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Doppler Systems LLC

Radio Direction Finders and Direction Finding Systems

High Frequency Radio Direction Finder

Covering the HF bands from 1.5 - 10 MHz our HF direction finder electronically creates a rotating directional antenna.  A simple AM receiver demodulates the received signal and our DF processor extracts the bearing information from the audio output of the receiver.  The system is optimized to work on near vertical incident skywave, NVIS, transmissions and can direction find all types of signals including AM, FM, SSB, any type of digital modulation, and even noise sources.

Loop antennae manufactured by Wellbrook Communications, are used for the receiving antennas. These antennae exhibit high bandwidth, low noise and are compact in size allowing for ease of transport and system setup.  The loops are one meter in diameter and they are mounted on tripods with the base of the antenna approximately 2 meters off the ground.  The antennae are arranged so that the N, E, S and W antennae are positioned in a square with a diagonal distance of 0.707 wavelength at the geometric center of the frequency band of operation.  For a 4-8 MHz version this would be 123 ft.  There are two more loops, NS and EW,  which are mounted near the center of the array. The loops are oriented so as to produce the same pattern as would be the case if dipole antennae were used. That is, since the null in a loop is normal to the plane of the loop, antennae N, NS and S are all oriented to be in the NS plane and antennae E, EW and W oriented to lie in the EW plane.

The HF Direction Finder uses our DDF7000 series processor and an AM receiver packaged into an easy to transport Pelican case.  Two antennas and the requisite cabling for them are housed in a single case.  The summer/combiner is housed in a weather proof NEMA enclosure to be mounted outside.  A search receiver is also provided allowing the operator to listen to the received signal.

Our TargetTrack and User interface software provide the user with easy display of the measured bearings.  Multiple systems in different geographical locations can be linked via the internet to enable geolocation of a RF source within regional boundaries.


DF Method Synthetic Directional Beam patented with "Smooth Summing"
Frequency Range 1.5 - 10 MHz
Accuracy < 10 deg rms
Resolution 0.1 deg
Sampling Rate 2 samples per second
Averaging Adjustable from 1 to 20 samples
Rotation frequency Adjustable (250, 500, 1000, 2000 Hz)
Voltage Range 105 - 220 Vac (12 V power supplies furnished)
Power 20 Watts
Temperature Range -25 °C to 85 °C (antenna)
CE Compliant

Per EN 61000-6-2, EN 61000-6-4 AND EN 301 489-1

HFDF Block Diagram
Block Diagram of the HF Direction Finder
Doppler High Frequency DF Antenna Arrangement of HF Direction Finder Antennas
HF Direction Finder Loop Antenna HF Antenna Arrangement
Doppler HF Direction Finder in Operation
HF Direction Finder Test Setup in Arizona Desert