How can I measure LTEM TX power after the antenna impedance matching circuit

[Carla31zv]

Hello,

I’m currently working with a custom board based on the nRF9160 SiP, and I would like to measure the LTE-M TX power after the antenna impedance matching circuit. Ideally, I’d like to perform this measurement using an nRF9160 DK to help automate the RF testing process.

I’m aware that the %RFTEST TX AT command provides the transmitted power, but this measurement is taken at the antenna output, not after the matching circuit.

I was considering using the %RFTEST RX command on the development kit to capture the transmitted signal from the custom board. However, from my understanding, direct communication between two nRF9160 devices in this context is not supported.

Is there a recommended way to measure the TX power after the impedance matching circuit using a development kit, or any other method you suggest for automating this measurement?

Thank you in advance for your help!

Best regards,

[mathiaso]

Hi, Carla.

I'm not quite sure I'm following why you would want to measure the output power after the antenna's matching network. Do you mean between the ANT pin and the antenna-matching network, where the connector is placed on the nRF9160 DK? Would you be able to illustrate and/or describe your setup and what you want to achieve more in detail?

Best regards,
Mathias

[Carla31zv]

Hello, yes it is after antenna's matching network of my custom board, pin ANT_4G. Here you can see my setup: 

[mathiaso]

Thank you, Carla.

What was the reasoning behind adding that matching network, with those specific values?

As can be read in the PS, the ANT pin is already matched to 50 ohms. Your connector, differently from what would be the case if it were an antenna, likely has an impedance of 50 ohms as well. This is also the reason why the nRF9160 DK has a matching network for the antenna but not for the connector.

[Carla31zv]

Thanks for the explanation. 

I would like to know—as mentioned in this ticket—whether it's possible to measure the transmitted signal power from one nRF9160 DK using another nRF9160 DK.

Also, can these operations be performed using the AT command %RFTEST?

[mathiaso]

Carla31zv said:

I would like to know—as mentioned in this ticket—whether it's possible to measure the transmitted signal power from one nRF9160 DK using another nRF9160 DK.

Ok, understood. For this purpose, you should use a spectrum analyser, rather than a DK. The DK would likely not give very precise measurements, but I don't know what you're planning to use them for?

If using the TX test %XRFTEST at any time, beware of the caution about restricted bands.

[Carla31zv]

Precision in measurement is not a top priority for me. I was trying to use the AT command %XRFTEST RX to enable the RF receiver and measure the signal power sent by another devkit. However, I believe this isn't feasible because one devkit transmits on uplink frequencies, while the other receives on downlink frequencies