Radio interference signals are mainly electromagnetic energy that enters the receiving device channel or system through direct or indirect coupling. It can affect the reception of received signals required for radio communication, resulting in performance degradation, quality deterioration, information errors or loss, and even blocking the communication. Therefore, it is generally said that the fact that useless radio signals cause the quality of useful radio signals to decrease or damage is called radio interference.
Previously we have an article about the analysis and solutions of antenna interference in satellite communication, including polarization interference, adjacent frequency interference, forwarding interference, etc. Please click here to read the full article.Today we will focus on analyzing how to interfere with radio from several aspects, such as physical obstacles, weather conditions, electromagnetic interference (EMI), solar activity, atmosphere, and frequency bands. For example, heavy rain can reduce the signal strength of 12 GHz by 20 dB per kilometer. Solutions include using higher frequencies to obtain clearer paths or placing antennas to avoid reflective surfaces and interference sources. Please go ahead for further details.
1. Obstacles in the physical realm
Obstructions in the physical realm have a lot to do with radio waves, and they can interfere with or weaken the signal—depending on the type of obstruction and its density in the path. Whether it’s urban, rural, or climate change, understanding the impact of various materials and environments can help more effectively design solutions to improve clarity and range.
The number and density of buildings, especially tall concrete and steel buildings, is a significant factor in metropolitan environments. Concrete has a very high attenuation rate and can significantly weaken radio signals. Consider a medium-sized concrete wall, and depending on its thickness, a radio wave will lose 10-15 dB of signal strength with each wall it passes through. For example, in a densely populated urban environment, with various walls in the path of both the source and receiver, the signal can drop by 70% as it tries to penetrate multiple layers of material. Of course, add in metal surfaces, which are highly reflective and can cause multipath interference, with reflected signals interfering with the direct signal. In these environments, placing the receiver close to a window can minimize the damping effect of the wall, as glass has a much smaller disruptive effect on radio wave strength, with only about 3 dB of signal strength lost per pane of glass.
Vegetation in natural outdoor environments can also cause significant interference. Trees, especially those with tall, wet leaves, tend to absorb and scatter radio waves. In fact, for the 2.4 GHz band (the band widely used for Wireless Fidelity), a single tree can cause signal loss of up to 10-15 dB, and in densely forested areas, a row of trees squeezed together can reduce the range of a 2.4 GHz signal by nearly 50% compared to an open field. This effect is even more pronounced during rainy or high humidity weather, as the added moisture further enhances the leaves’ absorption capacity. During seasonal changes, such as in the summer when the leaves are thickest, the signal attenuation can be as much as 10% to 20% compared to the winter when the trees have lost their leaves.
Other obstacles to radio wave propagation include mountainous or hilly terrain. These are natural obstacles that are difficult for radio signals to bypass, especially high-frequency signals that rely on line-of-sight transmission. For example, in mountainous areas, FM signals can lose about 20% to 40% if there is a peak or ridge between the transmitter and receiver. More sensitive UHF frequencies, such as those used in television broadcasting, in the 300 MHz to 3 GHz range, can experience losses of more than 50% if terrain blocks line-of-sight transmissions. For example, a broadcast tower might be located behind a mountain, and its range to a receiver on the other side of the mountain would be only 30% of the normal range compared to a flat area. Solutions for such areas often involve placing repeater stations at intervals at points of elevation or along valleys to maintain signal continuity.
Inside buildings, the structure and composition of walls and furniture can also greatly affect radio wave strength: partitions offer little resistance, typically producing only about 2 to 3 dB of signal loss per wall. In contrast, metal-reinforced walls, thick concrete, or firewalls can experience losses of up to 20 dB per barrier. For example, in a typical office building, a Wi-Fi signal operating at 5 GHz can drop by 50% or more from the middle of a floor to a corner, depending on the wall material and the type of exposed metal objects (perhaps a filing cabinet or duct wall).
2. Weather Condition
Variations in radio wave propagation depend greatly on the type of signal and the frequency at which it is transmitted. Other factors that can cause fluctuations in radio signal clarity and range include rain, fog, snow, and thunderstorms—all of which can affect radio signals, especially those transmitted at high frequencies. This knowledge is critical when using radio communications, as weather attenuation can sometimes be severe and can affect the reliability of communications.
Rain is probably one of the most common weather conditions that affect radio signals, and this effect increases with frequency. Above 10 GHz, rain attenuation becomes a problem that can affect satellite and microwave communication systems. Heavy rain with an intensity of about 50 mm/hour can reduce signal strength by up to 20 dB/km at frequencies around 12 GHz. At 30 GHz, heavy rain can reduce signal strength by up to 30 dB/km. Satellite communication systems can rely on adaptive power control to cope with this, or temporarily switch to a higher transmission power when rain falls, which requires more additional energy.
Fog and humidity can also affect high-frequency signals, though to a much lesser extent than rain. While the particles in fog are very fine, they can cause scattering at frequencies above 20 GHz. For example, in dense fog (less than 100 meters of visibility), signals around 30 GHz may attenuate by 2 to 3 dB per kilometer. In wireless communication networks that utilize this high frequency range, such as some 5G systems, range and reliability may be reduced by up to 20% on foggy days compared to clear days. In addition, high humidity exacerbates this effect: signal strength may decrease by about 1 dB per kilometer at 90% humidity compared to 50% humidity.
Snow has varying effects on radio waves, depending on the density and moisture of the snowflakes. Dry and powdery snow generally has little effect on signal strength, but wet snow may cause attenuation similar to light rain. For example, for frequencies around 15 GHz, signals may attenuate by about 5 dB per kilometer when the moisture content of the snow mixture is greater than about 15%. In addition to this type of signal loss, snow accumulation on antennas and transmission equipment increases reflections and refractions, which generally weakens the clarity of the signal. Using antenna covers in snowy areas can mitigate this effect, reducing the potential for interference.
