Please don't use the cardboard. It is bound to bite you at some point if it absorbs moisture. No good can come from that, and its been mostly proven that the shield is not really grounding out, but could. It is coated. There are several alternatives such as a thin piece of plastic, 2 strips of electrical tape, 3d printed versions, etc. Search the forum and you will find many. I have the mRo in use with the original shield and it picks up great. I will say my other Solo (rev B) has the 3DR v2 shield and it works great as well. Not as many satellites, however it was immediately noticeable that it had improved its cold start performance. Personally I think the GPS thing has been blown a bit out of proportion for most individuals who's units worked perfectly out of the box. I say this as someone who fretted over all this tirelessly, and now have tried most every combination. In the end my solo worked fine for my purposes out of the box, but I had to try them. YMMV