CAD transmit preamble length should match duration of receiver sleep cycle

[scott2b]

"There is support for Channel Activity Detection in the current Radiohead libraries for RFM95W. The function isChannelActive() places the module into CAD mode and returns true if activity is detected. Set the transmit preamble length to match the duration of the receiver sleep cycle. From my understanding of the datasheet, preamble length in symbols = cycletime * BW / 2^SF. So, for 1 second cycle at 500 kHz and SF7, preamble = 1 * 500000 / 128 = 3906 symbols."

https://lowpowerlab.com/forum/low-power-techniques/any-success-with-lora-low-power-listening/