Important note about the Doppler II:

• Jacques has obsoleted the Doppler II, but firmware and boards may still be available - see the Doppler II Modifications Page for more info.
  

Abstract:

Jacques Brodeur, VE2EMM, has 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 is 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.

AVAILABILITY:

• Q:  Where can I get this firmware?
• A: This firmware is now available in the form of pre-programmed PICs (only) be available from the author:  Please send email if you have any questions.  Note that these chips are usually shipped code-protected.
  
• Q:  Which chips are used?
• A:  The main processor for the Doppler I uses a PIC16F876A;  The Compass rose and Comb Filter use the PIC16F819;  The "mini" comb filter uses the PIC12F683;  The Doppler III "Clock" uses the PIC12F675.  A PIC16F877A is currently used for the main processor for the Doppler II and Doppler III alternate firmeware although testing is being done with the PIC18F series.
• Q:  Why is the firmware available on two different types of processors?
• A:  The PIC16F877A has been used as it has been large enough to accomodate the current feature set although the addition of more features will likely require the use of the larger processors - which may be plugged in with no modifications.  If you can think of some feature that would be advantageous to add, please feel free to contact me to see.
  
• Q:  How much do the chips cost?
• A:  Recently, I have been charging as follows (all prices in US Dollars)  Please note that these prices are subject to change!:
• $13 - Main processor for Doppler II or Doppler III alternate firmware - you must specify whether you want the Doppler II or Doppler III firmware.  For the version using the PIC18F series, the main processor will be $15.
  
• $12 - Main processor for the Doppler I alternate firmware.
  
• $7 - Compass rose display chip.  This chip is required for the Doppler III, as are certain minor modifications - see the Compass Rose page for more info.
• $5 - "Clock generator" chip.  If you already have a working Doppler III and wish to change to the alternate firmware, you will not need this chip:  You will only need it if you are building it and do not already have the chips.  This clock generator is not required for the Doppler II.  Also note that the .HEX file for this processor may be found below if you have the ability to obtain and program PIC12F675's yourself.
  
• $7 - Comb Filter to remove the switching tone from the received audio.  This is for the "full-sized" comb filter.  Important note:  This filter is designed to filter a tone of precisely 500.8 Hz - the switching frequency of the original Doppler II firmware and the alternate firmware for both the Doppler I, II and III units:  If used on the original Doppler III firmware, a different frequency will be required - please note this if you are interested!
• $5 - The "mini Comb Filter."  This works much like the above comb filter, except that it has fewer available modes and it uses an 8-pin PIC in a smaller package.
• $5 - A PIC-based TDOA unit.  If you are interested in this unit, please note that its firmware is still being developed, but the prototype seems to work nicely - but if you get one, I expect feedback from you as to how to improve it!
  
• Shipping/handling and "hassle factor" - If you order just one or two of the smaller chips (8 or 18 pin) then shipping/handling will probably be $3.50.  If you order a complete set of chips for the Doppler III, it will probably be be in the $5-$6 area.  Please ask!  Please note that any incurred taxes and/or tariffs are the responsibility of the recipient of the chips.
  

Doppler III Filter Clock object code:

Please note that object code for the Doppler III filter clock is available here.  Note that this code is functionally identical to the original - but is not in any way based on the original code as far as I know.  This .HEX file is targeted to be programmed into a PIC12F675 and simply outputs a 98.04 KHz signal with a 20 MHz input drive signal - that is, it simply divides the 20 MHz input by 204 by using a bunch of "watchdog restart" instructions to delay toggles of the output clock line.  This filter clock rate yields a bandpass frequency very close to 500 Hz.

Disclaimer:

This code was originally based on that of the original Montreal Doppler II DF unit by 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, Jacques cannot reasonably be asked to offer any support or assistance regarding them!

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 DF-related questions?  If so, you may send email to the address below:

Do not click on the address above - simply type it into your email client

For further information, go to the Unofficial VE2EMM Doppler Information page.

This page updated on 20080716