How to Accurately Measure Wi-Fi Antenna Power: From a Smartphone to a Spectrum Analyzer

Wi-Fi antenna power is a key parameter determining the range and stability of a wireless network. But how can you determine the actual performance of your equipment when manufacturers often quote theoretical values? In this article, we'll explore 5 Practical Measurement Methods — from simple smartphone apps to professional tools available only to engineers.

You will learn how they differ isotropic power (EIRP) And transmitter power, Why dBm more important mW for analysis, and how to correctly interpret the results. We will also reveal Why even an expensive antenna with a claimed 9 dBi performance can perform 5 dBi worse than a cheap one if installed incorrectly.

1. Theoretical basis: what exactly are we measuring?

Before taking measurements, you need to clearly understand which parameters affect signal strength:

• 📡 Transmitter power (TX Power) — is measured in dBm (decibel-milliwatt) or mWThis is the "raw" power that a router or access point produces. to the antenna.
• 🔄 Antenna gain — is indicated in dBi (decibels relative to an isotropic radiator). For example, an antenna TP-Link TL-ANT2406A has a gain of 6 dBi.
• 📶 EIRP (EIRP) — equivalent isotropically radiated powerThis is a combined figure that takes into account both transmitter power and antenna gain. In Russia and the EU, EIRP is limited by law: 20 dBm (100 mW) for 2.4 GHz and 30 dBm (1 W) for 5 GHz.

The formula for calculating EIRP is simple:

EIRP (dBm) = Transmitter Power (dBm) + Antenna Gain (dBi) – Cable Loss (dB)

⚠️ Please note: Most countries have strict EIRP limits for Wi-Fi equipment. Exceeding these limits (for example, with powerful antennas or amplifiers) may result in fines from communication regulators. Before modifying equipment, check the current standards in official sources.

Why is this important? Because Measuring antenna power separately from the transmitter is pointless — it always works in conjunction. Even if you buy an antenna with amplification 15 dBi, but connect it to a router with the transmitter power 10 dBm, the real EIRP will be only 25 dBm (minus cable losses).

2. Method 1: Software measurement via a router

The most accessible way is to use the built-in tools of the router. Most modern models (ASUS RT-AX88U, Keenetic Ultra, MikroTik hAP ac³) allow you to see the current transmitter power in the web interface.

Instructions for popular brands:

Please note: many routers show power in percent (for example, 100%), but this relative value. To convert it to absolute dBm, you need to know the maximum power of your model. For example, if the router supports a maximum 20 dBm, then 50% = 17 dBm (20 – 3 dB).

Make sure that the power is not limited by the country regulator (EU/US/RU)

View the current TX Power value in dBm or %

Check if the "Auto" mode is enabled - it can reduce power when overheating.

Record values ​​for both bands (2.4 GHz and 5 GHz)-->

3. Method 2: Mobile applications for signal analysis

If you don't have access to your router settings (for example, if you rent an apartment with Wi-Fi), you can estimate the signal strength using your smartphone. Apps like WiFi Analyzer (Android) or NetSpot (iOS/macOS) show the signal strength in dBm from your access point.

How does this work:

1. Install the app and connect to your network.
2. Bring the phone as close to the antenna as possible (1–2 meters away).
3. Write down the value RSSI (Received Signal Strength Indicator) in dBm.
4. Compare with reference values:

• 🟢 From -30 to -50 dBm - excellent signal (the antenna is working at maximum).
• 🟡 From -50 to -70 dBm — average level (cable losses are possible).
• 🔴 Below -70 dBm - weak signal (check the antenna connection).

Important: This method indirect - it shows power accepted signal, not transmittedHowever, if the RSSI near the antenna is worse -60 dBm, this is a clear sign of problems with the transmitter or cable.

WiFi Analyzer (Android)

NetSpot (iOS/macOS)

inSSIDer (Windows)

Other

I don't use it-->

4. Method 3: Professional PC Utilities

For more accurate measurements, desktop programs that work with Wi-Fi adapters are suitable. The best options are:

• 🖥️ inSSIDer - shows signal strength in real time, supports channel filtering.
• 📊 Acrylic Wi-Fi — a professional tool with the ability to record packets and analyze the spectrum.
• 🔍 Wireshark + adapter in monitoring mode - for experts (requires skills in working with packages).

Example of use inSSIDer:

1. Connect an external Wi-Fi adapter (recommended) Alfa AWUS036ACH for accurate measurements).
2. Run the scan in the program.
3. Find your network in the list and look at the column Signal (dBm).
4. To analyze the transmitter power, bring the adapter as close as possible to the antenna (10–20 cm).

The advantage of this method is the ability to see real power in different channelsFor example, if there is a signal on channel 6 -45 dBm, and on channel 11 - -60 dBm, this may indicate interference or a faulty antenna.

5. Method 4: Using a Spectrum Analyzer

For engineering tasks (for example, setting up corporate networks) they use spectrum analyzers — devices that display signal strength in real time, broken down by frequency. Popular models:

• 📡 Rohde & Schwarz FSH3 — a professional device for laboratories.
• 🔧 Wi-Fi Explorer Pro (for macOS) - a software analyzer with adapter support Wi-Spy.
• 💻 Ubiquiti airView - free software for devices Ubiquiti.

How to take measurements:

1. Connect the analyzer to the antenna or place it close to the signal source.
2. Set the frequency range (eg. 2.412–2.484 GHz for Wi-Fi 2.4).
3. Run a scan and find the power peak on your channel frequency.
4. Compare with maximum permissible values ​​(eg. 20 dBm for the EU).

