Hi,
?
I hacked the standalone mode by adding another trace showing the combined gain of the LNA and PGA during a sweep.? If the AGC is enabled then the gain can be read in Register 0x69 bits 4-0
The vertical scale for the gain is 5dB/division.? T
he yellow trace is the 0-255 RSSI value from the SI4432,? I was too lazy to change the scale at the side for the quick hack.This is how the gain varies with agc enabled (x69 = x60).? The dBm value at the peak includes the correction for the filter/mixer loss, and yes I know it should say dBm not dB - fixed after the photos were taken.
Interesting how the gain drops early, and the spike at each change of gain.? Also interesting how the gain starts increasing before we get to the main signal spike.? Presumably the gain algorithm is working on the signal strength before the FIR filter?
Fixing the gain at the value the ALC chose, 37dB we get this:
go up to 43dB and we see some spurious signals and the peak RSSI drops - ADC overload?:
Drop down to 25dB and the peak RSSI stays at -13dBm but the minimum detectable signal level increases:
So it looks like the AGC does a great job of setting the best gain level, the RSSI value is compensated for the gain change, but there are unwelcome spikes at the changes in gain.? Perhaps some sort of on-demand "Optimise gain" button is needed where the gain at the peak (or perhaps the minimum through the sweep) is recorded and then used to keep a fixed gain throughout the sweep.
I tried detecting a change in gain then delaying and retaking the reading, but that did not offer an improvement.? Perhaps there is some instability and the gain is swapping between different levels?
73
M0WID
