Modern users rarely consider the physics of radio waves until their internet service starts lagging at the most inopportune moment. Low speeds are often caused not by the internet provider, but by simple signal attenuation on the way from the router to your device. To understand the real situation, it's not enough to look at the number of bars in the corner of your smartphone screen, as this indicator is extremely inaccurate and subjective.
To obtain objective data, it is necessary to measure the power level of the received signal in logarithmic units dBm (decibels relative to milliwatts). This parameter allows engineers and advanced users to accurately determine the location of "dead zones" and how efficiently an access point is operating. Unlike abstract icons, the numerical value provides a clear indication of connection quality.
In this article, we'll discuss how to properly take measurements, which tools to use for different operating systems, and how to interpret the results. You'll learn to distinguish between normal and critical signal levels and understand when it's time to relocate your router or purchase an amplifier.
Understanding units of measurement and ranges
Before we begin practical measurements, it's important to understand the scale we'll use to evaluate connection quality. WiFi signal strength is measured in negative decibel-milliwatt (dBm) units. This may seem strange, but the closer the value is to zero, the stronger the signal. For example, -40 dBm is significantly stronger and better than -80 dBm.
The signal transmitted by the router usually has a power of about 20 dBm (100 mW), but when passing through walls, furniture and other obstacles, it quickly loses its energy. Attenuation This occurs for various reasons: concrete walls absorb radio waves more strongly than drywall, while metal structures can completely block the signal. Therefore, the reading in the far room can drop to critical levels.
It is important to understand the difference between the 2.4 GHz and 5 GHz frequency ranges. Range 2.4 GHz has better penetration ability, but is often overloaded by neighboring routers and household appliances. The range 5 GHz Provides higher speeds, but its signal attenuates faster when passing through obstacles. Measurements must be taken separately for each network.
⚠️ Attention: Don't confuse signal strength (RSSI) with channel bandwidth or connection speed. A high data plan won't help if the physical signal strength is too weak to support stable modulation.
Below is a table to help you classify the values obtained during measurements:
| Value (dBm) | Signal quality | Description of the situation |
|---|---|---|
| -30 ... -50 | Excellent | The device is located in close proximity to the router. |
| -51 ... -60 | Good | Stable operation, high speed, typical for one room. |
| -61 ... -70 | Average | Short-term speed drops are possible, suitable for web surfing. |
| -71 ... -80 | Bad | Unstable connection, possible interruptions, video may buffer. |
| -81 ... -90 | Critical | There is a connection, but data transfer is almost impossible. |
Measurement on smartphones and tablets (Android and iOS)
Mobile devices are the most accessible tool for initial WiFi network diagnostics. However, default operating system settings often hide precise technical data, displaying only a graphical indicator. For detailed information, specialized apps are required.
On the platform Android The situation is most favorable. The system provides apps with broad access to the WiFi module, allowing them to see not only the current signal strength but also a list of all available networks with their channels and frequencies. A popular and free tool is WiFi Analyzer or WiFi Man from Ubiquiti. These programs display a real-time graph, allowing you to walk around your apartment and observe how the signal level changes.
For users iOS (iPhone, iPad) are less fortunate due to Apple's security restrictions. Third-party apps from the App Store are not allowed to display the exact signal strength in dBm for the currently connected network in a convenient format. The only legal way to obtain this data is through the hidden engineering menu.
How to enable the engineering menu on iPhone
Go to the App Store and download the AirPort app (without launching it). Then open the Compass app and press and hold the center of the screen for a few seconds. A hidden Field Test Mode menu will appear. Look for the RSSI parameter or measure it using third-party scanners by connecting the device to a PC.
When taking measurements with your phone, it's important to hold the device in one hand and avoid covering the antenna area (usually the top or bottom of the phone) with your palm. The human body also absorbs radio waves, so the results may be distorted if you constantly change the position of your smartphone.
Diagnosing WiFi on Windows computers
The Windows operating system also hides detailed wireless connection parameters from the average user, but provides powerful built-in command-line tools. You don't need to download third-party software to get basic signal strength information.
The fastest way to find out your current signal strength is to use the command line. Press the key combination Win + R, enter cmd and press Enter. In the window that opens, enter the command:
netsh wlan show interfacesIn the list that appears, find the "Signal" line. It will be displayed as a percentage. While it's not in dBm, the conversion is fairly straightforward: 100% corresponds to approximately -50 dBm and above, and 0% corresponds to -90 dBm and below. For a more in-depth analysis, you can use third-party utilities such as Acrylic Wi-Fi Home or inSSIDer.
