We have tried first round of test, very very simple setup, to just make sure all can work and what is the performance by default without any optimize.
- A pair of module, both flashed with get_started sketch
- receiver module powered by 9V battery (on board xc6206 only support up to 6V, this is wrong)
- transmitter module powered by FT232RL at laptop to see serial output result.
- Laptop send packet, both module run in “ping-pong” mode, so lucky it should have round-trip feedback.
- A pair of module, transmitter module flashed with radiohead RF95 reliable client sketch, receiver module flashed with radiohead RF95 reliable server sketch.
- transmitter module powered by lithium battery, powered and send data packet.
- receive module powered by FT232RL laptop, receive data and send hello back
- Both module soldered spring coil 433MHZ antenna.
Some points we already know:
- The on board nrf24duino can reach TX power +7dbm, we use default sketch, not sure if can make it better.
- No 2.4G wifi connection to interfere, laptop wlan even turn off.
- Not test voltage, not test current, not power TX power. Just rough test.
- Wifi range, data could congest is a busy channel selected, can use a scanner.ino to find good/bad channel.
- 0 => 2400 Mhz (RF24 channel 1)- wifi start
- 1 => 2401 Mhz (RF24 channel 2)
- 76 => 2476 Mhz (RF24 channel 77) standard
- 83 => 2483 Mhz (RF24 channel 84) — Wifi goes to about here
- 124 => 2524 Mhz (RF24 channel 125)
- 125 => 2525 Mhz (RF24 channel 126)
- 250KBPS instead of 2MBPS could greatly improve the range.
- dBm Tx power set to +13dbm on this round of test (set by default), could set to 20dbm (or 23dbm):
- // Defaults after init are 434.0MHz, 13dBm, Bw = 125 kHz, Cr = 4/5, Sf = 128chips/symbol, CRC on
- // The default transmitter power is 13dBm, using PA_BOOST.
- According to manufacture, set bandwidth bigger can get longer distance.
- With a dipole antenna like that, the signal tends to go out in the shape of a doughnut, so the angle may not have it is the most optimum position which would be both sender and receiver perfectly flat with antenna sticking straight up so the signal is polarized the same and in the optimum position for rx/tx
- A buck/boost LDO regulator could fully drink the power of lithium battery.
- The giant metal railing that could impact the signal in a number of ways, should be avoid.
- A big high voltage transmission tower is behind the receiver.
Quick image took during test.
Test Result of NRF24duino :
- Get about 40-50 meters sight transmission distance, over this distance, packet will lose 50-90% .
- On 40 meters sometimes can send ok, but failed on round-trip check.
- PCB antenna should be face and point to receiver direction to get better result.
- Use Phone GPS to see two modules, maximum distance 800 meters, signal complete 100% lost on 900 meters. On 800m still can get 100% data packet.
- SX1278 can reach 3KM, so there are still much can be improved.
This is not very promising result, will check if anything wrong on code or hardware, and test again.
- TX power set on 13dbm, not full power, need more test.