Measuring DVB-T Signals - Digital Video and Audio Broadcasting Technology - page 411

elaborate method in the Measurement Guidelines [ETR290]. In practice,
the DVB-T spectrum is in most cases simply measured by using three
markers, setting one marker to band center and the others to +/- (DVB-T
channel bandwidth/2 + 0.2 MHz). With an 8 MHz channel, this results in
test points at +/- 4.2 MHz relative to band center and +/- 3.7 MHz for the 7
MHz channel. Fig. 21.31, shows the spectrum of a DVB-T signal after the
mask filter (critical mask). The DVB-T standard [ETS 300 744] defines
various tolerance masks for various adjacent channel allocations.

*
*

RBW 10 kHz
VBW 100 kHz
SWT 10 s

Delta 2 [T1 ]
-55.44 dB
3.700000000 MHz

Ref -10 dBm

*

Att 15 dB

*

-10

Marker 1 [T1 ]
-30.46 dBm
212.500000000 MHz

A

-20

Delta 1 [T1 ]
-52.45 dB
-3.700000000 MHz

1 RM
CLRWR

*

1

-30

-40

-50

PRN

-60

-70

-80

1

2

-90

-100

-110

Center 212.5 MHz 1.5 MHz/ Span 15 MHz

Date: 19.MAY.2005 13:42:15

Fig. 21.31. Spectrum of a DVB-T signal measured after the mask filter (critical
mask)

In practice, the following shoulder attenuations are achieved:

• Power amplifier, undistorted: appr. 28 dB

• Power amplifier, equalized: appr. 38 dB

• After the output BPF: appr. 52 dB (critical mask)

Usually the tolerance masks listed in Table 21.3. (uncritical mask) and
21.4. (critical mask) are used for evaluating a DVB-T signal (7 and 8 MHz
bandwidth). In the corresponding documents (DVB-T Standard
[ETS300744], System Specifications), the ratio with respect to channel
power at 4 kHz reference bandwidth is usually specified. If the spectrum
analyzer does not support this resolution bandwidth, it is possible to select
a different one (e.g. 10, 20 or 30 kHz) and the values can be converted.
10lg(4/7610) = -32.8 dB and 10lg(4/6770) = -32.2 dB correspond to the
attenuation with respect to the total signal power of the DVB-T signal with
4 kHz reference bandwidth in the useful DVB-T band. If another resolu-