what size/kind of wire do we need for the loop?

you can use a mildly shielded wire. up to 125' long.. best if 1 foot past loop line. single strand wire 20 ga -32 ga can be buried 2 feet or 2 feet above

its for a carpet track maybe 5 feet to cover track - i think the coax yellow wire to splitter box is fine but the wire we have now keeps breaking on small wire from after splitter loop side