Digital Signal Processing Reference
In-Depth Information
of 3 to 10 times the resolution bandwidth, i.e. 300 kHz, is selected. To
achieve a certain amount of averaging, a slow sweep time of 2000 ms is
set. These parameters are needed because we are using the RMS detector
of the spectrum analyzer. The following settings are then used:
•
Center frequency: center of the DVB-T channel
•
Span: 20 MHz
•
Resolution bandwidth: 30 kHz
•
Video bandwidth: 300 kHz (due to RMS detector and logarithmic
scale)
•
Detector: RMS
•
Sweep: slow (2000 ms)
•
Noise marker: channel center (resultant C' value in dBm/Hz)
DVB
−
T
−
signal
_
bandwidth
C
[
dBm
]
−
10
lg(
)[
dB
];
resolution
_
bandwidth
Fig. 21.5.
Spectrum of a DVB-T signal
The level indicated in the useful band of the DVB-T spectrum (Fig.
21.5.) depends on the choice of resolution bandwidth (RBW) of the spec-
trum analyzer (e.g. 1, 4, 10, 20, 30 kHz) with respect to the bandwidth of
the DVB-T signal (7.61 MHz, 6.66 MHz, 5.71 MHz). In the literature
(DVB-T standard, systems specifications), 4 kHz is often quoted as refer-
ence bandwidth but is not always supported by spectrum analyzers. At
4 kHz reference bandwidth, the level shown in the useful band is 38.8 dB
(7.61 MHz) or 32.2 dB, respectively, below the level of the DVB-T signal.
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