The situation where an internet provider only extends fiber optic cable to the property line or the roof of a building, but the signal is lost within the building itself, is familiar to many. The solution to this problem is wireless data transmission technology, known as WiFi radio bridgeIt's not magic, but a complex engineering process that allows gigabits of information to be transmitted over the air without loss of quality.
The operating principle is based on the conversion of electrical signals into electromagnetic waves of a specific frequency. Two antennas pointed at each other create a virtual cable, which is physically impossible to break without interfering with the line of sight. Understanding the physics of this process will help you avoid common mistakes during equipment installation.
Physical principles of wireless communication
Any radio channel is based on the use of radio waves, which are part of the electromagnetic spectrum. The 802.11n, ac, and ax WiFi standards use the 2.4 GHz and 5 GHz frequency bands. These waves propagate through space at a specific speed, close to the speed of light, but their behavior is highly dependent on obstacles and the atmosphere.
The key parameter is wavelength, which is inversely proportional to frequency. The higher the frequency (for example, 5 GHz), the shorter the wavelength and the more the signal attenuates when passing through obstacles, but the more data can be transmitted per unit of time. This is why 5 GHz bridges require perfect line-of-sight, while 2.4 GHz bridges are more penetrating but slower.
There is also a concept Fresnel zoneThis is the ellipsoid of space between the transmitting and receiving antennas. For stable channel operation, this zone must be at least 60% free of obstacles (trees, buildings). If a tree branch encroaches on this zone, the signal will be reflected and interfere, causing a drop in speed.
⚠️ Caution: Metal structures, siding, and even wet foliage can completely block the signal. Make sure the beam path is clear not only visually but also within the Fresnel zone.
Transmitter power and receiver sensitivity determine the link's range. However, blindly increasing power isn't always effective, as it can lead to receiver saturation and signal distortion. A balance between transmit power and antenna quality is the key to success.
Equipment operating modes: Point-to-Point and Point-to-Multipoint
When designing a network, it's important to choose the right topology. The most common and stable option is the Point-to-Point (PtP)In this setup, one device operates as an Access Point (AP), emitting a signal, and the other operates as a Station (Client), receiving it. This ensures maximum throughput, as the entire airtime resource is shared between just two devices.
If it is necessary to distribute the Internet from one tower to several houses, the mode is used Point-to-Multipoint (PtMP)Here, a single, powerful base station (AP) broadcasts to a sector antenna, and client devices are installed in homes. In this mode, the speed is divided among all connected clients, and the more clients there are, the less each one gets.
- 📡 PtP: Ideal for connecting two buildings, maximum speed and stability.
- 🏘️ PtMP: Suitable for providers distributing Internet throughout the village.
- 🔄 WDS/Mesh: Modes for expanding coverage inside the perimeter are less stable for external bridges.
Modern equipment, for example, from Ubiquiti or MikroTik, often has proprietary protocols that improve point-to-multipoint operation by dynamically allocating transmission time (TDMA). This avoids collisions when multiple clients attempt to communicate simultaneously.
Frequency range selection and the influence of interference
The 2.4 GHz band has historically been the busiest. It's used not only by neighbors' WiFi routers, but also by Bluetooth devices, baby monitors, microwave ovens, and wireless CCTV cameras. Using this band for a backbone connection is only worthwhile in dire straits or over very short distances.
The 5 GHz band offers significantly more clear channels and lower noise levels. Channel widths can reach 40, 80, and even 160 MHz, which is critical for high speeds. However, as mentioned earlier, 5 GHz is less able to bypass obstacles and is more susceptible to absorption by rain.
There's also the 60 GHz band (the WiGig standard), which offers incredible speeds but only works over very short distances (up to 200-300 meters) and is vulnerable even to dense fog. Choosing a frequency is always a compromise between range, speed, and airborne noise.
| Parameter | 2.4 GHz | 5 GHz | 60 GHz |
|---|---|---|---|
| Range | High | Average | Low |
| Penetration | Good | Bad | Absent |
| Speed | Low | High | Very high |
| Interference | Many | Moderately | Minimum |
When setting up equipment, it's necessary to conduct a site survey. Many modern access points have a built-in spectrum analyzer that displays channel occupancy in real time. Ignoring the spectrum analysis stage is the main reason for unstable operation of radio bridges in multi-apartment areas.