These programs create heat maps and graphs showing not only your signal strength but also the noise floor. SNR Signal-to-noise ratio (SNR) is a critical parameter. Even a strong signal is useless if the noise level in the air is even higher, which is often the case in apartment buildings.
☑️ Check WiFi on Windows
When using a laptop for measurements, ensure you don't shield the antenna with your body. Built-in antennas in laptops are often located around the screen or on the bottom of the case. Rotating the device 90 degrees can change the reading by several decibels.
Professional methods and equipment
When setting up a network in an office, a large home, or a public space, amateur methods may not be enough. Professionals use specialized equipment to create precise heatmaps. This allows you to visualize coverage and identify areas where the signal is reflected or absorbed.
For such tasks, external WiFi adapters with the ability to connect an external antenna and a monitoring mode are used. Chip-based adapters are an example. Atheros or Ralink, which support packet injection and detailed traffic analysis. Standard USB dongles often have weak antennas and don't provide a complete picture.
There are also portable spectrum analyzers, which look like small tablets with antennas. They can distinguish WiFi signals from interference generated by microwave ovens, Bluetooth devices, or baby monitors. This equipment is expensive, but essential for complex diagnostics.
⚠️ Attention: The interfaces of professional software (such as Ekahau or AirMagnet) may change with the release of new versions. Always consult the software manufacturer's official documentation for up-to-date calibration instructions.
When conducting a professional audit, it's important to consider not only horizontal signal propagation but also vertical signal propagation. A router's signal propagates in a donut-shaped (toroidal) pattern, so coverage above and below the router is often worse than to the sides.
Factors affecting measurement accuracy
The resulting figures are not constant. WiFi signal strength is dynamic and can change every second. This is influenced by many factors that need to be kept in mind when interpreting the data. If you see fluctuations in the values, this doesn't necessarily indicate a hardware malfunction.
One of the main causes of fluctuations is multipath propagation. The signal reflects off walls, mirrors, floors, and furniture, creating interference. At one point in the room, the direct and reflected signals can combine, amplifying each other, while at a neighboring point (10 cm away), they cancel each other out. Therefore, measurements should be taken on average, staying in the same area for several seconds.
Wall materials play a crucial role. Reinforced concrete, metal siding, tinted glass, and even aquariums can all block the signal. Water It is an excellent absorber of microwave radiation, so the kitchen or bathroom often become areas of poor reception.
Network load is also worth considering. While this has a greater impact on speed than RSSI, during peak load periods, some routers may reduce transmission power or prioritize certain devices over others, which indirectly impacts perceived connection quality.
What to do if the signal strength is low
If measurements show values below -75 dBm in the locations where you plan to work, you need to take action. Simply increasing the transmitter power in the router settings (if such an option is available) rarely solves the problem completely and can lead to device overheating.
The first step should always be optimizing placement. Elevate the router, move it away from niches, cabinets, and sources of interference (microwaves, cordless phones). Sometimes moving the access point by 50 centimeters can dramatically change the coverage.
If rearranging the router doesn't help, consider installing additional equipment. This could be a second router in access point mode, a mesh system, or a repeater. Mesh systems are the gold standard today, as they create a single, seamless network, automatically switching devices to the nearest point with the best signal.
Why can a repeater make the situation worse?
A repeater receives the signal, decodes it, and transmits it further. This process takes time and, more importantly, cuts the actual connection speed by at least half, as the device cannot simultaneously receive and transmit data on the same frequency. Furthermore, the repeater also replicates all the noise it picked up from the main router.
Does WiFi version (4, 5, 6) affect range?
Standard WiFi 6 (802.11ax) uses OFDMA technology, which allows for more efficient data packaging. While the physical transmitter power remains similar to WiFi 5, WiFi 6 devices are better at "hearing" weak signals and can maintain a stable connection at lower RSSI levels than older devices.
Can weather affect indoor WiFi?
Weather doesn't directly affect indoor signal strength. However, if your router is located near a window and there's a heavy rainstorm or snowstorm outside, water droplets and snowflakes can scatter radio waves, slightly weakening the signal coming from outside (if you're using your neighbor's WiFi) or passing through the wall. Inside a dry apartment, the effect is negligible.
Should you buy high gain antennas?
Replacing the standard antennas with more powerful ones (for example, 5 dBi or 9 dBi instead of 2 dBi) changes the antenna pattern. The signal becomes flatter and has a longer range in the horizontal plane, but penetrates less efficiently through floors. This is useful in long apartments, but is useless in multi-story houses.
How often should the signal be re-measured?
Once after setting up the network, testing is usually sufficient. However, if you've rearranged the furniture, bought a new aquarium, installed a mirrored wall, or your neighbors have purchased a powerful router, it's worth repeating the measurements. The RF landscape of your apartment is not static.