The amplitude of the original signal (before notch 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 either the
analog or digital generator frequency. If the Generator Control
mode is Analog Audio Generator, then the notch will track the
analog generator. If it is one of the digital modes, the notch will
track the embedded audio signal on the digital generator.
.
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. For the analog analyzer, 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. The THD must
also be less than about 10% THD+N. For the digital analyzer, the
signal must be above about -80 dBFS. If the signal amplitude is too
low, tuning operation will cease and the display will read ‘Low’.
& For a more
detailed discussion of
units, see page 3-26.
& For more
information on
Generator Control
Modes, see page 3-13.
4 Functions
THD+N (Total Harmonic Distortion plus Noise) Function Descriptions
4-8 ATS-1 Dual Domain User's Manual
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