First, the purpose of the test
Frequency hopping is a good way to resist external interference and multipath fading, which divides the frequency into separate physical channels. LoRa wireless communication is no exception, and channels need to be divided by frequency. LoRa's center frequency and communication bandwidth can be dynamically set. This experiment aims to test the relationship between bandwidth and channel division.
Second, the test method
As shown in the figure above, connect the two iWL881A to the PC through the USB to serial port. Modules support shell commands and can set BW (bandwidth) and Freq (frequency). After receiving the data, the RX module prints to the PC screen via the UART.
Third, the test data
Fourth, the test summary
1. From the "test data", the division of the channel is closely related to the bandwidth. Consider the security isolation:
Channel spectrum = 1.5 * bandwidth, the frequency band is distributed along the center frequency. For example: BW=125kHz, Fc=470MHz, the channel distribution is as shown in the figure below (example 5 adjacent channels):
2. Because of the deviation of the crystal oscillator and related circuits, the channel is often not strictly developed along the set center frequency, for example, BW=125kHz, Fc=470MHz, theoretically the channel is 469.9MHz~470.1MHz, and the test channel is 469.975MHz~470.1MHz. . This is also the reason why the channel spectrum is set to 1.5 times the bandwidth.
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