QDXQDX: QRP Labs Digital Xcvr (transceiver)
Operating manual, firmware 1.08

QDX operating manual; firmware 1_08

1Contents

Contents.......................................................................................................................................................................... 2
1. Introduction.................................................................................................................................................................3
2 Operating instructions..................................................................................................................................................4
3 Firmware Update procedure......................................................................................................................................11
4 Terminal Applications.................................................................................................................................................14
4.1 PC terminal emulator..........................................................................................................................................14
4.2 Entering terminal applications mode...................................................................................................................15
4.3 Exiting terminal applications mode.....................................................................................................................15
4.4 Configuration.......................................................................................................................................................16
4.5 Band configuration..............................................................................................................................................24
4.6 Audio filter sweep................................................................................................................................................27
4.7 RF filter sweep.....................................................................................................................................................28
4.8 Input analysis.......................................................................................................................................................29
4.9 Image sweep........................................................................................................................................................33
4.10 CAT command test............................................................................................................................................35
4.11 CAT monitor.......................................................................................................................................................40
4.12 Log file...............................................................................................................................................................41
4.13 Transmitter test.................................................................................................................................................44
4.14 Factory reset......................................................................................................................................................45
4.15 Update firmware...............................................................................................................................................45
4.16 Exit terminal......................................................................................................................................................45
5. Troubleshooting Transmit issues...............................................................................................................................45
6. Resources.................................................................................................................................................................. 47
7. Document Revision History.......................................................................................................................................47

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1.

Introduction

The QDX is a high performance, four-band 5W Digital modes transceiver with CAT control andbuilt-in USB sound card. QRP Labs presents QDX, a digital transceiver with a ratio of performance
to price not available until now.
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Four band 80, 40, 30 and 20m; 5 W from 9 – 10V supply
Clean single signal output (zero residual carrier, zero unwanted sideband)
Solid state PIN-diode switched Low Pass Filters and solid state Band Pass Filters
Solid state transmit/receive switching
High performance embedded-SDR SSB receiver using 110dB 24-bit stereo ADC chip
Built-in USB sound card: 48ksps 24-bit stereo
Built in USB Virtual COM port serial for CAT control
Si5351A Synthesized local oscillator with better than 0.001Hz resolution and high precision
25MHz TCXO reference as standard
Built-in signal generator
Built-in suite of configuration and analysis tools
Lifetime free firmware upgrades with QRP Labs Firmware Update (QFU) bootloader foreasy firmware update on any OS with no extra software, or drivers, or programming
hardwareAll SMD components pre-installed by factory, only through-hole component soldering by the
kit constructor
Receive current: 100-150mA; Transmit current 1.0 – 1.1A (9V supply, 5W output)
Only three connectors: USB (audio and serial for CAT), Power and RF
Optional smart aluminium extruded enclosure measuring just 89 x 63 x 25mm

No test equipment is required to build, align and operate this digi modes transceiver. There are noalignment tasks.
Assembly of the transceiver is covered in a separate document, along with design details(theoretical explanation) and performance measurements.
NOTE: QDX-M, the single band version of QDX, uses the same firmware as QDX. Thismanual applies to QDX-M equally.
This document describes operation of QDX, and applies to the firmware version specified. Thismanual will get you started with QDX and your WSJT-X or other digi modes software in minutes.

PLEASE READ THE BASIC ASSEMBLY AND USE INSTRUCTIONS IN
THIS MANUAL VERY CAREFULLY BEFORE APPLYING POWER TO
THE BOARD!

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2Operating instructions

Operation of the QDX transceiver is really simple. There are only three/four connections:
1. DC Power: use a regulated wellsmoothed DC supply of not morethan 12V; it should be capable of up
to 1A current supply. The connector
is a 2.1mm barrel type (outside
diameter 5.5mm).
2. RF: a standard BNC connector toyour antenna system
3. USB: USB type B connector (astandard USB type A to B cable isrequired) for Audio and CAT control.
4. PCB Rev 3 (and corresponding
enclosure Rev 3) has a 3.5mm jack connector as a PTT output; it can drive grounded or+5V PTT signal requirements and/or can be used for external auxiliary controls such asantenna switching if desired.

