KA7OEI's Amateur Radio Direction Finding (ARDF) Page


This page contains various links related to Amateur Radio Direction Finding (ARDF) - also known as "Foxhunting" or "DFing"

Pages related to VE2EMM's "Montreal Doppler" units:

Jacques Brodeur, VE2EMM, has designed several excellent microprocessor-based "Doppler" type DF units described at his web site (see the links below.) These units works along the same principles that the so-called "Roanoake" DF units do - but the addition of a microprocessor (to do the generation of switching signals and processing of the received audio) adds additional flexibility.  If there are any questions, please use the contact information on the respective page(s.)

Important notes:


Links to Official VE2EMM Web pages relating to the Montreal Doppler units

Please visit these pages first if you are interested in the Montreal Doppler units.  Please note that the "Doppler I" and "Doppler II" units may not be supported by Jacques, VE2EMM.  Where practical, reproductions of the original web pages are provided as a reference.

The "Doppler I" (a.k.a. "VE2EMM 32 LED  Doppler Direction Finder") has been obsoleted by Jacques, but the boards are still available from FAR circuits and alternate firmware is still available.

Please note that the original "Doppler I" (32 LED Doppler direction finder) web page is no longer online, but:
The "Doppler II" has been obsoleted by Jacques, but the boards are still available from FAR circuits and alternate firmware is still available.

Please note that the original Montreal Doppler II web page is no longer online, but:

Note:  The following pages are not official pages of VE2EMM and do not necessarily involve his direct contributions.  For questions about the contents of these pages, please use the contact information contained on them.

Other pages related to the Montreal Doppler units - construction and circuit board availability:
Can you "DF" digital voice signals?

The question has been asked:  With new, digital voice systems such as D-Star and APCO-25, can those signals still be located?

To answer this, let's do a quick review:  There are two general types of DF (Direction Finding) techniques:
  • Signal strength.  These use the strength of the signal - often using a directional antenna such as a yagi - to determine the direction from which the signal is arriving.
  • Phase-detection techniques.  These include systems such as two-antenna "TDOA" or the rotating "Doppler" systems that can, in one of several ways determine something about the direction of the incoming signal.
The "signal strength" system doesn't really care what mode or bandwidth is being used:  As long as the signal can be detected in some way, one can determine its direction.  This could be done using a field-strength meter, a receiver specially designed for direction-finding, or even the S-meter of an existing receiver.

For the phase-detection systems, it turns out that many of the systems designed for analog reception will work with narrowband digital systems, such as D-Star.  Note, however, that the "bandwidth-limited noise" nature of the D-Star  (and similar) signals may reduce accuracy and sensitivity of some units somewhat, depending on their design and filtering.

For DFing a narrowband digital signal, one would continue to use the same analog receiver as before in conjunction with the signal meter or direction-finding unit.  Of course, if one wanted to "hear" the audio being transmitted on the digital signal being tracked, you would need to use a digital receiver (such as a  D-Star-capable receiver) on a separate antenna to do so.

Note that DFing of wideband digital signals (those that are much wider than an standard FM signal, such as the 128kbit D-Star found on 23cm) will likely require "Signal strength" techniques as the phase information imposed by antenna switching (for example) is likely to be badly diluted.

The "alternate firmware" for the Doppler II and III has been tested with D-Star signals and found to work very well.  The "Doppler I alternate firmware" and the original Montreal Doppler firmware versions have not been tested, but is also expected to work just as well as they all function using the same, basic techniques.

KA7OEI's pages pertaining to the Montreal Doppler 1, 2 and 3 DF units:

The following pages are maintained by KA7OEI:  Questions about these pages should be directed using the contact information on these pages rather than to Jacques.

"Alternate" firmware for the Montreal Doppler units:
 Other related pages:

Interfacing Doppler DF units with computers and GPS receivers for moving-map displays:

With relatively little effort, it is possible to use a computer (a modest laptop - 200 MHz Pentium-class or faster) along with a GPS receiver equipped with NMEA output, and the Montreal Doppler II or III units to produce a mobile, street-level moving-map display that can display converging bearings on received signals.  There are at least two low-priced software packages that can do this:

Other pages at this site having to do with Doppler RDF:

These pages discusses other devices used with the Montreal Doppler units, but these could be applied to direction-finding units as well.

  • An Add-on Pelorus for the Doppler II (or III) - This page describes an outboard compass-rose display unit that is driven by "Agrelo" formatted data output from the serial port.  This display has been "obsoleted" by the use of the "Alternate Firmware" for the Doppler II, Doppler III, and the compass rose display.
  • An add-on Pelorus using an OLED Display - This project was done mostly to evaluate the use of Organic LED (OLED) displays that are becoming available.  This unit operates from the serial port (using "Agrelo" format bearing/quality data) and provides a graphical representation of the bearing, history, and quality of the signal being received.
  • Audio comb filter for switched-antenna RDFs - When a switched-antenna RDF system operates, an audio tone (used to determine the bearing) results.  This page describes a PIC-based DSP comb filter that can remove this tone (if desired) to make the on-signal modulation more intelligible.  Note:  Even with the comb filter enabled, one can still discern the presence of multipath by the "sound" of the audio and multipath-generated sidebands that get through the filter.
  • DF Antenna Arrays - This page describes some typical antenna arrays (for mobile and home use) that may be used with RDF systems.
  • A "Pre-processor" for Doppler-type DF units - This unit may help to detect and prevent distorted/bad bearings from being received by the DF unit.


    • Miscellaneous other pages having to do with Amateur Radio Direction finding (ARDF)

    These pages contain information on how ARDF gear works as well as the building of other pieces of equipment.

    Note:  The reader should be aware that the authors of the links on this page do not necessarily endorse any of projects, circuits, designs or vendors mentioned above.  The level and satisfaction of performance as well as efficacy and safety of any of the above circuits is largely based on the skill and experience of the operator.  Your mileage may vary.

    Do you have any DF-related questions?  If so, you may send email to the address below:
     
    Say it aloud - 'dee eff at double-you double-you double-you dawt yew ess ess sea dawt com'
    Do not click on the address above - simply type it into your email client

    Go back to the KA7OEI main page

    This page updated on 20091130

    Note:  This page (and other pages on this site) are not "official" pages of VE2EMM.  These pages are simply set up to aid those who have built or might build the described equipment.