Externally excited electric synchronous machine

An externally excited electric synchronous machine, comprising:

• a machine rotor including a rotor shaft and a machine rotor coil that is non-rotatably arranged on the rotor shaft, the machine rotor coil supplied with DC voltage during operation and providing a magnetic rotor field;
• a machine stator including a machine stator coil that is fixed relative to the machine stator, the machine stator coil providing a magnetic stator field during operation, the magnetic stator field interacting with the magnetic rotor field such that the machine rotor rotates about an axial axis of rotation during operation;
• a signal transmission device for contactless transmission of an operating signal corresponding to the DC voltage to the machine stator;
• wherein the signal transmission device includes (i) on the machine rotor, a signal coil connected in series with the machine rotor coil and (ii) on the machine stator, a magnetic field sensor that detects a magnetic field provided via the signal coil during operation;
• wherein the signal coil is arranged on an axial end-face of the rotor shaft;
• and
• wherein the magnetic field sensor extends axially into the signal coil.