Drivers
No additional drivers are required for operation with most Linux distributions, Apple Mac or MS
Windows 10 or Windows 11.
For older versions of MS Windows, it may be necessary to install a driver for the serial port
because this driver is not on your computer already by default. This driver is available from the ST
Semiconductor website at https://www.st.com/en/development-tools/stsw-stm32102.html and isapplicable to 98SE, 2000, XP, Vista®, 7, and 8.x Operating Systems. There is a description for
installation on Windows 7/8 on the QRP Labs QLG2 page http://qrp-labs.com/qlg2 so if in doubt,
please check this.

Linux special note
On Linux systems, a particular problem can occur. When the QDX Virtual COM (Serial) connection
is detected, the PC thinks that a modem has been connected and starts trying to send it Hayes
AT-commands dating back to 1981, implemented on Hayes’ 300-baud modem. Yes! 40 years
ago…
The Operating System attempting to send AT commands to your QDX will certainly messeverything up. Not least because when QDX receives a carriage return character, it will enter
Terminal Applications mode; this will send all sorts of characters back to the PC (as QDX thinks it
is now talking to a terminal emulator) and it will disable CAT command processing, so your PC digi
modes software will not be able to talk to QDX. Disaster.
To fix this you need to issue the following commands to disable ModemManager:

sudo systemctl stop ModemManager
sudo systemctl disable ModemManager
sudo systemctl mask ModemManager
QDX operating manual; firmware 1_08

4This will permanently stop ModemManager. If for some reason, you actually DO need
ModemManager operational, for some other reason… well there IS a way to stop it just for QDX…
but Google will be your elmer on this!

Additional information from Greg Majewski:
There is another Linux service, BRITTY, that does the same. BRITTY is a Braille service foraccess by sight impaired people. I have encountered the problem with the G90 and Ubuntu on alaptop (Ubuntu full version), Raspberry Pi 3 with Raspberry OS and the Orange PI 800. Here arecommands that remove BRITTY:
sudo systemctl stop brltty-udev.service
sudo systemctl mask brltty-udev.service
note output: Created symlink /etc/systemd/system/brltty-udev.service→ /dev/null.
sudo systemctl stop brltty.service
sudo systemctl disable brltty.service
These commands are similar as used for Modem Manager service.

WSJT-X configuration
Next it is necessary to set up WSJT-X to communicate with QDX. We will use WSJT-X as theexample, because it will be what most people are using. But other software will be identical (forexample JS8Call) or similar. There are two parts to the set-up – firstly to choose the right USB
Sound card, and secondly to set up the CAT communication so that WSJT-X can control the QDXvia the serial comm port.
Open the WSJT-X settings window (from the File menu) and select the Audio tab. Select “QRPLabs QDX Transceiver” as the input and output sound card. The below screenshot shows how it
looks on my system, which is Linux (Xubuntu 18.04). It will look different on Windows, Mac andperhaps other Linux distros but the basic idea will be the same… you should see something in thedrop-down which says something about QDX, and that’s the sound card to select.

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Next click the “Radio” tab in the settings window, which sets up the CAT control communication.
The following four settings need to be changed, and are illustrated in the diagram below:•

Rig will be set to None by default, click the drop down and choose “Kenwood TS-440”
which should work well with QDX. On some other software, if you find that TS-440 is notpresent in the list or does not work properly, you could try “Kenwood TS-480”. More details
about CAT and debugging any CAT problems are in another section of this manual, where
the CAT test terminal screen is described.

