RadioHeadModem.c

// Defaults:
// Bw = 125 kHz
// Cr = 4/5
// Sf = 128chips/symbol
// CRC on
RH_RF95::ModemConfig modem = {0x72, 0x74, 0x00};

void setBandwidth(uint32_t bw) {
  uint8_t index;
  uint32_t bandwidths[] = {
    7800,
    10400,
    15600,
    20800,
    31250,
    41700,
    62500,
    125000,
    250000,
    500000
  };
  for (index = 0x00; index < 9; index++) {
    if (bw <= bandwidths[index]) {
      break;
    }
  }
  modem.reg_1d = (modem.reg_1d & 0x0f) | (index << 4);
}

void setSpreadingFactor(uint8_t sf) {
  if (sf < 6 || sf > 12) {
    return;
  }
  modem.reg_1e = (modem.reg_1e & 0x0f) | (sf << 4);
}