frequency domain reflectometry (FDR)

Frequency-domain reflectometry (FDR) is a frequency sweep used to localize the frequency behavior and reflections of transmission media in terms of frequency.

According to the procedure, frequency-domain reflectometry involves sweeping in which the frequency of a carrier frequency is continuously changed in such a way that the frequency range of the cable to be measured is covered. The swept frequency is fed into the high-frequency cable to be measured and partially reflected at inhomogeneities and impedance deviations. The reflected signal portion is transmitted back to the transmitter. It has the frequency of the sweep signal, but a different phase. At the receiving end, the amplitude of the reflected signal is related to the transmitted signal amplitude.

The results are determined at discrete frequency points and contain more information than time-domain reflectometry(TDR), since both the location of the inhomogeneity - of a connector, adapter, cable defect - and the reflected frequency and characteristic impedance are displayed. The FDR method is also characterized by a high dynamic range, which can be up to 100 dB, and offers high resolution for long cables.