General Signal Viewing > DPX Spectrum
DPX Primer
When you widen the box to cover a broader range of frequencies, software computes the density sum for
the included pixels in each column inside the box. The aggregate density value for this box is the average
density, calculated by adding the column density sums then dividing by the number of columns. For a 100%
result, there must not be any hits above the top edge of the box or below its bottom edge. In other words,
every waveform drawn across the graph entered the box through its left side and exited the box through its
right side, with no excursions out the top or bottom. Figure 24 demonstrates this principle on a CW signal.
As you can see on the left-hand side, no amplitudes exist above or below the box; the density of the signal
is 100%. On the right hand side, there are signals below the box, therefore the density is less than 100%.
Figure 24. Density of signals de
fi
ned within an area. Left: Correct measurement of a CW signal. All columns in the
box include the signal. Right: Incorrect measurement area. The measurement is accurate, but probably not what you
expected. Some columns in the box contain no hits, so they contribute zeros to the calculation of average density.
The density measurement box’ vertical size and location are always set in dB and dBm, no matter what
units you have selected for measurements. (Amplitude control panel > Units tab) The box is not draggable
when the selected units are linear (such as Amps, Volts, Watts…), though you can still adjust its size and
location using the Frequency and Amplitude controls in both the DPX Settings > Density and Trigger >
Event tabs. Since the vertical scale is non-linear, a box of constant amplitude changes visual height as it
changes vertical position, a disconcerting effect if you are trying to drag it.
Figure 25. DPX Density control panel is used to de
fi
ne the area of interest for DPX density measurements.
A readout will appear somewhere in the graph. If the box is off-screen, the readout will be accompanied by
an arrow pointing towards the invisible box. Grab this readout with your mouse or
fi
nger and drag the
density readout to the area you want to measure.
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RSA6100A Series Real-Time Spectrum Analyzers Help
Summary of Contents for RSA6100A Series
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