For me, my electronics is not as good as my development skills ;-). But I gave it a try. According to the datasheet the NRF24 will consume about 14 mA max. My cable is 2 m max, so then the resistance is 0,16ohms. So if I understand correctly the voltage drop would be 0,00224 volt. Sounds neglegtable to me? Also; can't I just measure the voltage at the end of the cable once it's connected to the RPI?
At the stackoverflow page somebody says: "In an answer on a Microchip forum, Jan Axelson, author of 'Serial Port Complete', claims a maximum cable length of 10' for the SPI bus. Other posts have mentioned the same figure.". So 10" is about 3 metres, so I am within that range. I do understand though that this isn't a preferred thing to do.
Which makes me wonder how other people handle this. I mean; I think ideally you'd want the radio that is connected to the controller in the most 'center' way of the home, right? So do people just hange the Pi and the whole shebang to the ceiling? I'd rather put the controller in the closet where my modem and router are, and then only wire the receiver to outside the closet. Isn't there a better way to do this?