AX8052F143 spectrum behavior dependent on packet data

Hi all,

We are testing the modulation spectrum of an AX8052F143 using the Regulatory Tests provided by de AXRadioLab. I have attached the PhyLayer used (First picture below, COMDPhyLayer) As you can see, we are using GMSK modulation. Then, running the TX_PN9 Regulatory tests, the spectrum analyzer shows a perfect GMSK spectrum as expected. However, when the TX_1010 test is run, the spectrum is completely different, showing something similar to an AFSK modulation. Between both tests, we didn’t change anything from the configuration parameters. And looking at the code of the test, we cannot see any difference between both test cases apart from the data to send. So, is this issue expected? Has anyone ever come up with the same problem? Or maybe the TX_1010 is actually doing modulation changes that explain the different signal spectrum?

I have attached the screenshots achieved too. Second picture (COMD_1010) is the spectrum achieved with the TX_1010 test, and third one (COMD_PN9) is the one with the TX_PN9 test.


If anyone has experienced the same behaviour, I would appreciate your help.

Many thanks!

Irene Guitart

@irene.guitart

“RX PN9”, “TX PN9”, “RX PN15”, “TX PN15”, “RX PN17”, “TX PN17” are similar
to “RX 1010” and “TX 1010”, except that the BER measurement is performed
using a pseudo-random data stream. In PN9 mode, the data stream is
generated using the polynomial x9+x5+1, in PN15 mode, the polynomial
x15+x14+1 is used, and in PN17 mode, the polynomial x17+x12+1 is used.

Thank you for using our community forum.

Hi Martin,

Thank you for your response.

Then, if only the data of the packet changes in the test, does it make sense this difference between spectrum? Because seems that the modulation has been modified in the TX 1010 test. Do you expect that the micro varies the spectrum in function of the data packet sent?

Regards,

Irene

thanks for you support, but my question is different: when I use 0101 sequence, I’m not able to get the right spectrum (so the right modulation, MSK). Otherwise when I use PN9 packet, the spectrum is right (MSK). The configuration parameters are the same.
Can you explain the reason?

@irene.guitart
We will take a look at the wave-forms for both and get back to you on community forum.

Ok! Many thanks. I’ll wait for your feedback.

@irene.guitart

We tested today with the board that we have in hands, we figured since the AX8052F143 has an AX5043 radio core which would be similar to the AXM0F343 which also has the same radio core we will see if the issue would be reproduced.

PN9 mode : There was no problem noticed @ 436.7 MHz

TX1010 The problem was noticed intermittently @ 436.7 MHz

image

image

When TX1010 is used, it seems the VCO locking is unstable. Sometimes the spectrum view is good, sometime its bad, when it’s bad there is strong 2nd Harmonic tone. The VCO seems is not working properly.

We are using AXM0F343-256-915MHz board without external inductor, but we are configuring it into 436.7MHz. Similar to your case, using he F143-Mini-DVK which is available for 868 MHz only

When using a 436.7MHz board we recommend using an external inductor to fix this issue as recommended for the aforementioned frequency.

Thank you for using our community forum!

Hello Martin,

Many thanks for your information. It has been very helpful for our studies.

Regards,

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