Ben Harpe (left), Isaac Struhl and Alex Wuff pose with a prototype of one of their radio frequency sensors.Courtesy of Distributed SpectrumIn 2021, while perfecting their technology for detecting military communications and jamming, Alex Wulff, Ben Harpe and Isaac Struhl beta tested their work on a civilian population: their Harvard classmates.The engineering students built a few dozen prototypes of small, low-cost radio sensors and asked their friends to put them in their rooms, then walked around campus talking on handheld radios to refine their detection algorithms.We had some very funny looks from some of our classmates, recalled Wulff.The company they founded while seniors at Harvard, Distributed Spectrum, is now getting come-hither looks from national security agencies and investors. The trio say theyve won $7 million in contracts over the past year from the Department of Defense and an intelligence agency they cant name. Tuesday, they announced that theyve raised $25 million in a Series A funding round led by the venture capital firms Conviction and Shield Capital, and the tech entrepreneur and investor Nat Friedman.Distributed Spectrums radio frequency detection technology impressed retired Army Gen. Stanley McChrystal, who commanded U.S. and international forces in Afghanistan. He views them as a cheaper, more nimble alternative to the bulky, multimillion-dollar equipment from companies like Raytheon and L3Harris that the military has long relied on. Because it's inexpensive and you can just put it everywhere, it's going to allow you to cover things you could never cover before, said McChrystal, who is advising Distributed Spectrum and invested in the company.Harpe, 26, and Wulff and Struhl, 25, say their sensorsthe smallest of which weighs under a pound and is the size of a thin stack of cocktail napkinscontain about $1,500 to $2,000 worth of commercial hardware, including software-defined radios and power-sipping Nvidia Jetson minicomputers. Outfitted with AI algorithms that automatically identify signals and pinpoint where theyre coming from, the devices promise to give soldiers in the field an awareness of the threats around them without the need for highly trained signals intelligence officers to interpret the data.There's a huge need to understand, hey, I'm detecting something out there. What is it? Is it a threat to me? said Wulff, CEO of the startup, which is now based in New York City.That need is perhaps most visible in Ukraine, where an intense, invisible battle is being waged with radio waves. Russian and Ukrainian soldiers communicate with cell phones and handheld radios; bombs and missiles are guided to their targets by satellite signals; and soldiers wearing FPV goggles remotely pilot explosive-laden drones. Meanwhile electronic warfare specialists blast out radio noise to jam their enemys communications or spoof their guidance systems.Both sides are constantly changing their transmission and jamming techniques, at a speed that outmatches the abilities of traditional automated detection systems that are based on libraries of signal patterns that can take weeks to update.Its a preview to what U.S. troops could face in a war with an advanced adversary like China, and one that makes it clear signals intelligence officers will have a far more difficult job than they did in Iraq and Afghanistan.As we transition to great power competition at the scale of the entire Pacific Ocean, there's just no way that we're going to be able to have that level of understanding spread out across that large of an area, said Wulff. The only solution is to automate some of this.Distributed Spectrum was born out Wulffs concept for a senior thesis project to try to replace expensive and bulky radiofrequency sensing hardware with lots of cheap, software-powered devices. With Harpe and Struhl, he saw a business opportunity in the commercial wireless market where the trio could help telecom companies monitor interference and make better use of their spectrum.But a 2021 hackathon sponsored by the Defense Department changed their plans. There they learned the military was facing a really hair on fire problem: it often struggled to determine whether battlefield communications systems were being jammed or were just malfunctioning.They won the $25,000 grand prize by coding a system to detect radio-frequency attacks on military vehicles in real-time, impressing Pentagon officials who helped orchestrate a collaboration with Special Operations units to try out their technology.Theyve since landed development contracts with the Army, Air Force and Navy for an array of applications: soldier-portable devices that offer alerts for approaching drones or nearby enemy cellular signals, stationary systems to monitor for activity around military bases and networks of sensors to detect anomalies in the radio spectrum across wide areas that might be a tipoff to the presence of unfriendly forces.Last fall the company won $150,000 and a shoutout from outgoing Defense Secretary Lloyd Austin in a competition for concepts for electronic warfare tools suitable for use in the vast, watery reaches of the Indo-Pacific region.Wulff, Harpe and Struhl say theyve deployed a handful of their sensors with a partner in Ukraine whos strapped them to drones that are used to locate enemy jamming devices and hidden troops on the battlefield.The Defense Department is a hard place for small startups like Distributed Spectrum to make inroads, but Sarah Guo, founder of the VC firm Conviction, likes the companys chances given the acumen of its founders and their early success in winning contracts. There is real energy in the department to work on this problem. I think that's all you can really ask for at an early stage company, she said.