nr51822: No radio with custom PCB

[Henry]

Hi,

I have created a custom PCB that more or less follows the Nordic SmartBeacon design: Beacon_V2.pdf

Instead of BAL-NRF01D3 I used the BALF-NRF01D3 as this is supposed to be compatible with the QFAAG0 chips, which I use.

So now, when I load the SmartBeacon FW, everything seems to operate fine: LED pulsing, change to orange LED on button press (DFU mode)...

But what is missing is that I cannot capture any signal on my iPhone on the custom PCB... With the original Smart Beacon HW everything works fine. On the custom PCB I use the same shape and dimension PCB antenna.

I already switched from external 32Mhz crystal to internal but everything stays the same.

Now, how can I find out what is going wrong? Is there a way to see wether the soldering of the Balun was ok?

Thanks for your help!

Henry

[Asbjørn]

It's difficult to tell from your screen shot, but it looks like the ground plane is missing, at least on the top top layer. Do you have a ground plane incorporated into your board? The antenna will not work as intended if there's no ground plane no the board.

Secondly, if the ground plane is insufficient, you should still get a couple of inches of range. Could you test by holding the phone very close/on top/under the beacon and see if you get any readings at all out of it.

I've recommended this as a debug option for many customer, it's to check the VDD_PA pin on the board. It will go up to 1.8 V when the chip is actually transmitting. So you should see that VDD_PA goes up to 1.8 V with an oscilloscope for every time you expect the beacon to send a package.

You should also verify that the external 32/16MHz crystal is actually starting up.

[Henry]

Dear Asbjørn,

Thanks for your help. I redesigned the PCB, please see the updated version above. Do you think that this should be sufficient?

I am still not so confident due to the fact that even on very close distance, I was not able to get any signal. But as you said, maybe the lack of GND plane did create so much interference that the signal was killed completely.

Do you see at first sight anything wrong in my design?

In regards to the balun, I use the BALF-NRF01D3 version (instead of BAL-...). This should be compliant with the NRF51822 QFAA G2 chip I use. In the Balun datasheet (page 5) it says that no capacitor is needed (in contrast to the BAL-.. version). Does this mean I can leave out the capacitor from the PI network?

Thanks Henry

PS: Dont think my oscilloscope is capable of measuring 16MHz