Thunderstorms further complicate radio wave propagation. The most important component of a thunderstorm is lightning, which generates powerful electromagnetic pulses that interfere with radio signals over a wide frequency range. A single lightning strike within 10 km of a receiver generates an electromagnetic pulse powerful enough to cause a 20 dB spike in signal noise on an FM radio channel. This interference usually lasts only a few milliseconds, but successive lightning strikes can create a persistent source of interference. Thunderstorms also cause other disturbances in the ionosphere that affect HF (high frequency) signals between 3 and 30 MHz; these disturbances are characterized by random variations in signal path and quality.
Antesky 3.7m antenna with de-ice system heating reflector assembled
3.Electromagnetic interference (EMI)
Types of Electromagnetic Radiation
Different electrical devices emit electromagnetic wave frequencies that can interfere with radio communication signals. EMI can come from a variety of sources, from home appliances and cell phones to complex machinery in industry; each of these sources can have different effects on radio signals depending on their distance, power, and frequency. It is important to understand the effects of EMI and how to eliminate them, especially in urban or industrial areas where high concentrations of interference sources are common.
Home appliances, such as microwave ovens, fluorescent lights, and even cordless phones, can add to EMI in the home. The most prominent cause of interference to Wi-Fi networks that use the same frequency is microwave ovens that operate at a frequency of approximately 2.45 GHz. A typical microwave oven can generate EMI levels strong enough to reduce Wi-Fi signal strength by up to 20 dB within a range of 3 to 5 meters. This interference can cause a noticeable drop in Internet speed and connection stability. To minimize this effect, Wi-Fi routers and devices can be placed as far away from microwave ovens as possible, and they should also operate on different frequency bands, such as 5 GHz instead of 2.4 GHz, to keep the signal clearer.
In industrial environments, EMI is more noticeable due to the presence of heavy machinery and electrical equipment. Most industrial machinery typically operates at very high power levels and generates significant EMI over a wide frequency range. For example, electric motors used in a business may radiate enough EMI to reduce radio signal strength within 10 meters of the motor by 30 dB or more, depending on the power level and insulation of the motor. These extremely high-power bursts of EMI come from welders, arc furnaces, and other high-energy equipment; they can cause significant interference to nearby radio systems. Shielding equipment and installing EMI filters on sensitive equipment can help reduce these interferences in factories and other industrial environments.
In medical environments, EMI is a significant concern, especially for sensitive equipment such as MRI machines and heart monitors. MRIs are powered by high magnetic fields and radio waves, which can radiate EMI that can interfere with other equipment within a radius of about 100 meters. One study estimated that MRIs can reduce the signal of radio communication equipment operating in the same frequency range by about 40 dB. To combat this, hospitals designate certain EMI-free zones where communications equipment and sensitive electronic equipment are properly shielded or filtered to reduce interference. In addition, equipment within these zones is designed to meet strict EMI standards so as not to interfere with the safe treatment of patients or the proper operation of life-support equipment.
Solar activity
Solar activity, especially at long distances and at high altitudes, can severely affect the propagation of radio waves. Solar flares, sunspots, and solar winds can disturb Earth’s ionosphere – a vital layer that radio waves need to pass through to reflect back to Earth. These solar events can cause fluctuations in the density of the ionosphere, which can affect signal strength, clarity, and transmission range in various frequency bands; especially high-frequency radio communications, which are commonly used for aviation and maritime communications.
For example, a solar flare releases a large amount of energy in the form of radiation, which can reach Earth in a matter of minutes. The interaction of a solar flare with the ionosphere can produce sudden ionospheric disturbances in the D layer, which in turn begins to absorb high-frequency radio waves between 3 MHz and 30 MHz. During a strong solar flare event, high-frequency signals can lose up to 20 dB, transmission range can be reduced by more than 50%, and global communications can be interrupted for hours. In extreme cases, such flares can cause high-frequency radio blackouts, making signals unusable for hours on the sunlit side of the Earth. This can cause severe interference, especially in emergency and military communications, which rely heavily on the high-frequency frequency range for long-distance coverage.
Sunspots also affect radio wave propagation. During the roughly 11-year solar cycle, increased sunspot activity enhances the reflection of HF signals from the ionosphere, allowing for an increase in the range of certain frequencies. During periods of peak sunspot activity, HF radio operators can achieve even greater signal propagation distances, sometimes achieving a “jump” of 2,500 miles on a single bounce. At the other end of the spectrum, when sunspot activity is at its lowest, HF signals lose some of their increased propagation ability, reducing their range by about 30 percent. In fact, this is why operators notice that signal attenuation can reduce the effective range of a 10 MHz signal by as much as 500 miles during periods of low sunspot activity compared to peak sunspot activity.
Atmosphere
These atmospheric layers are very important for the behavior of radio waves, especially in their long-distance propagation. Each atmospheric layer affects radio signals differently, depending on the frequency and environmental conditions; namely, the troposphere, stratosphere, and ionosphere. This will help in understanding the above effects, and thus managing and optimizing radio communications for specific applications such as broadcasting, aviation, and marine navigation.
Frequency Band
The most important role of the frequency band is its ability to determine how radio waves adapt to their environment: propagation distance, interference sensitivity, and obstacle penetration. Different frequency ranges react differently to the same environmental conditions; therefore, some frequency bands are more suitable than others for certain applications. Understanding how the frequency band affects the properties of radio waves can help us choose the best frequency for broadcasting, communication, and data transmission applications.
