I've finally made a little progress over the last two days. Lots of background reading on the excellent SX12XX library and some tinkering to make a portable radio modem for future testing
Here's the transmit end soldered up to a little bit of prototyping board I had lying around, which it turned out was the perfect size to fit the E28+breakout, Arduino Pro Mini, and voltage reg! All powered off a tiny 2S LiPo at the moment. The antennas are external Happymodel ELRS-intended and are supposedly 5dB...
The voltage divider is included for battery monitoring. I modified the 'varying power' library examples (numbers 10/20) to include sending one battery voltage packet per test and print serial bytes in a slightly more interpretable format for a python script to read and save to csv.
Just as a proof of concept, I looked at how RSSI/SNR vary with Tx power and RF attenuation, see below:
- TC1 = line of sight, 3-4m separation
- TC2 = as TC1 but cross-polarised antennas
- TC3 = several brick walls of attenuation
- TC4 = as TC3 but cross-polarised antennas
(and yes, the axes are intentionally the wrong way around since it's easier to fit the plots on a horizontal screen this way!)
Clearly something is working right as RSSI drops off linearly with Tx power! SNR performance leaves a bit to be desired but seems that @NeverDie had similar results. Not very exciting but showing the setup is correct for now and I can move on to some more interesting things.
Next up is to have a look at implementing the PA/LNA on the E28 modules and seeing what kind of difference I get in performance. Spotted the RX/TX_EN pins in the library documentation so I'll give those a go