Chapter 10 441
Analyzer Options and Block Diagrams
Option 190 DVB-C Service Menus
For the 8 MHz channels, R=50, B=38 and A=1 which yields 243.4 MHz.
For the 4 MHz channels, R=35, B=27 and A=0 which yields
246.85 MHz. For the 2 MHz channels, R=49, B=38 and A=2 which
yields 246.571 MHz. The two separate keys,
DECIMAL PLL N and
DECIMAL PLL R, are used to enter the 2 values and contain the default
values for the 8 MHz channel: 9720 (2602 hex) for the N word and
32869 (8065 hex) for the R word.
SHOW AGC VALUES will take a single AGC (signal) reading at the input
of the Option 190 demodulator input and display it both as a hex value
and as its equivalent `gain' (for example, the amount of downconverter
attenuation to subtract). With a signal at the input, by entering a value
into
DNCVRTR ATTEN and reading the AGC value returned by {SHOW
AGC VALUES}}, you can accomplish manually what the DLP automatic
level setting algorithm does. Note that if you want to duplicate the
value of attenuation shown during a measurement and the
measurement set the analyzer attenuator (AT) to 0 dB, you'll also have
to (manually) set AT to 0 dB.
The
AGC HOLD RUN key allows you to freeze the AGC circuit when
toggled to HOLD.
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