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Digital modulation as per FCC

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dapu

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Sorry, it may be a little long post, please feel free to skip to next para. I have been learning electronics, and i came across a 2.4g RF module (XN97L) which got me interested in it. After working, and banging my head with google translate and chinese datasheet of this product, I finally feel confident that I have understood how to use it. Its very much similar to NRF24l01s out there, except it allows me to configure some BB_CAL, RF_CAL etc stuff. I initially started making a project on home automation using this, now after making some progress on it. I plan to use this and try my luck with selling some locally in my country, and in future maybe expand it to big startup. I understand that I need to meet regulations like FCC part 15, ETSI etc. for different countries for this transceiver module.

So what I was wondering is that will this module (XN297L), by any chance will qualify under FCC part 15.247? as GFSK is digital modulation, now given that this module supports "data-whitening/scrambling" and has maximum 13dbm of output power, and I plan to use no more than 8dbm, so no antenna gain is required either. I know it is not possible to say without proper tests and checking all technical stuff, but I am wondering if it will qualify under that digital modulation category, so I can get my product FCC certified in future by making small adjustments etc. In some papers I read online, they say that it is only valid for DSSS, whereas BLE also uses GFSK and it qualifies under digital modulation (not FHSS). Also page 4 of this paper here (https://www.semtech.com/images/datasheet/fcc_digital_modulation_systems_semtech.pdf), assuming same applies to 2.4G also. Please let me know, if I have not put forward my question correctly, and sorry for any mistakes in my understanding if any, as I am still learning about this.

Some details of that module :
Operating frequency 2400 Mhx to 2483 MHz
Phase-locked loop frequency step 1 MHz
Crystal frequency 16 MHz
Data rate Min 0.25 Mbps Max 2 Mbps

Δf 250K Modulation Frequency Offset @ 250Kbps Typical 125 Khz Max 150 KHz
Δf 1M Modulation frequency offset @ 1Mbps Typical 160KHz Max 300 KHz
Δf 2M Modulation Frequency offset @ 2Mbps Typical 320 KHz Max 550 KHz

FCH250K Channel spacing @ 250Kbps 1 MHz
FCH1M Channel spacing @ 1Mbps 1 MHz
FCH2M Channel spacing @ 2Mbps 2 MHz

PRF Typical Output Power Min 2 dBm , Typical 8dBm , Max 13 dBm
PRFC Output power range Min -35dBm Max 13 dBm
 

FSK modulation is relatively, but not totally, constant envelope. so much of the output spectrum is simply derived from how the FM deviation index is set. Sometimes there IS an analog, or a digital approximation to an analog, baseband filter before the modulated oscillator...and that can be set to "round off" the sharp digital corners...also helping in lowering adjacent channel interference.

I would say you have a very good chance of meeting the FCC emissions mask limits, (remember to check the harmonics too), but you need to set one up on a bench with a spectrum analyzer attached, and tweak the programmable registers until it looks good!
 

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