24/7 Intruder Detection Using Real-Time Spectrum Analyzer
Since the end of the Cold War in 1991, the international threat scenario has changed. Nowadays it is based on terror. The inflow of illegal refugees poses another safety risk. Thus, one of the burning issues for civil and military agencies is the protection of national borders, requiring gapless situational awareness along widely stretched lines that have to be monitored 24/7. With the new SignalShark, engineers at Narda Safety Test Solutions, an L3 Technologies company, have succeeded in developing a powerful, mobile, real-time spectrum analyzer (RTSA) that creates new capabilities for this Herculean task.
Narda’s RF engineers have designed this latest, handheld, direction-finding instrument specifically for rapid and reliable detection, analysis, classification and localization of RF signals between 8 kHz and 8 GHz. Figure 1 shows a partial block diagram of the instrument. Two, independent digital down-converters enable the spectrum of the signal to be observed and demodulated at the same time, independently, within the real-time bandwidth. With its high real-time bandwidth of 40 MHz, the SignalShark can display all the detected RF signals present in entire communication channels in real time. Dynamic range is another highlight of this handheld device. High dynamic range determines the ability to reliably capture low-level signals that, in inferior instruments, would be unseen in the presence of higher-level signals or hidden in the intrinsic noise.
Combining handheld RTSAs with stationary units is a proven and affordable technique for effective border control. State-of-the-art, mobile RTSAs are able to receive and reliably analyze any communication or RF signal in the area. As a commercially available instrument, the SignalShark can directly demodulate AM and FM signals and route them to the installed speakers or headphones. If border patrol agents receive the analog signals from a walkie-talkie conversation, they can listen to what the intruders are talking about. For digital radio signals, the internal solid-state drive of the RTSA records the digital data simultaneously over an extended time period. This enables the patrol to record and collect all information, i.e., all different signals in the air—even coded ones—to decode later with suitable software on a laptop or in the laboratory.
When a communication signal is detected, it is critically important to retrieve its content. Narda’s new SignalShark is able to record I/Q data and stored measurement values in internal memory. By using the frequency, bandwidth and time-domain functions, it is possible to manually pre-classify GSM and private mobile radio communication signals. With the help of a connected laptop PC and special evaluation software, I/Q data with up to 20 MHz bandwidth can be streamed via the SignalShark’s 1 GbE port. Coded data and meta data, such as time, date, length of communication and the identities of communication partners, are a few examples of the information that can be obtained.
Most handheld spectrum analyzers do not support real-time measurements. Any that do will usually be limited to 10 MHz bandwidth. The SignalShark has a big advantage, providing 4× this bandwidth and able to analyze and record in real-time with up to 40 MHz bandwidth. This is greater than the entire 35 MHz wideband of GSM 900, meaning the SignalShark can capture all detected signals in the GSM 900 band at once, without loss. It does not matter if the intruder changes the frequency, the border guard records the whole GSM 900 band.
In border control, real-time spectrum analysis enables complete detection of short-term signals, i.e., signals that only occur sporadically and are easy to miss. Using conventional methods, these signals are hard to capture and a considerable time is required for detection. If the border patrol looks at a frequency band for a typical public access mobile radio communication between 410 and 430 MHz with the SignalShark handheld analyzer, every signal in this span, including all pulsed signals regardless of duration, will be captured.
If an intruder tries to “hide” under a normal commercial signal, the border patrol can still detect this in the spectral distribution. The SignalShark shows this directly on its display (see Figure 2). While observing the signal, the border patrol agent can move a manual antenna to see if the small signal under the large one gets stronger or weaker, enabling the direction of the signal source to be determined. Narda’s new handheld analyzer makes this signal visible in the midst of other larger signals. Tracking the signal with the help of a fully automatic direction-finding antenna, the bearing can be detected in seconds.
HIGH SENSITIVITY ENABLES COVERING WIDE AREAS
The power level of a hostile transmitter, the terrain profile and the sensitivity of the receiver determine the maximum detection distance between the surveillance station and the intruder, i.e., the maximum distance where the receiver can still detect the intruder’s outgoing signal. Noise figure is one key indicator of the sensitivity and quality of the receiver; the lower the noise figure, the better the sensitivity. As a general rule, reducing the noise figure by 6 dB provides twice the detection distance between the transmitter and receiver. Higher quality analyzers typically have a noise figure of about 22 dB. In comparison, the SignalShark has a noise figure of 15 dB with the preamp off. With an antenna this improvement more than doubles the detection distance, and 4× more area can be monitored—a huge improvement in situational awareness, which makes monitoring endangered national borders much faster, lower cost and safer for the border guards.
Narda Safety Test Solutions GmbH