The modern world is impossible to imagine without radio communication, and a significant part of this huge spectrum is occupied by the world. ultrashortwave. It is this range that provides FM radio, television, mobile communications and satellite navigation, without which no modern car or gadget can do. Understanding their physical properties allows not only to use the technique more effectively, but also to understand the causes of interference or unstable signal reception in various terrain conditions.
The VHF range covers frequencies from 30 MHz to 300 MHz, although in the everyday sense they often include higher frequencies used in VHF communications. Electromagnetic radiation In this sector of the spectrum behaves in a special way, differing from long and medium waves in its ability to bend obstacles worse, but have high noise resistance and sound quality. For a driver or radio enthusiast, knowing these nuances can be a crucial factor when choosing an antenna equipment.
In this article we will discuss the physical nature in detail. ultrashortwavemethods of their distribution in the atmosphere and practical application in various fields of activity. We will pay special attention to how the terrain and weather conditions affect the quality of communication, and also consider the technical aspects of signal reception and transmission.
Physical characteristics and frequency range
Ultrashort waves (UFW) occupy an intermediate position between short waves and ultrahigh frequencies. Their wavelength ranges from 10 meters to 1 meter, which dictates specific requirements for the design of antennas and transmitters. Unlike lower frequencies, VHF propagates primarily within line of sight, which limits the range of communication to the horizon if repeaters are not used.
A key feature is the high frequency of oscillations, which allows broadband signals such as stereo sound or video stream to be transmitted. Signal modulation This range is often performed by frequency method (FM), which provides excellent audio quality and resistance to atmospheric noise. However, the high frequency also means that the signal is easily absorbed by dense materials and reflected off metal surfaces.
⚠️ Attention: When installing antennas to operate at VHF frequencies, it is critical to consider the height of the lift. Low installation of an antenna on a car or building drastically reduces the communication range due to the curvature of the earth’s surface.
For the precise configuration of the equipment, it is necessary to know the specific frequency corridors. The following is a table of distribution of the main sub-bands:
| Sub-range | Frequency range (MHz) | Wave length (m) | Principal application |
|---|---|---|---|
| Lower VHF | 30 – 50 | 10 – 6 | Service, taxi service. |
| Medium VHF | 66 – 74 | 4.5 – 4 | Old Broadcasting (USSR) |
| FM band | 88 – 108 | 3.4 – 2.7 | Broadcasting, music |
| Aviation | 108 – 137 | 2.7 – 2.1 | Communication with pilots, navigation |
Thus, spectral distribution It allows efficient use of frequency resources, allocating separate bands for different needs. This prevents interference between rescue services, commercial broadcasting and amateur communication.
Features of radio signal propagation
Spreading ultrashortwave It is very different from the long wavelengths that can circle the globe. VHFs move almost straight, like light, so the zone of confident reception is limited by the line of sight of the antennas of the transmitting and receiving devices. Any obstacles – hills, tall buildings, dense forests – create a radio, where the signal can disappear completely or become extremely unstable.
However, there are atmospheric phenomena that can significantly increase the communication range. Under certain conditions, temperature and humidity occur troposphericWhen the signal circles the Earth's surface at distances of hundreds of kilometers. This phenomenon is often observed over water surfaces or during periods of sudden temperature changes.
It is also important to consider the multipath effect. The signal can be reflected from buildings or mountains, coming to the receiver from different directions and with different delays. This causes distortions known as "echoes" or whistles in speakers. Directed antennas and noise reduction systems are used to combat this.
Antenna systems for VHF range
Effectiveness of working with ultrashortwave It depends on the quality and type of antenna used. Because the wavelength is small, the antenna sizes are also compact, allowing them to be installed on even small vehicles. The most popular are pin antennas (GP - Ground Plane) and directional designs of the type "Wave channel" (Yagi).
For stationary objects, such as repeaters or bases, antennas with a high gain are often used. They allow you to “break” the distance to remote correspondents. On cars, the trade-off between aerodynamics, appearance and efficiency is important. Magnetic antennas popular due to the ease of installation, but inferior to the cut-in efficiency due to the smaller area of contact with the body, which serves as a counterweight.
- 📡 Pin antennas: omnidirectional, ideal for communication with moving objects, do not require accurate guidance.
