The invention refers to single-ended test of a loop with the aid of a transceiver, wherein an input impedance (Zin(ƒ)) of the loop is generated. The transceiver has a digital part, a codec and an analog part and is connected to the loop. With the aid of a transmitted and a reflected broadband signal (vin, vout) an echo transfer function Hecho(ƒ)=V(f)out/Vin(f) is generated, which also can be expressed as H echo ⁡ ( f ) = H ∞ ⁡ ( f ) ⁢ Z in ⁡ ( f ) + Z h0 ⁡ ( f ) Z in ⁡ ( f ) + Z hyb ⁡ ( f ) . Here Zh0(ƒ), Zhyb(ƒ) and H∞(ƒ) are model values for the transceiver. In a calibration process a test transceiver, with the same type of hardware as the transceiver, is connected to known impedances, replacing the loop. Hecho(ƒ)=V(f)out/Vin(f) is generated for the known impedances and the model values are generated and are stored in a memory in the transceiver. The stored model values are then used when the input impedance (Zin(ƒ)) for the loop is generated after a measurement of the broadband signal (Vin, vout) is performed.