Rohde & Schwarz R&S FSL3 - Digital TV Measurement Examples

Cable TV Measurements (Option K20) R&S FSL
1300.2519.12 2.70 E-11
If the transmitter's (DUT) local oscillator does not provide the exact nominal carrier frequency (CF), a
c
arrier frequency error results. The carrier frequency error is displayed in the result table of the
Overview measurement.
f
f
measuredCFidealCF
errorfrequencycarrier =__
Good local oscillators have low phase noise. Phase noise causes an unwanted phase modulation. The
Cable TV Measurements option measures the phase jitter that corresponds to the variance of the phase
error. .(/) represents the phase difference between the (noisy) measurement meas(/) signal and the
ideal transmit signal ref(/). The phase jitter is only evaluated at symbol instants, i.e. for
symbol
Tt = 
{
}
(
)
{
}
{
}
)()()(_
2
2
*
 ErefmeasEjitterphase ==
A non–flat frequency response of the analog hardware (amplifiers) or the transmit channel
(reflections or echoes in the TV cable) causes inter–symbol interference (ISI). To much ISI leads to
wrong symbol decisions in the QAM measurement demodulator. The QAM measurement demodulator
can suppress the channel's influence by filtering the receive signal with the inverse of the channel's
response. This operation is done by the so–called equalizer. With the equalizer activated (see Digital
TV Settings dialog box in Fig. 2-51), the EVM and MER values decrease by the ISI which was removed
by the equalizer. Activating the equalizer leads to two things: First of all the equalizer is trained based
on the received data of the current measurement (Freeze Equalizer option deactivated). Furthermore,
the measured signal will be filtered / "equalized'' with the previously estimated equalizer filter. If the
equalizer has reached a stable state and the channel does not change (time invariant channel) the
equalizer can be frozen by activating the Freeze Equalizer option. By this means the equalizer will not
be trained anymore but will still equalize the signal. Please also refer to the Echo Pattern measurement
(channel analysis).
The term n(/) is the synonym for any kind of distortion and thermal noise that has not been covered by
the transmitter and distortion model of Fig. 2-50 yet. In classical communication theory n(/) is modeled
as additive white Gaussian noise (AWGN).
EVM and MER result parameters are calculated based on the error vector signal, which corresponds to
the difference between the measurement signal meas(/) and the ideal transmit signal ref(/). The error
vector signal is only evaluated at symbol instants, i.e. for
symbol
Tt =  .
To a certain extend the QAM measurement demodulator is insensitive to distortion, but if there is to
much of it, erroneous symbol decisions may occur and the results will not be valid anymore. A
possibility to check this is to have a look at the constellation diagram. If the clouds around the
constellation points are getting much bigger than the (horizontal and vertical) decision borders or if
there is even only one single big cloud, this will be a strong indication for a faulty QAM analysis. The
QAM measurement demodulator of the Cable Measurements option was designed by taking the
transmitter and distortion model from above (see Fig. 2-50) into account.
Digital TV Measurement Examples
These measurements are set up to carry out single channel measurements of digital TV signals. The
settings for digital TV measurements are described in section Digital TV settings. The test setup for the
following measurement types is provided in section Digital TV test setup.
The digital TV measurements offered by the Cable TV Measurements option can be divided into two
groups:
 spectrum analyzer measurements
 measurements based on the measurement QAM demodulator