Cable TV Measurements (Option K20) R&S FSL
1300.2519.12 2.78 E-11
Echo Pattern measurement (channel analysis)
This measurement determines the magnitude of the channel impulse response in respect to the
corresponding time delay. Damage of TV cables causes unwanted reflections of the TV signal. These
reflections lead to echoes in the TV receiver. These echoes can be seen by looking at the echo pattern
trace. If the unit of the x–axle is changed into meters or miles (this requires knowledge of the
propagation speed of the cable, i.e. the velocity factor) the location of the cable damage can be
measured. This kind of measurement is sometimes referred to as distance–to–fault measurement: as
the position of a peak in the echo pattern trace represents the distance between the faulty part of the
cable and the location of the R&S FSL.
Test setup:
Refer to the section Digital TV test setup.
Procedure:
1. Press the MEAS key.
2. Press the Digital TV softkey.
3. Press the Channel Analysis softkey.
4. Press the Echo Pattern softkey.
5. To change the unit from Rs to km or miles:
Press the Velocity Factor softkey to define the velocity of propagation for the unit conversion.
Press the Unit softkey to select the unit.
6. To zoom into the echo pattern, press the Zoom softkey.
7. To adjust the input attenuator, press the Adjust Attenuation softkey.
8. Press the RUN key.
Fig. 2-56 Digital TV Echo Pattern measurement
9. To get correct measurement results the equalizer should be activated. A non–flat frequency
response of the cable channel may cause demodulation errors and thus corrupt the measurement
results. Inter–symbol interference can be suppressed by the use of the equalizer.
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