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The Serial Port drop-down must be set to the correct port where QDX is connected. On my
Linux system it is either “/dev/ttyACM0 or /dev/ttyACM1. On Windows systems it will be a
COM port numbered COM1, COM2 etc. Unfortunately unlike the USB Sound, the serial port
name doesn’t contain the text “QDX”. If you are unsure which port to choose for QDX, theeasy way to find this is as follows. Unplug QDX. Restart WSJT-X. Look in Settings -> Radioand make a note of the list of serial devices. None of these are QDX (because you
unplugged it). Now close WSJT-X, plug in QDX, start WSJT-X and again look in Settings ->QDX operating manual; firmware 1_08

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Radio, and now you should see a newcomer in the list of available ports. The newcomer is
QDX!
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Note that none of the Serial Port Parameters need to be changed, leave them all at theirdefaults. Even the baud rate 9600 is unimportant because it is irrelevant to the USB VirtualCOM Port which is a virtual port over USB, not a real physical serial port.

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Change the Poll Interval to 10 seconds, the default will be rather chatty with QDX which
probably is not a problem, but anyway I feel more comfortable with the less frequent polling.
QDX has no capability to alter its operating frequency for example by itself, it can only do soat the command of WSJT-X over CAT; therefore the polling is actually redundant anyway.

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Change PTT Method from the default “VOX” to “CAT”. VOX means “voice operated
exchange” or “voice activated transmission”; the radio will automatically switch to transmit,
when incoming audio is detected. With PTT Method set to CAT, when WSJT-X wishes tostart a transmission, it will send an actual CAT command to QDX informing it to start thetransmission, before sending the audio. This CAT command causes QDX to switch from
Receive mode to Transmit mode (and back again afterwards). “CAT” is preferable to “VOX”
because if system sounds are accidentally routed to your “QDX” sound card as output, thenwith VOX that will enable the QDX transmitter and try to transmit the sound.

•Now click the “Test CAT” button and after a few seconds, it should turn Green to indicate
successful communication with QDX.

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NOTE 1: If you are using other software than WSJT-X or JS8Call, then QDX CAT commands
should still work with this software. If you encounter difficulties then it is possible that your software
is trying to communicate with QDX using CAT commands that are not supported by QDX. In thesection of this manual on the CAT Test utility (in the QDX Terminal applications), you will find alisting of the CAT commands supported by QDX. Another useful utility is the log file, which will let
you record all CAT commands received and investigate any issues. If CAT commands are missing
for your application, QRP Labs can add support for them easily.
NOTE 2: As mentioned above, CAT control of transmit/receive switching is recommended. If you
INSIST on using VOX, QDX can support that. For example, you may be using a software
application which does not support CAT control of transmit/receive switching and can only use
VOX. In that case you should change the QDX transmit/receive switching mode from CAT to VOX
in the QDX terminal Configuration utility, which is described in the terminal applications section ofthis manual.

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NOTE 3: The Data Bits, Stop Bits, Handshake should not need to be changed; however several
users have reported that changing them to the settings shown in the orange box has resolved
some issues with CAT reliability on Windows Operating Systems.

WSJT-X “Pwr” Slider
The only other point to note is that WSJT-X should be operated with the power slider at the
maximum setting. This point is discussed further in the QDX design section which explains thatbest accuracy in determining the audio tone frequency being sent by the PC, is when the Pwr is at
the maximum setting. There is no point to using any setting other than maximum, because QDX
only ever transmits at full power (5W), there is no way for it to transmit at a lower power output
under command of WSJT-X. If you wanted a lower power output, you would need to use a lower
supply voltage. Furthermore, QDX cannot be “over-driven” by too high volume, in the way that a
SSB transceiver could.
Therefore the “Maximum” setting for the Pwr slider is highly recommended, it is the optimum
setting for QDX operation.

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QDX Status LED
The front panel of QDX contains a 3mm red Status LED. The operation of this LED is as follows:•

Quick flashing (flickering) for first 5 seconds after power up: if you disconnect power now,then next time you power up, QDX will be in firmware update mode. During this fiveseconds QDX is also operating normally in Receive mode. After five seconds, the LED will
go to a steady on (lit) state.

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Slow flashing: QDX is in firmware update mode (refer to the Firmware Update procedure
section of this manual). If you did not wish to be in firmware update mode and have enteredfirmware update mode inadvertently, simply power down QDX and re-apply power; QDX
will now be in normal operating mode again (quick flashing for the first five seconds, seeabove).

