Important note about the Doppler II:

• The Doppler II was obsoleted by the late Jacques Brodeur, VE2EMM, but the "alternate" firmware is still be available - see the Doppler II Modifications Page for more info.
  

Abstract:

The late Jacques Brodeur, VE2EMM, designed an excellent microprocessor-based "doppler" type DF unit described at VE2EMM's Montreal Doppler II page that drives the antenna switching circuit, updates the display, and does signal processing to determine the bearing.  Please note that this firmware was not supported by Jacques himself - please read the disclaimer.

This unit 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.  For a bit of information about the newer Montreal Doppler III unit, go to the "Montreal Doppler III" page.

This "Alternate Version" firmware is based on the original code written by Jacques for the Montreal Doppler II but these new features have been added independently without Jacques' direct involvement.  Note that it contains equivalents of some of the features found in the newer Montreal Doppler III unit as well as a few others!

Preliminary operating instructions for this firmware may be found on the Operating Manual page.

This new firmware has the following modifications/improvements:
 

The arrangement of the main display of this new firmware showing dual graphical and numerical bearing displays:  This display is identical for both the Montreal II and III versions.
Go to the Operating Manual page for more information.

• New graphical compass rose.  The original Montreal Doppler II code displayed a clever, but difficult-to-decipher graphical 32 point compass rose display.  The intent was to provide a visual representation of the bearing of the received signal with respect to the current location.  The problem is that with the 16 character, 2 line display, the compass rose was extremely "squashed" and it took more than a quick glance to try to figure out the bearing.  This new firmware provides a smaller, but more intuitive compass rose showing the current bearing in a form that resembles an analog clock (but with only a minute hand...)  This new display only displays 16 points of the compass, but owing to the small size of this display, more resolution would be of questionable benefit.
• Sliding average.  Also displayed is a sliding average consisting of up to 32 readings (including the current one.)  Because this average is updated with each new reading, a high average setting does not slow the update rate like the integration does.  Also, because it calculates the average based on the amplitude vectors of the original readings, its operation has much the same effect as the 8-capacitor roanoake filter - a real benefit to the users of an Doppler II without the switched-capacitor filter!
  
• Doubled update rate.  In the original Montreal Doppler II code, new readings were not being taken while the display was being updated, most notably when the integration was set to 1.  This has been changed so that up to 20 readings per second are available on the serial port and/or the Compass Rose display.  One may select between the current reading or the average reading to be output on the serial port.
• A dual compass rose.  Actually, there are two compass roses on the display.  The one of the left displays the current bearing while the one on the right displays the sliding average of past readings as long as they are above the minimum quality value.  This additional display can provide the following benefits:
• If the signal is very noisy and seemingly random (as is often the case when operating mobile amongst urban clutter) an averaged reading can go a long way towards being able to determine a likely bearing.  Being that this average bearing is weighted according to quality, poor bearings won't affect the average as much as good, solid ones.
• A smaller integration rate may be used.  Often, the minimum integration (e.g. none) is more than adequate.  In this setting, about 20 readings per seconds are displayed, completely updating the "average" about 1.3 times per second.  Because this average is sliding, it is also updated at the same 20 readings per seconds - but the result is significantly smoothed.
• Because the averaging is only done on "good" quality signals (those above the selected "minimum" quality level) it will "freeze" the display when the signal disappears, showing the average.  Because the original Doppler II would continue to process the signal for a short time after it had disappeared (owing to the integration) it was likely that the last reading displayed was likely erroneous, having been based on the squelch noise burst and having nothing to do with the original signal.  This "average" display mitigates this problem, as only a few of the last (erroneous) readings are contributing to the overall average.  (Note:  The audio level detect modification for the Doppler II noted below improves this even more!)
• Dual numerical displays.  For both displays, the bearing and signal quality is displayed.  In addition to the "sliding average" bearing, the averaging display also shows the "average" quality for that same bearing.  In addition, the current integration rate is displayed, along with either an "S-meter" reading (if connected to the receiver) or audio input level - selectable by the user.
• Support for a "raw" audio level meter.  One of the overlooked features on the Montreal Doppler II unit (something corrected with the Montreal Doppler III) was a means of detecting the "raw" audio level.  On the original Montreal Doppler II code, the audio level is computed from the processed input data - but this is rather slow to respond, particularly if a higher integration rate is used.  The result of this (as mentioned above) is that it takes a moment to detect that an input signal has disappeared and to stop processing, the result being is that the final bearing(s) may be bogus.  Being able to measure the audio level as it comes from the audio audio peaking filter (the first-stage filtering, outside the microprocessor) allows much faster response to the disappearance of audio.  This means that the most recent good reading may be "frozen" on screen when the signal disappears and the squelch closes.  This input audio level is displayed as a graphic on the screen - along with the "gating" status (e.g. whether or not the audio input is too low to allow display of  a reading) with the "gating" threshold being adjustable. Note that for the Montreal Doppler II, this feature requires a simple modification of the main board involving cutting of two traces, the installation of one jumper, and the addition of 3 resistors, a diode, and capacitor.
• Differential outputs for 4 antennas.  In addition to the 4, 6, or 8 antennas (and selectable drive polarity) of the original Montreal Doppler II unit, when 4 antennas are selected, the "other" 4 output pins (the connections for antennas 5-8) provide an opposite-polarity drive signal for differentially-driven antenna switches.
• Vector-based "quality" calculation.  The quality of the signal is now based on the quality of the resolved directional vector itself rather than just amplitude.  This permits better quality assessment of signals that are noisy and/or "multipathy" and thus improve the likelihood of rejecting signals with poor quality and prevent their contribution to the calculated direction.
• Support for a Compass Rose display without using the RS-232 port.  A larger compass rose (Pelorus) is a highly desirable accessory - which is precisely why the newer Montreal Doppler III has one integrated with it.  Originally, the Montreal Doppler II could "drive" an external compass rose only via the serial port, but it would be nice to not have to tie it up the serial port this way - especially if one wishes to put the compass rose in the same enclosure AND use an external computer/GPS receiver.  This new code can provide a synchronous data output to drive a compass rose like the one used on the Montreal III unit - and it is, in fact, compatible with the original Montreal Doppler III compass rose display and the updated firmware for the Montreal Doppler III's compass rose.  Note that this feature requires a simple modification of the Doppler II's main board (simple cutting) and, of course, the addition of a compass rose display like that used with the Montreal Doppler III. One may select either the current reading or the average reading to be displayed on the compass rose.
• Improved GPS multiplexing.  NMEA sentences from a GPS receiver are "passed through" the serial port, allowing the user to have both devices on a single serial port.  The original firmware "froze" while it waited to synchronize to the incoming GPS data.  In this firmware, the GPS passthrough multiplexing is completely transparent to the user and does not, under any conditions, affect normal operations.  Additionally, support for 19200, 38400, 57600, and 115200 baud has been added.
• "Adaptive Filtering" for a switched-capacitor filter.  This feature allows a very fast response to brief signals - even if the filter is set to respond "slowly."  If an 8-capacitor "Roanoke-type" switched capacitor filter is present (as on the Doppler III, or if one is added to the Doppler II) an additional modification will automatically switch this filter to a "fast response" mode when it disappears.   This allows two things to happen:
• Remenants of the "old" signal are quickly removed from the filter, allowing it to start "fresh" when a new signal appears.  When a new signal appears, it is not affected by previous "history."
  
