nRF51422 issues with 2nd harmonic FCC testing

[Danny]

Hi,

I'm using the attached circuit and we recently took our product to FCC testing and failed the 2nd harmonic because we were transmitting too much power.

I'd like to tune the pi network based on your white paper nWP-017 and I think I have an understanding of how to do so.

My question is, once I tune the pi filter will C26 throw everything out of balance? What is C26 used for?

Any additional advice or suggestions would be greatly appreciated!

We're at an EMC testing facility and we have access to a network analyzer. We measured the impedance of the antenna and it's feed line and we're at 48 ohms for the real part and we're at -10 for the imaginary part. It seems that the antenna is pretty well matched to 50 ohms as I would expect.

Thanks, Danny

[Danny]

We ended up passing EMI testing with this circuit:

What makes me nervous is that we removed C26 with a zero ohm. Our performance was 10dB higher than the previous circuit and we passed all harmonics.

Is there something that I should be concerned about. We can reliably transmit and receive data in this configuration and we are passing EMC testing. I guess when it works, it works but I can't help but think we should be doing something different.