- 📡 Directional antennas: They have a narrow beam, allow you to receive weak signals from a particular direction, ignoring interference from other sides.
- 📡 Logarithmically periodic: Broadband designs covering the entire range of VHF at once are often used for monitoring.
When choosing an antenna, you need to pay attention to its resonant frequency. The antenna, tuned at 145 MHz, will operate inefficiently at 430 MHz, despite both being ultra-short wavelengths (in the broad sense of VHF/UHF).
Applications to navigation and communication
Scope of application ultrashortwave It's extremely wide. In aviation, this range is the main for voice communication of controllers with pilots. Signal stability and absence of atmospheric interference make VHF indispensable for flight safety. Navigation also relies on these frequencies to coordinate ship operations in ports and coastal waters.
In the automotive industry, VHF is used in long-range communication systems (CB-band is adjacent to VHF, but the communication of truckers often goes to 27 MHz, while taxis and delivery services use VHF / UHF). Digital TV and DAB+ broadcasting are also based on these frequencies, providing consumers with high quality media content.
Special attention should be paid to satellite navigation (GPS, GLONASS). Although the carrier frequencies of satellites are higher (L-band, about 1.5 GHz), the principles of propagation and reception of signals are much similar to classical VHF. The accuracy of positioning depends on the quality of reception of these signals.
Impact of interference and methods of protection
Despite the high noise resistance, ultrashortwave They are affected by industrial interference. Noise sources can be power lines, faulty car ignition systems, low-quality LED lamps and industrial equipment. These interferences create a “noise carpet” that can completely silence a useful signal.
To protect against interference, power filters, shielded cables and high-quality connectors are used. In the receiving technique, narrow-band filters are used, which pass only the desired frequency range, cutting off all the excess. Also effective is the use of directional antennas that physically do not "see" the source of interference if it is outside the main lobe of the directional chart.
In urban environments saturated with electronics, noise levels can be critical. Therefore, for professional work, you often have to travel out of town or use complex antenna systems with a high signal / noise ratio.
☑️ Signal reception quality check
Development prospects and future of the range
Technology is not in place, and the range ultrashortwave It's still evolving. Digitalization of broadcasting (the transition from analog FM to digital DAB+) allows more data to be transmitted with better sound quality at the same frequencies. The spectral efficiency of modern modulation techniques is increasing, allowing more channels to be placed in a limited frequency resource.
However, the congestion of the spectrum is also increasing. With the development of the Internet of Things (IoT) and wireless sensors, free frequencies are becoming less and less. Engineers have to find new trade-offs, use cognitive radio that automatically finds free frequencies, and improve signal encoding techniques.
The future lies in hybrid systems, where VHF communications are combined with satellite and cellular. This will ensure continuity of communication even in the most remote corners of the planet, where there is no coverage of mobile operators.
⚠️ Attention: Using high-powered transmitters outside the permitted ranges or without a license can result in severe fines and interference with air communications, which is a criminal offence.
Frequently Asked Questions (FAQ)
Why is FM radio bad at catching tunnels and under bridges?
Ultra-short waves propagate within line of sight and do not easily circumvent large obstacles. A tunnel or bridge creates a physical shield that blocks the radio wave’s direct path from the transmitting antenna to the receiver. Some modern tunnels have special radiating cables installed to solve this problem.
What is the difference between VHF and UHF?
Both ranges are ultrashort wavelengths. VHF (Very High Frequency) covers 30-300 MHz, while UHF (Ultra High Frequency) covers 300 MHz 3 GHz. UHF has a smaller wavelength, better penetration through building walls, but requires more complex antennas of smaller size. VHF is best distributed in open areas and in the forest.
Can I improve the reception of VHF with simple foil?
Theoretically, the foil can act as a reflector for a directional antenna, focusing the signal. However, artisanal designs often disrupt the antenna’s alignment with the feeder, resulting in the signal reflected back into the cable and the reception worsening rather than improving it. It is better to use certified amplifiers or antennas.
Does the communication range depend on the transmitter power?
Yes, increasing the power of the transmitter directly affects the communication range, but only up to a certain limit determined by the horizon of sight. After the signal rests on the horizon, further increase in power will give a slight increase in range, but improve the quality of the signal at limiting distances.