"How do I get programmed chips?"
If you are interested in the chips mentioned here, send me an email! At the present time, the following programmed chips are available:
Important notes for those interested in
the source and object code:
The late Jacques Brodeur, VE2EMM, designed several excellent
microprocessor-based "Doppler" type DF units described at his web
site (see the links below.) These units work along the
same principles of the so-called "Roanoake" DF units - 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.)
Links to the legacy
VE2EMM Web pages relating to the Montreal Doppler
Please note that circuit boards are still available from FAR circuits (see the links below) and the "Alternate" firmware for the Montreal Doppler 1, 2, and 3 units is still available from me.
Note that the chips that may be available from FAR circuits would NOT be the programmed with the "Alternate" firmware!
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 from this site.
Please note that the original "Doppler I" (32 LED Doppler direction finder) web page is no longer online, but:
- Here is a copy of the "Doppler I" (32 LED) web page from a 2003 web archive. This web archive may or may not include complete copies of all links, pictures and files.
- Here is a .PDF representation of most of the original 32 LED "Montreal Doppler" ("Doppler I") web page and
- Here is a .ZIP file containing the web page images, PCB trace file, source code, and .HEX file.
- For additional information about the "Doppler I" see the "Doppler I Alternate Firmware" page.
- The "Alternate Firmware" for the Doppler I is still available - go here for more information on pre-programmed chips.
The Montreal Doppler II
The Montreal Doppler II - This is a microprocessor-controlled "Doppler" type of RDF unit roughly based on the "Roanoke" design, but using some DSP techniques to process the audio signal.The "Doppler II" has been obsoleted by Jacques, but the boards are still available from FAR circuits and alternate firmware is still available.
Why "Alternate" Firmware?
Occasionally I get asked how the "Alternate" firmware for the Montreal Dopplers came to be.
I purchased my original Montreal Doppler II from Jacques himself some years ago. Unfortunately, something went wrong with the programming of the chips and they didn't work: Since I already had a programmer and "C" compiler, I wrote a simple test program and verified that the hardware was working correctly.
Upon emailing Jacques he kindly sent me a .HEX file of the object code and upon programming it into the chip, everything worked fine. This started a series of correspondences about some minor bug-fixes and changes - some of which he kindly did. Then one day, after not having heard from him for several months, he sent to me his original source code in an email and said that it was a gift: Surprised, I replied and thanked him.
With the code in hand I gradually tweaked the code more to my liking, adding new features and some additional processing and display options that Jacques, in our correspondence, indicated that he would have like to have done, but didn't get around to it. When the "Doppler III" came out I bought another set of boards from him and with the similarities of hardware, quickly adapted my re-worked "Doppler II" code to work on the new platform.
Ultimately, only a small portion of the original Doppler II code remained - Some of the low-level signal processing and the general layout of the Doppler II menu structure - which I personally preferred over the Doppler III's menu system: Occasionally, upon making major changes and producing stable software I would email the source code to Jacques.
And so it is today: I've since ported a pin-compatible version of the original "Doppler I" hardware and added about all of the features that I and a few others can think of and the code is very stable - so not too much has been added to it recently - but if someone who uses it has a great idea, I'm all ears!
Please note that the original Montreal Doppler II web page is no longer online, but:
Can you "DF" digital voice signals?
The question has been asked: With new, digital voice systems such as D-Star, Yaesu's System Fusion 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:
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. (The 'EMM units describe here have no problems at all with D-Star!)
For DFing a narrowband digital signal one could use "normal" (non-D-Star) analog receiver 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 avoid data corruption due to the "switching tone") 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 are also expected to work just as well as they all function using the same, basic techniques.
DFing one station amongst several in a TDMA environment:
There is one notable exception to the above with regard to "narrowband" digital voice operation and that has to do with those modes that involve TDM (Time-Domain Multiplexing) - that is, the "sharing" of several transmitters on the same frequency. In this mode independent users' transmitters will take turns, briefly transmitting during their assigned "slot", allowing the re-use of the same frequency for several users at the same "time." Clearly, this can cause confusion of "traditional" direction-finding techniques - particularly those of the "Doppler" type as there is no obvious way to separate the two.
Typically, the radios operating in these modes require that they be configured to transmit some sort of identification which means as long as the user has appropriately configured the radio - and as long as you have access to one - you should be able to identify the user. Barring that, if you have a radio and are able to differentiate the transmissions of the "station of interest" from those of other stations using the frequency it may be possible to get general bearings of the station through the use of a directional antenna such as a Yagi and attenuator. Finally, it will be highly likely that not all users on the frequency will always be transmitting at the same time, leaving transmission of the "station of interest" by itself, making it easier to employ more conventional means of location!
The one exception to this rule thusfar is if the digital voice system in question is being used by more than one operator in a TDMA (Time Division Multiple Access) scheme such as is available with DMR: If there are two stations transmitting on one frequency in a time-interleaved manner, directional readings can be confused. In the case of a "Doppler" type system that is inherently omnidirectional, if both signals are audible the likely result will be nonsensical readings. If one is using a Yagi it may be possible to isolate the two, distinct transmitters, but this will depend on the relative strength of the two signals with respect to each other, the separation of their bearings, the prevalance of reflections/multipath and a few other related factors - not to mention needing to be able to discern one signal from the other to determine which one is actually being sought!
If the signal source is very close and strong then the use of attenuators, directional antennas, etc. can help isolate it from other, weaker TDMA signal on the same frequency, allowing both types of systems to be used.
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:
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.
This page updated on 20150820
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