Add Support for SX1276 (902-928 MHz LoRa)

[John Gorkos]

I have the US-ISM version of the TTGO T-Beam, with the SX1276 chip and tuned for 900-928 ISM in the US. I would like to use the T-Beam as an IGate/Digi at 913.500Mhz.

Ideally, this would be a simple configuration option in the config file. I've attempted to switch line 19 in TaskRadiolib.cpp from:
_radio = new SX1278(_module);
to
_radio = new SX1276(_module);
And it builds, loads, and seems to run correctly, but never receives anything. I have verified the transmitter is working correctly, and have received packets from a transmitter on the same bench with other LoRa receivers. I'm assuming the syncword is 0x12, but I can't find verification in the code. As a side request, the ability to set syncword would also be nice.

Happy to provide any additional information. I'm looking to use the following LoRa setup:
"lora": {
"frequency_rx": 913500000,
"gain_rx": 0,
"frequency_tx": 913500000,
"power": 20,
"spreading_factor": 7,
"signal_bandwidth": 125000,
"coding_rate4": 5,
"tx_enable": true
},

Thank you,
AB0OO

[John Gorkos]

Ahh, it was a bad LoRa module. It had enough magic smoke to fake it, but not enough to work. Replacing SX1278 with SX1276 does, indeed, work.