• Within 50-100 milliseconds of the new signal being detected, the Roanoke filter is returned to its orginal settings.  At this instant, the Roanoake filter is already "pre-loaded" with some bearing information about the "new" signal and from that point on, the original setting of the filter (as set by the "damping" control, if present) will take over, providing the "slow" filtering.  This allows a very fast response to the appearaince of a "new" signal - even if the damping is set to provide a "slow" response.

Use of the "alternate" firmware on the Montreal Doppler III:

• Supports the Compass Rose display.  With the current firmware, the current reading, the averaged reading, or even both may be displayed simultaneously.
• Utilization of the Doppler III's audio level metering capability.  This audio level is shown on the display using an icon.  "Gating" of the readings (e.g. starting and stopping) based on the audio level is also supported.
• A reworked menu interface.  While the Doppler II has 4 buttons used to navigate around the menus, the Doppler III has a potentiometer and one button:  This change necessitates a different method of selecting and changing menu items.
• When in the normal display mode, the pot is used to adjust the integration rate (or, if so-configured, the amount of averaging) and the button sends the current reading (selectably the current reading or the average) out the serial port, if enabled.
• On other menus, the pot is used to move a cursor that selects menu items and the button is used to change the selected item.
• Because of the ease of adjustment when using the potentiometer, a wider selection of integration/averaging settings is available from the main display
• Serial output and/or GPS passthrough.  Just like the original Doppler II firmware, one may select a continuous output stream of bearing/quality data, have the data sent on a selectable timed interval, or configure to manually send the bearing at the push of a button.  Optionally, data from a connected GPS receiver may be passed through.  The serial bearing data being output (in "Agrelo" format) may be either the current or the averaged reading.

Preliminary operating instructions for this firmware may be found on the Operating Manual page.

• Getting the firmware described at this site

Disclaimer:

This code was originally based on that of the original Montreal Doppler II DF unit by the late Jacques Brodeur, VE2EMM, and full credit is given to him for this fine work.  Because the additional modifications are my own and were not done with his involvement!

Although good faith efforts have been made to make certain that the operation of the hardware/firmware is as described, it is possible that "undocumented features" (bugs) may be present:  It is through testing, use, and feedback from the users that projects such as this may be improved, and the user is asked to be understanding of this fact.  This firmware is strictly intended only for non-commerical amateur-radio use and any other use is in violation of applicable laws.

Additional note:  Neither the author or UARC officially endorse any vendors mentioned above or assume any responsibility for the use of the devices/products described herein.  The level and satisfaction of performance of any of the above is largely based on the skill and experience of the operator.  Your mileage may vary.

Do you have any questions on this or other DF-related topics?  Go here.

This page updated on 20120316