IRC Ghost Atto Duo User manual
Rev 1.4 - Oct 2020
Introduction, and History
Back in early 2013, when FPV was still in its infancy, and mini-quads hadn’t been invented yet,
ImmersionRC introduced the EzUHF 433MHz remote control system.
In the early days, this system was used for some of the most iconic fixed-wing FPV flights, pushing
limits out past 10s of km.
Since then, FPV has evolved massively, and now, 7 years later (4 years after development started), it
is time to bring a new innovative R/C link to the market.
Ghost doesn’t run on 433MHz, nor does it run on 868/900MHz. Ghost uses an innovative new
chipset on the 2.4GHz band for some very good reasons.
Why 2.4GHz, Are We Nuts?
At first glance this seems to be a questionable design decision, after all, shouldn’t ‘UHF’ systems run
on 433MHz, or 868/915MHz?
In Europe, the 868MHz band, commonly used for controlling hobby-class drones, has a couple of
serious limitations. Firstly, the entire (legal) band is only 2MHz wide (vs. 76MHz for 2.4GHz). This is
just not enough bandwidth to run more than a small number of systems simultaneously, and is just
not suitable for racing.
Secondly, duty-cycle limitations which allow other potentially life-saving equipment (fire alarms,
home automation, medical systems) to co-exist on this band, make it a poor choice for low-latency,
high duty-cycle model control.
The chirp-spread-spectrum technology used by the Internet of Things (LoRa WAN, etc.) when run on
the 2.4GHz band has some serious advantages, including:
- Tiny antennas, 2.4GHz antennas are only 36% of the size of the equivalent on 868MHz
- Much wider band, 76MHz vs. 2MHz on 868MHz (or 26MHz on 915MHz)
- Much better sensitivity (= much longer range) than traditional 2.4GHz systems
- Much better selectivity (adjacent channel rejection) than traditional 2.4GHz systems
- Much smaller directional antennas for the really crazy long range missions
- More range than 99% of pilots need, and with a higher gain (but still small) Tx antenna,
comparable range with 868/915MHz systems.
- Enough bandwidth to run 150Hz+ modes using the advantages of LoRa modulation
- Lower power consumption than Sub-GHz systems for longer radio battery life
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Specifications
Ghost General
Frequency Range, Ghost 2G4
2406 - 2479MHz 3
Ghost Protocol
Modulation
Chirp Spread Spectrum + Adaptive FHSS 3
(With LBT for EU versions)
Binding
Bidirectional, with confirmation and protocol negotiation
RF Profiles
Initially 4, Race, Pure Race, ‘Normal’, and Long Range, more to come
Ghost JR Module Transmitter
Uplink Tx Power
16uW - 350mW (100mW EU) (+/- 0.5dB) 3
Frame Rate
222.22Hz (purerace), 160Hz (race), 55Hz (normal), 15Hz (long range)
Format
Standard JR Module, tested with most common OpenTx compatible radios.
Antennas
Twin antenna, with Tx-side diversity. Antennas are 2.1dBi Dipoles
Compatibility
Any R/C Tx which accepts JR modules (Taranis, etc. )
Serial Formats
SBus, GHST 1 - Auto-Sense
Firmware
USB Upgradable (with OTA updates for receivers)
Power Supply
6V-20V, 1.75W @ 350mW, ~250mA at 7.4V
Ghost Atto/Zepto Receiver
Downlink Tx Power
+13dBm
Sensitivity
-117dBm in Long Range mode, less in Race modes
Serial Formats
SBus, SBus-Fast (200k) , SRXL-2 (400k), GHST 1, SBus Inverted 2
Firmware
Over-the-air (OTA) upgradable
Power Supply
5V recommended, 3.6-6.0V (no more than 6.0V!)
vTx Control
Tramp control from ‘T’ pin on Rx, regardless of selected serial format
Atto Dimensions
14.8mm x 11.5mm, 0.6g (w/o antenna)
Zepto Dimensions
10.0mm x 10.0mm, 0.38g (w/o antenna)
General Features
Tx-side Spectrum Analyzer
Supported, full frequency range
Rx-side Noise Floor Analysis
Auto on power-up, or on demand from the tx
1
GHST protocol available in a custom OpenTX build at product first shipment (IRC Website)
2
Sbus is inverted by definition, SBus Inverted flips it over so that it doesn’t require inverters on F4 FCs
3
Some specifications vary depending upon the regionally-specific product SKU
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Getting Started
OpenTx Configuration
The Ghost transmitters, and high frame rate + low latency that they can supply, are optimized for a
new OpenTx protocol, GHST.
For transmitters which do not yet support this protocol, either download one of the ‘Nightly OpenTx
Binaries’ from the Ghost page on the ImmersionRC website, or use the commonly-available SBus
protocol.