What is signal polarization?
Polarization is the orientation of an electromagnetic wave in space. The antennas at both ends of the bridge must have the same polarization (vertical or horizontal). If one antenna is rotated 90 degrees relative to the other, the signal will be almost completely lost (losses of up to 20-30 dB).
Mounting and adjusting antennas
The success of establishing a radio link depends 90% on the quality of installation. Antennas must be firmly secured to masts or brackets to prevent them from swaying in the wind. Even the slightest movement of a highly directional antenna can lead to a broken connection.
The process of adjusting the antenna's direction is called alignment. Professional equipment has signal strength (RSSI) LEDs directly on the body, which light green when perfectly aligned. If this isn't possible, a second person will be required to monitor the signal strength in the web interface via a radio or phone.
- 🔩 Use stainless steel fasteners and lightning rods.
- 🌧️ Seal all connectors with self-absorbing tape.
- 📏 Keep your distance from metal surfaces (at least 1 meter).
The cable route is also important. The longer the cable between the antenna and the switch, the greater the attenuation. For WiFi, it's best to use low-attenuation cable (such as RG-6 or specialized copper-clad Ethernet cable if the length is short) and keep it as short as possible.
⚠️ Caution: Before ascending to a height, check the completeness and functionality of the equipment on the ground. Descending to replace a forgotten patch cord is a waste of time and a safety risk.
☑️ Check before installation
Setting up network equipment
After physical installation, comes the logical configuration phase. First, you need to change the default IP addresses of your devices so they are on the same subnet as your computer but don't conflict with the main network. Static addressing is typically used for bridges.
In the device interface (often this is 192.168.0.1 or 192.168.1.1) you need to select the operating mode. For the side where the Internet is, set Access Point (or Bridge AP), for the remote side - Station (or Client). It's important to disable the DHCP server on the client side so that the main router distributes addresses.
Example of static IP for a bridge:IP: 192.168.88.2
Mask: 255.255.255.0
Gateway: 192.168.88.1
Pay special attention to security. Be sure to enable encryption. WPA2-AES or WPA3An open radio channel is a security hole in your local network. The password should be complex, as it would be easy for an attacker to intercept the WiFi handshake.
It's also worth disabling unnecessary services (Telnet, HTTP if HTTPS is available) and changing the default management ports. Some administrators recommend isolating the radio bridge in a separate VLAN to prevent an attacker from gaining access to the internal network if the equipment is compromised.
Diagnostics and troubleshooting
Even a perfectly configured bridge can malfunction. The first indicator of problems is the parameter CCQ (Client Connection Quality) or similar metrics depending on the vendor. It indicates the percentage of useful transmission time. If CCQ falls below 80-90%, it indicates interference or reflection issues.
A common problem is equipment "sticking." Radio modules can overheat or accumulate errors in the buffer. This can be solved by setting a reboot schedule, for example, once a week at night. This is standard practice for telecommunications equipment.
If your speed has dropped sharply, check to see if a tree has grown in the beam's path or if a new building has appeared. Seasonal changes (leaves in summer, bare branches in winter) can affect signal transmission, especially at 5 GHz.
In challenging noisy environments, changing the channel width can help. Narrowing the channel from 40 MHz to 20 MHz will reduce the maximum speed but improve the signal-to-noise ratio, making the channel more stable.
What is the maximum range of a WiFi radio bridge?
Theoretically, directional antennas can extend a link 50-80 km. However, in practice, for stable operation without repeaters, it is recommended not to exceed a distance of 10-15 km for the 5 GHz band and 3-5 km for 2.4 GHz due to the curvature of the earth's surface and the Fresnel zone.
Does the antenna need to be grounded?
Yes, mast grounding and lightning protection are essential. A rooftop antenna is an ideal lightning rod. Even if lightning strikes indirectly, the induced voltage can burn out expensive equipment. Use special Ethernet surge protectors.
Is it possible to connect three dots into a line?
WDS mode allows connecting multiple access points, but this reduces the overall channel throughput proportionally to the number of hops. For three access points, it's better to use a star configuration with a central base station or set up a separate bridge between the remote access points.