Hiya, I moved my emonPi to an outbuilding and needed to boost the EmonTH signals.
I found emonTH Range testing. It mentioned a “ground plane” which I tried with some success on the emonPi but I couldn’t work out how best to do it for the emonTH (I tried various orientations of the ground plane and the emonTH but couldn’t find a combination that made much difference).
I also found Improving RF Signal. As a result I screwed a 165mm length piece of wire (a single strand from a dead network cable) as an extra aerial to the GND (3rd screw from the left) of the emonTH.