Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
Issue link: https://electronicsmilitarydefense.epubxp.com/i/350588
Technology Detecting And Locating Hidden Signals And Interferers In Military Operations Spectrum analyzers can be used to neutralize electronic warfare threats. By Eric Hakanson T oday's warfare depends on wireless technologies for successful military deployment and operations. This reliance has created a wave of tactics that focus on disabling signal transmissions through the use of GPS, radar, and other types of jammers, as well as bugs and various interferers. Additionally, militia groups and terror organizations continue to utilize hidden signal techniques to communicate with each other covertly while coordinating their military actions. This era of electronic warfare has led to arming soldiers with more than weapons and radios. Interference-hunting and spectrum-monitoring tools, such as handheld spectrum analyzers and directional antennas, are now standard defense tools (Figure 1). The armed forces rely on these instruments to detect and locate jammers that may interfere with essential commands as well as eavesdrop on hidden conversations between terror cells. Given the sensitive nature of the signals that need to be detected and the environments in which these operations are conducted, the handheld spectrum analyzer must have key performance and design parameters. One essential specification is dynamic range, as it allows military personnel to detect small signals in the presence of large signals that may be nearby in the radio frequency (RF) spectrum. Handheld spectrum analyzers that can see a small signal 90 or 100 dB below a strong signal while both are present should be used when on patrol. Another key capability is a fast sweep speed with a low resolution b a n d w i d t h . This allows the spectrum analyzer to conduct fast sweeps while still displaying all the required detail. A 1 MHz span is useful for many types of interference hunts. Soldiers need a handheld spectrum analyzer that can use a 1 kHz resolution bandwidth to create a noise floor below -130 dBm, with an update rate of three to five sweeps per second to achieve fast results. Detecting Bursty Signals Being able to reliably detect bursty signals is vital in the efforts of field troops to locate intermittent or bursty emitters. For example, the Spectrum Master MS2720T (Figure 2) features a burst detect function that can take up to 20,000 measurements per second, allowing soldiers to capture emitters as narrow as 200 µs and even less. Captured spans can be as wide as 15 MHz and as narrow as 20 kHz, so they can focus on signals of interest. A display update of up to five times per second allows frequent display updates, so signal changes will be quickly seen. There are other useful features for tracking down inter- ference sources. A spectrogram displays occurrences over time, so locating intermittent interfer- ers is easier. Signal strength measure- ment, coupled with a directional antenna, makes finding rogue transmitters much simpler as well. An audio indicator of the signal strength allows patrols to find the transmitter without having to look at the display, allowing soldiers to concentrate on what is around them. New interference hunting tools can further aid the military. Antenna handles now are designed with a magnetic compass and a GPS and can accept various antennas. These help preserve the antenna pattern, which is extremely important when plotting data on the spectrum analyzer. Combining the Electronic Military & Defense Annual Resource, 4th Edition 36 Figure 1: Handheld spectrum analyzers are being used by soldiers to detect and locate jammers in the field. Figure 2: The Anritsu Spectrum Master MS2720T allows military personnel to capture emitters as narrow as 200 μs.