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Tool/software:
Hi TI team,
My customer wants to develop an IoT product in the 924.6 MHz band.
Please answer our customer's questions.
IoT transceiver usage conditions
1. Frequency: 924.65 MHz and 924.7 MHz
2. Bandwidth within 10KHz
3. Modulation : 2-FSK
4. Communication : Simplex
Question:
1. Is it possible to set the total bandwidth to 10KHz, 10KHz or less, or other bandwidths by varying Frequency Deviation & Data rate?
2. Is there a mode where frequency stability (±1 KHz) can be checked in CW mode?
3. There was a phenomenon that PLL locking was not possible while using a transceiver from another company.
1) The frequency offset occurs from 924.6 MHz to approximately 1.2 KHz when power is on.
2) Frequency flow at 924.6 MHz (slowly shifting CW waveforms)
If CC1120 is not satisfied with the relevant performance, please recommend another transceiver.
Hi,
Just a few comments regarding your questions.
Q.1 We're using the CC1120 and derivatives of these parts with a higher transmission bandwidth than OCBW=10KHz. You may need to confirm you're refering to the Transmitter's occupied bandwith with the 2-FSK modulation scheme ?!? Or are you refering to the receiver bandwidth ? Regarding the former, from memory the CC1120 should be able to be configured via its registers so that you obtain the OCBW to be about 10KHz, but you will need to measure this to confirm. Adust the deviation and data rate to get just under 10KHz by measurement.
Regarding Q2. You will need to measure this by setting the CC1120 in CW mode at a particular frequency, then adjust accordingly to get the required frequency. There is also a Tx autocalibration mode that you can configure that "pulls" the transmitter back into calibration once in a while (say every 4 Tx or more etc). This would allow you to ensure the frequency stability with time. Also ensure the Quartz Crystal (32 or 40MHz) you're using is of a low PPM type with regards to frequency drift etc.
Q.3 not sure what this means ?!? the CC1120 is a transceiver and PLL locking is handled by the device. Are you refering to the particular frequency range you are using ? Check the datasheet if your frequencies are within the device's specifications.
Q.4 Again, you need to measure this a set accordingly using the frequency setting's registers, and also ensure the frequency calibration registers are set accordingly to ensure auto-calibration. The autocalibration is set to be active during transmissions, but not sure if it is also active in CW mode. You may need to perform modulated transmissions (say with ASK mode or similar) to measure the drift when doing real transmissions ... Or it might also work fine with 2-FSK with a very low baud rate ...
Q.5 Slow drifting CW when in CW mode might be observable for various reasons. One of them is that if you keep the transmitter in CW mode at full output power, some self heating effects will effect the frequency drift, or there may be drift from the crystal with time. However, most transmissions are usually in burst mode and the CC1120 is not in permanent Tx mode all the time, so self heating may not be as relevant and may not be a real problem. You may need to set your own acceptable limits for your application, and realise that in CW mode there are self heating effect, but this CW mode is not a real mode that you'll be using in the real world etc.
You might consider the CC1125 for tighter specifications but it is also more expensive ...
Hope this helps in some way. Cheers, MM
Hi,
This is possible and please refer to SmartRF studio for the register settings.
Please start with the generic 868/915/920 MHz PHY for the Narrowband as shown below. This can be set to 924.650024 MHz and 924.699951 MHz.
This has a Rx bandwidth of 10 kHz. It is possible to use 8 kHz Rx bandwidth on the CC1120. Using a small Rx bandwidth is dependent on the data rate and crystal tolerance.