If sending by r.f., I think you’re aware that you need to make sure each emonTx sends using a different NodeID.
If one is connected serially, you can give it a Node ID offset in emonHub - which in effect means the default value of 0 can be increased to put it onto one of the pre-programmed definitions in emonHub. e.g. the original NodeID sent by the emonTx serially was 15, to move it to 17:
(N.B. - use the correct interfacer!)