MultiNav Pro+ BLE - does TX power scale down automatically at short range?

The MultiNav Pro+ doesn't do automatic TX power scaling based on measured path loss out of the box, but you can absolutely manage it yourself through the AT+TXPWR command if your firmware can estimate link quality from the RSSI feedback - at 50-200m you're probably sitting on like -60 to -75 dBm which means you could drop TX power significantly and still have tons of margin. Honestly for your solar/supercap setup I'd just set a conservative fixed power level for normal ops and only kick it up when RSSI drops below a threshold, way simpler than a full adaptive loop and your battery situation will thank you.

@James Martinez yeah your instinct is right and the approach you've already outlined is basically what I'd do too. At 50-200m you've got so much link margin to burn that you could probably drop TX power by 10-15 dBm and still have a rock-solid connection, which translates to meaningful current savings on the radio side.

 

The threshold-triggered approach is genuinely simpler to tune and debug than a full closed-loop adaptive system — just pick a conservative RSSI floor like -80 or -85 dBm as your "kick up" trigger and you're done. One thing worth adding though: build in a little hysteresis so you're not toggling power back and forth if RSSI is bouncing around near the threshold. Something like "kick up at -85, step back down only if RSSI holds above -70 for N consecutive readings" keeps it stable without a lot of complexity.

 

Also worth thinking about is your supercap sizing against worst-case cloudy stretch — the Power/Program Kit's 5-min charge / 24-hour runtime spec was designed around running the full module stack, so if you're already using that, your headroom is probably better than you think even at higher TX power. But yeah, lower power for normal ops is just good practice regardless.

Yep Barbara's approach is solid, and to add to it - if you're already polling RSSI for other reasons, you can feed that into a really simple hysteresis loop so you're not constantly toggling power levels and burning extra write cycles on the config. I did something similar on a LoRa node last year and ended up with like 3 power tiers (short/mid/long) triggered by RSSI thresholds, worked great and the logic was maybe 20 lines of code total.

Seconding the 3-tier approach Jennifer mentioned - I'm running almost exactly that on a solar node right now and honestly the hysteresis is the key part, without it you'll get this annoying flicker around the threshold boundaries that wastes more power than it saves. One thing I'd add: log your RSSI samples over a few days before you set your thresholds, because depending on your environment the numbers can shift more than you'd expect with weather/multipath and you want some real data before you hardcode anything.

John's point about logging first is huge - I spent way too long tuning thresholds on gut feeling before I actually pulled the data and realized my RSSI was swinging almost 15dB between morning and afternoon just from foliage moisture on a partially obstructed path. Definitely do a few days of passive logging before you commit to anything, and if you can swing it, grab samples across different weather conditions since your solar situation means cloudy days are exactly when you need the power budget to behave predictably.

Thomas nailed it on the foliage thing - I saw similar swings on a partially-wooded path and it caught me completely off guard. One thing worth adding: if your supercap is small enough that cloudy-day power budget is tight, I'd actually bias your thresholds a bit conservatively (lower power tiers trigger earlier than your data strictly suggests) since the cost of occasionally running at slightly more TX power than needed is way less than the cost of a brownout resetting your node mid-session.

One more thing to stack on Susan's conservative threshold idea - if you can read your supercap voltage over ADC, tie that into the tier logic too so at low SoC it forces down to the lowest TX power regardless of RSSI, basically a "limp mode" that prioritizes survival over link quality. Saved me on a similar solar build where a week of overcast just slowly drained the cap to the point where even my conservative RSSI thresholds weren't enough.

Joseph's limp mode idea is exactly right and I'd actually extend it slightly - if you're already reading supercap voltage for that, consider logging those voltage samples alongside your RSSI data so you can see how the two correlate across weather events, makes it way easier to tune the SoC threshold so you're not dropping to low power too early on a slightly cloudy day vs actually needing to conserve hard.

Richard that's a really clean idea - having the RSSI and cap voltage on the same timeline makes it way easier to spot if your thresholds need seasonal tweaking too, since a "normal cloudy day" in summer vs late fall can hit the cap pretty differently depending on your panel angle and how much ambient you're actually catching.

Charles that's a good call on seasonal drift - one thing I'd add is if you have spare flash or even just EEPROM, snapshot those correlated samples with a timestamp so after a full year you can actually go back and see if your thresholds still make sense rather than just guessing from memory.