I am using two RFM95 LoRa Radios to transmit and receive messages and would like to maximise the range of the radio. I am currently using the following settings:
#define FREQ 915E6 #define TX_PWR 20 #define SPREAD_FACTOR 12 #define BANDWIDTH 125E3 // #define CODING_DENOM 5
This all works fine but when I decrease the bandwidth of the radios to 62.5E3 (which should increase the range) the radios seem to stop working. The datasheet seems to state that this bandwidth should be supported.
I just wondered whether anyone knew why this might be? I found the following (from someone who I believe posts here):
A low bandwidth signal, such as 7.8kHz will give the best (longest distance) performance, but with the low cost components used in the Hope and Dorji LoRa® modules a transmitter and receiver may not talk to each other at this bandwidth. The receiver has a frequency capture range, this is the percentage difference allowable in relation to the bandwidth that the transmitter and receiver can be apart in frequency in order for the receiver to pick up the transmitters signal. This percentage is typically 25% of the bandwidth.
Low bandwidths of 20.8kHz have been used for long range trackers and they do give better performance, but care is needed as devices used at this bandwidth may not talk to each other unless a frequency calibration factor is measured and applied. Once communication is established at low bandwidth a form of automatic frequency control can be used to adjust the receivers base frequency to keep it within the capture range.
EDIT: In case it matters, I am testing the radios at very short range (<30cm) and without aerials.