DVB-S Measuring Technology - Digital Video and Audio Broadcasting Technology - page 276

15.4 Measuring the Shoulder Attenuation
The DVB-S signal within the wanted DVB-S channel should be as flat as
possible, i.e. it should not exhibit any ripple or tilt. Toward the edges of
the channel, the DVB-S spectrum drops off filtered with a smooth roll-off.
There are, however, still signal components outside the actual wanted band
and these are called the 'shoulders' of the DVB-S signal. The aim is to
achieve the best possible shoulder attenuation of at least 40 dB. [ETS
300421] specifies a tolerance mask for the DVB-S signal spectrum but, in
principle, the satellite operator can define a particular tolerance mask for
the shoulder attenuation.
The signal spectrum is analyzed using a spectrum analyzer and simple
marker functions.
Fig. 15.3. DVB-S spectrum with “shoulders“
15.5 DVBS Receiver Test
The testing of DVB-S receivers (set-top boxes, s. Fig. 15.4., and IDTVs) is
accorded great significance. For these tests, DVB-S test transmitters are
used which can simulate the satellite transmission link and the modulation
process. Such a test transmitter (e.g. Rohde&Schwarz TV Test Transmitter
SFQ, SFU) includes, in addition to the DVB-S modulator and upconverter,
an add-on noise source and possibly even a channel simulator. The test
transmitter is fed with an MPEG-2 transport stream from an MPEG-2 gen-
erator. The test transmitter then supplies a DVB-S signal within the range
of the first satellite IF (900 - 2100 MHz). This signal can be fed directly to
the input of the DVB-S receiver. It is then possible to create various signal
conditions for the DVB-S receiver by changing numerous parameters in
the test transmitter. It is also possible to measure the bit error rate as a
function of the C/N ratio. Such test transmitters are used both in the de-