Two-way radios have been used for decades in various industries, from emergency services to construction, and even for recreational purposes like hiking or camping. While they appear simple, the communication process that happens between two or more radios is governed by complex physics. At the heart of this process is signal propagation. Understanding how radio signals travel, or propagate, through different environments is key to using these devices effectively.
In this blog, we’ll explore what two-way radio signal propagation is, the different types of propagation pathways , the factors that affect how signals travel, and how propagation pathways impacts the range of communication.
What is Two-Way Radio Signal Propagation?
Signal propagation refers to the way radio waves travel from one point to another. In the case of two-way radios, this means the journey the signal takes from the transmitter (the radio sending the message) to the receiver (the radio receiving the message). These signals are electromagnetic waves, which can travel through different mediums, such as air, water, or even solid materials.
Two-way radios use radio frequency (RF) energy to communicate. When a user speaks into the radio, their voice is converted into an electrical signal, modulated onto a radio wave or sent in digital packets, and transmitted into the air. The receiving radio captures this wave, decodes it, and converts it back into sound. While this might sound straightforward, the journey of the radio wave can be affected by many factors.
Types of Two-Way Radio Signal Propagation
1. Line-of-Sight (LOS) Propagation
Line-of-sight propagation is the most common type of signal propagation for two-way radios, especially those operating at very high frequencies (VHF) and ultra-high frequencies (UHF). As the name suggests, this type of propagation occurs when the transmitting and receiving antennas are within a direct line of sight of each other. The signal travels in a straight line between the two radios without interference from obstacles.
Examples of LOS Propagation:
- Communications in a cellular network
- Communications between two handheld radios in an open field
- Communications between a ground radio and an aircraft in flight
2. Ground-Wave Propagation
Ground-wave propagation occurs when the radio signaling pathway travels along the surface of the Earth. This type of propagation is typically used by radios operating in lower frequency ranges, such as the medium frequency (MF) band. Ground-wave signals follow the curvature of the Earth, allowing them to cover longer distances than line-of-sight signals in some cases.
Examples of Ground-Wave Propagation:
- Maritime radio communication
- Long-range AM radio stations
3. Sky-Wave (Ionospheric) Propagation
Sky-wave propagation, also known as ionospheric propagation, involves radio waves that are transmitted into the atmosphere, where they are reflected or refracted back to Earth by the ionosphere, a layer of the Earth’s atmosphere. This type of propagation is common for radios operating in the high frequency (HF) band, and it allows transmitter signals to travel over vast distances by bouncing between the Earth and the ionosphere.
Examples of Sky-Wave Propagation:
- Amateur (ham) radio operators communicating across continents
- Shortwave amateur radio radio broadcasting
4. Tropospheric Propagation
Tropospheric propagation occurs when radio waves travel through the troposphere, the lowest layer of the Earth’s atmosphere. In this mode, signals are refracted (bent) by variations in temperature and humidity within the atmosphere. This type of propagation is most common in VHF and UHF frequencies and can lead to enhanced range over flat terrain or bodies of water.
Examples of Tropospheric Propagation:
- Extended-range VHF radio communication over coastal areas
- Radio signals traveling long distances during weather phenomena such as temperature inversions
Factors Affecting Two-Way Radio Signal Propagation
Now that we understand the different types of signal propagation, it’s important to recognize the factors that influence how radio waves travel. These factors can either enhance or hinder communication, depending on the circumstances. They effect both digital and analog transmissions. Tridon Communications engineers consider these factors as we optimize your communication system. Let’s explore some of the more common factors affecting two-way radio signal propagation:
1. Frequency
Frequency spectrum plays a critical role in signal propagation. Lower radio frequencies, such as those in the HF band, tend to travel longer distances and can reflect off the ionosphere, allowing them to cover vast areas. Higher frequency signals, such as those in the UHF band, are more likely to follow a line-of-sight path and are often absorbed or blocked by obstacles.
Key Points About Frequency:
- Lower frequencies (e.g., HF) are better for long-distance communication via sky-wave propagation.
- Higher frequencies (e.g., UHF) provide clearer communication over shorter distances but are more prone to being blocked by physical barriers.
2. Obstacles
Physical obstacles between the original signal and the receiver, such as buildings, trees, mountains, and hills, can significantly affect radio signal propagation much like an object between you and the sun will block light waves. Line-of-sight radio signals are particularly sensitive to obstructions. When an obstacle blocks the direct path between two radios, the signal may be weakened, reflected, or scattered. This can lead to reduced range and poor communication quality.
Types of Obstacles:
- Urban areas: Buildings and other structures can block or reflect radio signals, leading to weaker reception.
- Forested areas: Dense foliage can absorb radio waves, reducing signal strength.
- Mountains or hills: Large landforms can completely block line-of-sight signals, making communication impossible in some cases.
3. Weather Conditions
Weather can also influence radio signal propagation. Certain atmospheric conditions can enhance or degrade radio communication. For example, temperature inversions (where warm air sits above cooler air) can cause radio signals to travel farther than normal due to tropospheric refraction. Conversely, heavy rain, snow, or fog can attenuate (weaken) signals, especially at higher frequencies.
