How to measure the conducted RF power

It is sometimes useful to characterize the RF power generated by the module on an evaluation board. The module typically operates in a frequency-hopping mode, which makes it difficult to measure the power conducted from the module. For this reason, nomac_test exposes the "--tone" function, which causes the module to emit a non-hopping quasi-continuous-wave tone.

To characterize the power conducted by an evaluation board's module, perform the following steps:

  1. Connect the evaluation board to a PC using a mini-USB cable. Note the COM port enumerated by the evaluation board. If necessary, first install the USB drivers for the evaluation board.
  2. Connect the evaluation board's SMA connector to a reliable power meter or spectrum analyzer using coaxial cable. Be sure to insert enough attenuation in the path to prevent damage to the instrument.
  3. Using nomac_test, send the "--mac_set 0" command to set the module to use MAC mode 0 (NoMac mode). Refer to this article to learn how to use nomac_test. Be sure to address the correct COM port.
  4. Using nomac_test, send the "--antenna_set 1" command to ensure the module conducts the RF tone to the evaluation board's SMA connector.
  5. Using nomac_test, command the module to transmit a continuous-wave tone using the "--tone" command appended with the desired frequency and power. For example, the following picture shows how to command an evaluation board at COM21 to transmit at a frequency of 915 Mhz and power of 26 dBm.

 

  1. Record the power measured by the power meter or spectrum analyzer. Be sure to account for any attenuation in the path (connectors, attenuators, cable loss, etc).
  2. Stop the transmission by sending a different command to the module, such as "--reset_mcu".

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