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Steady LED on state: QDX is in normal Receive mode operation•

LED pulsates pleasantly, its brightness modulated with a sinewave, with a 1Hz rate (onceper second)•

LED flashes 2 times in quick succession, repeating every 1 second: the PC host software
application is sending audio to QDX, and QDX is detecting and measuring the incoming
audio, however the volume is too low (refer to Troubleshooting section, below).

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LED flashes 1 time for 0.1 seconds, repeating every 1 second: the PC host software
application has activated PTT but the QDX is not detecting any audio signal from the PC(refer to Troubleshooting section, below).

Operate!
Once CAT is configured and working, and the QDX sound card is chosen, just operate WSJT-X as
you would normally! You can choose the desired band 80m, 40m, 30m or 20m from the WSJT-X
screen and WSJT-X will communicate with QDX via CAT, to cause QDX to switch in the correctfilters.
This QDX manual is not the place to include tutorials on various digi mode operation or particularapplication software such as WSJT-X, such guides are readily available and written very much
more thoroughly than I could hope to achieve!

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3

Firmware Update procedure

On occasion QRP Labs may make available updated firmware for QDX, in order to deliver bug
fixes or functionality enhancements.
QDX contains a new firmware update procedure for STM32-series microcontrollers, called QFU(QRP Labs Firmware Update) which provides the following features:•

Easy – anyone can do the firmware update•

No additional hardware required: only a standard USB A-B cable (or micro-USB cable if
you have installed a micro-USB connector)•

No additional software required: just the standard file manager application that is alreadyavailable on any PC•

No drivers: no special drivers need to be installed, the existing drivers on any modern PC
operating system are used•

Works on any PC Operating System: and in the same way: Windows, Linux, Mac•

Secure: firmware files are published on the QRP Labs website and are encrypted using
256-bit AES encryption technology

Entering bootloader (firmware update) mode:
QDX provides two possible ways to enter firmware update mode:
1) On powering up QDX, you will see the QDX status LED flickers quickly for 5 seconds after
power up, then illuminates solidly. If you power down QDX during this 5 seconds, then apply
power again, QDX will now boot up in QFU (Firmware Update) mode.
2) Select the “Update firmware” menu option in the QDX Terminal (see subsequent section ofthis manual). QDX will then enter firmware update mode.
In firmware update mode, the status LED flashes slowly.

Exiting bootloader (firmware update) mode:
QDX provides two possible ways to exit firmware update mode:
1) Update the firmware! After updating the firmware, QDX will automatically reboot in normal
operating mode.
2) Power down QDX, and re-apply the power again. QDX will reboot in normal operating mode.

USB Flash memory stick emulation:
In the firmware update mode, the QDX pretends to be a USB Flash memory stick, having a
4MByte capacity and implementing a FAT16 file system. This virtual “Flash stick” contains two
files:
1. the firmware program file of the QDX microcontroller. You may read the file from QDX, orwrite a new one, just by dragging files in your file manager application.

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2. EEPROM contents: the QDX configuration and log file (if enabled). Again, you can read thefile from QDX or write a new one to QDX, simply by dragging files in your file manager
application.
On entering the Firmware update procedure, a pop-up window should appear on your PC. On mysystem (Linux XUbuntu 18.04) it looks like this:Click the OK button.
The File Manager window will then open, and on my system looks like this:QDX operating manual; firmware 1_08

