R&S FSH
Cable Measurements
1145.5973.12 4.115
E-11
When SPECTRUM is selected, the R&S FSH turns off
the tracking generator and displays the spectrum over
the frequency range of the DTF measurement. To
indicate that the R&S FSH is in the spectrum mode,
DTF Spectrum is displayed in the top right-hand corner
of the screen. Otherwise, the R&S FSH uses exactly
the same settings as it did for DTF measurements.
The spectrum mode is used to check if there are any
spurious signals in the frequency range of the DTF
measurement. These are most likely to be present if
the cable under test is connected to an antenna.
When REFLECTION is selected, the R&S
FSH
measures the return loss over the frequency range
which has been selected for the distance-to-fault
measurement. This means, for example, an antenna
can be matched without altering the test setup. The
R&S FSH automatically switches the VSWR Bridge
R&S
FSH-Z2 or R&S
FSH-Z3 to the VSWR
measurement mode if REFLECTION has been
selected.
To indicate that the R&S FSH is measuring return loss,
DTF refl. cal is displayed in the top right-hand corner of
the screen.
Further information
Setting the span
If automatic setting (AUTO SPAN) is used, the R&S FSH automatically selects the span based on the
cable length and cable model entered. The shorter the cable under test, the greater the selected span.
If the center frequency is too high or too low for the cable length in question, the R&S FSH
automatically adapts it to the required span.
The R&S FSH calculates the span from the cable length as follows:
2048
1024
CL
2
v
c
1023
Span
r
0
=
,
where
c
0
= velocity of light
v
r
= velocity factor of cable
CL = cable length
1024 = number of pixels calculated
2048 = number of pixels included in inverse Fourier transform
If, in the case of short cable lengths, the 3 GHz frequency range of the R&S FSH is not sufficient to set
the span obtained with the above formula, the number of pixels calculated for displaying distance to
fault is reduced accordingly.
If the span is set manually, the R&S FSH calculates 1024 points as in automatic setting. Since,
however, not all 1024 points are valid owing to the restricted frequency range, the R&S FSH displays
