NRF7002 Radio test RX_CAP 2 trigger

[Julianstj]

Hello,

I'm testing the IQ feature of the radio test. According to the documentation on https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/wifi/radio_test/sample_description.html  , the last IQ test documentation for RX_CAP 2 , it should only trigger off WLAN packet.

I put a NRF7002 DK in an RF chamber and ran the wifi scan test application as well, and it saw no frames and no detected devices.

WiFi scan application building and output:

nrf\samples\wifi\scan

west build -b nrf7002dk_nrf5340_cpuapp -- -DCONFIG_WIFI_MGMT_RAW_SCAN_RESULTS=y

Scan request done
Scan requested
Scan request done
Scan requested
Scan request done
Scan requested
Scan request done
Scan requested
Scan request done

However, when I run the radio test application with rx_cap 2 similar to the documentation, it does dump IQ samples. I did init 144 and init 1 to try both 2.4GHz and 5GHz wifi bands, and both triggered the IQ dump.

radio test build and run

west build -b nrf7002dk_nrf5340_cpuapp

uart:~$ wifi_radio_test rx_capture_length 10000wifi_radio_test rx_cap 2
************* RX capture data ***********
FD5FDF
036022
FC3030
043FCC
FDFFB7
FC2038
048013
015FE0
00BFD5
039FDE
03D011
022012
005FCE
010FC9
01BFE7
FF5FCC

I would expect that, a device in a sealed RF chamber, with no other boards, and wifi scan showing nothing, that the IQ dump shouldn't trigger. If I look at the IQ dump frequency content, it does show an arc around the center, which seems to point towards it trying to detect something. Is this a known behavior of RX_CAP 2 operation?

Thanks!

[Håkon Alseth]

Hi,

 

"rx_cap 2" will enable raw access to the radio, meaning no checksums or address matches etc. It dumps out raw data from the demodulator.

If I look at the IQ dump frequency content, it does show an arc around the center, which seems to point towards it trying to detect something.

Without seeing the shape/form/magnitude, it is hard to state exactly what it is, but given that this was measured in a shielded chamber, it has to be coming from the design itself. What you're describing sounds like a Receiver local oscillator leakage (RX-LO), meaning a small leakage from the receiver logic inside of the nRF7002.

 

Kind regards,

Håkon

[Julianstj]

Hi Håkon,

Here's the data I captured in the chamber, at channel 1 and channel 144, along with the script I used to parse the data. 

Raw data from the demodulator is perfect, that's what I want. The statement about rx_cap 2 says "To capture AGC adjusted baseband samples after WLAN packet detection" , so AGC adjusted baseband samples is fine, but the WLAN packet detection part. Based on my measurement, it isn't WLAN packet detection but something else? If it's in an RF chamber I wouldn't expect it to trigger or give IQ samples at all. Or is that not how the code is operating?

My goal is to have IQ samples that correspond with a specific packet, so I'm very interested in the "after WLAN packet detection" component. I was surprised that I stuck the board in the chamber, see nothing on wifi scan, but still see IQ data come back when running rx_cap 2.

Thanks!

EvalBoardLogs.zip

[Håkon Alseth]

Hi,

 

My apologies, I have misinformed you previously:

Håkon Alseth said:

"rx_cap 2" will enable raw access to the radio, meaning no checksums or address matches etc. It dumps out raw data from the demodulator.

"rx_cap 0": Unfiltered output, i.e., ADC output. Please note that analog filter in RF is applied on these samples. Digital filter in baseband is not applied. This is at 40MHz sampling rate (ADC sampling rate).

New
"rx_cap 1" : Filtered output, i.e., both analog filter in RF and Digital filter in baseband are applied. Output is at 20MHz sampling rate.

"rx_cap 2" : Filtered output. Output is at 20MHz sampling rate. Only difference compared to "rx_cap 1" is that capture should be triggered after packet detection.

 

When you have set "rx_cap 2" and placed the device in a shielded box, with no other traffic around, it should not output any data. I have reported this as a bug back to R&D for further investigation.

 

Julianstj said:

Raw data from the demodulator is perfect, that's what I want.

It sounds like rx_cap 0 or 1 is the mode that you want, based on your preference wrt. digital filtering on or off.

 

Kind regards,

Håkon

[Julianstj]

Hi Håkon, that makes sense, thank you for the additional details and looking forward to hearing more details. I do actually need it to be triggered by packet detection, as I do not want to have IQ samples constantly, but only during packet times.

Please let me know if there is any experiment I can collect data from to help debug. 

Thank you!