What Are the Interferences to Radio Waves? What Are the Interferences to Radio Waves?

Radio interference refers to the phenomenon that occurs during radio communication, where some electromagnetic energy enters the receiving system or channel through direct or indirect coupling, resulting in a decrease in the quality of useful received signals, information errors or loss, or even blocking communication.

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.

The solar wind, also emitted by the sun, also affects the structure and behavior of the ionosphere. This solar wind immediately causes distortions in the Earth’s magnetic field as it approaches the Earth, and can lead to auroral ionization in the polar regions. This in turn creates unpredictable radio wave propagation. As a result, HF and VHF signals decay very quickly or even disappear completely. For example, during strong solar storms, VHF signals (30 MHz to 300 MHz) are scattered more strongly by scintillation, causing variations of 10-15 dB over a few minutes. This effect is strongest over polar regions and can therefore affect flights that rely on VHF communication and navigation systems, as the loss of signal coherence can be as high as 40% during these disturbances.

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.

The troposphere is the lowest layer of the atmosphere. This layer has a strong influence on the VHF and UHF frequencies used in television, radio, and cellular communications. Tropospheric ducting is the phenomenon of radio waves bending due to the refraction effects of temperature and humidity gradients in this layer. Under conditions of high humidity and temperature inversions – when a layer of warm air overlies a layer of cooler air – VHF signals can propagate beyond the normal line-of-sight range, up to 500 km, compared to the usual range of only 50-100 km. On the other hand, this ducting can also cause interference between distant stations on the same frequency due to signal overlap and attenuation when the weather changes. For example, a temperature inversion over the sea can interfere with a distant radio or television station, affecting the reception quality of local broadcasts.

Above the troposphere, the stratosphere has no significant direct effect on most radio frequencies, as it lacks the dense gases and particles needed to reflect and refract signals. However, the stratosphere indirectly contributes to such tropospheric waveguide events by increasing the temperature inversion layer at the boundary with the troposphere. However, the stratosphere has little or no direct effect on radio signals, and even under abnormal temperature conditions, radio signals (especially those at VHF and UHF frequencies) suffer slight refraction when passing through the stratosphere, but these effects are negligible compared to the effects of the troposphere. Under normal conditions, a 150 MHz VHF signal only suffers a negligible loss of about 1-2 dB when passing through the stratosphere.

Above the stratosphere, the ionosphere has the most significant effect on the propagation of radio waves in the high frequency (3-30 MHz) range. This layer consists of multiple layers of ionized particles, whose density varies day and night due to ultraviolet radiation from the sun. During the day, high frequency waves are absorbed by the D layer of the ionosphere, causing signal attenuation and reducing signal strength, sometimes by up to 20 dB, with the greatest effect on frequencies below 10 MHz. At night, the D layer dissipates and high-frequency signals can be reflected from the higher F layer, enabling long-distance propagation of thousands of kilometers. This propagation is called sky-wave propagation and is the basis of international broadcasting and amateur radio. However, the density of the ionosphere varies greatly, especially due to solar activity. During solar maximum, ionospheric disturbances can reduce the clarity of high-frequency signals by 30% or more, making reliable long-distance communications unreliable.

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.

The low-frequency band extends from 30 kHz to 300 kHz and has a strong ability to propagate over long distances due to low atmospheric absorption. Low-frequency waves can propagate along the surface of the earth up to 2,000 kilometers, a propagation called ground wave propagation. For example, low-frequency bands are used in navigation systems and maritime communications because their long wavelengths easily pass through water and can reach great distances without much interference. On the other hand, to transmit low-frequency waves, giant antennas hundreds of meters long are required. This limits the use of low frequencies in many practical applications. In addition, while low-frequency waves are insensitive to physical obstructions, their limited data carrying capacity makes them unsuitable for modern high-speed data applications.

In the HF band of 3-30 MHz, signals can reach great distances of thousands of kilometers by reflection from the ionosphere, thus enabling “sky wave” communications. The HF band is suitable for international broadcasting, amateur radio, and military communications. In contrast, HF signals are susceptible to the effects of the atmosphere, which is almost entirely controlled by the day-night cycle. During the day, the D layer of the ionosphere absorbs HF signals below 10 MHz; this can sometimes reduce the effective range by half compared to the nighttime period. At night, when the D layer breaks up, these frequencies can travel farther because they are reflected from the higher F layer. However, this HF band is susceptible to solar activity; for example, during a solar flare, it can reduce the clarity of HF signals by up to 70% in just a few hours. Therefore, it cannot be relied upon for long-distance communications.

The VHF band is between 30 and 300 MHz and is used for FM broadcasting, TV broadcasting, and two-way communication systems. Because VHF waves propagate primarily by line-of-sight (with limited diffraction around obstacles), their effective range is limited to about 50-100 km, depending on the height of the transmitter. As a result, buildings and hills can block VHF signals. This band is less effective in urban areas. However, the VHF band offers an excellent balance between range and quality, with relatively little interference from ambient noise compared to lower bands. For example, FM radio broadcasts between 88 and 108 MHz, providing high-quality audio for up to an 80 km radius from the transmitter. An unusual atmospheric condition called tropospheric ducting can retransmit VHF signals hundreds of kilometers beyond the horizon for short periods of time, sometimes allowing FM stations to be received at great distances, but this effect is unreliable.

The UHF band (300 MHz to 3 GHz) is used for broadcast television, cell phones, and Wi-Fi. Its wavelength is much smaller than that of AM radio or FM radio signals, making it ideal for carrying large amounts of data—this is true in applications such as video transmission and high-speed Internet access. On the downside, UHF signals have a limited range and are more susceptible to physical obstacles than longer wavelength radio waves. For example, 900 MHz UHF signals used in mobile communications can be attenuated by as much as 20 dB when passing through concrete walls; this reduces effective indoor coverage accordingly. Atmospheric absorption in the UHF band is high, especially in humid conditions, attenuating the signal by about 1 to 2 dB per kilometer in high humidity conditions. Despite these limitations, UHF frequencies are widely used in urban areas due to their high data capacity and compatibility with compact antennas suitable for portable devices.

Antesky 1.0m automatic flyaway antenna on site

Antesky Science Technology Inc. was built in 1985, we’re mainly engaged in the design and manufacture of satellite communication large satellite dish,VSAT antenna,TVRO antenna, Portable flyaway antenna and relevant control and tracking system. We have a selected range of antenna in the frequency band, such as C-band, Ku-band, X-band, L-band, S-band, Ka-band, DBS-band.

If you are looking for any other satellite communication dish or related accessories, please send Antesky an inquiry via sales@antesky.com. Thanks!