The article describes the variety of types of UAVs, including multi-rotor systems and aircraft platforms, their advantages and limitations.
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In modern conditions, the use of unmanned aerial vehicles (UAVs) is becoming increasingly popular and important, especially in the military and intelligence sectors. Communication between the UAV and the ground station is a key condition for the successful completion of tasks. However, not everyone understands how complex this system is and what factors affect its stability. In this article, you will learn how the main transmitting and receiving devices on board the UAV work, including GPS modules, telemetry modems and video transmitters.
Communication from the ground station to the drone is carried out using radio, so it is worth considering the physics of the process in more detail, but without resorting to high-level matters.
Let’s consider the radio transmission systems installed on UAVs.
In essence, the module is a GPS signal receiver with a calculator, installed as far as possible from equipment that creates electromagnetic guidance. It is usually installed away from equipment that can create electromagnetic interference. This module is critically important for orientation in space and accurate positioning of the drone. There are several satellite navigation systems: American GPS, European Galileo, Russian GLONASS and Chinese Beidou.
For the user, they all work approximately the same, but there is one nuance – the more satellites the receiver “sees”, the more accurately it determines the coordinates. Some receivers support one navigation system, others – several at once. The latter have an advantage, because, receiving more signals, they work more accurately and are better protected from GPS spoofing. This is when the electronic warfare station jams the real signals of the satellites and replaces them with fake ones, forcing the drone to incorrectly determine its location.
A telemetry modem is a receiving device designed to exchange information between a ground station and a UAV. From the ground station, it sends commands for execution, and from the UAV, it receives information received from sensors (for example, speed, current consumption, voltage, position in space) to the ground station. It is usually the main control channel for the UAV.
A video transmitter is a device that transmits images from UAV cameras to a ground station. It is the most visible device on board a UAV, so it should not be turned on unnecessarily (this applies only to UAVs that store photos on board), observing the radio silence mode. This mode reduces the possibility of the enemy using electronic warfare (EW) means.
Polarization is the directionality of the vector of the electric component of an electromagnetic wave in space. There are: vertical, horizontal, and circular polarization.
Simply put, radio waves have a property called polarization, which depends on how the antenna is positioned. If the antenna is vertical, the wave will also be vertically polarized, if horizontal, it will be horizontally polarized. For the connection to be stable, both antennas — on the drone and on the remote control — must be set up the same way, that is, located in the same plane. At short distances, the difference is almost imperceptible, but the further the drone is, the more this affects the signal quality: it begins to deteriorate sharply.
UAVs used today consist of standard modules operating at standard frequencies. Telemetry most often operates at frequencies of 433 MHz, less often 91 5 MHz, and even less often 865. There are telemetry modules operating at frequencies of 2.4 and 5.8 GHz. The video transmitter, as a rule, operates in the ranges of 1.2 GHz, 5.8 GHz, less often 2.4 GHz. Sometimes the telemetry modem and video transmitter are combined into one device operating at high frequencies (2.4 and 5.8 GHz). The control panel – 2.4 GHz, 433 MHz. GPS (all systems) operate at frequencies of 1.1 – 1.6 GHz.
The radio signal is highly dependent on the presence of obstacles. These include both natural and artificial objects, as well as electromagnetic fields that can interfere with the signal transmitted between the ground station antenna and the UAV. Any object in the signal path can become an obstacle, and the level of influence depends on the material: wood degrades the signal slightly, brick is stronger, and metal and reinforced concrete almost completely block it.
Even objects such as utility poles or ordinary chain-link mesh can cause unexpected problems. In addition, the radio environment in the flight area should be taken into account – when many devices operate simultaneously on the air at similar frequencies, this can create significant interference. The UAV’s own equipment, in particular servomotors, can also become a source of interference.
It is worth mentioning separately about natural and man-made anomalies, such as waste heaps or dumps with a high metal content. Their influence has been noticed repeatedly, although its nature is sometimes difficult to explain. Such anomalies are usually detected through experiments, and the results are taken into account when planning future flights.
Air humidity also has a great influence on signal propagation. The higher the humidity, the worse the communication quality, and accordingly, the smaller the range of the complex. In addition, it is necessary to take into account that with a change in humidity, obstacles that previously did not affect the range change their properties. For example, low “green grass”, which did not cause problems in dry weather, after rain becomes a serious obstacle to the passage of a radio signal.
The forest always creates interference for radio waves. Depending on the level of humidity and temperature, it can both absorb and reflect the signal, which makes the conditions for wave propagation unpredictable. Because of this, placing a ground station in a forest or even on the edge of a forest is undesirable, since the quality and range of communication can deteriorate sharply. The optimal place for a ground station is where there are no trees, bushes or other similar obstacles in the path of radio waves. This will ensure stable and reliable communication during the flight of the UAV.
