A radio frequency applicator and method for heating a geological formation is disclosed. A radio frequency source configured to apply a differential mode signal is connected to a coaxial conductor including an outer conductor pipe and an inner conductor. The inner conductor is coupled to a second conductor pipe through one or more metal jumpers. One or more current chokes, such as a common mode choke or antenna balun, are installed around the outer conductor pipe and the second conductor pipe to concentrate electromagnetic radiation within a hydrocarbon formation. The outer conductor pipe and the second conductor pipe can be traditional well pipes for extracting hydrocarbons, such as a steam pipe and an extraction pipe of a steam assisted gravity drainage (SAGD) system. An apparatus and method for installing a current choke are also disclosed.