The Ghost transmitter auto-senses the R/C control protocol, no need to set anything.
For more details on the OpenTx build, along with the telemetry sensors that it supplies, refer to
section ‘OpenTx Custom Builds for GHST’ later in this document.
Make sure to disable the Internal RF when using the Ghost. Newer OpenTx builds will
enforce this, but will mean that if Internal RF is enabled, GHST doesn’t appear in the protocol list.
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Binding
Binding SUCKS, it really does. How many times have you had to tear apart a model to get access to
some buried bind button. How many times have you received a new ‘BNF’ model only to have to
scour the internet for an out of date manual that tells you which of the identical-looking three
buttons on the model are the bind button, and whether you need to press it while deftly plugging the
battery (three hands would be useful for this), or just after power up. How many times have you had
to find some ‘secret’ betaflight ‘CLI’ command to figure out how to bind an SPI receiver?
Then once you do find the button does the Tx need to be in E8, E16, E32, or JJAJ mode to bind
successfully?
Ghost attempts to be a little different.
New Receivers
New Receivers are shipped with bind mode enabled. For new receivers, just power them on, power up
the Tx, enter the Binding menu, and start the bind sequence.
The Rx LED will be blue when in bind mode.
The Tx will show the binding confirmation, if successful, with the ID of the receiver, and the firmware
version installed on it.
Note: To prevent surprises if the bind button is pressed during flight, the bind button is deactivated
30 seconds after the Rx is powered up. Simply cycle Rx power to re-enable if bind was intentional.
Deja Vu Binding
Deja Vu Binding records all receivers used by a Ghost transmitter and can bind to them in the future
without the need to touch the bind button on the receiver.
Receivers, after powered on, and before they have a valid connection to a Ghost transmitter,
periodically scan for transmitters attempting to bind.
This feature also enables the Ghost Updater to transfer firmware updates only for receivers that you
own.
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Receiver Pinouts
2G4 Atto
The smallest of the Ghost receivers, the Atto is optimized for use in race/freestyle quadcopters.
it has the following pinout:
Receiver Protocols
Ghost receivers support a number of common protocols, selected during binding.
Each has its own merits, and performance characteristics.
PWM should be used for fixed-wing flight, with 4 PWM outputs capable of driving servos, and motor
ESC.
SBus is offered (with it’s ‘Fast’ variant) as a compatibility mode, since it is supported by most flight
controllers, whether running Betaflight, iNav, PX4, etc.
SRXL-2 is the preferred protocol for Betaflight 4.2 and later, since it supports passing Link Quality
(LQ) to the OSD for a little more confidence while flying.
The GHST protocol is not supported by flight controllers at Ghost release, but will be added shortly
after.
Protocol
Frame Time
Baud Rate
Packet Duration
Channels
Telemetry
PWM
20ms
N/A
N/A
4
None
SBus
Same as RF
100k
3ms
12
None
SBus Fast
Same as RF
200k
1.5ms
12
None
SRXL-2
Same as RF
400k
800us
12
LQ passed as RSSI
GHST
Same as RF
TBD
TBD
TBD
Yes
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Receiver Wiring
SRXL-2 Wiring to Betaflight Flight Controllers
SRXL-2 is a bidirectional protocol which requires connecting via a single wire to a UART TX pin, NOT a
RX pin. This is the preferred protocol for Ghost receiver hookup until the GHST protocol is ported to
betaflight.
Note that F4 flight controllers may require a ‘cli’ command to enable the high speed SRXL-2 mode:
set srxl2_baud_fast = ON
Specification
Value
Gnd
Ground
5V Power
Clean 5V Power, from FC pin
Serial Out
Wire to TX pin on an unused UART. No inversion required (incompatible with most S.Bus inputs)
Serial In
Optionally wire to Tramp Telemetry pin, for Ghost control of Tramp vTx channel
NOTE: When using SRXL-2 with Betaflight, an internal setting in Betaflight does not allow
Ghost’s Long Range mode to be used. For Long Range mode (for the moment), use SBus, or
SBusFast instead of SRXL-2.
This will be resolved when the native GHST protocol is ported to betaflight.
SBus Wiring to Betaflight Flight Controllers
SBus, unlike SRXL-2, requires an inverted UART signal. Flight controllers that support S-Bus generally
have a dedicated S-Bus input, with any required inverters.
Ghost does allow SBus to be wired to a non-inverted UART input on the FC by selecting the ‘SBus Inv’
mode while binding. This causes Ghost Rx to emit a pre-inverted SBus signal.
Specification
Value
Gnd
Ground
5V Power
Clean 5V Power, from FC pin
Serial Out
Wire to SBUS pin on an unused UART. FC pin generally labelled SBus
Serial In
Optionally wire to Tramp Telemetry pin, for Ghost control of Tramp vTx channel
NOTE: If your Flight Controller does not detect a valid serial connection from the Ghost Rx,
ensure that the
Ports
tab in the Betaflight Configurator only has one
single port
enabled for
Serial Rx. If more than one is selected, the serial Rx will not work.
