Boonton 1121A, Инструкция по эксплуатации

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Operation Section 3
3-9
3-23. Special Distortion Measurement Modes. Spe-
cial functions 12 and 13 are provided to preset and hold
specific input level and distortion ranges. Refer to
paragraph 3-65. Special function 17 extends the mea-
surements sampling period to provide a more consistent
reading in the presence of noise. Using special function
14, notch filter tuning can be held at specific frequencies
to aid in tuning the notch filter in the event that a stable
frequency measurement cannot be achieved or to enable
notch filter tuning to frequencies other than the funda-
mental. As with all amplitude measurement functions, the
rms, average, or quasi-peak detector type can be
selected using special function 70, 71 or 72, respectively.
Special functions 80 through 86 select logarithmic
distortion level display units in dBV or dBm.
3-24. SINAD Measurement Function.
The Model 1121A
measures SINAD (signal-to-noise and distortion) in the
same manner as the distortion measurement except that
the notch filter is tuned and held at the source frequency
to permit measurements in the presence of large amounts
of noise. If an external oscillator is used, it must be tuned
to within 3% of the source frequency setting. The AC
measurement techniques are similar to those used in the
level measurement function yielding fast settled
measurements. Measurement bandwidth is selectable to
reject noise while accurately preserving harmonic
components. The combination of harmonics and noise is
displayed as a percentage of the total input signal
consisting of fundamental, harmonics and noise.
3-25. SINAD Measurement Display Units.
SINAD
measurements are only displayed in dB units. To select
the SINAD measurement function simply depress the
SINAD key which illuminates both the key’s LED and the
KYBD legend in the ANALYZER display.
3-26. Special SINAD Measurement Modes.
Special
functions 12 and 12 are provided to preset and hold
specific input level and SINAD ranges. Refer to
paragraph 3-65. Special function 17 extends the
measurements sampling period to provide more
consistent readings in the presence of noise. When
measuring large amounts of noise (0 to 10 dB SINAD),
the notch filter turning may become indeterminate and
causes the
to be displayed. Special function 15 is
designed to disable the message in this
circumstance. As with all amplitude measurement
functions, the rms, average, or quasi-peak detector type
can be selected using special function 70, 71 or 72,
respectively.
3-27. S/N Measurement Function.
The Model 1121A
measures S/N (signal-to-noise) by alternately turning the
source output on and off and displaying the ratio of the
two measurements. The measurement techniques are
similar to those used by the level measurement mode.
Measurement bandwidth is selectable using the filters to
reject out of band noise or provide industry standard
weighting characteristics.
3-28. S/N Measurement Display Units.
S/N measure-
ments are only displayed in dB units. To select the S/N
measurement function simply depress the S/N key which
illuminates both the key’s LED and the KYBD legend in
the ANALYZER display.
3-29. Special S/N Measurement Modes.
Special func-
tion 17 extends the measurement sampling period to
provide more consistent readings in the presence of
noise. Special functions 40 through 49 are used to
program the amount of delay between the signal
measurement and noise measurement to allow time for
the device under test to respond to the change in
amplitude. As with all amplitude measurement functions,
the rms, average, or quasi-peak detector type can be
selected using special functions 70, 71, and 72.
3-30. Using the Ratio Mode.
The Model 1121A enables
all measurement modes to be displayed as a relative
value to a previous measurement value. In a ratiometric
measurement, such as flatness response, amplitude
measurements at various frequencies are displayed
relative to a reference level at a frequency of 1 kHz.
Another sample of a ratiometric measurement is the
measurement of the percent of AC ripple on a DC level.
3-31 Ratio Measurement Display Units. Ratiometric
level measurements are displayed in % or dB units
whereas relative frequency measurements are displayed
in Hz or kHz. To select the ratio mode simply depress an
analyzer measurement key such as LEVEL followed by
the RATIO key. The LEDs of both keys will be
illuminated along with the KYBD legend in the
ANALYZER display. When the next measurement cycle
is complete, the measurement value will become the ratio
reference and the display will indicate 100.00%, 0.00 dB
or 0.000 Hz depending on the previous log/linear display
mode.