for the Montreal Doppler
and III RDF units
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
Modifications Page for more info.
The late Jacques Brodeur, VE2EMM, designed an excellent
"doppler" type DF unit described atVE2EMM's
pagethat drives the antenna switching
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
DF units do - but the addition of a microprocessor (to do the
of switching signals and processing of the received audio) adds
flexibility. For a bit of information about the newer
Doppler III unit, go to the "Montreal
Doppler III" page.
This "Alternate Version" firmware is based on the original code
by Jacques for the Montreal Doppler II but these new features
added independently without Jacques' direct involvement.
equivalents of some of the features found in the
III unit as well as a few others!
Preliminary operating instructions for this
be found on the Operating
This new firmware has the following
The arrangement of the main
display of this new
firmware showing dual graphical and numerical bearing
display is identical for both the Montreal II and III
versions. Go to the Operating
page for more information.
New graphical compass rose. The original
II code displayed a clever, but difficult-to-decipher graphical
compass rose display. The intent was to provide a visual
of the bearing of the received signal with respect to the
The problem is that with the 16 character, 2 line display, the
rose was extremely "squashed" and it took more than a quick
to figure out the bearing. This new firmware provides a
but more intuitive compass rose showing the current bearing in a
resembles an analog clock (but with only a minute hand...)
display only displays 16 points of the compass, but owing to the
size of this display, more resolution would be of questionable
Sliding average. Also displayed is a sliding
consisting of up to 32 readings (including the current
Because this average is updated with each new reading, a high
setting does not slow the update rate like the integration
Also, because it calculates the average based on the amplitude
of the original readings, its operation has much the same effect
8-capacitor roanoake filter - a real benefit to the users
Doppler II without the switched-capacitor filter!
Doubled update rate. In the original
II code, new readings were not being taken while the display was
updated, most notably when the integration was set to 1.
been changed so that up to 20 readings per second are available
serial port and/or the Compass Rose display. One may
the current reading or the average reading to be output on the
A dual compass rose. Actually,
compass roses on the display. The one of the left displays
bearing while the one on the right displays the sliding
of past readings as long as they are above the minimum quality
This additional display can provide the following benefits:
If the signal is very noisy and seemingly random (as is
when operating mobile amongst urban clutter) an averaged
reading can go a long way towards being able to determine a
Being that this average bearing is weighted according to
bearings won't affect the average as much as good, solid ones.
A smaller integration rate may be used. Often, the
(e.g. none) is more than adequate. In this setting,
per seconds are displayed, completely updating the "average"
times per second. Because this average is sliding,
it is also updated at the same 20 readings per seconds - but
is significantly smoothed.
Because the averaging is only done on "good" quality signals
the selected "minimum" quality level) it will "freeze" the
the signal disappears, showing the average. Because the
Doppler II would continue to process the signal for a short
it had disappeared (owing to the integration) it was likely
reading displayed was likely erroneous, having been based on
noise burst and having nothing to do with the original
"average" display mitigates this problem, as only a few of the
readings are contributing to the overall average. (Note:
level detect modification for the Doppler II noted
Dual numerical displays. For both
the bearing and signal quality is displayed. In
the "sliding average" bearing, the averaging display also shows
quality for that same bearing. In addition, the current
rate is displayed, along with either an "S-meter" reading (if
to the receiver) or audio input level - selectable by the user.
Support for a "raw" audio level meter.
features on the Montreal Doppler II unit (something corrected
Montreal Doppler III) was a means of detecting the "raw" audio
On the original Montreal Doppler II code, the audio level is
the processed input data - but this is rather slow to respond,
if a higher integration rate is used. The result of this
above) is that it takes a moment to detect that an input signal
and to stop processing, the result being is that the final
be bogus. Being able to measure the audio level as it
the audio audio peaking filter (the first-stage filtering,
microprocessor) allows much faster response to the disappearance
This means that the most recent good reading may be "frozen" on
when the signal disappears and the squelch closes. This
level is displayed as a graphic on the screen - along with the
status (e.g. whether or not the audio input is too low to allow
of a reading) with the "gating" threshold being
Montreal Doppler II, this feature requires a simple
modification of the main board involving cutting of two
installation of one jumper, and the addition of 3 resistors, a
Differential outputs for 4 antennas. In
the 4, 6, or 8 antennas (and selectable drive polarity) of the
Montreal Doppler II unit, when 4 antennas are selected, the
pins (the connections for antennas 5-8) provide an
signal for differentially-driven antenna switches.
Vector-based "quality" calculation. The
the signal is now based on the quality of the resolved
itself rather than just amplitude. This permits better
of signals that are noisy and/or "multipathy" and thus improve
of rejecting signals with poor quality and prevent their
the calculated direction.
