How Do I Get the Maximum Output Power Indicated on the USRP Manual?

Updated Jan 29, 2019

Reported In

Hardware

  • USRP-2952
  • USRP-2950
  • USRP-2953
  • USRP-2954
  • USRP-2955

Issue Details

I use the example Tx Streaming (Host).vi to increase the Output Power value in the front panel until the power displayed by the spectrum analyzer no longer increases.
The maximum power obtained is much smaller than the maximum power indicated in the USRP manual (Maximum output power: 17 dBm to 20 dBm).
I tried to send three signals with different frequency values (783MHz, 2.5GHz, 5.1GHz) signals, and the measured maximum transmit power is much smaller than the nominal value. How do I get the maximum output power indicated on the USRP manual?

Solution

The nominal maximum power value in the USRP manual is the value measured with a single frequency signal transmitted.
The maximum output power of different frequency points is also different, which is related to the frequency response of the system.
The maximum output power is related to the gain of the USRP front-end amplifier, and the measurement results vary with the value of the gain.
The method of modifying the gain can refer to the following figure. Modify the Amplitude value of  Generate Waveform(Multi-Array).vi. 
Take USRP-2953 as an example. If we want to get the maximum output power:
  1. Run Tx Streaming (Host).vi send a signal with a frequency of 2GHz;
  2. Set  the Output Power parameter to 20dbm;
  3. Set the Amplitude parameter to 0.5;
  1. The signal power measured by the spectrum analyzer is 12.98dbm;
  2. Set the Amplitude parameter to 1;
  3. The signal power measured by the spectrum analyzer is 18.53dbm (Maximum output power: 17 dBm to 20 dBm);

Additional Information

The USRP RIO is not a calibrated device platform. The device has gain offset tables (correction data) which enables the user to measure input signal power and set a reference level on the device or transmit a signal at a set power level. 

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