I feel like I must be missing something obvious because no one else is asking about this, but how do you make relays work? The most explanation I can find is that 'high gain' antennas can't be used as relays but 'low gain' antennas can. There seems to be nothing in-game that tells you if an antenna is high gain or low gain, so right off the bat I'm basically just guessing based on which antennas looks like an omnidirectional and which ones look like dishes. The in-game descriptions give the antenna type as 'direct' or 'relay', and that definitely doesn't correspond to omni or dish antennas, but I've tried building a relay based on that in-game description instead and it still doesn't work. I found something online that says you have to 'flag' your low gain antenna as 'relay', but... how do you do that? There's no option for that when you right click an antenna, either in the VAB or in flight. There's nothing for the antennas that can be toggled in the planner.