and from +40dBV/dBm to -130dBV/dBm in the Log
mode.
Figure 3-11. Noise vs. Frequency.
3-46. Dynamic Range.
3-47. For operating purposes, the dynamic range of a wave
analyzer can be defined as the ratio of the largest to
smallest signals it can measure for a given range setting. The largest signal that can be measured (full-scale sensitivity) is
determined by the INPUT SENSITIVITY, amplitude VERNIER and AMPLITUDE REF LEVEL settings. The smallest signal that can be measured is determined by:
a. instrument-induced distortion and spurious
b. display range
c. internal noise floor (maximum sensitivity)
3-48. Distortion and Spurious. When the OVERLOAD
light is off, the instrument-induced distortion and spurious
is more than 80 dB below full scale.
3-49. Display Range and Noise Floor. When the volts scale
is selected, the smallest signal that can be measured is
approximately 10% of full scale. Thus, the dynamic range is
about 20 dB as long as the noise floor is more than 20 dB
below full scale. When the Log 90 dB scale is selected,
displayed readings of less than -80 dB are not specified. The
dynamic range is 80 dB as long as the noise floor is more
than 80 dB below full scale. When the Log 10 dB scale is
selected, the dynamic range is 10 dB as limited by the
display range.
3-50. Meter Scales.
3-51. Refer to Figure 3-12 for the following discussion.
The 3581 SCALE buttons permit selection of three scale
settings: Volts (linear). Log 90 dB and Log 10 dB.
3-52. Voltage Scales. When the Volts SCALE button is
pressed and the amplitude VERNIER is in the CAL |
position, the meter indicates signal amplitude in rms volts
(average responding). There are two voltage scales on the
meter. These are scales C and D. Scale C ranges from 0 to 1
and scale D ranges from 0 to 3.2. The full-scale sensitivity is
indicated by the white window on the INPUT SENSITI-
VITY switch dial. If the full-scale sensitivity is 10V, IV,
0.1 V, etc., read the meter using scale C. If the full-scale
sensitivity is 30V, 3 V, 0.3 V, etc., read the meter using
scale D. Refer to Paragraph 3-56 for further information
concerning the use of the linear scales.
Figure 3-12. Meter Scales.
3-53. Log Scales. When the Log 90 dB or Log 10 dB
SCALE button is pressed and the amplitude VERNIER is in
the CAL position, the meter indicates signal amplitude in
dBV or dBm as selected by the front panel Calibration
switch. When the VERNIER is not in the CAL position, the
meter indicates relative amplitude in dB.
3-54. There are two logarithmic scales on the meter. These
are scales A and B. When the Log 90 dB SCALE button is
pressed, the meter can be read using scale A which ranges
from 0 dB to - 90 dB. For absolute measurements, a reading
of 0 dB corresponds to the full-scale reference indicated by
the white window on the INPUT SENSITIVITY switch
dial. The absolute signal level is the algebraic sum of the
full-scale reference and the meter reading. For example, if
the full-scale reference is - 40 dB and the meter reading is
0 dB, the signal amplitude is - 40 dBV or dBm. Similarly, if
the full-scale reference is - 20 dB and the meter reading is
- 40 dB, the signal amplitude is - 60 dBV or dBm.
3-55. When the Log 10 dB SCALE button is pressed, the
meter scale is expanded to 1 dB per division over a 10 dB
range. The meter can then be read using scale B which
ranges from 0 dB to - 10 dB. The Log 10 dB scale can be
read in the same manner as the Log 90 dB scale. A reading
of 0 dB corresponds to the full-scale reference indicated on
the INPUT SENSITIVITY switch dial. The full-scale refer-
ence can be adjusted from 0 dB to - 70 dB using the
AMPLITUDE REF LEVEL switch. The absolute signal level
is the algebraic sum of the full-scale reference and the meter
reading. Refer to Paragraph 3-65 for further information
concerning the use of the log scales.
3-56. Using the Linear (Volts) Scales.
3-57. For amplitude measurements using the linear scales,
the full-scale sensitivity is determined by the INPUT
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