the Montreal Doppler II hardware to utilize features
of the alternate firmware
Important notice - please read:
These modifications apply only to a Montreal Doppler II unit
that has been fitted with the alternate firmware. This firmware
based on code originally written by Jacques for the Montreal Doppler
The alternate firmware allows these additional features to be used
the Montreal Doppler II unit:
Audio level metering:
Audio level metering. Measuring the audio level being
the main peaking filter allows the quick and easy setting of the audio
input level. While the original Doppler II firmware had only a
audio level indicator, it had several major drawbacks:
This audio level was derived from the processed audio
higher the integration rate was set, the longer the time between each
sample. If the integration was set to, say, 16, it could take
a second before the unit responded to changes in audio.
If the audio disappeared during a sample with the integration
fairly high, the resulting bearing may be inaccurate.
If additional filtering (such as the Add-on
Filter) the response to the
of the input signal will depend on the bandwidth of the filter.
set to be very narrow, this response may take more than a second.
Audio-based gating of bearing updates. Having the audio
at an "early" audio stage allows for a rapid response to the
of the audio. If the audio drops below a preset level, the
bearings may be "frozen." This allows readings to be
using the receiver's squelch as well as preserving the last bearing
the signal has disappeared.
Synchronous Serial Compass Rose data output:
The Montreal Doppler III has an synchronous serial output (SPI-type)
that feeds a 36 LED compass rose display that shows the bearing.
This firmware also provides a compatible serial output to such a
This data stream is compatible with the original display supplied with
the Doppler III unit as well as the Alternate
Note: It is presently unknown if just the
rose display board is available. The schematic/details of this
board may be found on the Montreal Doppler III page. For
on the alternate
firmware for this display, use the contact information at the
of this page.
Clock output for an outboard switched-capacitor filter:
A "Roanoake-type" 8-capacitor switched-capacitor filter may be added
to the Doppler II: The new firmware outputs a clock that may be
to directly drive an
Add-on Switched-capacitor filter.
Figure 1: Schematic
diagram of the added
audio level detector.
The ground is tied to any convenient ground on the circuit board.
Audio level meter modifications:
Some minor modification of the Doppler II circuit board must be done
in order to connect the audio level detector input. These
are as follows and are noted in the diagram:
Pin 4 of IC3 (the main processor) must be isolated from the +5
bus. This involves two cuts and the addition of
The trace between pins 4 and 5 of IC3 must be cut. Click
here for a picture of the cut/jumpered traces.
The trace between pin 4 of IC3 and one leg of R7 (a 2.7k
A jumper is added from pin 5 (or 6) of IC3 (or a trace
connected to it)
to the now-disconnected leg of R7.
The audio detector components (see schematic) are then
added. Click here
for a picture of the completed modifications.
After this is done, use an ohmmeter to verify that there is no
continuity between the +5 volt supply and pin 4 of IC3. Also
that there is continuity between pin 5 of IC3 and the newly-jumpered
of R7 and verify that both of these do have continuity
the +5 volt supply bus. Note: There may be some high
readings between pin 4 of IC3 and the +5 volt supply, but these may be
due to the input circuit of IC3 itself. If the trace wasn't
severed, the reading will be in low-ohms range (e.g. less than 10
Do not use an analog ohmmeter set to the "1 ohm" or "10 ohm" scale for
this sort of measurement! Do not omit the 470 ohm resistor:
Without it, the modification may not be reliably detected.
Figure 2: This
display shows the detected
status of the
modifications for audio level metering ("LVL Mtr"), the data output to
the compass rose ("ROSE") and the clock output for the added
switched capacitor filter("SCF")
The output of the peaking filter (IC2, pins 6 and 7) is
an envelope detector as depicted in the schematic in Figure 1.
detector is connected
to pin 4 of IC3. For this modification, pin 4 must be isolated
from the +5V power
supply bus and a jumper added to reroute the +5V bus as described above.
Once this modification is installed, the firmware must be instructed
to detect these modifications. This may be done one of two ways:
Press and hold the two center buttons while applying power.
will cause the firmware to display the compile date and check for the
modifications. This does not erase stored EEPROM
settings. The compile date is not shown on versions 7A and
newer, as the version number appears on the startup screens.
Press and hold all four buttons while applying
does the same as the above in addition to resetting the EEPROM
It is unnecessary to clear the eeprom contents after installation.
With these buttons pressed, the startup sequence will include a display
showing the detected status of the modifications, as shown Figure
Figure 3: This
display shows the display without
detected audio level hardware. Note the "square with line" icons
around the quality reading on the left side of the screen in leiu of
"audio level" icons.
If you are successful, the detected status of the audio level
and the SPI interface for the compass rose will be displayed. If
the displayed status is "1" (as shown in Figure 2)
firmware has detected that the modifications have been done, and a
"0" of the circuit board traces appear to be in their original
Another indication that this modification may be successful is that "N/A"
under the "AFGATE" parameter in the last menu.
Note: This modification is detected by checking to see
if pin 4 of IC3 is tied to the +5 volt bus. It cannot
the actual presence of the added circuitry - only that pin 4 has been
Synchronous serial output modifications for the
This modification is straightforward:
Remove the jumper the connects pins 23 and 24 to ground.
is located on the top side of the board.
Cut the trace between pins 23 and 24.
Pin 23 (RC4) is connected to the clock input of the
and pin 24 (RC5) is connected to the data input of the compass
Once this modification is complete, the procedure for forcing detection
(e.g. holding buttons down while powering up, as mentioned above) is
The firmware simply detects the presence of this modification by
to see that neither pin 23 or 24 is grounded It cannot
the actual presence of a compass rose or any other hardware.
indication that this modification may be successful is that "N/A"
under the "ROSE" parameter in the last menu.
Switched capacitor filter clock output:
This modification simply detects whether or not pins 9 and 10 of IC3
still connected to each other: It cannot detect the actual
of the switched capacitor filter or any other hardware.
Adaptive filter modification (firmware version
7A and newer):
In firmware versions 7A and newer, an "Adaptive filter" feature is
available. To use this, one must already have done the "Audio
Level Meter modification and have a switched-capacitor filter
installed. This modification involves isolating pin 5 from the +5
volt bus (a simple matter of cutting the trace between pins 4 and 5
if you have already done the "Audio Level Meter" modification - see above for more information) and using
this signal to operate an analog gate (such as a 4066) by "short out"
the damping control.
What if you do not have the switched-capacitor filter
installed? As long as you have the "audio level metering"
installed, you can get most of the benefit if the "Average Clear"
function is used. The added switched-capacitor filter provides
additional filtering when needed (that is, when the "damping" or "Q"
control is turned up) but while this improves performance in the
presence of weak/noisy/heavily-modulated signals, it greatly slows the
response to brief transmissions. The adaptive filtering (described
here) causes the filter to automatically switch back to a "fast"
mode when the currently-monitored signal goes away as well as help
"pre-load" the switched-capacitor filter with some of the new signal
when it appears, before switching to the "slow" mode, as set with the
Schematics/additional details of this modification will be
added shortly - send an email to the address below if you want more
Do you have any questions on this or other DF-related
topics? Go here.