Trying to boost a weak wireless network signal often leads to a paradoxical situation: instead of the expected speed increase, the user experiences a complete loss of speed.
The reason for this result in the overwhelming majority of cases is an incorrectly selected connecting element, namely Wi-Fi antenna cable, which simply “eats up” the entire useful signal on its way to the receiver.
In this article, we'll take a detailed look at why regular "TV" cable isn't suitable for 2.4 GHz and 5 GHz frequencies, how to calculate the permissible cable length, and which connector type to choose for your router.
The Physics of the Process: Why Length Matters
At the frequencies used in wireless networks, the cable ceases to be a simple conductor and becomes a complex circuit element that introduces signal attenuation.
The higher the frequency of the transmitted signal, the more it resists passing through the conductor, turning into heat or radiating out through the screen.
For the range 2.4 GHz Losses in a cheap cable can be up to 0.5 dB per meter, which seems insignificant, but over a length of 5 meters you will lose 2.5 dB, which is equivalent to a decrease in transmitter power by half.
The situation is even more critical for the range 5 GHz, where attenuation increases almost twofold when using the same material.
⚠️ Caution: Do not attempt to use a standard terrestrial television coaxial cable (RK-75) to connect the antenna. Its internal structure is not designed for gigahertz frequencies and will act as a jammer rather than a conductor.
The main parameter to look at when choosing is attenuation, measured in decibels per 100 meters (dB/100m).
A good cable should have the lowest possible value for this parameter, but low attenuation always comes at the cost of thickness and rigidity of the product.
Basic types of cables for Wi-Fi equipment
There are many brands on the market, but in the Wi-Fi equipment industry, a few specific types of coaxial lines have become the de facto standard.
The most common and affordable option is RG-58, which often comes with cheap antennas.
Its diameter is about 5 mm, and the attenuation at 2.4 GHz reaches 30 dB at 100 meters, which makes it suitable only for very short sections of up to 1-2 meters.
A more advanced solution is RG-6, which is thicker (about 6-7 mm) and has better insulation, but even it is not ideal for professional use.
The gold standard for building outdoor links and connecting powerful antennas is considered to be a cable of the type LMR-400 (or its analogues like Ecoflex-10).
Its diameter is 10.3 mm, which provides excellent protection against losses - only about 20 dB at 100 meters for the 2.4 GHz frequency.
However, due to its thickness and rigidity LMR-400 It is difficult to install in hard to reach places and requires the use of specialized N-type connectors.
- 📡 RG-58 — a budget solution for patch cords up to 1 meter long, flexible and inexpensive.
- 🏠 RG-6 — a compromise option for indoor antennas, but not suitable for long outdoor routes.
- 🚀 LMR-400 — a professional choice for lines from 3 to 15 meters long with minimal losses.
- 🔌 Ecoflex-10 — European analogue of LMR-400, often used in Ubiquiti and MikroTik equipment.
Table of signal losses depending on length
To make a final decision, you need to calculate the losses for your specific situation.
Below are the average signal attenuation data at 2.4 GHz for popular cable types.
Please note that for 5 GHz the loss values will be approximately 30-40% higher.
| Cable type | Diameter | Loss (dB/100m) | Max. length (without critical losses) | Application |
|---|---|---|---|---|
| RG-58 | 5.0 mm | ~30 dB | up to 2 meters | Internal patch cords |
| RG-6 | 6.6 mm | ~22 dB | up to 3-4 meters | Short indoor connections |
| LMR-240 | 6.1 mm | ~18 dB | up to 5 meters | Flexible jumper cables |
| LMR-400 | 10.3 mm | ~8 dB | up to 15 meters | Main street lines |
| LMR-600 | 15.0 mm | ~5 dB | up to 25 meters | Base stations and powerful links |
As can be seen from the table, the use of cable RG-58 A 5 meter long cable will result in a 1.5 dB signal loss, which may not be noticeable, but 10 meters of such a cable will “kill” the signal almost completely.
That is why for distances over 3 meters The only reasonable choice is a cable of the LMR-400 type or its direct analogues.
Connectors and impedance matching
No less important an aspect than the cable itself are the connectors with which it is terminated.
In the world of Wi-Fi equipment, the impedance standard is 50 Ohm, and all components of the circuit must comply with this value.
Using 75 ohm connectors (commonly used in television equipment) will result in mismatch, standing waves, and signal reflection back into the transmitter, which may even damage the router.
The most common types of connectors are:
- 🔩 SMA — the most popular connector for home routers and access points, has a thread.
- 🔌 RP-SMA — a variation of SMA with reversed contacts (needle in socket), often found on TP-Link and D-Link equipment.
