All of these statements are wrong. Where did you come up with this stuff?The problem with twin lead was that stray signals could be picked up that interfered with the antenna signal.
It was found that the twin lead could be covered with foil that was grounded to stop this interference.
However, coax is better at preventing this interference and is cheaper to manufacture.
OK! If I'm wrong tell me why! Shielded twin lead was developed to prevent extraneous signal pickup. Also, unshielded twin lead had to be kept away from any metallic object by at least 6" or it would short circuit the antenna signal. This was unnecessary with shield. It could be strapped directly to the tower rather than use stand offs!All of these statements are wrong. Where did you come up with this stuff?