Many users face situations where their router is located far from the location where stable internet is needed, or the signal in a particular room is too weak for comfortable operation. The solution often involves installing an external directional or omnidirectional antenna, which can pick up the signal in places where standard devices fail. However, even the most powerful and expensive antenna will not work effectively if it is connected to the router using the wrong cable.
In this article, we'll take a detailed look at the technical nuances that affect connection quality. You'll learn why length matters, the differences between insulation types, and how to correctly calculate signal loss in decibels. Understanding the physics of radio wave propagation will help you avoid common installation mistakes and save money on purchasing the components you really need.
We won't delve into complex mathematics, but we will examine the key parameters to pay attention to in a store or when ordering components. Coaxial cable It's not just a cable, but a complex engineering structure whose quality determines your internet speed. Let's determine exactly what you'll need to create a reliable signal reception system.
Why Cable Selection Is Critical for Wi-Fi
At the frequencies at which Wi-Fi operates (2.4 GHz and 5 GHz), radio signals behave differently than in low-frequency circuits. Any transmission line connecting the receiver and the transmitter introduces attenuation. Signal attenuation It is measured in decibels per meter of length and directly depends on the quality of the cable and its diameter.
If you choose a wire that's too thin or cheap, most of the energy gained by the antenna will simply be dissipated as heat within the braid and core before it reaches the router's circuit board. As a result, you may end up with a worse internet connection with an antenna than without one, simply because the loss over the length exceeds the antenna's gain.
Impedance matching is also important to consider. The standard for Wi-Fi equipment is 50 ohms. Using a cable with 75 ohms (often used in TV antennas) will create a mismatch, and some of the signal will be reflected back into the antenna, creating standing waves and distorting the transmitter.
Basic types of coaxial cables for radio frequencies
There are many brands on the market, but not all are suitable for Wi-Fi signal boosting. The main differences lie in the diameter of the central core, the dielectric material, and the quality of the shielding braid. Coaxial cable consists of a central copper core, insulation, screen and outer sheath.
The most popular standard in the world of professional equipment is the RG (Radio Grade) series. However, there are significant differences within this series. For example, RG-58 is often used in radios, but for Wi-Fi, it is already considered a compromise solution due to relatively high losses at gigahertz frequencies.
For fixed antennas and long cable runs, experts recommend using low-attenuation cables. These have a larger diameter and often use foamed polyethylene as a dielectric, which reduces dielectric loss. LMR cables (for example, LMR-200, LMR-400) are a modern analogue of RG and show significantly better results.
- 📡 RG-58 - thin cable, suitable only for very short connections (up to 1-2 meters), high losses.
- 📡 RG-213 / LMR-400 - thick, rigid cable with minimal attenuation, ideal for outdoor applications.
- 📡 LMR-200 / RG-8X — a compromise option, more flexible than thicker counterparts, but with higher losses, good for indoor installation.
- 📡 RG-6 - TV cable, strongly not recommended for Wi-Fi due to 75 Ohm resistance and high losses.
When choosing between flexibility and attenuation, it's always best to prioritize the latter if the cable runs longer than 3 meters. Rigid cable is more difficult to install, but it will ensure stable speeds.
The Silver Plating Myth
Is it worth paying extra for a silver-plated core? At Wi-Fi frequencies, the skin effect (current displacement to the surface of the conductor) already occurs, but in small-diameter copper cables, the benefit of silver is minimal compared to increasing the copper core diameter. It's better to use thicker copper than thinner silver.
Calculation of attenuation and the influence of path length
Cable length is the enemy of signal. The longer the cable, the more decibels it "eats." It's important to understand that attenuation is nonlinear with frequency: at 5 GHz, losses will be approximately 1.5 times higher than at 2.4 GHz for the same cable.
If you plan to install an antenna on a roof or a tall mast, every extra meter must be justified. Using a signal booster between the antenna and the cable is possible, but it requires power and proper configuration; otherwise, you could overload the router's input. It's simpler and more reliable to choose a cable with a lower attenuation coefficient.
⚠️ Attention: Don't try to extend the cable using twisted cables or cheap adapters. Each connection introduces additional loss (approximately 0.2-0.5 dB for a high-quality connector) and compromises the cable's integrity.
Let's look at a comparative attenuation table for popular cable types at 2.4 GHz. The numbers show how many decibels of signal are lost for every 10 meters of length.
| Cable type | Diameter (mm) | Attenuation (dB/10m) | Recommended length |
|---|---|---|---|
| RG-58 | 5.0 | ~22 dB | up to 2 meters |
| LMR-200 (RG-8X) | 6.1 | ~12 dB | up to 5 meters |
| LMR-400 (RG-213) | 10.3 | ~6 dB | up to 15 meters |
| Heliax (Corrugated) | 12.0+ | ~3-4 dB | professional lines |
As the data shows, using RG-58 cable 5 meters long will turn a powerful antenna into a useless piece of metal, absorbing almost 99% of the signal. Therefore, it's best not to use it for outdoor antennas thinner than 7-8 mm.
