Principle and Procedures of DTF Measurement
Measurement Procedures
 Read out the cable characteristics from USB memory
 Set the rough value of distance to discontinuity point or cable length
 Press the “CF/SPAN: Auto Set” key
 Select either
 In case of 50Ω:Equip MA430 with 50Ω terminator
 In case of 75Ω:Equip with adapter cable MC313 and 50Ω/75Ω adapter MA310. Equip with MA310 75Ω terminator.
 Execute the normalization
 Remove the terminator and connect the cable under test.
A waveform of the cable in frequency domain is observed
 Switch the mode to distance domain (Execute the Inverse Fourier Transform)
These processes are executed in MSA438TG automatically
$$
\begin{cases}
・\text{IFT}:
\\ \quad
f(t)=\frac {1}{2π} \int_{∞}^∞ F(jω) exp[jωt]dω
\\
・\text{The time domain data is obtained}:
\\
・\text{The time domain data is transformed into the distance domain}:
\\ \quad
\text{Distance＝Time×(Propagation velocity)}\\
・\text{A waveform on distance domain is displayed}
\\
\end{cases}
$$
image:A waveform on distance domain is displayed
 Measure the distance to the discontinuity point with a marker
 Save the measurement result in the USB memory
Data saved in USB memory
Parameters related to measurement
DTF Relative Propagation Velocity 0.659 Nominal Attenuation (dB/m) at 1GHz 0.787 Cable Attenuation(dB/m) 0.00 Cable Length (m) 15 Length SPAN (m) 98.84 Factory Name BLD Cable Type RG58A 58C START f (MHz) 62.5 STOP f (MHz) 562.5 
1001 points waveform data on distance domain
spect_DTF 0 0 47.84 ～ ～ ～ 1000 98.84 56.13

Principle of DTF measurement
For this measurement, “TG OUT” of MSA438TG is divided into the cable under test and “RF IN” of MSA438TG by the DTF adapter. When a discontinuity point exists, the reflected signal returns to the DTF adapter. The half of reflected signal is input to the “RF IN” thorough the DTF adapter. The combined two signals of this reflected signal and “TG OUT” are input to “RF IN”. The mutual interference occurs corresponding to the frequency and the distance to discontinuity point of the cable. Therefore, peaks and bottoms are continuously generated on the frequency axis, and its frequency corresponds to the distance to discontinuity point. The reflection at the discontinuity point appears as a peak when this frequency domain data are converted into the time domain data by the inverse Fourier transform. And after then, the distance to discontinuity point is gotten by the multiplication of the appearance time of the peak and the propagation velocity. As the horizontal axis value of the marker measurement, the distance is displayed instead of the frequency in spectrum analyzer mode. Therefore, the distance can be directly read when the marker is moved to the peak. The processing mentioned above is done at each sweep.