The hunt for rogue RF signals
Tektronix unveiled the RFHawk, a digital handheld device that hunts, locates and classifies both analog and digital rogue radio frequency transmissions. It is targeted to the surveillance and security sector, where speed is paramount, said Bob Hiebert, general manager of wireless test solutions for Tektronix.
“The sooner they can find the bad guy, the sooner they can prevent a bad thing from happening,” Hiebert said.
The RFHawk had been in development for three years. Tektronix got the idea for the device when it learned that the military had adapted spectrum scanners and analyzers the company had developed for the cellular market to use for surveillance applications.
“With the spending going on in security and [anti-]terrorism activities, that looked like a good place to go,” Hiebert said.
The growth of digital wireless technology has caused a major headache for the surveillance and security sectors. So much RF spectrum is being used that it has become increasingly difficult to distinguish between legitimate and illegitimate transmissions, Hiebert said.
“In the past, you could find a bad guy by the presence of an RF signal. The problem now is that there’s so much RF spectrum being used that distinguishing between what’s supposed to be there versus what’s not supposed to be there is really difficult,” Hiebert said. “Secondly, the nature of the digital signals themselves masks their true nature. CDMA is a derivative of military spread spectrum, which was developed as a way to avoid detection.”
A real-world example of a crowded RF landscape where it is challenging to determine which signals shouldn’t be there can be found in Iraq, where the U.S. Army now finds itself in a bit of a quandary. Insurgents have been using a wide variety of wireless devices — including cell phones, cordless phones and garage-door openers — to detonate improvised explosive devices, or IEDs. To combat this, the Army has been engaged in the wholesale jamming of RF signals. But this has resulted in an unwanted byproduct: the jamming also has been affecting the Army’s own transmissions. (See “Army’s jamming strategy blows up,” MRT March, page 26.)
The RFHawk not only would hunt for such illegitimate transmissions and ferret them out, it would help users create a profile in order to have a better idea of what they were looking for in the future, according to Hiebert.
“When [an IED] goes off, they can capture [the transmission] to see what it looks like, so they can characterize the signal that triggered the detonation,” he said.
There are other examples much closer to home. For instance, drug traffickers use illegitimate transmissions to converse with each other along the U.S./Mexico border, Hiebert said. Other examples can be found in U.S. prisons.
“They’re actually looking for crime lords that are running their empires from behind bars,” Hiebert said. “They get their electronics confiscated, but somebody smuggles them a cell phone.”
The RFHawk’s location capability is provided via a mapping application. However, it is the device’s ability to classify the signals that makes it truly unique, according to Hiebert. “This is the magic,” he said.
The device uses spectral correlation analysis to compare identified signals with known signal types in the area. RFHawk users can visually compare the shape of the questionable signal with the shape of known signals in the area to determine whether the questionable signal is indeed a problem.
“You can think of this as an RF-fingerprinting tool,” Hiebert said.
When a signal is determined to be a threat, the RFHawk pinpoints the location, aided by the device’s directional antenna and its ability to generate signal-strength readings that are linked to GPS and in-building maps, which enables rapid narrowing of the search area. In addition, the RFHawk, which lists for $38,900, logs and stores measurement data for each rogue signal that’s identified.
