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Key Function Descriptions
Key Descriptions
The FFT results are displayed on the spectrum
analyzer in a 10 dB per division logarithmic scale. For
the horizontal dimension, the frequency at the left side
of the graph is 0 Hz, and at the right side is 300 divided
by the sweep time. Also, peak search marker is
activated.
The FFT function is commonly used to measure AM in
the presence of incidental FM. In this case, performing
an FFT on the demodulated, zero-span AM signal, will
result in a component (shown at 0 Hz) that depicts the
power in the carrier of an AM signal. Other components
are shown at the power level of the AM sidebands, with
FM sidebands rejected. The amplitude accuracy of
these sidebands is affected by the effective filtering of
the resolution bandwidth filter (equivalent to a
low-pass filter with a cutoff frequency equal to half the
resolution bandwidth) and the video filter.
Aliasing can occur when modulation rates on the
carrier are higher than one-half the sample rate for the
zero-span signal, or 300 divided by the sweep time. The
aliasing can be reduced by using a narrower resolution
or video bandwidth.
Front-panel key access:
Not available in normalized mode. Turns FM
FM DEMOD ON OFF
demodulation ON or OFF. If no marker is active and
the frequency span is greater than 0 Hz, pressing FM
DEMOD ON OFF automatically places a marker at the
center of the trace and demodulates the frequency at
that marker position. Turning FM demodulation on
turns off AM demodulation, if it is active. When the
frequency span is greater than 0 Hz, a 100 kHz
bandwidth is used during the demodulation, regardless
of the bandwidth annotated on the screen. When the
span is equal to 0 Hz, the displayed bandwidth is used.
In either case, the video bandwidth is not applied to the
demodulation.
Front-panel key access:
Changes the focus of the display on E-series
FOCUS
instruments. Press FOCUS, then use the data keys, the
step keys, or the knob to adjust the focus. The focus
ranges from 0 to 255; the current value appears in the
active function block. When FOCUS is pressed, STORE
FOCUS appears on the menu. Press STORE FOCUS to
store the new focus value. The overall display focus can
only be affected a small amount. EC-series instruments
do not require adjustment and are not adjustable.
238
MEAS/USER
AUX CTRL
Chapter 4
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