Cable Measurements
R&S FSH
1145.5973.12 4.106
E-11
Press the DEFINE USER MOD softkey.
Select ATTENUATION... and confirm with the
ENTER key.
The current cable attenuation is displayed in the value
entry box in dB/m or dB/ft, depending on the unit of
length selected in the setup menu.
Confirm the current cable attenuation with the
ENTER key or enter a new cable attenuation and
confirm with the ENTER key or the DEFINE USER
MOD softkey.
The cable attenuation can be found, for example, in
the manufacturer's data sheet for the cable in question.
Preselecting the cable length:
The R&S FSH uses the cable length to determine the optimal span for the measurement. The longer
the cable under test is, the smaller the span used by the R&S FSH. The R&S FSH also calculates the
cable attenuation from the selected cable model and the length setting so that the magnitude of the
reflection at the fault is measured correctly. If the graphics display mode is selected for the results, the
R&S FSH scales the x axis so that it represents the total length of the cable.
If the entered cable length is less than the actual cable length, the R&S FSH does not display the faults
of the complete cable. A reflection at the end of the cable will not be shown. However, deliberately
entering a cable length that is too short is a good way of increasing distance-to-fault accuracy for a fault
that is near to the measurement plane. If the entered cable length is greater than the actual length, the
measured values for lengths beyond the cable length are useless because they are caused by multiple
reflections. If the length of the cable is not known precisely, it is best to enter a length that is about 20 %
to 50 % greater than the best estimate of the cable length.
Press the CABLE LENGTH softkey.
The R&S FSH opens the cable length (CABLE LEN)
value entry box and displays the current length setting
in meters or feet. The unit of length is selected by, and
depends on, SETUP: LOCAL SETTINGS: UNIT OF
LENGTH.
Using the numeric keys, enter the cable length in
meters and terminate the entry with the ENTER
key or one of the unit keys, or
Using the rotary knob (1 m steps) or the cursor
keys (10 m steps) adjust the cable length.
The minimum cable length is 3 meters or 10 feet. This value is determined by the maximum frequency
range of the R&S FSH. A cable length of max. 1000 m can be entered. The maximum cable length that
is suitable for measurements depends on the cable attenuation. Since the test signal must be twice
routed through the cable, the signal reflected at the cable end arrives with twice the cable attenuation in
attenuated form at the input of the power divider. Dynamic range decreases with increasing cable
length.
