442 Chapter10
Analyzer Options and Block Diagrams
Option 190 DVB-C Service Menus
IQ Constellation
If SHOW KEYS ON OFF in the Service menus is set to ON, a Service key
will be present in the IQ Constellation menu. All the keys on this
Service menu are duplicates (for convenience) of keys under Service
menus discussed in the menu sections, except
Osc Control. Osc Control
leads to a menu which allows control of both the 240 MHz PLL and
71.1 MHz oscillators.
PLL OFS - 0 + is a 3-way toggle key. This key will offset the 240 MHz
PLL oscillator by −200 KHz when a demod based measurement is
started and the “−” is underlined or by +200 KHz when the “+” is
underlined. This key is also a left-over from prototype days when we did
not have control of the 71.1 MHz oscillator.
PLL Custom is also a left-over from prototype days and is a duplicate of
the
Custom Freq menu key described in the Downconverter Test section.
TUNE 71.1 OSC shows the current state of the 71.1 MHz oscillator and
allows you to enter a new state (“tune number”). Note that even though
the automatic retune algorithm will only select the lower (“1”), centered
(“2”) or upper (“3”) states, you can enter values here from 0 to 7. The “0”
state is twice as low as the “1” state, the “4” and “5” states are don't
cares', the “6” is twice as high as the “3” state and the “7” state is 3
times as high as the “3” state. It turned out that only the lower,
centered, and upper states were required by the automatic retune
algorithm to compensate for the temperature drift of the 71.1 oscillator.
RETUNE ON OFF is a duplicate of the same key in the Service menus
described in the menu sections.
SHOW SEQUENCE will display the 71.1 MHz oscillator tune state
numbers used during the last full signal acquisition sequence. A “2”
means only tune state 2 was required. A “21” means that states 2 then
1 were tried. A “213” means that 2 then 1 then 3 were tried.
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