Bluetooth Antenna Problem

[FlavioPiracicaba]

Hello,

   I created a sucessfull code for nRF5340-DK working with bluetooth, uart etc. I am using the Bluetooth NRF52 dongle

to test. When I upload the firmware to nRF-DK works perfectly, it's sending and receiving packets.

  Then I created a customized board with an external antenna. This board has 32KHz Crystal.

  The power supply is working well with 3.3volts

  These are the related parts of schematics

The antenna's track width is 9.84mil and below is the rf grounded dieletric. This

track width was calculated by Altium Design and I used an external tools to confirm

if it was correct.

This is the stack-up of the first two layers. The board has four layers.

Top Solder	Solder Resist	0.010mm
Top Layer	Copper	0.018mm	Red
Dielectric 2	FR-4	0.122mm
GND	Copper	0.018mm	Brown

We don't have a Spectrum Analyser at our lab. We don't have tools to do RF simulations too.

In order to know if there is a problem with antenna circuit I  removed the L6 and C27 and installed a wire.

I don't know if could work but I tried.

This image you can see the wire. Wire's lenght is 15mm

 I tested again and is not working. I am open to hear suggestions.

 I already tried to change from external crystal to internal RC as 32KHz generator. Didn't work.

Thanks,

[Kenneth]

Hello,

If you don't have access to equipment do measurements, you may consider using a pre qualified nRF5340 module in your design, this will ensure qualified design that also pass radio regulations around the world. For a list of modules: 
https://www.nordicsemi.com/Nordic-Partners/3rd-party-modules 

The 32kHz crystal affect timing (such as for instance sleep intervals and maintaing a connection), however in your case it seems you have a fundamental problem with getting the radio to work, in such case the problem is related to the 32MHz crystal. So I guess the question then is what 32MHz crystal you have used in your design, and if you have potentially adjusted the load caps in accordance with possible CL parameter for the 32MHz in your design. If you can provide partnumber and CL for the 32MHz crystal used I can take a look at the parameters.

Also, have you done any debugging to find if the code seem to run normally?

Best regards,
Kenneth

[FlavioPiracicaba]

Crystals:

32KHz: XL1/XL2 is 9HT11-32.768KBZC-T.

32MHz: XC1/XC2 is KC2016K32.0000C1GE00

There isn't capacitors installed on the crystals.

I done the debug, the code is running,  but the Bluetooth is not broadcasting. I can't see the client as I can when I use the development kit.

Thanks,

Flavio

[ketiljo]

I Flavio

Is this the 32 MHz oscillator you're using? https://www.digikey.no/en/products/detail/kyocera-avx/KC2016K32-0000C1GE00/5322520

If so, you need to switch to a proper crystal. This is a complete oscillator that needs to be powered separately. From the schematic, it looks like you meant to use a crystal here. 

Best regards,

Ketil Aas-Johansen

[FlavioPiracicaba]

Correct, The Pin 4 of cristal is wrong connected. Must be powered.

I will try to fix it and I will reply you.

Thanks,

Flavio.

[ketiljo]

Hi Flavio

You can't use this crystal oscillator at all. The problem with this is that it has a PLL to generate the frequency. The phase noise is too large so the receiver won't work. You need to use a proper crystal.

Cheers,

Ketil

[FlavioPiracicaba]

Hi Ketil,

I specified a crystal, not a PLL. I don't know what's happened. Now I will replace by this one:

ECS-320-8-37-CKM-TR3 (32 MHz ±10ppm Crystal 8pF 60 Ohms 4-SMD). 

Do you know if it will work well?

Thanks,

Flavio.

[ketiljo]

Hi Flavio

Yes, this should be good.

Cheers,

Ketil