Pascal.
Eric TsaiMy understanding is that the total radiated power of the LoRa module is a combination of
1) transmit power on the output stage (AT+TXP)
2) antenna gain (AT+ANT).
Valid values for AT+TXP are 0-20 (dB).
Valid values for AT+ANT are -128 to 127 (dBi), defaults to 3, which is the antenna that it’s certified for. The AT command document states that the AT+ANT is used to help adhere to transmit power regulation (FCC, etc..)
If you enter a really high value for antenna gain (say AT+ANT=15) and set the max AT+TXP=20, does the mDot actually dial down your transmit power (AT+TXP < 20) to meet FCC, despite your setting? In effect, the firmware is de-rating TXP based on what you enter for ANT?
I’m confused how this ANT value is useful. If we decide to save power by using a larger gain antenna, we’re going to need to go through the FCC certification anyways, in which case we’ll be tuning the TXP value down and probably don’t want the LoRa stack applying an ambiguous de-rating.
On the other hand, if we use a lower gain antenna than the certified 3dBi one, it doesn’t make a difference if we remember to modify ANT or keep it at the default, because no de-rating will occur. Is that right?
Jason ReissThe AT+TXP and AT+ANT effects will be changed for the US915 in the next release. The current release will subtract the gain from the output power
Under FCC the maximium conducted output allowed is 1 W (30 dBm)
Depending on the number of channels enabled and the datarate used this limit may be 21 or 24 dBm
Antenna gain up to +6 dBi is allowed with 1 W.
Higher than +6 dBi must dial back the conducted power the amount of gain over 6 dBi
The mDot library will use the antenna gain and tx power settings to stay below.
PascalDoes that mean we can increase the output power by pretending the antenna gain is terrible?
For example, TXP is set to 20dBm.
What happens if I set ANT to -128??
I need to know this because my firmware will allow for configuration changes in the field and I need to know which configuration parameters and their feasible ranges I need to account for.