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
PWM Operation for micro-Fixed wing
The Atto receiver may be used for fixed-wing applications with up to 4 servos without any additional
hardware.
Pinout for PWM mode is as follows:
Specification
Value
CH1
SBus Output ‘S’
CH2
Telemetry Input Pin ‘T’
CH3
‘3’ Pad on bottom side of PCB
CH4
‘4’ Pad on bottom side of PCB
Note: Production PCBs have ‘3’ and ‘4’ marked on the bottom of the board, pre-production doesn’t have the
markings, but pad location and function is the same.
Specification
Value
Power
20mW downlink
Sensitivity (approx)
Variable, -112dBm Normal Mode, -106dBm Race/PureRace
-117dBm Long Range
PWM Channels
4
UARTs
One, Serial_TX/Telemetry
Protocols
SBus, SBus Fast (200k)
USB
None
Firmware Upgrades
Over the air (OTA)
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Link Quality (passed as RSSI)
If using the SRXL-2 protocol, link quality is automatically communicated to BetaFlight.
If using other protocols, the link quality may be passed down an unused R/C channel, and betaflight
configured to that channel’s value as RSSI.
And enable the value in the OSD setup (if present):
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Direct Tramp Control
To control the frequency and power of a Tramp HV/Tramp Nano vTx, simply run a single wire from
the ‘T’ pin of the Ghost to the ‘TEL’ pin of the Tramp.
Note that this replaces any connection between the Tramp and the Flight Controller, which is not
required with direct control.
To set the channel/power, joystick click left from the main Ghost screen.
Move up/down to change settings, then click Send.
Note that Receivers will remember the requested vTx parameters, and will reload them into the vTx
upon next powerup.
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Updating Firmware
JR Module
Connect your PC to the Ghost JR module using a micro-USB cable.
Press the Start Update button to start the procedure.
If for any reason the Ghost Tx display does not turn on, power up the module with the joystick
pressed to force boot load mode.
Receivers
All Ghost receivers are updated using an over-the-air technology during binding.
If a Rx firmware update was necessary, once complete,
don’t immediately power down
the Rx,
leave it for 10-20 seconds to finalize the update. (LED will flash a few times to indicate update
progress)
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Antennas
JR Module Transmitter
The JR module is equipped with two antenna connectors, creating a diversity antenna configuration
even for tiny micro-sized quads equipped with a single antenna.
To comply with current FCC regulations the JR module uses RP-SMA (reverse-polarity SMA)
antennas, an unfortunate departure from ImmersionRC’s traditional SMA bias.
If only one antenna is available, the Antennas
menu may be used to configure which antenna (or
both) is used. < for the left antenna, > for the right
antenna, and <> for both.
Running the Ghost transmitter without antennas, or without an antenna on the port(s) selected
in the Antennas menu can cause permanent damage, and should be avoided.
An alternative antenna for the JR module side is TrueRC’s Singularity.
Currently this is only available in an SMA version, but a RP-SMA version is expected to be available
before Ghost customer shipments.
Note that for any antenna used on the Ghost transmitters equipped
with dual SMAs, it is advisable to orient them about 90 degrees from
each other, in a ‘V’.
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Atto Receiver
The IRC qT Antenna - Balanced Dipole
The Atto receiver ships with a small balanced dipole antenna, which does not have a ‘ground’ and
‘live’ end. Both antenna elements are ‘balanced’. This means that the common practice of finding the
‘ground’ end of the antenna, and placing it near Carbon Fiber is not recommended.
Mount the antenna with the elements as far as
possible from carbon fiber, or other materials,
and somewhere with a good view of the
ground-based Tx for most model orientations.
When integrating the antenna into a model,
keep in mind that if the antenna gets ripped off
of the quad/plane during crash, you don’t
really want to rip the U.FL connector off of the
Ghost Rx.
Try to restrain the antenna cable possibly in
part of a 3d printed part so that if the antenna
does get destroyed in a crash, only the
antenna needs replacing.
Self Adhesive Flexible Antennas
An antenna that was popular with testers during the development of Ghost is the TaoGlas FXP73. A
tiny, lightweight self-adhesive antenna that integrates nicely into 3d printed ‘flip sticks’, or fins on
mini quads. Also superb for fixed-wing models, where it can be simply stuck onto the wings made of
foam or balsa.
These antennas are available from most online electronics stores, including Mouser, and Digikey, for
just a few dollars.
Part number is: FXP73.07.0100A
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Antenna Placement
The Ghost receiver is incredibly sensitive, and works best when distanced from the typically high
power video transmitter antenna of long range drones.