The spectrum analyzer shows not only the power but also channel congestion, which helps optimize network settings. For example, if your signal on channel 6 has a strength 15 dBm, but there is a powerful interference nearby 18 dBm, it's worth changing the channel.

⚠️ Attention: High-precision spectrum analyzers (e.g. Keysight N9912A) cost tens of thousands of dollars and require calibration. For home use, software solutions like Wi-Fi Explorer or adapter Wi-Spy DBx (~$200).

6. Method 5: Calculating power based on technical specifications

If you don't have access to the equipment, but know its parameters, you can calculate EIRP theoreticallyFor this you will need:

• 📄 Transmitter power (indicated in the router datasheet, for example, 17 dBm For TP-Link Archer C7).
• 📡 Antenna gain (written on the body, for example, 5 dBi).
• 🔌 Cable losses (depending on the cable type and length; for RG-58 — ~0.6 dB/m at 2.4 GHz).

Example calculation for a router ASUS RT-AX58U:

Transmitter power: 20 dBm (max for EU)
Antenna gain: 4 dBi (built-in)
Cable length: 0 m (antenna is not removable)
EIRP = 20 + 4 – 0 = 24 dBm (exceeds EU limit by 4 dBm!)

If the result exceeds local standards, the router automatically reduces power. You can check this in the device logs (section Wireless Log or System Log).

Why might the calculated EIRP differ from the actual one?

Actual power depends on:

- Router temperature (when overheated, TX Power drops by 2–5 dBm).

- Quality of the antenna soldered connections (oxidation of contacts results in losses of up to 3 dB).

- The presence of amplifiers or attenuators in the circuit.

- Firmware adjustments (some alternative firmware like DD-WRT allow you to bypass restrictions).

7. Typical errors in power measurements

Even experienced users make mistakes that distort results. Here are the most common ones:

• 📏 Incorrect distance — RSSI measurements should be taken at a fixed distance (e.g., 1 m from the antenna). Standing too close will result in inflated readings due to the near-field effect.
• 🌡️ Ignoring temperature — When the router heats up, the transmitter power may drop by 20–30%. Measure after 10–15 minutes of operation under load.
• 🔌 Bad cables - cheap coaxial cable (for example, RG-59) can "eat" up to 50% of the power. For accurate measurements, use LMR-400 or LMR-600.
• 📶 Interference from other devices Microwaves, cordless phones, and nearby Wi-Fi networks distort the results. Conduct measurements in a "clean" environment or use a spectrum analyzer.

Another common mistake is confusion between dBm and dBi.Remember:

• dBm — absolute power (for example, 20 dBm = 100 mW).
• dBi — relative antenna gain (dimensionless value).

dBm = Max. power (dBm) – (100 – % power) × 0.1

Example: maximum 20 dBm, current power 80% → 20 – (100–80)×0.1 = 18 dBm.-->

FAQ: Frequently Asked Questions about Wi-Fi Antenna Power

Is it possible to increase the antenna power above the legal limits?

Technically yes, with the help of amplifiers or modified firmware (for example, DD-WRT). However, this breaks the rules communications regulators (in Russia - Roskomnadzor, in the EU — ETSI). Fines for individuals can reach 50 000 ₽, and for legal entities - 500 000 ₽.

Legal ways to improve coverage:

• Use antennas with directed radiation (for example, TP-Link TL-ANT2424B by 24 dBi).
• Set up additional access points in mode Mesh.
• Go to range 5 GHz (there is less interference and higher throughput).

Why does my 9dBi antenna perform worse than the stock 3dBi antenna?

This is a typical situation when users do not take into account radiation patternHigh gain antennas (from 7 dBi) have narrow beam - They "shoot" a signal in one direction, but poorly cover the space around.

Solutions:

• Check the antenna tilt angle (optimally - 45° for home conditions).
• Replace with omnidirectional antenna (for example, Alfa APA-M25 by 7 dBi).
• Use 2-3 antennas with lower gain (5–6 dBi), located at different angles.

How to check antenna strength on a smartphone without apps?

Android and iOS have hidden menus for network diagnostics:

• Android: dial in the phone app ##4636##, select Wi-Fi information → Wi-Fi signal strength.
• iPhone: go to Settings → Wi-Fi, click on the "i" symbol next to your network. Field RSSI will show the power in dBm.

Limitation: These methods only show accepted signal, not transmitter power.

Does cable length affect antenna power?

Yes, and very much so! Losses in a coaxial cable depend on:

• Cable type:
  • RG-58: ~0.6 dB/m at 2.4 GHz, ~1 dB/m at 5 GHz.
  • LMR-400: ~0.2 dB/m at 2.4 GHz, ~0.3 dB/m at 5 GHz.
• Frequencies: on 5 GHz losses are 30-50% higher than 2.4 GHz.
• Connector quality: each connector (eg. SMA) adds ~0.1–0.3 dB of loss.

Example: If you use RG-58 10 m long for a 5 GHz antenna, the loss will be ~10 dB. This means that half power gets lost in the cable!

Is it possible to measure antenna power with a multimeter?

No. The multimeter measures constant voltage or resistance, but not the high-frequency Wi-Fi signal. To measure power in dBm, you need:

• Specialized RF wattmeter (For example, Bird 4022).
• Spectrum analyzer with power measurement function.
• Wi-Fi adapter with support monitor mode and software like Acrylic Wi-Fi.

Trying to connect a multimeter to the antenna may disable it due to the high frequency signal.