Creating a wireless communication system over a distance of 10 kilometers is an ambitious task, requiring precise engineering calculations and high-quality materials. Standard household routers are unable to provide a stable channel over such a distance without the use of specialized equipment. directional equipmentIn this article, we will examine the process of creating a highly efficient antenna system capable of creating an air bridge between two points.
To implement this project, it's essential to understand the physics of radio wave propagation in the 2.4 GHz band. At distances greater than 5 km, not only the gain becomes critical, but also signal purity, as well as the absence of interference. Homemade designs can be more cost-effective than factory-made counterparts, but require strict adherence to geometry.
The team of authors has prepared a detailed guide based on proven designs for Bi-Quad antennas and parabolic reflectors. We'll cover every step, from purchasing materials to final beam alignment. Keep in mind that even minimal dimensional deviations can reduce the device's efficiency by 30-40%.
Theoretical foundations and design choice
Before you start soldering, you need to decide on the antenna type. For a distance of 10 km, the optimal solution is to use parabolic antenna or "double square" designs with a reflector. These devices have a narrow beam pattern, allowing energy to be concentrated in a narrow beam, penetrating distances.
The key parameter is gainFor reliable reception at 10 km in line-of-sight conditions, you'll need an antenna with a gain of at least 15-18 dBi. Standard whip antennas are useless here, as their signal dissipates in all directions.
⚠️ Warning: Using homemade power amplifiers may violate the laws of your country. Make sure the final EIIM (equivalent isotropically radiated power) does not exceed the permitted limits (usually 100 mW or 20 dBi in total).
There are several popular designs that have proven effective in the field. The choice depends on the materials and tools available.
- 📡 Bi-Quad: Easy to manufacture, requires minimal soldering, and is easy to configure.
- 📡 Parabolic (Offset): Uses a satellite dish as a reflector, providing maximum gain.
- 📡 Wave channel (Yagi): Difficult to fine tune at 2.4GHz, but has excellent directionality.
Necessary materials and tools
Assembly quality directly impacts the result. Using oxidized wires or inappropriate solder will result in signal loss at the antenna input. The main component is a copper wire with a diameter of 2-3 mm. Aluminum is not recommended, as it is difficult to properly weld. tin and solder.
A sheet of galvanized iron, aluminum, or even the bottom of an old saucepan with a diameter greater than 20 cm is ideal for creating a reflector. The larger the reflector's surface area, the better it focuses the signal. You will also need coaxial cable low-attenuation cable such as RG-6 or RG-58, but a dedicated 50-ohm WiFi cable is better.
☑️ Shopping list
The instrumentation should be standard for a radio amateur. A caliper is critical, as the dimensions of the components are measured in millimeters. An error of 1 mm at 2.4 GHz can shift the resonant frequency.
- 🔧 A soldering iron with a power of 40-60 W for good heating of copper.
- 🔧 Calipers or precision ruler.
- 🔧 Metal hacksaw or wire cutters.
- 🔧 Sandpaper for cleaning contacts.
Calculating the Bi-Quad Antenna Geometry
A Bi-Quad antenna consists of two squares joined at the center. The length of the square's side is calculated based on the signal's wavelength. For a frequency of 2.4 GHz (centered at 2440 MHz), the wavelength is approximately 123 mm. The side of the square is equal to a quarter of the wavelength.
Formula for calculating the side of a square: L = 71 / f (GHz)For 2.4 GHz, the square side should be approximately 30-31 mm. The distance between the conductor and the reflector is also critical and should be 0.25 * λ, that is, about 31 mm. Compliance with these dimensions ensures resonance systems.
