Impedance tensor and tipper vectors, known to connect the electromagnetic surface components for plane-wave excitation, are shown to be uniquely defined for horizontal electric or horizontal magnetic dipole sources. Two independent source polarizations are needed for their estimation in practice. Analysis of impedance tensors and tipper vectors for a layered half-space shows that the impedance tensor can be antidiagonalized by rotating the measurement system so that one of the measurement directions coincides with the direction to the transmitter dipole. The tipper vector points towards the transmitter dipole. In the static limit, all transfer functions are real, and simple analytic results for a homogeneous half-space show that impedance elements are proportional to the inverse of the product of conductivity and distance between source and receiver, while the tipper vector is a unit vector pointing towards the transmitter dipole.