links. Different transmission protocols can also be used in one frequency band. For example, Bluetooth and WiFi use the same frequency band of 2.4 – 2.5 GHz, but different transmission protocols.

Here is a list of the most common radio standards:

Bluetooth: Some small toy drones for children use Bluetooth for data transmission. The outdoor range is approx. 100m. This may cause interference with WiFi networks or microwave ovens. There are also remote controls that send the control signals to the cell phone via Bluetooth and the cell phone is connected to the drone via WiFi.

Wi-Fi: Many common drone sets (drone, camera, battery and remote control) are operated in conjunction with a cell phone and a suitable app. The WiFi standard is used to control the drone and to transmit the video signal. Realistic ranges of WiFi connections are 200-300m. Some higher quality remote controls reach ranges of up to 2km. This also depends on the environmental conditions. Thereby mountains, forests weaken the signal. Likewise, the frequency band allocation has a major impact on the range. When your drone reaches the maximum range, the first thing to be disturbed is the video signal, control data is usually still transmitted in sufficient quality. Always keep in mind, however, that the ranges at which drones may be operated are usually regulated by law.

DSSS or FHSS: Direct-sequence spread spectrum (DSSS) and frequency-hopping spread spectrum (FHSS) are standards for the common radio remote controls of model vehicles or model airplanes. Here you can operate different models with one remote control. The range of this standard is approx. 2km.

27.12 MHz or 40.68 MHz: Analog signals are usually transmitted in this frequency band. As a general rule, the transmission of video signals and control signals should be transmitted separately in different frequency ranges. For example, a drone can be controlled in analog mode at 40.68 MHz, and the video signal is transmitted by means of 2.4 GHz transmission. (The same is true for control signals using 2.4 GHz signal and video signals on 5.8 GHz)

How does a drone send a video and what is FPV?

Videos are normally transmitted in a frequency band of 2.4 GHz or 5.8 GHz. Mostly the WiFI standard or the analog PAL or NTSC standard is used. Everything else works the same as for transmitting control signals.

FPV (first-person view) is a method of controlling a drone from the perspective of the pilot flying with it. A camera mounted on the drone will transmit the video signal to the pilot in real time on FPV goggles or a monitor. When the camera is mounted on a gimbal, the accelerometers of the FPV goggles can be used to control the camera position on the drone using head movement.

FPV races are very spectacular. In these races, small very fast drones fly simultaneously through a parkour. The drones are very light and the camera is fixed to the frames of the drone. Flying such drones using FPV requires a lot of practice, a fast reaction time and flying skills.

Do I need a smartphone to fly a drone?

In the small drone sector, the WiFi standard is increasingly being used for data transmission. In this case, the smartphone is used as a display for video transmission. Professional drones are flown with a better radio remote control and if a video signal is needed, this is transmitted to a screen via a separate radio transmission.

On some flight controls, flight parameters can be adjusted during flight. By means of Bluetooth or WiFi the flight control is connected to a cell phone. Using an appropriate app, the pilot can change parameters such as sensitivity to control signals.

Do I need internet to fly a drone?

No, you don't need internet to control a drone. The WiFi connection is only used to transmit the data from the cell phone to the drone. The only situation where the internet can be used is when using maps. Maps are used in conjunction with autopilots. The software uses the GPS signal of the drone and downloads the appropriate map. This can also be circumvented by saving the relevant maps locally on the cell phone, tablet or computer beforehand and using them offline.

How far does the radio transmission to a drone reach??

This depends on the radio transmission used. Bluetooth has a range in the open field of approx. 100m, WiFi 200-300m and DSSS or FHSS can transmit data up to 2km. In general, drones should always be operated within visual range.

What is interference?

Interference is a superposition of waves, in our case electromagnetic waves. When two waves with the same frequency meet they interact with each other. When a wave trough meets a wave crest, the waves cancel each other out. When a wave crest and a wave crest meet, the signals overlap. In both cases the transmitted data are useless. For this reason, you should not operate a WiFi controlled drone in the settlement area, as there are usually many home networks here.

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