Datasheet

6 | WWW.TEK.COM
APPLICATION NOTEInterference Hunting
Deeper Signal Insight
As discussed in the previous section, the sweeping nature of
traditional spectrum analyzers limits the POI when analyzing
short duration signals. This problem is particularly acute when
we need to make “Over The Air” (OTA) measurements. When
monitoring for interference the spectrum analyzer must mimic
the sensitivity of the victim receiver. By default, most spectrum
analyzers will set the RBW filter as a ratio of the span setting.
Figure 3 shows an OTA measurement of an LTE downlink
signal. In this example it is very difficult to visually discriminate
the signal due to the wide RBW filter.
Figure 4 shows the same span, but with the RBW filter set to
1kHz. The full LTE downlink signal can now be measured and
the RTSA can easily discriminate narrow band or low-level
signals.
The Real Time Difference
Figure 5 shows the Digital Phosphor Spectrum (DPX) display.
Like a classic spectrum analyzer, it shows frequency vs.
amplitude information. In addition, the pixels in the display
have added color which indicates how often RF energy is being
measured at that pixel. The DPX measurement also allows
you to specify a decay function, providing a phosphorescent
effect which mimics the effect of displays found in CRT
based oscilloscopes. It adds the dimension of periodicity to
the display, showing you how often a signal is actually being
measured in the span of interest.
This form of real-time spectrum display lets you “see” what
your receiver “sees,” and provides greater insight into what
exactly is happening over the span of interest.
Monitoring the Spectrum for Long
Periods of Time
To effectively identify the source of interference it is important
to collect as much information as possible about how the
spectrum is changing over time. The DPX measurement
provides much detail, however, it doesn’t provide enough
information about the potential effects of interfering signals. By
their nature spectrum displays are not able to show the time
interleaving of signals. Employing a “zero-span” measurement
would provide good detail about pulse amplitude and duration
but lack frequency information.
FIGURE 3. This is an example of how an LTE signal looks OTA.
FIGURE 5. A real-time spectrum analyzer display shows much more information
than a traditional display.
FIGURE 4. A real-time spectrum analyzer with a 1kHz RBW filter improves
visibility on a LTE signal.