MODEL SOUNDS DopplerFX User manual

Model Sounds Inc.
DopplerFX® Rev. 03
REFERENCE MANUAL
January 20, 2021

DopplerFX®Rev. 03 Reference Manual Page 2 of 17 Published: January 20, 2021
© Model SoundsTM Inc.
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DopplerFX®Rev. 03 Reference Manual Page 3 of 17 Published: January 20, 2021
© Model SoundsTM Inc.
CONTENTS
CHAPTER 1 - GETTING STARTED –THE BASICS ...................................................................................4
Purpose of the DopplerFX Feature........................................................................................................ 4
How Does The DopplerFX Feature Work?............................................................................................. 4
Some Simple Math That Explains Doppler Frequency Shift.................................................................. 5
What is GNSS? ....................................................................................................................................... 6
Caution About Using Other GNSS/GPS Receivers .............................................................................. 7
CHAPTER 2 –MOUNTING THE DOPPLERFX ACCESSORY BOARD .........................................................8
CHAPTER 3 –HOW TO CONNECT YOUR DOPPLERFX ACCESSORY BOARD ...........................................9
DopplerFX Accessory Board Connections ............................................................................................. 9
Orientation of the 4-Wire Accessory Cable Connector......................................................................... 9
Powering the DopplerFX Accessory Board.......................................................................................... 10
CHAPTER 4 –HOW TO OPERATE YOUR DOPPLERFX ACCESSORY BOARD .......................................... 11
RC Inputs on the ShockWave 3 Module Supporting the DopplerFX Feature ..................................... 11
Setting The Observer Position Remotely............................................................................................. 11
Enabling/Disabling The DopplerFX Feature......................................................................................... 12
The DopplerFX LED Indicator............................................................................................................... 12
Range of Doppler Shift Enhancement................................................................................................. 12
CHAPTER 5 –THE DOPPLERFXSETTINGS.TXT FILE............................................................................. 13
CHAPTER 6 - HOW DO I KNOW WHEN I HAVE A SATELLITE FIX? ....................................................... 14
The Effects of Weather on the Time To First Fix ................................................................................. 14
Using System Sounds for DopplerFX Event Notifications ................................................................... 14
CHAPTER 7 –THE DOPPLERFX BOARD BACKUP BATTERY................................................................. 15
CHAPTER 8 –LIMITATIONS.............................................................................................................. 16

DopplerFX®Rev. 03 Reference Manual Page 4 of 17 Published: January 20, 2021
© Model SoundsTM Inc.
CHAPTER 1 - GETTING STARTED –THE BASICS
PURPOSE OF THE DOPPLERFX FEATURE
The Model Sounds Inc. DopplerFX feature is unique in the model RC world.
It is a feature of the ShockWave 3 sound module and is enabled by the DopplerFX accessory board
that communicates with the ShockWave 3 sound module using two signal wires. The DopplerFX
accessory board takes its +3.3 Volt power from the ShockWave 3 sound module over the same four
wire cable that provides the serial two wire data link.
The concept of the DopplerFX feature is that it provides an enhanced Doppler frequency shift
experience to a ground observer while the model aircraft or helicopter is in flight. Doppler shift is the
change in pitch of a sound as the source gets closer, then gets further away, e.g. like an ambulance,
fire engine or police siren. Due to its own motion, every model aircraft produces its own natural
Doppler shift as it approaches towards and recedes from a stationary observer on the ground.
But because a scale model aircraft’s speed is fairly slow compared to the speed of sound, especially
when flown at a realistically slow scale speed, its natural Doppler shift is quite mild in effect. If the
model is outfitted with our ShockWave 3 sound system, this DopplerFX accessory board can provide
increased Doppler frequency shift to the engine and gunfire sounds played back by the sound module.
This can make the model sound as though it is travelling at 350km/hr when its actual speed is only
50km/hr, for example.
HOW DOES THE DOPPLERFX FEATURE WORK?
When the sound system is first powered up by the pilot, once a GNSS (e.g. GPS) satellite fix has been
acquired, the DopplerFX feature will record the accessory board’s position. This is called the Observer
Position. Then as the aircraft moves away from or towards the Observer Position, either on the
ground, or in the air, the DopplerFX accessory board continuously updates its position and altitude at
up to 10 times per second and the ShockWave 3 sound module will calculate its speed and position
relative to the Observer Position.
Then, depending on its speed and whether it is approaching towards, or receding from, the Observer
Position, the ShockWave 3 sound module will compute what the relative Doppler frequency shift
should be to simulate the plane’s actual speed multiplied by the Speed Multiplication Factor. It then
changes its playback speed appropriately.

DopplerFX®Rev. 03 Reference Manual Page 5 of 17 Published: January 20, 2021
© Model SoundsTM Inc.
SOME SIMPLE MATH THAT EXPLAINS DOPPLER FREQUENCY SHIFT
Doppler shift (in the light from stars) was first identified and named after the Austrian physicist
Christian Doppler, who described the phenomenon in 1842 and his theory was tested for sound waves
by the Dutch chemist Buys Ballot in 1845.
Doppler shift in
sound is a time
compression of
the sound
wavefronts
(wavelength
compression) due
to the source’s
motion.
V = f x λwhere
V = velocity
(speed of sound),
f = frequency, and
λis the
wavelength of the
sound.
Therefore f = V / λ and since V, the speed of sound, is constant, more or less, if the wavelength λ
decreases, as when the sound source is approaching you, then frequency f goes up.
Conversely if the wavelength λincreases, as when the sound source is receding from you, then
frequency f goes down.
And when the source is immediately at your location when it is nether approaching or receding f, the
frequency you hear, is the same as the source’s own frequency.
It is important to realize that, under normal circumstances, the source’s sound frequency does not
actually change at all. It is only due to the wavefront compression and stretching due to its motion that
the sound a fixed observer hears appears to change.
The DopplerFX feature implemented in the ShockWave 3 sound module enhances this natural effect
by applying additional frequency shift at the source to emulate a much higher speed.