How to Measure Wireless Link PA Output Power

Introduction

In wireless communication systems, verifying the output power of the Power Amplifier (PA) is a critical step during development and production testing.

If a customer reports no RF output or abnormally low transmit power, it does not necessarily indicate hardware damage. In many cases, the issue may be related to configuration, test method, or even soldering quality.

This guide explains how to measure wireless link PA output power using Continuous Transmission (Continuous TX) mode.

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When Should You Use Continuous TX Mode?

Continuous TX mode is recommended when:

• RF output appears unstable or intermittent
• Measured transmit power is lower than expected
• You need a steady signal source for spectrum analyzer or power meter testing

This mode forces the device to transmit continuously at full duty cycle, making measurements more reliable.

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Step 1: Enable Continuous TX Mode

Use the following AT commands:

AT+CFUN=0         // Soft power-off  
AT^DSONCTX=1,14300,5,"25",0,0,0  
AT+CFUN=1         // Power on  

Parameter explanation:

• 1 → Enable Continuous TX
• 14300 → Frequency = 1430 MHz
• 5 → Bandwidth = 20 MHz
• "25" → Transmit power (dBm)
• 0 → Single antenna
• 0 → Not single tone
• 0 → QPSK modulation

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Step 2: Measure Output Power

After enabling Continuous TX mode:

1. Connect the RF port to:
   • Spectrum analyzer, or
   • Power meter
2. Verify:
   • Output power level (dBm)
   • Signal stability
   • Spectrum characteristics

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Step 3: Disable Continuous TX Mode

After testing, disable the mode:

AT+CFUN=0         // Soft power-off  
AT^DSONCTX=0      // Disable Continuous TX  
Reboot  

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Troubleshooting Low Output Power

If the transmit power is still very low in Continuous TX mode, consider the following:

1. Soldering Issues (Very Common)

Poor soldering between the module and baseboard can cause RF signal loss.

Check:

• RF-related pins
• Ground connections
• PA signal path

2. Incorrect Configuration

Verify:

• Frequency settings
• Bandwidth selection
• Power level limits

3. Hardware Limits

If configured power exceeds device capability, the system will cap it at the maximum supported level.

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Advanced Example: 2.4 GHz Single-Tone Test

AT+CFUN=0  
AT^DAOCNDI=08  
AT^DSONSBR=64,24015,24814,65,8060,8259,66,14279,14679  
AT^DSONCTX=1,24415,2,"25",0,1  
AT+CFUN=1  

Key points:

• Frequency: 2441.5 MHz
• Bandwidth: 5 MHz
• Single-tone mode enabled (ideal for RF calibration)

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Key Parameters Summary

Parameter	Description
<mode>	0 = Disable, 1 = Enable Continuous TX
<freq>	Frequency (unit: 100 kHz)
<bandwidth>	1.4 / 3 / 5 / 10 / 20 MHz
<power>	-40 to +40 dBm
<tx_mode>	0 = Single antenna, 1 = Dual antenna
<single_tone>	0 = Modulated, 1 = Single tone
<modu_type>	QPSK / 16QAM / 64QAM

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Conclusion

Using Continuous TX mode is the most effective way to measure wireless link PA output power accurately.

If low output persists under this mode, the issue is unlikely to be software-related and is often caused by hardware factors such as poor soldering or RF path issues.

By following this method, engineers can quickly isolate and diagnose PA-related problems in wireless systems.