Established in 1981, Doppler Systems Inc. designs and manufactures radio direction finding equipment for amateur, commercial and government users. Fixed-site and mobile units are available for frequencies between 50 and 1000 MHz.

Doppler's direction finders operate on the simulated Doppler principle utilizing a patented constant impedance, smoothly varying RF summing unit for high sensitivity and high dynamic range. Three series are currently offered - 5900 series, 6000 series, 6100 series.