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QDX appears as a removable USB Flash device named “QDX”, and the folder two files. The
firmware file in this example is named shows a single file which is the firmware version file,
1_00_001.QDX in this example. The EEPROM file is always named EEPROM.QDX. You can read
and write EEPROM files in order to make and restore backup copies of your configuration etc.
The firmware file name must not be longer than 8 characters, and cannot contain punctuationor spaces; the file extension must be no more than 3 characters. This is because the file systememulation is FAT16 and these are the specifications of the FAT16 format.
You may check the properties of the file and will note that it is a 119.5K file. QDX firmware images
are always a 119.5K file. The creation date and modification date etc. have not been set, because
it was important to minimize the size and complexity of the QFU bootloader, in order to maximize
the space available to the application firmware.
You may copy the existing firmware file to another directory of your computer. Crucially, to do thefirmware update, all you need to do is copy the new firmware file to this QDX “Flash disk”.
Download the new firmware file from the QRP Labs website, unzip it, and simply drag it into thefolder where the existing firmware file version is shown. Or copy and paste it, however you wish.
The file on the QRP Labs website is a ZIPPED file, please be sure to unzip it to get the .QDX
file before copying it to QDX.
As soon as you copy the new file to the QDX QFU “flash drive”, the QDX QFU bootloader erases
the current program from its memory and installs the new one.
The QDX firmware is 256-bit AES encrypted and this means:•

The encrypted QDX firmware file will only work on a QRP Labs QDX board, it cannot be
installed on any other board, even one containing the same processor.

•

No other firmware file will work on the QRP Labs QDX board except an official QRP Labs
encrypted QDX firmware file.

The procedure will vary slightly for different Operating systems but in all cases is just a simple
matter of copying the new firmware file to the emulated QDX QFU USB Flash drive.

The above firmware update procedure works on ANY modern OS because the QFUbootloader emulates a USB Flash memory stick with the USB Mass Storage Device (MSD)
class, for which drivers are already present.
The QFU bootloader implements a USB device stack (Mass Storage Device class), emulated
FAT16 file system, Flash erase/write, and 256-AES encryption.

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4

Terminal Applications

QDX provides a suite of applications which may be accessed via a Terminal emulator running on
your PC. These applications provide configuration utility, and various self-test tools. It is very
educational and interesting to experiment with these tools.
However, most QDX users need never use the terminal applications, it is not necessary forordinary operation of QDX with WSJT-X etc. The terminal applications are for the interested
user, or if you need to set up a particular configuration.
The terminal applications display everything as ASCII text in a 80 x 24 character window. It’s not
as polished as a dedicated graphical user interface software application for QDX would be.
However, it has the advantage of requiring no special software or drivers, and all the variations
that would have to be supported for different PC Operating Systems such as Mac, Windows andLinux, software installation procedures etc. Instead, all the applications are hosted and coded in
the QDX itself. The terminal emulator is only used to display the results. This keeps things simple
and low maintenance. After all, the terminal applications are useful bonus features rather thancore QDX functionality.

4.1 PC terminal emulator
I use Linux (XUbuntu 18.04) and I’m using the PuTTY terminal emulator. There are numerous
other terminal applications which will work fine. You may have your own favourite. They are allcapable of correct operation with QDX in its terminal mode.
I start PuTTY using command line “sudo putty” then connect to QDX on /dev/ttyACM1. Again as
before (refer to the Operating Instructions for connecting to QDX using CAT on WSJT-X) it isnecessary to know which serial port is being used by QDX. There is also a guide to identifying theserial port at http://qrp-labs.com/qlg2 (scroll down the page); or you could use WSJT-X.
Make sure WSJT-X is NOT running, when you connect to the QDX serial port using theterminal emulator. Only one PC application at a time can connect to Virtual COM Serial
ports.
Set the size of the terminal window to 80 columns and 24 rows.

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4.2 Entering terminal applications mode
Normally the QDX serial port is connected internally to the QDX’s CAT command interpreter. CAT
commands include text and numbers, each CAT command is terminated by a semicolon. CAT
commands never include a carriage return (enter).
Note that when the terminal is connected, you can actually type on your keyboard to send CAT
commands. For example, try typing FA; (just those three characters – no Enter at the end). The
text FA00007074000; will appear on the terminal. FA is the command to read or set VFO A, andthe result is 7.074 kHz, the default QDX startup frequency. HOWEVER, this is not a very
convenient or easy way to try out CAT commands, there is a CAT command testing application
which is much easier to use.
To switch to terminal applications mode, simply press the Enter key on your keyboard. Now theterminal applications mode will appear in your terminal emulator window, as shown below. The
screen shows the QDX firmware version (coloured yellow at top left), and a list of applications
coloured white. You may use the cursor keys to move the highlighted application up and down in
the list, and press Enter to select an application. Any application can be quit by pressing Ctrl-Q
which returns the terminal to the main menu screen.
Operation of each of the applications will be described in detail in subsequent sections.

