Hello Morse Micro team,
We are currently working with the MM8108 chipset in a setup where TX and RX signals are separated. Some boards use external PAs (for example, the GRF5509) on the TX path, while others use a bare MM8108 without a PA.
We’ve observed that in a mesh network configuration, the nodes without PA show a very high received signal strength (high RX signal) when receiving from a node with a PA, yet the RX data rate (or TX rate of the MM8108+PA side) remains unexpectedly low — typically below 8.8 Mbps.
There’s no noticeably high noise floor or instability in the link, which makes this issue puzzling. Our current hypotheses include:
- Possibly high ACLR or non-linearity introduced by the PA.
- A rate-control mechanism in the MM8108 firmware or MAC layer that might be automatically reducing the TX/RX rate in response to certain signal conditions.
Could you please provide guidance or suggestions on how to identify the root cause?
- Are there known conditions under which rate control intentionally limits the data rate?
- How sensitive is the MM8108 to PA linearity or ACLR performance?
- Are there recommended configurations or calibration steps when using external PAs with the MM8108?
Any diagnostic tips, firmware parameters, or test procedures to isolate the issue would also be very helpful.
Thank you for your support.
V