Section 3 Operation
3-14
3-64. Mode Alteration Functions. Codes 11 through 19
alter the normal operation of the Model 1121A. When
selected, the SPCL legend in the SOURCE display win-
dow will remain illuminated as an indication of the special
operating mode regardless of the function displayed.
3-65. The range-hold functions, 11 through 13, affect the
analyzer measurements by defeating the autorange ca-
pability. The input level or post-notch distortion range can
be held at its present value by entering the appropriate
special function code. Other ranges can be set and held
by selecting the desired analyzer measurement mode
and entering the level or distortion range directly into the
ANALYZER display window using the DATA ENTRY
keypad. Available level and distortion ranges for all an-
alyzer measurement modes are listed in Tables 3-4 and
3-5. It is not necessary to enter the exact full scale value
to set a range, rather the value need only fall within the
desired range. When a range is selected the appropriate
special code will automatically be activated and the SPCL
legend will be illuminated. Range-hold mode is cleared by
selecting an alternate analyzer function, using special
function 10 or initializing the instrument.
3-66. The notch-hold and ignore-tune-status functions, 14
and 15, affect the analyzer distortion and SINAD
measurement modes by defeating the auto-tune
capa-bility in the distortion mode and disabling the
tune-status information in the SINAD mode. Tune-status
information is unreliable in the presence of very high
amounts of noise (0 to 10 dB SINAD) resulting in the [ ]
message being displayed. The ability to select the
frequency of the notch filter enables the distortion mode
circuits to function as a programmable notch filter to
attenuate selected tones other than the fundamental.
These special modes can be activated by entering the
special code or by selecting the analyzer distortion mode
and entering the notch frequency directly into the
ANALYZER display window using the DATA ENTRY
keypad. Direct entry of the notch frequency will
automatically select Special 14 and the SPCL legend will
be illuminated. Notch-hold and ignore-tune-status modes
are cleared by using special function 10 or initializing the
instrument.
TABLE 3-6. OUTPUT LEVEL RANGES.
3-67. The unlock frequency function, 16, is provided to
speed repetitive frequency setting and measurements. In
normal operation a variable period of 20 to 200 mS is
required to measure the actual oscillator frequency,
calculate the frequency deviation and apply tine tune
correction. Inhibiting the frequency lock mode results in
faster operation at the cost of frequency accuracy. The
unlock mode is cleared by entering special function 10 or
initializing the instrument.
3-68. The slow detector function, 17, is provided to extend
the level measurement sampling time to provide more
consistent readings in the presence of noise. The level
measurement employs a period sampling technique
which adjusts the measurement period to include the
period of the dominant AC signal. This process is
extended to include low frequency components which
cause inconsistent readings. The slow detector mode is
cleared by using special function 10 or initializing the
instrument.
3-69. The output range-hold function, 18, is provided to
hold selected output level ranges. The active range at the
time the special function is activated will be held.
Available level ranges and resolution are listed in Table
3-6. Range-hold mode is cleared by entering special
function 10 or initializing the instrument.
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