Issue with LoRa long range modes and RFM95/RFM96

[ziplockk]

What I find interesting from the data collected is the RSSI very quickly drops to about -100dBm and stays there despite quite big changes of range . . . The moving radio pulls GPS location from a GPS receiver and sends this as its payload back to the static radio which logs the position and RSSI. Putting this onto google maps is simple enough.

[Russ Hedger]

ziplockk, could you try with the AGC turned off to see if that affects your RSSI?

RH_RF95::ModemConfig modem_config = {
  0x78, // Reg 0x1D: BW=125kHz, Coding=4/8, Header=explicit
  0xC4, // Reg 0x1E: Spread=4096chips/symbol, CRC=enable
  0x08  // Reg 0x26: LowDataRate=On, Agc=Off
};
rf95.setModemRegisters(&modem_config);

[ziplockk]

Good idea, will try and report.

Fd

[steve v]

For the RFM95 radios I find they always seem to work well using the off the shelf  sf128, and give me an open air range of better than 100 meters.

But when I switch over to the wider / slower configuration,   Bw31_25Cr48Sf512  some of the radios don't talk amongst the group.

When I investigate further  I found that the radios that do talk have the nominal  frequency of 915.000Mhz  +/-  3Khz

The radios that weren't talking in the group had a frequency of 915.00x   where the offset was greater than 4 Khz off

The solution to making everyone work was to measure the transmit frequency  with an accurate rf freq counter and then add the offset to the frequency in the sketch.

To get the RFM to transmit a steady CW frequency,  I just wrote a loop that on transmits a packet, with no pause for receive or acknowledge.  Doing this enables the frequ counter to lock onto the center frequency.

Now all of my Moteino RFM95 radios work with  an actual f of 915.000  +/-   1Khz   and the range is > 600 meters in a suburban setting with a 3 1/8 in ch wire antenna

[Felix]

steve, thanks for the knowledge sharing, any code snippet to support this solution you could illustrate?

[Russ Hedger]

Looking at steve v's configuration, I notice that the bandwidth is being set to 31.25 kHz. The crystals used in the RFM95W are reported to have too poor a tolerance to be reliable below 125 kHz. His manual calibration seems to work though!