R&S ESU Series, Руководство по эксплуатации

Страница: 142 / 855

Operating Manual 1302.6163.12 - 03 4.111
R&S ESU Instrument Functions
Analyzer Mode
4.8.4 Setting the Bandwidths and Sweep Time – BW Key
The BW key calls a menu for setting the resolution bandwidth ( RBW ), video band-
width ( VBW ) and sweep time ( SWT ) for the frequency sweep. The parameters may
be coupled dependent on the span (stop minus start frequency) or freely set by the
user. When working with a split screen display, the settings always refer to the active
window.
The R&S ESU offers resolution bandwidths from 10 Hz to 10 MHz in 1, 2, 3, 5, 10
steps.
Resolution bandwidths up to 120kHz are realized using digital bandpasses with
Gaussian characteristics. As far as the attenuation characteristic is concerned they
behave like analog filters but have a much higher measurement speed than compa-
rable analog filters. This is due to the fact that the transient response can be com-
pensated as a result of an accurately defined filter behavior.
Bandwidths above 120 kHz are realized using decoupled 5-circuit LC filters.
As an alternative to the analog filters, FFT filters are available for the bandwidths
between 1 Hz and 30 kHz. When working with bandwidths up to 30 kHz, the FFT
algorithm offers considerably higher measurement speeds with all the other settings
remaining the same. The reason is that with analog filters the sweep time required
for a particular span is proportional to (Span/RBW
2 ). When using the FFT algorithm,
however, the sweep time is proportional to (Span/RBW).
The video bandwidths are available in 1, 2, 3, 5, 10 steps between 1 Hz and
10 MHz. They can be set in accordance with the resolution bandwidth.
The video filters serve for smoothing the displayed trace. Video bandwidths that are
small compared to the resolution bandwidth average out noise peaks and pulsed
signals, so that only the signal average is displayed. If pulsed signals are to be mea-
sured, it is recommended to use a video bandwidth that is large compared to the
resolution bandwidth (VBW
≥
10 × RBW) for the amplitudes of pulses to be mea-
sured correctly.
For analog and digital filters, the R&S ESU has overload reserves of different mag-
nitude above the reference level. Due to the LO breakthrough the overload display
OVLD responds with digital filters with RBW < 100 kHz, as soon as the start fre-
quency is selected < 6 × RBW; for RBW = 100 kHz as soon as the start frequency
is below 3 MHz.