This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
Team,
we did RF measurements on one of our product based on CC430F and we noticed unexpected spurious emissions near the carrier frequency.
We did some experiments to investigate what is causing the unwanted emissions and we are not able to find the exact answer. We have the same PCBs with the same SW programmed but some of them have "good" spurious and some of them have spurious too high - see attached print screen of the measurement of spurious emissions near the carrier frequency.
The yellow trace is "good" and the blue is "bad".
We can share schematics and PCB layout offline if helpful.
Do you have any advise what part of HW could cause above mentioned spurious increase (perhaps xtal)?
The crystal frequency is 27,0 MHz. We would like to operate at 2 frequencies: 869,52 MHz and 868,3 MHz.
Thanks for your help
TI Customer
Yes, you are correct: The PCB which has blue trace has always this result and the same for the "yellow" PCBs.
We have not tried to swap the chip yet but we can try it.
This is the 5.9 Unwanted emissions in the spurious domain - 5.9.1.1 Unwanted emissions for a TX mode.
I forgot to mention that there is also the CC1190 RF Front End on the PCB - the schematic and the PCB layout corresponds to the reference design: CC1101–CC1190EM 869 MHz Reference Design (SWRR075.zip).
Marek
Does that mean that the measurements are done after the CC1190? If that is the case, how does the signal look like on the output of the CC430 (To be more exact at the input of the SAW filter, with the SAW filter removed)?
Yes, the measurements in the first post were done on the antenna connector (after the cc1190).
We swapped the CC430 on "good" and "bad" PCBs and the "close spurious" followed the chip. So the differences are in the CC430...
We also measured the spurious at the input of SAW with SAW removed - You can see the result on the picture below. The yellow trace is the measurement on antenna connector (CC430+SAW+CC1190), the blue trace is at the input of SAW with SAW removed. I think that the result is the same (of course the power is lower without CC1190).
Marek
- yes, we are going to use different output power settings in the two bands:
1. fc = 868,25 MHz, CC430 reg. value = 0x23, ef. radiated power is approx. 12,0 dBm.
2. fc = 869,52 MHz , CC430 reg. value = 0x3D, ef. radiated power is approx. 22,0 dBm.
- I do not have the plots of measurement according 5.9.1.1 in certified laboratory. You are right that you can not see the "fail" conditions on my plots - my measurement is only informative, in conductive mode and are done on the antenna connector. The certification measurement was done in radiated mode with connected antenna with gain approx. +7dBi. The fail conditions happened around the 867,75 MHz with RBW 10 kHz, which is in the frequency range f c - m ≤ f < fc - n, as you stated.
- I did my measurement only to investigate what causes the difference between the same PCBs with the same SW and register settings programmed.