September 27, 2016
The recipe for locating RF signal sources is one part science, one part art form, one part visual observation, and a sprinkle of luck. The best way to learn signal hunting is to track signals, as this gives field technicians a sense for how RF propagates and reflects, as well as how to determine what’s real and what’s not.
Locating RF signal sources is often challenging, because it involves a lot of physical activity as you change location to build evidence that points to the source’s location. It’s rarely comfortable, requiring hours of work – often times in less than perfect conditions. RF signal hunters must contend with heat, cold, wind, rain/snow, dust, and insects. One day they are atop a hill and the next they are standing on a rooftop. These scenarios can make each kilogram of equipment weight feel like five kilograms at the end of a long day. For these reasons, RF signal hunters want their equipment to be rugged, easily portable, and lightweight.
Keeping notes during an RF signal hunt is critical because after a while, it’s easy to forget what you’ve already looked at. The key tools for RF signal hunting are a map and a compass. A GPS is also sometimes used. Using a directional antenna, bearings from various locations plotted on a map can give a good sense for the approximate location of an RF signal. Paper maps have the advantage of being lightweight, but they lack the ability to change scale – marks on a map covering dozen square miles don’t help when you’ve narrowed the location down to a city block. Also, paper maps blow around in the wind, and are damaged by precipitation. Laptops and tablets offer maps that allow scaling, but they’re not typically very rugged and, like paper, they don’t like to get wet.
Need for Minimization
Minimizing the amount of equipment and tools is important from both a weight and complexity perspective. It’s impossible to simultaneously support a laptop, type on its keyboard, and manipulate the controls of a radio receiver. Much of the time, the solution is to set some or all of the equipment on a flat surface, but some locations encountered during an RF signal hunt might not be perfect for this. Ideally, you want something that can be body-worn and operated with only two hands.
Ease of movement is critical during an RF signal hunt. Getting into position to make measurements can involve squeezing through tight spaces, climbing onto a railing or ledge, or crawling under obstacles. Manipulating several pieces of equipment in these locations can be next to impossible.
A Better Way
To address these environmental issues, Anritsu’s Handheld InterferenceHunter MA2700A (figure 1) is a preferred option for RF signal hunting. When combined with an Anritsu handheld instrument (such as the Spectrum Master™, Site Master™, Cell Master™, and BTS Master™) the InterferenceHunter has a built-in GPS and compass. Maps are prepared for loading into the instrument using the easyMap software tool. Using the Interference Mapping tool, the GPS location and compass bearing of the InterferenceHunter is displayed directly on the map.
InterferenceHunter can be fitted with a variety of directional antennas and filters depending on the signal being hunted. No laptop is necessary and both the handheld instrument and the InterferenceHunter can be operated with two hands, improving mobility and reducing weight. Using the InterferenceHunter is a simple point-and-click operation – each time the trigger is pulled, a bearing line is created on the instrument’s map display. The RF signal source will be located near where several bearing lines converge, as shown in figure 2.
Once you’re in the general area of the RF signal source, mapping becomes less useful. At this point, most hunters use methods where the RF signal strength is indicated by the pitch of an audio tone. The aforementioned “Master” instruments offer this in the Signal Strength meter tool. Headphones with a standard 3.5 mm stereo plug are recommended, especially for outdoor use or high ambient noise situations.
Using these tips and the tools described can reduce the amount of time needed to successfully locate an RF signal source. For more information, check out a new white paper.