How to measure RF power of nRF52840 DK

[Sangbin]

Hi. 

I am using nRF52840 dk in windows 10 environment.

I want to measure the RF output power of a single nRF52840 using nRF52840 dk.

I succeeded in generating a burst signal (LE 1Mbps) at a fixed frequency by adjusting the number of channels to one

in "Direct Test Mode" using NRF CONNECT V3.3.1, and I was able to confirm the signal with a spectrum analyzer.

But problem is un-synchronous signal Spetrum analyzer and LE 1Mbps.

The signal I want to measure is

1.Tx output power (dBm).

2.2nd Harmonis.

Q1.The Tx ouput of nRF52840 is max 6dbm, and I want to see it as a fixed frequency continous signal rather than TDD signal.

This is to know the exact signal power(dBm) at a specific frequency with a spectrum analyzer.

Q2. If nRF52840 DK cannot output a signal corresponding to Q1, I would like to know how to measure a TDD signal such as LE 1Mbps by synchronizing with the trigger of SA.

It was difficult to use for the first time, but now I know that there is such a good page.

Please let me know if there is a good way!

Best regards.

[Andreas]

Hi,

 

1. You can click the 'Transmit packet type' drop down menu and select the 'constant' option. This will transmit a continuous, unmodulated carrier. If you want constant modulated carrier you need to use the radio test example, also found in the SDK.

2. Just configure the spectrum analyzer to use peak detector and trace max hold. It might take some time to 'catch' all of the spectrum and settle, but after some time it will display the same as a continuous carrier.

 

PS: 6dBm is measured internally in the spectrum analyzer, you need to add what is lost in the cable assembly between the nRF52 PCB and the spectrum analyzer.

 

Best regards,

Andreas

[Sangbin]

Thank you for your kind reply!

I have more question.

I'm using nRF connect v3.3.1 and lunch app named "Direct Test Mode". 

As your reply, "packet type" has constant option. but i can't find them. (so i attach my lunch app screenshot)

please confirm part that filled yellow.

So in my situation, i'm using packet type which named "PRBS9"

It also make it tx signal, but it is brusted rf signal.

I can measure rf power at trigger mode of Signal analyzer. but not incorrect power i guess.

Can you check my attached picture and help to find solve this problem? (using constant power)

Have a nice day!

Best regards.

[Andreas]

Hi,

 

OK, try updating to update to latest version (v3.3.3) and see if you can select constant then. Alternatively flash your board with the radio test example, found in our SDK under /examples/peripheral/radio_test/

 

As you say the PRBS and the other packet contents are bursted transmissions, or the packets are sent with a delay between each one. This is per the DTM spec. I am not sure I understand exactly how you trigger, but you do not need to worry about trigger at all. Just configure the spectrum analyzer to use peak detector and trace max hold. It will then report the peak sample measured at each sweep, and update the trace only if the measured value is higher than the previous one at that point in frequency. Which spectrum analyzer are you using?

 

Best regards,

Andreas

[Sangbin]

Hi. i'm using SA which named N9030B PXA.

when i measure triggered rf burst, it looks like modulated signal. (i attach photo)

so can you have any continous wave firmware or example code ? 

[Andreas]

Hi,

 

Not 100% sure with RBW=8MHz, try RBW=1MHz instead, but I think it is modulated yes.

 

FW for continuous wave is primarily radio test example in the SDK as mentioned, you can download this here:

 

Or flash this hex file, it just starts an unmodulated carrier on 2440 MHz: nrf52_unmod_ch40_sleep.hex

 

Best regards,

Andreas

[Sangbin]

Thanks to your support, i can measure the continous wave signal perfectely.

Is it set up at 6dBm output right? (i attached photo which i measure)

so i appreciate that your kindly reply.

and i have some question about hex file which you attached.

I want to set up the signal output at -10 / 0 dBm. 

But it is so difficult to me that fixing code because of hex file.

Can you support that this problem?

I would really appreciate that if you supported it as a hex file that can output -10dBm / 0dBm at the same frequency (2440MHz)

Best regard!