Support for a Compass Rose display without
port. A larger compass rose (Pelorus) is a
accessory - which is precisely why the newer Montreal Doppler
integrated with it. Originally, the Montreal Doppler II
an external compass rose only via the serial port, but it would
to not have to tie it up the serial port this way
if one wishes to put the compass rose in the same enclosure AND
external computer/GPS receiver. This new code can provide
data output to drive a compass rose like the one used on the
unit - and it is, in fact, compatible with the original
III compass rose displayand the updated
firmware for the Montreal Doppler III's compass rose.
this feature requires a simple modification of the Doppler II's
board (simple cutting) and, of course, the addition of a compass
like that used with the Montreal
Doppler III. One may select either the current reading or
reading to be displayed on the compass rose.
Improved GPS multiplexing. NMEA
receiver are "passed through" the serial port, allowing the user
both devices on a single serial port. The original
while it waited to synchronize to the incoming GPS data.
firmware, the GPS passthrough multiplexing is completely
the user and does not, under any conditions, affect normal
Additionally, support for 19200, 38400, 57600, and 115200 baud
This feature allows a very fast response to brief signals - even
filter is set to respond "slowly." If an 8-capacitor
"Roanoke-type" switched capacitor filter is present (as on
Doppler III, or if
one is added to the Doppler II) an additional
will automatically switch this filter to a "fast response" mode
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
When a new signal appears, it is not affected by previous
Within 50-100 milliseconds of the new signal being detected,
the Roanoke filter is returned to its orginal settings.
instant, the Roanoake filter is already "pre-loaded" with some
information about the "new" signal and from that point on, the
setting of the filter (as set by the "damping" control, if
will take over, providing the "slow" filtering. This
very fast response to the appearaince of a "new" signal - even
damping is set to provide a "slow" response.
Use of the "alternate" firmware on the
Note:While it is possible to simply "plug in"
alternate firmware into a Doppler II with no modifications at
some of the features on the
Doppler II require some simple board modifications - go the Doppler
II Modification page for more information.
alternate firmware, if all of the listed modifications are
the feature set of the Doppler II is the same as that of the Doppler
Perhaps the most useful feature for users of a Doppler II that
haven't added the
switched-capacitor filter is the addition of the sliding
average. As mentioned above, this simulates, in
much of the effect of the 8-capacitor "Roanoake-style" switched
capacitor filter present in the Doppler I and Doppler III. To
certain, the most flexible combination is to add such a filter to
Doppler II so that you have both. If you have a Doppler II without
the 8-capacitor switched-capacitor filter you will notice an
benefit in terms of filtering.
Use of the "alternate" firmware on the
Because of the similarity between the hardware on the Doppler II and
III units, it wasn't too difficult to modify the code to be able to
with either platform, the desired hardware configuration being
at compile time. This new firmware does everything that its
II equivalent does as well as taking advantage of the Doppler III's
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
This audio level is shown on the display using an icon.
of the readings (e.g. starting and stopping) based on the audio
A reworked menu interface. While the Doppler II has 4
to navigate around the menus, the Doppler III has a
button: This change necessitates a different method of
and changing menu items.
When in the normal display mode, the pot is used to adjust the
rate (or, if so-configured, the amount of averaging) and the
the current reading (selectably the current reading or the
the serial port, if enabled.
On other menus, the pot is used to move a cursor that selects
and the button is used to change the selected item.
Because of the ease of adjustment when using the
selection of integration/averaging settings is available from
Serial output and/or GPS passthrough. Just like the
II firmware, one may select a continuous output stream of
data, have the data sent on a selectable timed interval, or
to manually send the bearing at the push of a button.
data from a connected GPS receiver may be passed through.
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
For information about obtaining the
containing the described firmware, please refer to this web
This code was originally based on that of the original
II DF unit by the late Jacques Brodeur, VE2EMM, and full credit
is given to him
for this fine work. Because the additional modifications
and were not done with his involvement!
Although good faith efforts have been made to make certain
operation of the hardware/firmware is as described, it is
"undocumented features" (bugs) may be present: It is
use, and feedback from the users that projects such as this may
and the user is asked to be understanding of this fact.
is strictly intended only for non-commerical amateur-radio use
other use is in violation of applicable laws.
Additional note: Neither the author or UARC
endorse any vendors mentioned above or assume any responsibility
use of the devices/products described herein. The level
of performance of any of the above is largely based on the skill
of the operator. Your mileage may vary.
Do you have any questions on this or other DF-related
topics? Go here.