After further testing today we've discovered:
- The false carrier-detection actually seems to occur only at the sub-harmonic frequencies (868MHz / n), and we have noted problems at n = 2,3,4 ....8.
- We have verified this behaviour on multiple units (including two of our own CC1101 designs as well as the CC1101-CC1190EM 869MHz ref 2.1 board).
We used RF studio in continuous-RX mode with default settings to test with the CC1101-C1190EM module. The susceptibility was present across all default configurations for the CC1190 range extender mode.
We also verified the same susceptibility using the CC1101EM (ref1.0) in the same way.
Our lab test setup uses an HP8640B signal generator and passive magnetic probe, so it is possible we are creating more than the required 3V/m RF field, however the change in RSSI shown in RF Studio is substantial at these frequencies, even at relatively low HP8640B power levels. It is hard to see how Listen-before-talk (LBT) can work if we have to perform carrier sense correctly at no more than -90dBm, but the RSSI is higher than this when the unit is subjected to an RF field at these other sub-harmonic frequencies.
Any suggestions would be greatly appreciated.
Best regards
Hayden