Understanding how radio waves propagate, you can turn some obstacles to your advantage and use them as signal reflectors. For example, if there is a body of water (lake or river) between the UAV and the ground station and the air humidity is low, the water can reflect radio waves, increasing the communication range. However, this effect disappears or even becomes negative if there is high humidity or fog over the water – then the signal passes worse and can weaken significantly.
Another way to improve communication is to place a metal plate behind the antenna, such as a piece of corrugated iron or a sheet of roofing iron. This will create a kind of screen that will reflect the signal in the right direction, strengthening it. In some cases, bulletproof vests were even used for this. Taking into account such effects and their competent use can significantly improve communication efficiency and increase the operating range of UAVs.
Four types of antennas are most often used in UAV stations: pin, wave channel, patch, and clover.
There are some other types and schemes, but they work in a similar way. The pin and clover radiate equally in all directions.
Due to the fact that directional antennas do not radiate in all directions, but form them into a narrow beam according to their diagram, they provide a much longer communication range.
The directivity of an antenna determines how effectively it amplifies a signal in one direction compared to others. This can be seen on a special graph – a directivity diagram, which shows exactly how the antenna radiates radio waves. The main factor affecting directivity is the design of the antenna. Directional antennas concentrate the signal in a narrow beam, thereby providing a greater range and stability of communication compared to omnidirectional ones, which radiate the signal evenly in all directions.
The narrower the “petal” on the directivity diagram, the further the signal can spread and the better its quality will be. If you want to familiarize yourself with the formulas for calculating range and gain coefficients in more detail, they are easy to find in open sources.
The communication range depends on many factors, but the signal frequency has the greatest influence. The higher the frequency, the shorter the range, since high-frequency waves are less able to pass through obstacles. That is why low-frequency channels are used for telemetry, which is critically important for UAV flight, because without video the drone can still perform its tasks, but without telemetry it cannot.
The range also depends on the transmitter power and receiver sensitivity, but after a certain level of power increase it becomes useless. This is due to the fact that the signal propagates in a straight line to the limit of radio visibility, and then disappears sharply. Therefore, the main task is to ensure stable communication within this zone, and not to endlessly increase the transmitter power.
The sensitivity of the receiver also plays a role: the higher it is, the greater the range. However, if the signal is received against a background of strong external noise, improving sensitivity will not help, because the receiver will pick up not only the useful signal, but also interference.
Another way to increase the communication range is to use directional antennas with high gain and cables with minimal signal loss. This allows you to increase the signal level reaching the receiver, even without increasing the transmitter power. In general, the range is affected by many factors, and not all of them are obvious at first glance. Therefore, for optimal communication, it is important to take into account all these nuances and correctly configure the equipment.
In the radio frequency range of devices installed on board UAVs, the behavior of radio waves approaches the behavior of a light beam, and radio visibility approaches optical with increasing frequency. It is obvious that with height the distance of optical visibility increases and the distance of radio visibility increases. Below is a table of optical distances to the horizon, which fully corresponds to our radio horizon.
Based on the frequency data set out in paragraphs 2.5, 2.12 and the table in paragraph 213, it can be stated that a stable signal between the ground station and the UAV is possible only under the condition of direct visibility.
The UAV crew must understand that the location for installing the ground station should be chosen to ensure maximum radio horizon without obstacles and anomalies. The ideal option is to raise it, since placing the station at a height significantly increases the visibility zone and communication range. At the same time, the UAV take-off point does not necessarily have to be next to the ground station, and the antennas do not need to be constantly directed to the take-off point if we are talking about short distances. The most important thing is that during the mission the drone remains in the main area of action of the antenna, that is, within the main lobe of its radiation pattern. This guarantees stable and reliable communication.
EW (electronic warfare) is one of the most serious enemies for UAVs, second only to the mistakes of the crew itself. This topic cannot be ignored, because EW is intended to interfere with the operation of drones by creating radio interference for control and communication systems or by changing the conditions in which radio waves propagate. The methods of influence are divided into active ones, which generate interference, and passive ones, which reflect the signal, making it difficult for it to pass through.
There are also means of electromagnetic damage that work on the principle of a magnetron – they create induction currents in the electrical circuits of the equipment, disabling it. Fortunately, such means are not yet in the arsenal of the enemy in serial form. Therefore, we consider only those methods of EW that are actually used by the enemy.
The most common and most affordable method of electronic warfare is signal jamming. The principle of its operation is simple: a strong noise signal is sent at the same frequency as the drone equipment, which overlaps the useful one. This can affect various UAV systems.