4.3 Exiting terminal applications mode
When exiting terminal applications mode, do not simply close the terminal emulator window. Doingso will leave the QDX in terminal applications mode and it will not accept CAT commands. To
switch it back to CAT command mode, use the cursor keys to scroll down to the “Exit terminal”
option at the bottom of the list, and press Enter. The screen is now cleared, and QDX is back in
CAT command mode. Only then should you close the terminal emulator window.
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4.4 Configuration

The configuration screen allows entry of various QDX configuration parameters. The default
values are suitable for the vast majority of operating use. The following paragraphs describe eachconfiguration setting in turn. Use the up/down arrows to select the item you wish to edit. The
cursor is positioned at the last character of the value. Numeric values have a defined field length.
You can press the backspace key to delete the current entry in whole or in part, and type in the
new value. For non-numeric configuration parameters, you can use the left and right arrow keys tochoose between the available values.

TCXO Frequency
Default is 25000000 (25 MHz). This is the oscillation frequency of the QDX TCXO (Temperature
Controlled Crystal Oscillator) and is used for calculating Si5351A parameters for setting thedesired QDX operating frequency.
The supplied TCXO is a high precision component and will normally be found to be within (a one
standard deviation error of) +/- 5 Hz of the specified 25 MHz value. It is not normally particularly
necessary from an operating perspective, to have a more precise operating frequency than this.
Remember that the error is also scaled to the operating frequency. So a 5 Hz error at 25 MHz willtranslate to a 2.8 Hz error at 14 MHz.
However the perfectionists among you may wish to calibrate your operating frequency precisely –and this menu entry is for you!
To configure the correct TCXO reference frequency, you will need to measure your operating
frequency, deduce the error amount, and apply a correction to the TCXO frequency configuration
parameter.

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As an example, suppose your transceiver is set to a USB “Dial Frequency” of 14.0956 MHz and
WSJT-X is set up to transmit WSPR at 1500 Hz audio offset. This should result in a transmission
frequency of 14.097100 MHz. But let’s suppose that you measure it accurately, and you find that itis 3 Hz high, at 14.097103 MHz. Now what?
There’s an error of +3 Hz in your operating frequency. To work out the required correction to the
TCXO reference frequency configuration, calculate 3 Hz multiplied by a ratio of 25 MHz / 14.0971
MHz, which results in 3 Hz x 1.77 = 5.3 Hz.
Therefore you should increase the reference frequency by 5Hz. So move the highlight to the
TCXO frequency using the up/down cursor keys, then press the backspace key once, and type 5.
That will change the reference frequency to 25000005.
How about if you don’t have an accurate way of measuring your operating frequency? I havedeveloped tools for QRP Labs website to help you to use the WSPRnet reporting network to
determine your operating frequency quite accurately. To use these tools, simply use WSJT-X andQDX to operate as a 20m WSPR reporter (receiver) for several minutes, then look at this page:https://qrp-labs.com/images/wsprnet/rxerror.html
Look for your callsign in the list, which shows the error in your reception reports (operating
frequency error).
Alternatively, you may operate as a WSPR transmitter using WSJT-X and QDX, and the following
page will show your actual transmitting frequency:
https://qrp-labs.com/images/wsprnet/txfreq.html
Both of these QRP Labs pages are updated every two minutes. The analysis loads the last 5
minutes (approximately) of 20m WSPR reports from the WSPRnet website database. It crossreferences all the reports, analyzing the error of receiver stations by cross-referencing against
reports of the same transmitters by other stations. In this way calibration errors of all receiving
stations in the network are averaged out. The accuracy is generally within 1 or 2 Hz.

SidebandThis setting determines the demodulation sideband. Normally Upper Sideband (USB) is used forall digital modes, and is the default setting. If you wish to use Lower Sideband (LSB) for somereason, you can change it here. Use the left and right arrow keys to change between LSB andUSB.

