436 Chapter10
Analyzer Options and Block Diagrams
Option 190 DVB-C Service Menus
Dncvtr Test leads to a set of menus that allows the setup of various
Option 190 downconverter functions in a manner convenient to
troubleshooting, for example, no measurements are run. The softkeys
located under
Dncvtr Test are documented in the “Downconverter Test”
section.
Menu 2 of 3
RCVR CAL ON OFF allows you to enable or disable use of the Option 190
calibration by demod-based measurements. The Option 190 calibration
is a special factory calibration that allows us to compensate for the
linear distortion of the analyzer. This improves the channel response
measurement results as well asincreases the ability of the demodulator
to lock to a signal. The calibration “values” are kept in the analyzer
CMOS RAM memory and automatically uploaded by the analyzer
firmware to the Option 190 board set at power-up. If the cal is missing
or corrupt,
RCVR CAL ON OFF will remain in the OFF position (OFF is
underlined) and cannot be toggled ON. This key is the one exception to
the Setup keys: it does NOT retain its value through preset or power
cycles. The reason being the mode entry routine will automatically turn
RCVR CAL ON OFF to OFF (OFF is underlined) if it detects that the
Option 190 cal is missing or corrupted (and display a message). The
mode entry routine will also turn
RCVR CAL ON OFF to ON (ON is
underlined) if the CAL is OK. Pressing
DEFAULT SETUP key will set
RCVR CAL ON OFF to ON (if there is a valid CAL). The state of RCVR
CAL ON OFF is also shown in the “Diagnostic Data” section.
Dsp Evm Corr key leads to a menu which allows you to individually
enable or disable DSP based evm correction for each of the 3
bandwidths, 2,4 or 8 MHz. For example, the “8 MHz CH ON OFF” key
when set to ON enables DSP based corrections on 8 MHz channels. As
described in Modulation Accuracy (metrics) above, the 2 &4 MHz
bandwidths normally have this enabled, but not the 8 MHz bandwidth.
EVM CORR ON OFF enables DLP based evm corrections on channels that
do not have DSP based evm corrections enabled. The diagnostics data
(see the “Diagnostic Data” section) displays if DSP or DLP based evm
corrections are on for the current analyzer state.
CNTL A 1 0 allows you to toggle the preamp bypass switch
independently of
PREAMP ON OFF key. Selecting 1 puts the switch in
preamp mode, 0 puts the switch in bypass mode. This is useful for
troubleshooting the preamp drive circuits.
SHOW REVDATES key displays all three software revision dates:
the 8594Q QAM analyzer firmware (“F/W:”), Option 190 DSP firmware
(“DSP:”) and DLP.
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