Exact dimensions for 2440 MHz frequency
Square side: 30.5 mm | Reflector distance: 15-16 mm (for single) or 31 mm (for double) | Wire diameter: 2-3 mm | Reflector height: not less than 120x120 mm
To connect the cable, a method called "gamma matching" or direct connection to the center of the structure is used. The cable core is soldered to one corner of the square, and the braid is soldered to the opposite corner (or to the center of the jumper, depending on the circuit modification). It is important to ensure symmetry so that SWR (standing wave ratio) was minimal.
| Parameter | Value for 2.4 GHz | Admission | Impact on signal |
|---|---|---|---|
| Side of a square | 30.5 mm | ±1 mm | Resonance frequency shift |
| Distance to reflector | 31 mm | ±2 mm | SWR and diagram shape |
| Wire diameter | 2.0 - 3.0 mm | ±0.5 mm | Bandwidth |
| Reflector size | 120x120 mm | minimum | Side lobe level |
Assembly and soldering process
Start by preparing the reflector. If you're using sheet copper or steel, cut it into a square at least 12 cm on a side. The surface must be flat. If using mesh, the mesh size must be small, significantly smaller than the wavelength (less than 1 cm), otherwise the signal will pass through.
Next, bend the copper wire into two squares. At the point where the wires intersect (the center of the structure), they should be crossed, but not electrically connected at a single point if the circuit requires a break. Most often, the wire is bent into a figure-eight shape, and the ends are soldered. The cable connection point (the power point) should be thoroughly stripped.
⚠️ Caution: When soldering large-diameter copper wire, heat dissipates very quickly. Use a powerful soldering iron and active flux to ensure the solder penetrates the joint, rather than just dripping on top. Cold soldering will create nonlinear distortions.
The cable is connected as follows: the central core is soldered to one of the corners (or the center of the jumper), and the shielding braid is soldered to the other arm of the vibrator. The cable length from the connection point to the router should be as short as necessary, as each meter of cable introduces attenuation. For 10 meters of standard cable, losses can reach 3-5 dB, significantly reducing the range.
Weather protection
An antenna mounted on a mast is exposed to rain, snow, ultraviolet radiation, and temperature fluctuations. Copper oxidizes, which reduces conductivity and alters resonant properties. The plastic used to enclose the antenna should be radio-transparent (polypropylene, polyethylene).
The ideal enclosure is a plastic electrical box or a section of sewer pipe. The main thing is to avoid metallized materials. All joints should be sealed with silicone sealant. You can place a bag of silica gelto prevent condensation.
The antenna must be securely attached to the mast. At a height of 10-15 meters, the wind creates significant windage. If the antenna sways, the connection at a distance of 10 km will be constantly lost. Use stainless steel or galvanized clamps.
Setting up and adjusting the link
The most difficult step is pointing the antennas at each other. At a distance of 10 km, the Earth's surface appears flat, but it is necessary to take into account curvature of the Earth and obstacles. The Fresnel zone (the ellipsoid of space between the antennas) must be at least 60% free of trees and buildings.
To set it up, use a laptop with signal strength monitoring software installed (such as inSSIDer or the router's built-in utilities). Connect the antenna, turn on the router, and slowly rotate the antenna. Signal strength (RSSI) changes will be very sharp due to the narrow beam pattern.
Move the antenna horizontally and vertically in 1-2 degree increments, pausing to update the statistics. Once you find the point of maximum signal, secure the mounting brackets. If the signal is weak, check the polarization: the antennas at both ends of the line should be oriented the same way (vertically or horizontally).
What to do if the signal is unstable?
Instability may be caused by interference from other WiFi networks, radar, or microwave ovens. Try changing the channel in your router settings to a less crowded one (1, 6, or 11). Also, check that the beam isn't hitting a metal object that creates a reflected wave.
Can this antenna be used for 5GHz?
Yes, the principle is the same, but the dimensions need to be halved. For 5 GHz, the square side will be about 15 mm. However, cable loss at 5 GHz is significantly higher, so use only high-quality cable.
Which cable is best for 10 meters?
For long runs, use low-attenuation cable, such as LMR-400 or similar cables (5D-FB, 8D-FB). Regular thin RG-58 cable will eat up most of the antenna at such lengths.
Do you need a signal booster?
With a properly assembled antenna with a gain of 15-20 dBi and sensitive modern routers, an additional amplifier (PA) is often unnecessary and can even worsen the situation by introducing noise. First, maximize gain with a passive antenna.