Connectors and connection methods
The connector type determines compatibility with your router or access point. In the Wi-Fi world, the most common standard is SMA (SubMiniature version A). However, there's an important nuance here: connectors come with internal (Female) and external (Male) threads, and with or without a pin (Pin).
Routers typically use SMA-Female connectors (a female connector with a threaded connector on the inside), while antennas use SMA-Male connectors (a male connector with a threaded connector on the outside). The cable must have the corresponding mating connectors. Confusion between connector types (RP-SMA) often results in physical connection failure or damage to the central pin.
The quality of the soldering or crimping of the connector is critical. If the center conductor is loose or the shield is poorly pressed, parasitic inductance will occur, which will degrade the SWR (standing wave ratio). A high SWR means the signal is reflected back to the transmitter, which can lead to overheating and failure of the router's Wi-Fi module.
- 🔌 SMA - standard connector, thread on the outside of the socket.
- 🔌 RP-SMA — a connector with reversed polarity, the needle is on the socket, and the hole is on the pin (often in TP-Link, D-Link routers).
- 🔌 N-Type — a large sealed connector used in professional outdoor equipment.
- 🔌 TNC — a threaded connection with vibration protection, less common in everyday life.
⚠️ Attention: Never twist the connector by the cable itself. This will cause the central conductor to separate from the connector. Always grasp the metal part of the connector when tightening.
For making pigtails (short adapters) yourself, it's best to use ready-made factory-made products. It's virtually impossible to crimp LMR-400 cables properly at home without specialized tools (crimper and stripper).
Sealing and protection of street lines
If a cable is installed outdoors, it is exposed to harsh environmental conditions: ultraviolet radiation, rain, and temperature fluctuations. Regular PVC insulation cracks over time, allowing moisture to penetrate. Water in a coaxial cable changes its characteristic impedance and dramatically increases attenuation.
For external work it is necessary to use a cable with insulation made of polyethylene (PE), which is UV-resistant. It is usually black. The white cable is intended for indoor use only.
Cable entry points into equipment and joints must be sealed. The best solution is to use special self-absorbing tape. When heated, it turns into a viscous mass, completely filling the voids and blocking water penetration. Regular duct tape or electrical tape won't work here—they'll peel off within a season.
☑️ Street route inspection
It's also important to install a so-called "drip loop." Before entering the building, the cable should have a downward sag so that water drains from the lowest point and doesn't flow into the building or into the antenna connector.
Common installation mistakes
Even if you choose the right cable, improper installation can ruin everything. One of the most common mistakes is laying the cable near sources of interference. Power lines, transformers, and fluorescent lamps create electromagnetic fields that are induced on the cable shield.
Although the shielding in good cables (double shield: foil + braid) is quite effective, this rule should not be neglected. Avoid running Wi-Fi cables parallel to 220V wires at a distance of less than 20-30 cm. If crossings are unavoidable, run them at right angles.
Another mistake is excessive bending. Coaxial cable has a minimum bending radius (usually 10 times its outer diameter). If you bend thick LMR-400 cable at an acute angle, the internal structure will be damaged, the central core will shift relative to the shield, and the line parameters will change.
- 🚫 Tension — the cable must not be stretched like a string; it must lie freely or be attached with a sag.
- 🚫 Metal clamps — do not squeeze the cable with metal ties, use plastic clips or tapes.
- 🚫 Sharp edges - When passing through walls, be sure to use sleeves or corrugated pipes to avoid cutting the braid.
⚠️ Attention: Material specifications and operator requirements may change. Before purchasing a large quantity of cable, consult the equipment manufacturer's current specifications or official recommendations.
Following these simple rules will allow the system you create to work for years without having to climb onto the roof to replace a cable that has burned out from static or gotten wet.
Can you use a regular TV cable for Wi-Fi?
Technically, it's possible to connect them, but the results will be disastrous. TV cable (RG-6) has a characteristic impedance of 75 ohms, while Wi-Fi equipment is designed for 50 ohms. This mismatch will lead to signal reflection and loss. Furthermore, TV attenuation at 2.4 GHz frequencies is very high. Use only specialized 50 ohm cables.
What is the maximum cable length allowed without an amplifier?
For high-quality LMR-400 cable, the permissible length without noticeable signal degradation is up to 15-20 meters. For thinner cables (LMR-200), this limit is reduced to 5-7 meters. If greater length is required, it is necessary to elevate the access point (router) closer to the antenna and install twisted pair cable (Ethernet), which has no such limitations.
Does cable color affect signal quality?
The insulation color itself doesn't affect the electrical properties of the signal inside. However, color is important for operating conditions. Black cable contains additives that protect against ultraviolet radiation and is intended for outdoor use. White cable will quickly crack in the sun, moisture will penetrate, and the signal will be lost. Therefore, only black cable is suitable for outdoor use; any cable is suitable for indoor use.