nrf51 w/ RFAxis 2401C conducted power problem

[Alex]

We're using the nrf51 with the RFAxis (now Skyworks) 2401C amplifier, which is a fixed gain 20dBm amplifier. The goal is to have a longer range 'beacon' type product and the results so far are great. We have really good range and the signal quality looks good.

However, when setting the nrf51 to -4dBm output, we're running into issues with conducted certification testing (FCC). Specifically, we're failing the power spectral density requirement of 8dB.

Since this is a conducted test, there's little we can do 'on board' to fix (matching networks, etc). Do you have any suggestions on how to improve the conducted results? Below is our test setup:

• -4dBm output from nrf51
• +20dBm from amplifier
• Using FCC testing code which uses GFSK modulation and 1MB/s transmit rate

If we decrease the output power to -12dBm from the nRF51 we pass. That still gives an increased range over the solution without the amplifier, but would really like to use a bit more power if possible.

We're reaching out to Skyworks as well, but unsure how to proceed.

Thanks! Alex

[FormerMember]

Under which FCC rule does your device fail? Is it when testing for a "frequency hopping device"? If you plan to use BLE, your device should not be qualified as a frequency hopping device: While it does hop in frequency in connected mode, it doesn't in advertising mode. So it will fail the hopping requirements. Instead, the device should be qualified as a "Digital Transmission System" under FCC 15.247.