Probably something like this: HJ9HP-50 Heliax High-Power Air-Dielectric Coax https://www.alldataresource.com/Commscope-HJ9HP-50-HJ9-50-HELIAX-High-Power-Air-D

Probably something like this: HJ9HP-50 Heliax High-Power Air-Dielectric Coax https://www.alldataresource.com/Commscope-HJ9HP-50-HJ9-50-HELIAX-High-Power-Air-Dielectric-Coaxial-Cable-corrugated-copper-5-in-black-PE-jacket_p_376121.html https://www.alldataresource.com/Commscope-HJ9HP-50-HJ9-50-HE...