FCC Certification /Digital modulation minimum bandwitdth

RE: FCC Certification /Digital modulation minimum bandwitdth

LovejoySteph — Tue, 09 May 2017 05:26:31 GMT

Thanks AmbystomLabs for the previous comment.

As suggested by Bjørn Spockeli. I posted my question through the Mypage and they were able to help me.

They suggested to send random data, with the use of the radio test example to increases the bandwidth of the signal. Which seemed correct since I was only sending a fix data.

They also pointed that the radio was maybe not set up in BLE mode. Which was also correct since my radio was set to RADIO_MODE_MODE_Nrf_1Mbit

By modifying the radio mode to RADIO_MODE_MODE_Nrf_2Mbit and using the radio test example, I was able to obtain a 673 kHz bandwidh at 6dB

For the record, these are the result I obtain with 3 different radio mode:

RADIO_MODE_MODE_Nrf_1Mbit
RADIO_MODE_MODE_Nrf_2Mbit
RADIO_MODE_MODE_Ble_1Mbit

RE: FCC Certification /Digital modulation minimum bandwitdth

AmbystomaLabs — Thu, 04 May 2017 22:49:33 GMT

I just wanted to pass this along. Here is a sweep of our own design using the nRF52832. This is the output off of the pcb antenna close coupled to a test antenna. As you can see our 6dB bandwidth is about 654kHz. Plus we have good symmetry of the waveform. The center frequency is off by about 60kHz but that is well within the ppm spec for the crystal and bluetooth. Spectrum Analyzer Sweep

RE: FCC Certification /Digital modulation minimum bandwitdth

bjorn-spockeli — Tue, 02 May 2017 08:49:31 GMT

@lovejoy: Just letting you know that you can submit your schematics and layout through our Mypage support portal for a review by one of our RF Application Engineers. All files will be treated as confidential and will only be available to our Tech.Support staff.

RE: FCC Certification /Digital modulation minimum bandwitdth

LovejoySteph — Tue, 02 May 2017 05:38:06 GMT

Thanks AmbystomLabs for your answer.

I will definitely work on improving the matching between the output of the nRF and the antenna. Thanks again for your time and I will keep you updated if it worked.

RE: FCC Certification /Digital modulation minimum bandwitdth

AmbystomaLabs — Mon, 01 May 2017 16:23:19 GMT

Without extensive testing of your design, it is impossible to tell exactly what is going wrong on your test. However, there are a few things that stand out:

There is a little too much attenuation ahead of a spectrum analyzer. As a result the noise floor seems to be unusually high at about -40dBm. Or, maybe not. Hard to tell unless one spans out. The excess noise floor tends to compress the overall dynamic range one would see here.
Probably the most significant thing is the tilt in the waveform. It should be very symmetric. The most direct cause of the tilt is the lack of quadrature in the modulation. But since this is fixed inside the nRF the more likely cause is poor matching at the output of the nRF. Matching issues can wreak all kinds of havoc on the shape of the waveform from the reflected signals.

So, look at how good your matching is first.