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olliw42 / mLRS

2.4 GHz & 915/868 MHz & 433 MHz/70 cm LoRa based telemetry and radio link for remote controlled vehicles
GNU General Public License v3.0
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R9 MX (+ similar) only support 13 dBm? #139

Closed jlpoltrack closed 8 months ago

jlpoltrack commented 8 months ago

Recently acquired an R9 MX and the Lua returns 13 dBm when choosing the 17 dBm option.

Looking at the code I see a few things I don't understand:

  1. Max Power is limited to 15 dBm even though 17 dBm is allowed for continuous use in the datasheet: https://github.com/olliw42/sx12xx-lib/blob/main/src/sx127x.h#L253, https://github.com/olliw42/sx12xx-lib/blob/main/src/sx127x.h#L261
  2. The 15 dBm limit is applied when 17 dBm is asked for here: https://github.com/olliw42/mLRS/blob/main/mLRS/Common/sx-drivers/sx127x_driver.h#L49
  3. There's a 2 dBm negative offset applied that I don't understand (this is where the Lua gets the 13 dBm value): https://github.com/olliw42/mLRS/blob/main/mLRS/Common/sx-drivers/sx127x_driver.h#L53

So it seems that when using a 'bare' SX1276, when 17 dBm is asked for you only get 15 dBm but the Lua returns 13 dBm due to the offset.

Should 17 dBm be allowed? Where does this 2 dBm offset come from?

olliw42 commented 8 months ago

I can't tell you what's going on from scratch, but tell that this equation is at the bottom of it all: https://github.com/olliw42/mLRS/blob/main/mLRS/Common/sx-drivers/sx127x_driver.h#L45 (you should find it in the datasheet)

did I maybe got the signs for the 2's wrong?

jlpoltrack commented 8 months ago

did I maybe got the signs for the 2's wrong?

I think this is it. For Pout = 17 dBm, outputPower should be set to 15. 17 - (15 - 15) -> 17 - 0 = 17

Current code adds 2 when it should be subtracted.

In the actual power line the sign is reversed as well I think.

olliw42 commented 8 months ago

yes, looks like it is wrong in the two places