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]

The lack of ground plane may be the reason for why you don't see any RF output as the antenna would suffer. Normally you would be able to see at least a very weak signal if you have the phone and board touching each other, but not necessarily. It's good that you see the 1.8 V, that indicates that the chip at least is trying to transmit. Regarding the startup of the external crystal and measurement, is the oscilloscope able to measure up to 16 MHz?

[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

[Locky]

You still will want to keep the capacitor to tune the Antenna to your PCB. Its best to done with a full pi-network.

[Asbjørn]

This look like a good improvement with regard to ground. It look like a really small board, but to me it seems like you have added the amount of ground plane on both top and bottom layer that you could. Because of its small size it wouldn't be the best performing board, but you should be able to get some OK range with this one nevertheless.

You should move the trace that runs under the L1 component. It seems to be a button (BTN2 or 3?), but it could be something else that's powered. Avoid routing signal traces underneath the trace from the balun towards the antenna. Would it be possible to use a gpio on the opposite side of the chip to avoid this conflict?