Dear Board,
I can not figure out why the RSSI readings of the same incoming signal are hugely different, -35 with one RFM69W(2nd photo) connected through a bread board to a Moteino, and -90 with another RFM69W(1st Photo) just connected with a wires to a Moteino.
Is it because the ground plane is not big enough? How do I make them the same?
Please advise.
Signal strength depends on very many things. Your 2 setups are very different physically. Your antenna in relation with the ground plane and how orthogonal they are is very significant. This is going into antenna theory, I'm not an expert there but there are some threads in this forum (some sticky) that discuss some of these fine details.
You also want to make sure the "settings match the hardware".
In all reality when you expect the same results, you should have all things equal, certainly not the case in this setup you have.