Well spotted, I bought a roll of RG58 from a local supplier, ok I admit it was cheap, but I expected better, the lack of a good screen was made up for with the addition of a foil backed plastic wrap under the shield braid, similar to that seen in the pic above, the coax diameter wasn't even standard, but still marked up along it's length as RG58
I should check it's characteristic impedance, it's probably not even 50 ohm :headbang