Problem with Texas swra117d PCB antenna

[thpuch]

Hello,

in my design I used the antenna swra117d from Texas.

I am able to connect to my custom board with the nrf52 dongle and the nrf52 DK. 

Unfortunately I can not connect with my smartphone or the raspberry pi, nor I can not receive the advertising packages.

I used the nordic blinky example.

With the RSSI Viewer I see the advertising packages at strange frequencies like 2403 MHz and 2427 MHz.

Can it be that the frequency is wrong, maybe i got the matching network wrong?

Thanks in advance

Thomas

Texasswra117d.pdf

[Andreas]

Hi,

 

The layout has some deviations compared to our reference design, so the component values are probably not optimal. You should still see the signal (and you do), just lower signal strength. Also, you only have 1 component for matching the antenna, which might not be enough and it is not mounted anyway, this will potentially further reduce signal strength.

 

Seeing radio transmission at a higher frequency than expected might indicate too high crystal oscillator frequency. This is often the case if you have too small load caps on your 32MHz crystal (lower capacitance -> higher frequency). The small section I am able to see from your image does not really make sense, could you share the rest of the NRF52840 design as well or at least the 32 MHz crystal part? Also if possible the crystal part number you are using.

 

Best regards,

Andreas

[thpuch]

Hello,

thank you for your fast reply.

Attached is the complete design.

I am using the following crystal: 

• ABM3-32.000MHZ-B4Y-T
• CC4V-T1A-32.768kHz-12.5pF-10PPM-TA-QC

If I change the capacity from 12pF to 18pF, for the 32MHz, then it works fine.

Thank you for the hint!

Best regards

Thomas