The explosion of wireless technology means that RF signals are literally everywhere. And that mass congestion of RF exacerbates the problem of RF interference. And with more and more wireless devices permeating our lives, the possibility clearly exists for interference to affect the performance and reliability of the wireless technology across the board.
Tracking down where interference is coming from requires the right mix of tools and techniques. In this article, we’ll explain the premise of “interference hunting” by first discussing the different types of interference, and then get into the tools that can be used to detect it, supported by actual experiment results.
Categorizing Interference
RF interference is an issue that can lead to problems like dropped calls. There are three main types of interference.1 The first is co-channel interference, which occurs when multiple transmitters are transmitting signals on the same channel. Today, essentially all frequencies are being shared. The second is adjacent channel interference, which is caused by signals that interfere with communication in adjacent frequency channels.
The third type is impulse noise, which can result from imperfect shielding that allows energy to leak and interfere with RF devices. In addition, noise can result from partial device failures, as well as other sources like industrial machinery.
Detecting Interference with Real-Time Spectrum Analyzers
Detecting interference typically involves using a spectrum analyzer. Today, suppliers offer both swept-tuned and real-time spectrum analyzers (RTSAs). While a traditional swept-tuned spectrum analyzer can be used for interference detection, it does have certain limitations when compared with an RTSA.
Swept-tuned spectrum analyzers can display measurement data by continuously sweeping across a given frequency range from the lowest to the highest frequency. This functionality allows measurement data to be displayed for each measurement step in the specified frequency range. Thus, a user can observe a spectrum display as the analyzer continuously sweeps across a range of frequencies.
However, the sweeping functionality of a swept-tuned spectrum analyzer also affects its capability to measure interfering signals. Capturing an interference signal with a swept-tuned spectrum analyzer requires that signal be present (i.e., in an “on” state) when the analyzer performs its measurement at the frequency of the interfering signal. But since a swept-tuned spectrum analyzer sweeps across a range of frequencies, the possibility exists that the interference signal is not present (i.e., in an “off” state) when the analyzer performs its measurement at the interfering signal’s frequency.
Hence, an interfering signal that is present at some instances in time when the analyzer is sweeping also may not be present at the exact point in time when the analyzer performs a measurement at that interfering signal’s frequency. In this case, the interference signal would essentially be undetected. This scenario is obviously more likely when trying to detect short-duration signals.
RTSAs differ from traditional swept-tuned spectrum analyzers, as they do not actually sweep across a frequency range. Rather they can continuously capture spectrum information for any span as high as the RTSA’s maximum real-time span. This capability enables RTSAs to capture short-duration signals, making them an essential tool for RF interference detection.
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