Effects of Weather on Signal Propagation:
- Rain and snow: Water in the atmosphere can absorb and scatter radio signals, particularly at higher frequencies.
- Temperature inversions: These can create extended range by allowing signals to refract over longer distances.
- Fog and humidity: Can slightly weaken signal strength, though the effect is usually minor
4. Antenna Height and Orientation
The height and orientation of the radio’s antenna play a crucial role in signal propagation. In line-of-sight communication, higher antennas can overcome obstacles that might otherwise block the signal. Raising the antenna increases the effective range of communication by providing a clearer path for the signal to travel. Additionally, the orientation of the antenna (whether it’s vertically or horizontally polarized) should match between communicating radios to ensure the best signal reception.
Key Points About Antennas:
- Height: The higher the antenna, the greater the potential range of the signal.
- Polarization: Matching antenna polarization (vertical or horizontal) improves signal strength and clarity.
5. Interference
Interference from other electronic devices, radio stations, or natural sources can disrupt radio signal propagation. This interference can cause static, dropped signals, or reduced audio quality. Common sources of interference include power lines, electrical equipment, and other nearby radio transmissions.
Examples of Interference:
- Electrical interference from machinery or power lines
- Radio interference from other two-way radios operating on the same or nearby frequencies
- Natural interference from solar flares or lightning storms
How Signal Propagation Affects Range
The range of a two-way radio system is directly impacted by signal propagation. Depending on the type of propagation and the factors we’ve discussed, the range of a two-way radio can vary dramatically. Here’s how signal propagation can affect the range:
1. Line-of-Sight Range
For radios operating at VHF or UHF frequencies, line-of-sight propagation is the most common. The range is determined by the distance between the antennas of the two radios and any obstacles that may be in the way. In an open field, the range may be several miles, but in a city with tall buildings, the range could be much shorter due to obstructions.
Typical Line-of-Sight Range:
- Handheld radios: 1-5 miles, depending on terrain and obstacles
- Mobile radios: 5-10 miles with an elevated antenna
2. Extended Range via Ground-Wave or Sky-Wave Propagation
When operating at lower frequencies (such as in the HF band), ground-wave or sky-wave propagation can extend the range far beyond what is possible with line-of-sight communication. Ground-wave signals can follow the Earth’s curvature, allowing communication over distances of hundreds of miles. Sky-wave signals, popular with amateur radio enthusiasts, can travel thousands of miles by bouncing off the ionosphere.
Typical Extended Ranges:
- Ground-wave propagation: Up to 100 miles or more
- Sky-wave propagation: Up to thousands of miles, depending on ionospheric conditions
3. Range Variability and Atmospheric Conditions
Weather and atmospheric conditions can either enhance or degrade the range of two-way radios. Tropospheric refraction caused by temperature inversions can allow VHF or UHF signals to travel much farther than normal. On the other hand, rain, snow, or fog can reduce range by weakening the signal as it passes through the atmosphere.
Range Variability Examples:
- During a temperature inversion, a VHF radio that typically has a range of 10 miles might reach 30 miles or more due to enhanced signal propagation.
- During storms radio waves can become weaker due to electrical interference from lightning as well as snow, rain, and sleet.
4. Impact of Antenna Height on Range
Raising the height of the antenna can significantly increase the range of two-way radio communication. For example, a handheld radio with an antenna at ground level may have a range of only a few miles, but placing that same radio’s antenna on a tall building or tower could extend the range to 10 miles or more.
Antenna Height Range Increase:
- A handheld radio with a typical 1-2 mile range can achieve 10 miles or more with a properly elevated antenna.
5. Multipath Propagation
Optimize Your System for Maximum Range
Two-way radio signal propagation is a fascinating and complex process that depends on a variety of factors, including frequency, obstacles, weather, antenna height, and interference. Understanding these factors can help users optimize their radio setup for maximum range and clarity. By learning about the different types of signal propagation—such as line-of-sight, ground-wave, sky-wave, and tropospheric propagation—you can better predict how your radio will perform in different environments.
Whether you’re a professional relying on two-way radios for critical communication or a recreational user looking to stay in touch on a hiking trip, knowing how signal propagation works can make all the difference. By choosing the right frequency, adjusting your antenna, and being aware of potential obstacles or weather conditions, you can improve your two-way radio communication and ensure that you stay connected when it matters most.
Trust the Experts at Tridon
If you’re looking to enhance your communication systems and explore the benefits of wireless technology, contact Tridon Communications. Our experts can help you navigate the complexities of wireless communication and implement solutions tailored to your specific needs. Discover how Tridon Communications can help you stay connected in an increasingly wireless world.
You deserve the best, and Tridon is the right partner for your business. Whether you’re looking for voice or video communications we have what it takes to keep your business running smoothly in any situation – no matter how complicated they may seem. With over 40 years of experience, there isn’t anything we can’t handle when it comes to providing reliable service to companies across Western Canada.
