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R&S FSH
Cable Measurements
1145.5973.12 4.117
E-11
Measurement
The R&S FSH performs a sweep over 1024 test points to measure the sum signal of forward and
reflected waveform. It transforms the sum signal in the frequency domain into the time domain by
means of the inverse FFT (IFFT). The IFFT has a length of 2048 points. The data set is zero-padded to
2048 points and evaluated by means of a Hamming window before performing the IFFT. The R&S FSH
corrects the result of the IFFT by using the correction values from calibration.
It then calculates the IFFT result into length units from the cable parameters, light velocity and
frequency range. In addition, the R&S FSH considers the attenuation of the cable to be measured in
order to display the discontinuities with correct level.
Length measurement accuracy
The length measurement accuracy is primarily determined by the deviation of the cable data of the
cable model from the real cable data. Depending on the cable, the data may exhibit a tolerance of up to
10 %. This deviation directly affects the measurement error. A second factor of influence is the display
resolution of the R&S FSH. Its uncertainty is
±
1/2 pixel or 1/2 x (length/301).