custom nRF5340 board no bluetooth signal

[danny0007]

Hi Community,

I designed a similar board asThingy53, espacially the antenna parts are almost the same, except the RF switch, we replace it with another one (BGS12WN6E6327XTSA1), then we found there is some issue to make the switch work properly, so I just removed the RF switch and short the RF output to the short range antenna, which means, now only one anntenna is connected to the RF, even so, I cannot see any RF signal on the mobile phone. 

but the output from UART seems no problem:

*** Booting nRF Connect SDK v3.5.99-ncs1 ***
[00:00:00.303,100] <inf> Custom_board: Starting Custom_board...

[00:00:00.309,020] <inf> fs_nvs: 8 Sectors of 4096 bytes
[00:00:00.309,020] <inf> fs_nvs: alloc wra: 0, fd0
[00:00:00.309,051] <inf> fs_nvs: data wra: 0, 1c
[00:00:00.334,167] <inf> bt_hci_core: HW Platform: Nordic Semiconductor (0x0002)
[00:00:00.334,197] <inf> bt_hci_core: HW Variant: nRF53x (0x0003)
[00:00:00.334,228] <inf> bt_hci_core: Firmware: Standard Bluetooth controller (0x00) Version 54.58864 Build 1214809870
[00:00:00.336,456] <inf> bt_hci_core: No ID address. App must call settings_load()
[00:00:00.338,897] <inf> bt_hci_core: Identity: E6:BD:87:6D:09:49 (random)
[00:00:00.338,928] <inf> bt_hci_core: HCI: version 5.4 (0x0d) revision 0x218f, manufacturer 0x0059
[00:00:00.338,928] <inf> bt_hci_core: LMP: version 5.4 (0x0d) subver 0x218f
[00:00:00.342,742] <inf> Custom_board: Bluetooth initialized

[00:00:00.348,327] <inf> Custom_board: Advertising successfully started

the same code, if I compiled it for the nRF5340DK, the bluetooth signal can be observed. 

So I just curious if I did something wrong in my board files or something else? 

I have been strugled in this issue for a long time, please help me with it, thanks a lot!

Best regards

Danny

[JONATHAN LL]

Have you hade the design fully reviewed by us? 


My guess is that there is an issue with the antenna or RF path in some way and that this impacts the range, so maybe you need to be very close, try a few centimeters. And only have the PCB, if there is any casing or other material in the way or enclosing the antenna\PCB this might be a reason to why the RF is bad. 


Alternatively it might be the the clock, the 32MHz might be off and that can contribute to the issue. Make sure it is loaded correctly. 

Regards,
Jonathan

[danny0007]

Hi  JONATHAN LL 

1. it's not reviewed by you. I just checked the Thingy53 PCB file, found the followed differences:

Thingy53 PCB:

trace width: 0.6mm

grounded vias around the clear area of antenna .

My PCB:

trace width: 0.18mm:

I used this calculation, therefore I used 0.18mm RF trace width, is there anything wrong?

forgot to put grounded vias around the clear area of antenna.

I even put the PCB very close to the mobile phone, still can not see any siganl from my PCB.

2. I think I checked the 32M Hz crystal before, it's running, and all the other peripherals are running correctly, I2C, SPI, PWM...


Best regards
Danny

[JONATHAN LL]

Are there crossing traces directly under the RF path or is there a layer in between ?

Regards,
Jonathan

[danny0007]

yes, they are crossing traces directly under the RF path.

RF traces are on the TOP layer, the green traces are on the second layer, directly under the TOP layer.

Regards

Danny

[JONATHAN LL]

That is unfortunate as this will effect the performance as this causes a ground plane obstruction. You should still be able to see something coming from the antennas but effect might be reduces a lot. 

Here is a relatively easy explanation on how and why https://www.youtube.com/watch?v=EEb_0dja8tE&t=86s . 

Do you have access to a spectrums analyzer? or maybe you could try to use the RSSI viewer to see if there is a sure sine that something is going on. 

Regards,
Jonathan

[danny0007]

I measured it with a spectrum analyzer this afternoon,  we cannot see any valuable BLE signal from my PCB. 

For comparison purpose, we even put the taste probe near the 32.768K and 32M crystals, we can observe exactly the expected crystal frequency.  When we put the probe on the 2.2 nH inductor of the BLE output, nothing comes out. It seems there is no BLE signal from the chip at all.

Since there is no shieldbox available today, so we just shutdown our mobile phone, sometimes we observe a 2.4G signal, but not sure it's from my PCB or the WLAN in the building. Next week, we will get a shieldbox, so we can 100% make sure if there is some BLE signal from my PCB, probaly also not. 

I'm not sure, maybe something wrong with the customised board configuration regarding BLE? Until we get the shieldbox, how can we check it from software level and make sure there is no issue in configuration. 

[JONATHAN LL]

I would start by using the radio test sample and try and set the device in a constant carrier output mode. 

This way you will have something out on the RF at all times. 

https://github.com/nrfconnect/sdk-nrf/tree/main/samples/peripheral/radio_test 

Another alterative is this setup we use here for testing https://github.com/bheiskel/rf_test , you need an extra DK in addition to the device but it is easier to use. 

Regards,
Jonathan

[danny0007]

I have only nRF5340DK on my hand.

so I compiled the radio_test code:
https://github.com/nrfconnect/sdk-nrf/tree/main/samples/peripheral/radio_test 

Toolchain: 2.9.0

SDK: 2.9.0
with this configuration:

successfully compiled and flashed:

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But I see nothing on the mobile phone.