Doppler Systems, LLC specializes in manufacturing radio direction finding equipment and geolocation systems. Founded in 1981 by David Cunningham, the company has developed low-cost, professional-quality direction finders that are utilized by private enterprises, government agencies, and the amateur radio community. Doppler Systems' patented smooth summing technology enhances direction-finding sensitivity and accuracy, offering advanced solutions at competitive prices. Their products include fixed site, rack-mounted, mobile, and packaged direction finders, along with software like BearingTrack and TargetTrack. Doppler Systems operates from a facility in Tucson, AZ, where all products are manufactured in the US using local vendors.