Try to space the two antennas as much as possible if maximum range is required, as should be
common practice for any FPV control system.
U.FL Connector Care
The Ghost Atto receivers use U.FL connectors. These tiny high-frequency connectors require a bit of
care when removing and inserting.
When removing, try to pull vertically, with a finger-nail each side. Pulling to the side can damage the
antenna-side of the connector.
When inserting, make sure that the connector is lined up correctly before putting any pressure on the
connector. If it is lined up, it will easily click into place.
The supplied heat-shrink should be applied after connecting the antenna, and will keep the U.FL in
place, preventing any surprises in-flight.
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Betaflight OSD Configuration
When using SRXL-2 mode, or GHST mode, for the link between the Ghost Tx module and the R/C
radio, the link quality (for bidirectional modes) will be available for display on-screen in betaflight.
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Ghost JR Module User Interface
The main OLED user interface is navigated using the left/right joystick functions. The following
‘pages’ are available.
Note: Latency numbers in these images are from a PC-based simulator, and don’t reflect actual
performance.
Link Page
The link page is shown by default by the
transmitter, and contains all data relating to the
‘health’ of the control link.
The nois value is the detected baseline noise
level measured at the rx end at power up. Not so
interesting on 2.4GHz, but useful on sub-GHz
versions.
Status Page
The status page shows the current JR Module
bay voltage, along with a low voltage warning.
Note that the Rx version only shows when using
a bidirectional protocol (currently all protocols
but PureRace)
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Pack (Battery Pack) Status Page
Valid when using GHST protocol to
communicate with Betaflight. Shows the
betaflight-reported battery pack voltage,
current, and mAh consumed.
Only valid in bidirectional modes, such as Normal,
Race, and Long Range. Not valid in PureRace mode.
Channels Page
The channels page shows the positions of each
of the R/C channels. Up/Down to scroll through
all 12/16 channels..
Latency Page
The latency page shows an estimation of the
current system latency, using both fixed
elements, and measured values.
First page shows a summary, scroll up to see
more detail.
The ‘Locked’ value shows whether OpenTx sync
is active.
Latency Page (More Detail)
Frame : Current frame rate
RC dur: Duration of packet OpenTx to Ghost
RC lat: Latency of packet OpenTx to Ghost RF
RF dur: Duration of RF packet
RX dur: Duration of Ghost to FC packet
Total: Sum total of the above values
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
vTx Page
A Tramp (Nano, or HV), connected to the ‘T’ pin
of a Ghost Rx is controlled using the vTx page.
Scroll up/down to select the value to change,
scroll down to ‘Send’, and send the setting to
the model.
Pressing the center joystick button enters the setup menu:
Root Menu, First Page
Root Menu, Second Page
Use the Failsafe menu to set failsafe servo
positions for PWM Rx output mode only.
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Bind Menu
Receivers are bound from the Bind menu. This is
also where the receiver protocol is specified,
along with the channels on which the LQ and
RSSI values will be emitted.
Note: ‘Old Prot’, and ‘Force Up’ are present to
support early beta testers, and will be removed in a
future firmware release.
Mode Menu
The RF mode, and transmitter protocol is
selected in this menu.
For the RF Mode, ‘Normal’ is a good
compromise between long range, and race.
‘Race’ is great for the race track with 160Hz
frame updates, and bidirectional link.
‘Pure Race’ is for the bonkers racer, who wants
to live on the edge, with 222.22Hz frame
updates.
In the vast majority of cases the Tx Mode
(Protocol) can be left in ‘Auto’ mode.
In fringe cases, the protocol can be forced by
selecting Tx Mode Manual, and manually
selecting the protocol.
See Appendix B for details on regional settings.
Spectrum Menu
The Spectrum Analyzer may be used to analyze
noise floor on the 2.4GHz band.
Set the start/stop frequencies, and press Start.
Note that the vertical scaling is -40dBm at the top
of the display, and -127dBm at the bottom. No
auto scaling.
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
Antennas Menu
In most cases, leave these settings at their
default setting. Ghost will decide which antenna
to use for both Tx and Rx.
For ‘special cases’, such as using directional
antennas for extreme range, manually set the
desired antenna.
Tx Power Menu
Auto power mode will decide which power level
to use for the uplink transmission based on the
signal strength received at the receiver.
Note that in PureRace, a unidirectional mode, Tx
power in Auto mode defaults to 100mW (or the
max. allowed by the selected region)
Failsafe Menu
Used only when a Rx is set in PWM mode. Set
the servo positions to be used in the event of a
failsafe.
Note that for serial protocols (SBus, GHST,
SRXL-2) failsafe is indicated by missing packets,
as preferred by FC firmware authors.
ImmersionRC Limited, Kwai Chung, NT, Hong Kong, www.immersionrc.com
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