FS100A and XYMK5V are super cheap and super simple 433MHz modules. Some people report they work well, some that link is lost even at a range of few centimeters. I've decided to test that, and do a proper range test in open space.
With proper antennas, those little 433MHz modules can have a decent range. Who would expect that...

How FS1000A and XYMK5V work:    • How they work? 433MHz radios for Ardu...  

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