For example, if the telemetry channel is jammed, this can cause malfunctions or a complete interruption of control. Jamming the video transmitter prevents the transmission of images from the drone’s camera to the ground station, which makes it difficult to adjust actions, but is not critical for the flight itself. Jamming the GPS signal disorients the device, and if there are no other navigation systems, this often leads to the loss of the drone. The most dangerous scenario is the simultaneous jamming of telemetry and GPS, when the drone loses both control and the ability to determine its location.
There are no active ways to combat such interference yet. All that remains is to follow the recommendations: amplify the ground station signal, try to quickly leave the EW coverage area, and minimize radio visibility to reduce the likelihood of jamming.
Spoofing is a method of electronic warfare when the real GPS signal is replaced by a stronger fake signal coming from the enemy’s ground station. As a result, the drone receives incorrect coordinates and “thinks” that it is in a different location, which can lead to its being diverted to enemy territory.
Simply put, the spoofing station disguises itself as a satellite and transmits fake data about its position to the drone. This method is actively used, and the enemy has the appropriate equipment for this. It is possible to counteract spoofing if the crew notices the change in coordinates in time and begins to control the drone manually, guided by a magnetic compass or ground landmarks.
To reduce the risk of spoofing, it is effective to use more modern GPS receivers that can work simultaneously with several navigation systems, such as Galileo, GLONASS, BeiDou and GPS. This allows the drone to see more satellites and quickly detect a fake signal. In some cases, it helps to lower the flight altitude to hide from the spoofing station behind the terrain and get into a radio shadow.
The third method of electronic countermeasures is the interception of the control or telemetry channel. The electronic countermeasure station notices the signal from the remote control or modem, reads the key, determines the control protocol and with its signal with the same key, at the same frequency, intercepts the control for itself. In the case of such countermeasures, the one whose signal from the control equipment is stronger will win. As a countermeasure, UAV developers use all kinds of methods of encoding the control signal.
In addition to electronic warfare means, the enemy has electronic reconnaissance means that detect radio radiation, determine its location and determine the type of equipment with accuracy down to each specific device individually thanks to the unique signature of the transmitter (similar to fingerprints). Therefore, you need to know the safety rules and try to adhere to them as much as possible.
One of the devices that helps to increase radio security and makes it more difficult to determine the location of a UAV ground station is a false signal generator, or the so-called “deception”. It simulates the operation of the drone control panel, creating additional radio signals. Using several such decoys can significantly confuse the enemy, making it difficult for him to determine the real location of the crew, and thus increase the chances of safely completing the mission.
An old or faulty drone control panel can be used as a decoy. The main thing is to choose the right place to install it. It is best if it is a high point, for example, a lonely tree, the roof of a house or other similar structure that will effectively simulate the operation of a real transmitter.
The less the crew uses radio sources, the more difficult it is for the enemy to find their location. Therefore, unnecessary radio transmissions should be avoided: do not conduct radio conversations without urgent need, do not keep the control panel or ground station modem constantly turned on. If radio devices need to be turned on to configure or operate the UAV, it is advisable to place them so that the signal does not spread towards the enemy – behind natural or artificial obstacles that shield the radio signal.
It is worth paying special attention to mobile phones. If several active mobile signal sources suddenly appear in an area where there is usually no one, this may arouse the enemy’s suspicion. Also, the direction of the directional antenna should not be changed unnecessarily. During the flight, it should be adjusted only to follow the UAV, and not to other objects. Compliance with these rules significantly reduces the likelihood of detection of the crew.
It is worth remembering that enemy electronic intelligence units can keep a map of radio signal sources, recording the places where UAV crews previously worked. Therefore, it is undesirable to regularly use the same site for flights. It is best to have several alternative sites in the same sector and use them in a random order to make it difficult to track and predict your actions.
From the point of view of general security, it is necessary to minimize the leakage of information about upcoming flights. It is not necessary to warn neighboring units about the planned work with UAVs in a particular area for a long time. It is best to do this immediately before entering the site to reduce the risk of accidental or intentional disclosure of information. Such simple measures will help increase radio security and protect the crew from enemy intelligence.
Ensuring stable communication between the UAV and the ground station is critical for the successful completion of missions. However, this process is accompanied by numerous obstacles, both natural and man-made. The article examines the main factors affecting the quality of communication, from the correct choice of antennas and frequencies to taking into account weather conditions and possible anomalies. In addition, special attention is paid to countering electronic warfare and radio security measures that allow the crew to minimize the risks of hostile influence and maintain control over the device.
The use of modern GPS receivers, compliance with the rules for placing the ground station, competent selection of sites and the use of decoys significantly increase the chances of mission success even in difficult conditions. The ability to take into account all these factors allows the crew to effectively control the UAV, maintaining safety and ensuring the fulfillment of the assigned tasks.
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