Radios play a crucial role in various emergency situations, which is why devices like walkie-talkies are commonly used in rescue operations. Below, I’ll explain some basic knowledge about radios.
Definition: A radio refers to electromagnetic waves that propagate through free space (including air and vacuum), representing a specific limited frequency band. The upper frequency limit is 300GHz (gigahertz), while the lower frequency limit varies. In various RF specifications, common ranges include 3KHz–300GHz (as defined by ITU – International Telecommunication Union), 9KHz–300GHz, and 10KHz–300GHz.
Electromagnetic waves:
(1) Generation: When a rapidly changing electric current passes through a conductor, the conductor emits electromagnetic waves into the surrounding space.
(2) Propagation: Electromagnetic waves do not require a medium to propagate; they can travel through a vacuum as well as through a medium. The electromagnetic waves used in radio communication are called radio waves, which are electromagnetic waves within a certain frequency range.
(3) Relationship between frequency, wavelength, and wave speed: The speed of electromagnetic wave propagation in a vacuum is the same as the speed of light. In air, the speed is approximately the same as in a vacuum. The relationship among frequency, wavelength, and wave speed is: wave speed = wavelength × frequency, expressed with letters as:
Now let’s talk about some basic knowledge regarding walkie-talkies:
People often ask how far a certain model of walkie-talkie can transmit. To be honest, every time I’m asked this question, I find it quite hard to explain.
In the field of wireless communication, there is no technical parameter called "distance" because there are simply too many factors that can affect how far a wireless signal can travel.
Commonly used radio walkie-talkies generally operate on two frequency bands: 130-170MHz and 403-470MHz. These two frequency bands are also the ranges legally permitted for use by individuals or organizations.
Under normal circumstances, these two frequency bands propagate in a straight line. The sea is one of the more ideal environments for radio walkie-talkie communication on Earth, usually with no obstacles and minimal interference. However, in reality, even handheld walkie-talkies on the sea can only communicate effectively over a distance of about 10–20 nautical miles. This is because the Earth is round — if the distance is too great, the signal will be blocked by the sea in between. (So, installing the antenna higher can also increase the communication distance.)
Typically, when used in urban areas, obstacles have the greatest impact on the signal transmission distance. Professional walkie-talkies with power up to 5 watts generally achieve an actual communication distance of only about 2–5 kilometers in cities. In areas with high terrain, numerous buildings, or relatively enclosed indoor spaces, the communication distance may be even shorter. However, when supported by a system base station, the communication range of a walkie-talkie can reach several kilometers or even tens of kilometers (and if both walkie-talkies are at elevated positions, it can also reach around ten kilometers).
The 0.5W walkie-talkies sold on the market are advertised by manufacturers with a maximum communication distance of 3 kilometers. In reality, this communication distance is merely a theoretical calculation based on transmission power — meaning, the maximum communication distance of a 0.5W walkie-talkie under conditions with no obstacles and no electromagnetic interference. In actual use, due to varying user environments, differing background noise levels, and varying degrees of electromagnetic interference, the real communication distance usually does not reach 3 kilometers. Many users mistakenly believe that when using a walkie-talkie in a city, it can achieve a communication distance of 3 kilometers — but that’s highly unlikely. No manufacturer can predict the user’s specific environment, and therefore cannot provide an actual communication distance.
So when answering customers’ questions about distance (in terms of straight-line distance in a city), I think the following response is relatively objective: A. Handheld walkie-talkies: 5W professional models: 1–5 kilometers; 2W handheld models: 1–3 kilometers; 0.5W consumer models: 500–1000 meters. B. Vehicle-mounted walkie-talkies (usually around 25W in power): 5–15 kilometers.
Another way of putting it is:
In the field of radio communication, there is no such parameter as “communication distance.” This term usually arises because users are particularly concerned about it when buying a walkie-talkie — naturally, everyone assumes the farther the communication distance, the better. But in reality, the communication distance of a walkie-talkie is influenced by many factors.
The electromagnetic wave signals transmitted by walkie-talkies are subject to blockage and interference from buildings, mountains, trees, electromagnetic fields, etc., during transmission, affecting the actual communication distance and quality. Especially in cases of severe electromagnetic field interference, the communication distance can sometimes be very short or communication may even fail. Some attentive veteran users have noticed something puzzling and asked me: why is the communication distance of today’s walkie-talkies not as good as older models from years ago? The reason is that the electromagnetic environment today is worse than it was many years ago. In the past, walkie-talkies were not widely used, mobile phones were still luxury items, and electromagnetic interference was not serious. But now we are constantly surrounded by electromagnetic waves, so this phenomenon is unavoidable.
To put it in an easily understandable analogy: if you throw a stone into calm water, the ripples it creates will slowly spread out over a long distance. But if you throw several stones at once, you’ll notice that the ripples don’t spread as far, because the waves interfere with and cancel each other out. Similarly, mutual interference of electromagnetic waves affects the communication distance of walkie-talkies.
Experiments have shown that in urban areas, the actual effective communication distance of walkie-talkies is about 3 kilometers, while in suburban areas it can be slightly longer, around 4 kilometers. Of course, with some network support — such as setting up a repeater station — the communication distance of a walkie-talkie can exceed 5 kilometers, and with multiple base stations, it can even reach tens or hundreds of kilometers.
If you have high requirements for communication distance or are using the device in complex terrains, it is recommended to buy a 5W model. (The greater the power, the farther the distance. The maximum power of a walkie-talkie is 5W!)