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Doppler Systems LLC

Radio Direction Finders and Direction Finding Systems

The products on this page are no longer in production.  We do continue to support these products with customer assistance and repairs.  Contact the factory if you have need help with any of these products.

Series 6100 Radio Direction Finding System

The 6100 series radio direction finder provides a self contained system for mobile triangulation. Utilizing the Auto Track software program running on the user's laptop computer, lines of bearing may be recorded on a digital map. A GPS receiver is used to measure the tracking vehicle's location and heading which are displayed as an icon on the map. Lines of bearing (LOB) are also shown on the map originating from the icon. When the user determines that a valid bearing is displayed, the LOB is stored and the icon changes. By driving to another location and taking another LOB, the intersection indicating the emitter location is found. This process continues as the tracking vehicle closes on the emitter. The number of LOBs displayed may be limited to show only the most recent; however, all selected LOB data is written to a file that may be recovered later for analysis of the data.


The system is based on the DDF6002 display/processor unit which uses advanced digital processing to estimate the bearing angle. In addition, it provides the data multiplexing required to interface the GPS receiver, NBFM receiver, and optional flux gate compass with the laptop computer through a single serial RS232 port. The DDF6072 distributes 12 VDC power to all of the equipment. The figure below shows a complete series 6100 direction finding system.



DDF6002 Display/Processor

The DDF6002 display/processor drives the RF summer with the waveforms required to mix the four antenna inputs smoothly and to produce the simulated Doppler modulation at the selected sweep frequency. Audio from the receiver is processed to calculate a best estimate of the bearing angle. The DDF6002 may be used as a standalone homing type radio direction finder or it can be used with the Auto Track software as a triangulation system. When used with an appropriate receiver, the DDF6002 meets the following specifications:

SignalTrack Software

This Windows based program is supplied with the DDF6002. Serial data from the DDF6002 is decoded into the bearing angle, GPS latitude, longitude, heading and velocity. When a compass is used, SignalTrack uses its heading when the velocity is less than 4 km/hr; otherwise the heading is obtained from GPS. The tracking vehicle is located on the map image and displayed as an icon. The true bearing direction is displayed as a line from the icon on the map and is saved when the user presses the Insert key.

The program also provides control of the direction finder front panel controls and the receiver's frequency. A convenient auto-calibration can be set up if the location of a beacon transmitter (for example, a NOAA weather station) is known. For more information on this program, refer to SignalTrack.

Screen Image - AutoTrack Software


The DDF6074 is a compatible GPS receiver and antenna. The receiver is made by Garmin and is preprogrammed to provide the NMEA0183 messages GGA and VTG every 1 second. The GPS cable is wired to connect to a DDF6002 RS232 input and to the DDF6072 for power.

DDF6075 Compass

The DDF6075 compass is a version of the KVH model C100 which is recommended when operation is required when the tracking vehicle is stationary. (GPS does not provide heading information when the tracking vehicle velocity is less than a few km/hr). NMEA0183 message HDG is sent from the compass every 1 second. The DDF6075 includes compatible connectors for the serial data and power used in the series 6100 system. Care must be taken when placing this compass on the car to avoid magnetic structures.


DDF6072 Power Distribution Unit

The DDF6072 is a compact box that supplies 12 VDC power to the DDF6100 direction finder, receiver, laptop computer, GPS receiver and optional electronic compass. Twist lock connectors are used. The unit connects to the vehicle 12 VDC using a single auto power plug.