440 Chapter10
Analyzer Options and Block Diagrams
Option 190 DVB-C Service Menus
Downconverter Test
Dncvrtr Test in the Service Menus leads to a set of menus used to
troubleshoot Option 190 RF Downconverter boards. Note that pressing
it also sets up the analyzer for 0 span and routes the signal path to
Option 190 board set instead of the spectrum analyzer. Thus, if a signal
was present on the analyzer input, the screen will show only the
analyzer noise floor after pressing
Dncvrtr Test.
The Switch Control key leads to a menu which will allow you to select
one of the 5 possible paths:
1.
Spectrum Analyzer will route the signal back to the spectrum
analyzer. If you press this, the screen will show the signal (in 0 span)
if one is present on the analyzer input.
2.
Demod 8 Mz SAW will route the signal through the Option 190
demod, 8 MHz SAW filter path.
3. Demod 4 Mz SAW will route the signal through the Option 190
demod, 4 MHz SAW filter path.
4. Demod 2 Mz SAW will route the signal through the Option 190
demod, 2 MHz SAW filter path.
5. Demod Bypass will route the signal through the Option 190
demod, bypass (no SAW filter) path.
DNCVRTR ATTEN allows entries from 0 to 60 dB to set the amount of
attenuation. Note that only even integer values are actually utilized
and the value is set to 30 dB when entering the downconverter test
menu.
PLL Control leads to a menu which will allow you to select the 240 MHz
PLL oscillator frequency (based on the channel bandwidth):
1.
PLL 8 Mz Channel will set it to 243.4 MHz.
2.
PLL 4 Mz Channel will set it to 246.85 MHz.
3.
PLL 2 Mz Channel will set it to 248.571 MHz.
Custom Freq in the PLL Control menu leads to another menu which will
allow you to set the 240 MHz oscillator to a custom frequency by
specifying the `N' and `R' words which are sent as 19 individual (serial,
MSB 1st) bits to the National semi LMX2325 PLL chip. The highest 11
bits of the `N' word is used to load the `B' register, the next 7 bits are
used to load the `A' register, the lowest order bit always a 0 for `N'
words. The highest 3 bits of the `R' word are not used, the next bit is a 1
to specify the 32/33 prescalar, the next 14 bits are used to load the `R'
register, the lowest order bit always a 1 for `R' words. The frequency is
given by:
Fo = 10 MHz * N/R where N = (32*B)+A
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