Promax PROLINK-4 Manual De Instrucciones página 160

DVB-C channels tuning may require an adjusting process. It is recommended to follow
next procedure:
1.- From the spectrum analyser mode, tune the channel at its central
frequency.
2.- Switch to TV mode, BER measuring mode.
3.- If in the lower line of the screen does not appear MPEG-2 message (and
consequently BER is unacceptable), by turning the rotary selector deviate
the tuning frequency until MPEG-2 message appears. Finally tune channel
again to minimize the frequency deviation which optimizes the BER and
therefore minimize the BER.
If it is not possible to detect any MPEG-2 channel, make sure that digital signal
parameters are correctly defined and if signal level is too low, check that the 30 dB
attenuator is not activated (Attenuator 0 dB).
4.9.1.5.2 Measuring BER of COFDM Digital Channels (COFDM)
Press the rotary selector to access the COFDM signals parameters that must
be defined by user and that are described below:
1) Carriers
It defines the number of modulation carriers between 2k and 8k. To modify its
value, place the marker over the Carriers field by turning the rotary selector and
then press it: a menu will appear on the screen. Turning the rotary selector
select the desired value for the Carriers parameter and finally press it again to
validate.
2) Guard interval
The Guard Interval parameter corresponds to the time between symbols, its
purpose is to permit a correct detection in multi-path situations. This parameter
is defined according to the symbol length: 1/4, 1/8, 1/16, 1/32. To modify its
value, by turning the rotary selector, place the marker over the Guard Interval
field and then press it : a menu with the available values will appear. Turning
the rotary selector select the desired value and finally press it to validate. If
Guard Interval parameter is not known it is possible to assign the Auto option
for its automatic detection.
3) Channel BW (channel bandwidth)
Enables the channel bandwidth to be selected between 8 MHz, 7 MHz and 6
MHz. The selection of this parameter is essential for the correct operation of the
tuner, as it affects the frequency separation of the carriers.
Page 42
USER'S MANUAL. PROLINK-4
IMPORTANT REMARK
02/2003