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:
- 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.
- 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.
- 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.
- Using nomac_test, send the "--antenna_set 1" command to ensure the module conducts the RF tone to the evaluation board's SMA connector.
- 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.
- 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).
- Stop the transmission by sending a different command to the module, such as "--reset_mcu".