61
Instrument Functions
❙
MAX HOLD
: the trace indicates the maximum value that
has been measured up to that point in time. Intermittent
signals in the spectrum or the maximum of fluctuating
signals are easy to find with Max Hold.
❙
MIN HOLD
: the trace indicates the minimum value that
has been measured up to that point in time. With Min
Hold, sine signals within the noise can be highlighted or
intermittent signals suppressed.
❙
AVERAGE
: the R&S®HMS-X takes the level average over
consecutive traces. In the default setting, averaging is on
a pixel-by-pixel basis, sliding over the previous traces. The
average mode makes it easy to display sine signals in the
vicinity of noise.
❙
HOLD
: freezes the presently displayed trace. The
measurement is aborted. This allows subsequent
evaluation of spectra with the aid of the marker.
The selected trace mode function will be displayed at the
bottom right on the display (for example C/W for Clear/
Write).
6.7.1 Detector
A detector converts the video signal of a spectrum ana-
lyzer before it will be displayed. It functions pixel-by-pi-
xel, determining how the value of a pixel will be measured.
The R&S®HMS-X always measures the whole spectrum.
The trace only has 500 pixels in the x direction for display-
ing results. If a large span is selected, all the spectrum in-
formation must somehow be represented using only 500
points. Each pixel represents a frequency range equal to
span/500. For example, if the span is 3 GHz: 3 GHz/500 =
6 MHz. With a span of 3 GHz the minimum space between
two pixels is 6MHz.
Pushing the softkey DETECTOR will open the detector set-
tings menu. Following detector types are available:
❙
AUTO PEAK:
displays the maximum and minimum level
at each pixel for the frequency range represented by that
pixel, no signals will be lost. If the signal level fluctuates
(noise), the width of the trace will indicate the width of the
signal fluctuations (default setting).
Fig. 6.5: Simultaneous display of 3 traces
The smaller the span, the smaller the space between two pixels.
❙
SAMPLE:
Only displays an arbitrary point within a display
pixel. The sample detector should always be used for
measurements with span = 0 Hz, as this is the only way of
correctly representing the timing of the video signal.
The sample detector can also be used to measure noise
power as noise usually has a uniform spectrum with a
normal amplitude distribution. If the sample detector is
used for signal spectrum measurements with a span that
is greater than (resolution bandwidth x 501), signals may
be lost.
❙
MAX PEAK:
In contrast to the auto peak detector this
detector only finds the maximum value within the
frequency range associated with one trace pixel. Its use is
recommended for measurements on pulse-like signals or
FM signals.
❙
MIN PEAK:
yields the minimum value of the spectrum
within a pixel of the trace. Sine signals are displayed with
correct level, but noise-like signals are suppressed. The
Min Peak detector can be used to highlight sine signals in
the noise spectrum.
6.7.2 Trace Memory
With the softkey TRACE
MEMORY in the submenu ME-
MORY a trace can be transferred into the background
curve memory. By pushing the softkey SHOW MEMORY
the stored trace will be displayed and can be compared
with the presently displayed curve. The stored curve will
always be shown in white and thus can be easily differenti-
ated from the presently displayed curve. In order to let the
stored curve disappear, push the SHOW MEMORY soft-
key again.
6.7.3 Trace mathematics
The spectrum analyzer can subtract a stored trace from an
active trace and display the difference. If a trace is stored
under TRACE
MEMORY the difference between the
stored an the active trace will be displayed by pushing the
softkey TRACE MATH. In order to let the stored curve
disappear push the key TRACE MATH and select OFF.
Fig. 6.6: Display of a measured and a stored reference curve
The trace math function can not be used in HOLD mode.
Summary of Contents for HMS-X
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