Chapter 10 435
Analyzer Options and Block Diagrams
Option 190 DVB-C Service Menus
Menu 1 of 3
DIAGS ON OFF enables the display of the diagnostics data on
demod-based measurements along with the measurement results. This
data is shown as a small highlighted block on the screen. The exact
meaning of each of the data items is detailed in the “Diagnostic Data”
section.
IGNORE ON OFF enables a mode in which demod-based measurements
will ignore any QAM acquisition or measurement failure and show the
measurement anyway. This is useful to observe the constellation under
this condition since it can yield valuable clues about the particular fault
(spinning or random constellation). Note that this only ignores
acquisition or measurement unlocks; it will not ignore a 240 MHz PLL
unlock or level set failure.
KEYS ON OFF enables the following diagnostic and optional control keys
located elsewhere in the menus.
•
Service is located in the lq Constln menu.
•
AGC HOLD RUN and DNCVRTR ATTEN are shown during a continuous
(live) demod-based measurement.
DNCVRTR ATTEN is used to
manually enter a value of Option 190 downconverter attenuation
independent of the value set by the level-set algorithm, and display
in the diagnostic data. Useful information can be gleaned by
entering values different than that set by the level-setting
algorithm, then observing the effects on the constellation, or other
measurement.
Note that values are entered “blind” into the keypad, terminated by
dB; there is no visible active function area on the screen. Note also
that the diagnostic data does not change to reflect the new value of
downconverter attenuation. Also, only even values of attenuation
are utilized, due to only 2 dB steps are available on the board.
AGC
HOLD RUN (hold underlined) will freeze the AGC loop on the Option
190 demodulator input. This allows subtle effects to be observed
without being obscured by the action of the AGC loop.
•
VARIANCE SD 90% is located in the Modulation Accuracy menu. When
set to SD (SD is underlined), this will make averaged measurements
display the standard deviation instead of the 90% confidence value of
measurement variance.
•
METRIC ON OFF located in the SER, C/N Margin menu, when set to ON
(on is underlined) will make the SER measurement display the
EVM, or MER, that accompanies the measurement in a manner
identical to the channel response measurements.
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