Addressing Interference Problems Using Real-Time Spectrum Analysis

With the proliferation of wireless technologies now used in commercial, aerospace and defense (A&D) applications, interference problems are becoming more common and more severe. To mitigate these issues, many A&D systems are moving to higher frequencies, including the millimeter wave band.

Related design enhancements include the use of narrow radar pulses and highly encrypted communication signals. While these techniques and technologies can fend off the effects of externally generated interference, they make field troubleshooting more difficult. As a result, new tools and measurement technologies are needed to effectively maintain deployed systems. One such tool is real-time spectrum analysis (RTSA),which is especially effective for interference hunting and signal monitoring.

Keysight is offering a maximum real-time bandwidth of 10 MHz at frequency ranges up to 50 GHz (N995xA and N996xA models).



As signal environments become more complex, it is increasingly important to represent a large amount of measurement data on a single screen. This is essential for RTSAs that generate thousands of spectra per second, many more than can be discerned by the human eye. As an example, FieldFox with RTSA can produce >120,000 spectra per second, yet the average human eye can detect only 30 per second. Therefore, to take advantage of real-time results, each display update needs to represent about 4000 × 30 results in a useful way. The result are display in figure 1 below.

Figure 1: Density display with user-selected persistence time helps to convey the behavior of multiple signals occupying the same frequency channel.
Figure 2: A narrowband RF signal (red oval) “hiding” beneath a W-CDMA signal.

RTSA also can reveal signals within signals. In a highly dynamic environment, it can be difficult to see small signals with low duty cycles when the frequency content overlaps with signals that are wider, larger or more frequent. Fortunately, adjusting the persistence time can enhance the small differences that reveal elusive signals. Any situation in which signals can be separated by frequency of occurrence is a candidate for this approach (see Figure 2).


Keysight’s FieldFox handheld analyzers deliver precise microwave and millimeter wave measurements and possess key attributes that support routine maintenance, in-depth troubleshooting, and virtually anything in between:

  • Frequency coverage from 5 kHz to a maximum of 50 GHz.
  • Multiple capabilities, including cable and antenna tester (CAT), spectrum analyzer, RTSA, vector network analyzer (VNA), power meter, independent signal source, frequency counter and GPS receiver.
  • Rugged design meeting MIL PRF 28800 F class 2, type tested for IP 53 and MIL STD 810G 511.5 process 1 (explosive environment).
  • Field ready at 7.1 lb (3.2 kg) and a battery life up to four hours.

FieldFox key RTSA specifications are exceptional in field testing. For most over-the-air (OTA) applications, the maximum RTBW of 10 MHz is more than sufficient, because external interference typically occurs within a much narrower band. Another crucial spec is the probability of intercept (POI), which is the minimum duration for a signal of interest to be detected with 100 percent probability and measured with the same amplitude accuracy as when observing a CW signal. A FieldFox with RTSA has POI performance < 12.2 µs and can detect pulses as narrow as 22 ns. In general, FieldFox can see signals down to -150 dBm with the preamplifier activated and at narrow resolution bandwidth (RBW) settings.

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