- 🏗️ N-Type - a large, sealed connector used for outdoor antennas and thick LMR-400 cables.
- 📶 TNC — a threaded analogue of BNC, less common, mainly in industrial equipment.
⚠️ Important: When purchasing adapters or ready-made cables, carefully check the connector markings. SMA and RP-SMA connectors are visually almost identical, but are physically incompatible without an adapter, as they have different center pin locations.
For connecting thick trunk cable LMR-400 A pigtail (short adapter) is often used with a router with an SMA connector.
On one side it has an N-type (male) connector for connecting to a cable, and on the other side it has an SMA (male) connector for a router.
Try to minimize the number of such transitions, since each connection introduces additional losses of 0.1-0.3 dB.
What is VSWR and why is it important?
The standing wave ratio (VSWR) indicates how well the cable, connector, and antenna are matched. The ideal value is 1.0. If the VSWR is higher than 1.5, some energy is being reflected back. Poor matching (VSWR > 2.0) can lead to overheating and failure of your router's power amplifier.
Calculation of length and installation of the line
When planning your antenna installation, always aim to keep the cable as short as possible.
If it's possible to move the router closer to a window or antenna installation location, it's better to do so than to run a 15-meter-long expensive cable.
Optimal length for cable RG-58 does not exceed 1 meter, for LMR-400 — up to 10-15 meters without significant loss of quality.
When laying cables, observe the following rules:
- Do not bend the cable at a sharp angle (bending radius not less than 10 cable diameters).
- Avoid proximity to sources of strong electromagnetic fields (power lines, transformers).
- For outdoor installations, use cable with a UV-resistant polyethylene (PE) sheath, not PVC, which will crack in the cold.
☑️ Check before installation
Use electrical tape or special heat shrink tubing to seal the joints between the connector and the cable.
Water entering the coaxial cable instantly changes its wave impedance and leads to complete attenuation of the signal.
Common mistakes when choosing and installing
One of the most common mistakes is buying a ready-made "antenna" cable on the market without specifying its characteristics.
Sellers often offer thin black wire, claiming it is "reinforced", although inside it may be a steel core with poor shielding.
Such a cable at a frequency of 2.4 GHz will perform worse than no antenna at all, as it will add noise and losses.
⚠️ Important: If you're using an active antenna (with a built-in amplifier), make sure your router or switch supports power over Ethernet (PoE or Voltage Injector). Without power, this antenna won't work.
Another mistake is ignoring the quality of the connectors.
Cheap connectors can oxidize within one season, especially in outdoor conditions, resulting in a sharp drop in signal strength.
Give preference to connectors with gold-plated contacts and reliable threads.
Also, don't forget about mechanical strength.
Thin cables may not be able to withstand wind loads or tension, so for outdoor applications they must be secured to a supporting cable or mast using plastic ties.
Final choice and recommendations
Choosing a cable for a Wi-Fi antenna is always a balancing act between signal attenuation, cost, and ease of installation.
For interior work and short connections up to 1 meter, a high-quality one is quite suitable RG-58 or RG-174.
If you plan to install the antenna on a roof or mast, you can't skimp on cable: signal loss here will cost you all your network performance.
Always check your hardware specifications: some proprietary routers may require non-standard connector types.
A properly selected cable will ensure a stable connection and allow the antenna to reach its full potential.
Is it possible to extend the cable?
Extending a coaxial cable for Wi-Fi is highly undesirable. Each additional connection (joint) introduces losses and degrades the characteristic impedance. It's better to buy or make a new cable of the required length than to connect two pieces using an adapter.
FAQ: Frequently Asked Questions
Can you use a regular TV cable for Wi-Fi?
This is strongly discouraged. TV cable (RG-6, 75 ohms) has a different impedance than Wi-Fi equipment (50 ohms). This will lead to signal mismatch, signal reflection, and a loss of up to 30-50% of power, and may also damage the router's transmitter.
What is the maximum cable length for a Wi-Fi antenna?
For RG-58 cable, the maximum effective length is 1-2 meters. For LMR-400, it's up to 10-15 meters. Exceeding these values will result in cable losses exceeding the gain from installing the antenna.
What is the difference between SMA and RP-SMA?
The difference is in the contact arrangement. In SMA, the male connector has a pin in the center, and the female connector has a socket. In RP-SMA (Reverse Polarity), this is reversed: the male connector has a socket, and the female connector has a pin. They are not directly compatible without an adapter.
Do outdoor antennas need to be grounded?
Yes, if the antenna is installed higher than surrounding objects or in a lightning-prone region, grounding the mast and using lightning protection in the cable break is mandatory for the safety of equipment and people.