The THD+N reading is shown on the top left of the display. The top
left soft key selects the units for the measurement. If any units besides
% or dB are selected, the measurement only shows the amplitude of
the signal after filtering.
The amplitude of the original signal (before filtering) is shown in the
top center of the display. The top center soft key is used to select the
displayed units.
The top right corner of the display shows the current frequency. The
value displayed depends on the notch steering mode, which is selected
by top right soft key. This controls the center frequency of the tunable
notch filter. Three notch steering modes are available:
.
AUTO-TUNE – This causes the notch to be tuned to the
incoming frequency, as read by the frequency counter. The
display will show the current frequency counter reading.
.
GEN-TRACK – This causes the notch to be tuned to the
generator frequency.
.
FIX-TUNE – This causes the notch to be tuned to a frequency
specified by the user. The current tuning frequency will be
shown on the upper right of the display, and it may be adjusted
with the FREQUENCY controls. This will not give a valid
THD+N reading unless it is tuned to the fundamental frequency
on the input.
The AUTO-TUNE mode will automatically tune to an incoming
frequency. This is useful when making THD+N measurements on
signals generated by the device-under-test or at a remote location.
When running generator (internal) frequency sweeps, the notch will
automatically tune to the generator frequency, as in GEN-TRACK
mode.
Proper operation of AUTO-TUNE requires that the original signal has
sufficient amplitude for frequency counting and not too much
distortion. The signal amplitude must be greater than about 10 mV
within the audio band (20 Hz - 22 kHz) and greater than about 20 mV
outside the audio band. If the signal amplitude is too low, tuning
operation will cease and the display will read ‘Low’. The THD must
also be less than about 10% THD+N.
& For a more
detailed
discussion of
units, see page
4-71.
4 Operation
Operation Controlling the Analyzer : THD+N (Total Harmonic Distortion plus Noise)
4-26 Portable One Plus Access User's Manual
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