Closed S5NC closed 9 months ago
Let's take a look at the relevant datasheet sections (taken from DS.SX1261-2.W.APP, Rev. 1.2):
This references the SetPaConfig command:
The description of that command claims that deviceSel
should be used to selected between the SX1261 and SX1262 devices. So, does SX1262 really implement both a low power and a high power PA? I was not able to find that information in the datasheet.
That's really interesting, I hadn't thought of that. Maybe they meant to say "if high power PA model is selected" meaning SX1262. On https://www.semtech.com/design-support/lora-calculator if you select SX1262, your TX power options are limited to the range -9 to +22 dBm, but if you select the SX1261, you are limited from -17 to +14 dBm, this would be in line with this theory. The wording below also increased my suspicions:
And the below seems to imply that the range for both radios is having 32 options for power, for the SX1262 this would be 22 dBm to -9 dBm
However, an indication that there is both a high and low power PA in the SX1262 is the line, or maybe it is just because the PAs used are different?:
hpMax selects the size of the PA in the SX1262, this value has no influence on the SX1261
There are 8 possible values (inclusive, inclusive) from 0x00 to 0x07. -9 (high power mode minimum power), but lowering the power by 7 intervals using this would result in a minimum power of -16 dBm, not -17 dBm, besides one would expect an on/off toggle between a low or high power PA if there were two of them.
Now I check, it seems this may be you last year: https://forum.lora-developers.semtech.com/t/sx1262-tx-power-less-than-10-dbm/1354 I agree that it is ambiguous wording on their datasheet, but I am glad you could get a response from an official Semtech rep.
Honestly, I was always confused about the SX126x power configuration, there's just way too many magic parameters for me to like. I think that the reference about hpMax is just because the PA is different, though I never got too deep into that. And you are right, that is me from one year ago.
I think at some point the Semtech support guys mentioned a new release for the datasheet with some more information about previously undocumented features, so we'll see.
See 13.4.4 SetTxParams in the SX1261/2 and SX1268 datasheet. Use case: The SX1262's low power PA is assumed to have less noise than the higher power PA. A 9 dBm input is needed to reach the P1dB of an external PA. 9 dBm can be provided via the SX1262's high or low power PA, in this case it is best to provide it via the low power PA.