Default frequency
This is the default start-up frequency of QDX at power-on. It defaults to the 40m FT8 frequency
7.074 MHz. If you would like it to power up on a different frequency, you may edit thisconfiguration setting.

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VOX
If you want to use VOX (Voice Operated Transmission) then set this parameter to ENABLE. Any
incoming audio from the PC will then operate the Transmit/Receive switch and be transmitted.
When the audio stops, QDX will switch back to Receive automatically. The problem with this isthat any system sounds on your PC, if the PC is configured to deliver these to the QDX USB
sound card, will operate the transmitter and be transmitted.
The default setting “DISABLE” requires a CAT command from the PC host application (WSJT-X
for example) in order to enable the transmitter. This is discussed in this manual in the operating
manual section, on setting up WSJT-X for QDX.
If you wish to use software that does not support CAT Transmit/Receive switching, this may be
one reason why you would want to enable VOX.
If using VOX, you will also need to disable the CAT timeout feature (see below).

Rise threshold
This is a percentage signal level of maximum, above which the transmitter will be keyed down
(switched on). Its purpose is to ignore very low amplitude audio signals at the start of a raised
cosine keying envelope, whose audio tone could be decoded inaccurately due to quantization
error. This is discussed further in the Design section of this manual in the Audio Frequency
Analysis section. The default value of 80% should be fine for all purposes. The value should not
be set too close to 99%, since higher frequency audio where the number of samples per cycle issmall, may not contain a value sufficient to trigger this threshold in every cycle.

Fall threshold
This is a percentage signal level of maximum, below which the transmitter will be keyed up(switched off). Its purpose is to ignore very low amplitude audio signals at the end of a raised
cosine keying envelope, whose audio tone could be decoded inaccurately due to quantization
error. This is discussed further in the Design section of this manual in the Audio Frequency
Analysis section. The default value of 60% should be fine for all purposes. The value should notexceed (or be close to) the Rise threshold parameter, otherwise the transmitter will be repeatedly
keyed on and off falsely.

Minimum cycles
This parameter specifies the minimum number of audio cycles to use, in the measurement ofaudio cycle period, for audio frequency calculation. This parameter is used in conjunction with the
Minimum samples parameter: both conditions must be satisfied in order for an audio frequency
measurement to be completed. This parameter is discussed further in the Design section of thismanual in the Audio Frequency Analysis section. The default value of 1 should be fine for all
purposes.

Minimum samples
This parameter specifies the minimum number of audio samples to use, in the measurement ofaudio cycle period, for audio frequency calculation. This parameter is used in conjunction with the
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Minimum samples parameter: both conditions must be satisfied in order for an audio frequency
measurement to be completed. This parameter is discussed further in the Design section of thismanual in the Audio Frequency Analysis section. The default value of 480 should be fine for all
purposes.
Bearing in mind that there are 48,000 audio samples per second, a value of 480 specifies aminimum 0.01 second audio measurement period. In other words, there will be 100 measurementsof the audio frequency, per second, in this default configuration. This is sufficient to ensure thathigh audio frequencies are measured accurately. In the unlikely event that frequencies below
100Hz need to be measured, the “Minimum cycles” value (1) will ensure that a longer
measurement period is used, to measure one cycle.

Discard cycles
This parameter specifies the number of audio cycles (zero crossings) which are ignored, when
audio is first detected. The reason for this parameter is that in conjunction with the “Rise threshold”
parameter, it can be seen that the first audio cycle after the threshold is passed, is not a complete
cycle. The following zero crossing therefore needs to be discarded because its period
measurement will be too short. The default value of 1 should be fine for all purposes.

IQ ModeWhen IQ mode is enabled, the raw I and Q channels from the ADC are fed to the USB soundcard
directly, without any demodulation. This is suitable for people wishing to experiment with using
QDX as an SDR front end, with PC SDR software to demodulate I and Q channels.
IQ Mode is not suitable for use with WSJT-X and other Digi mode programs.

Japanese band limits
When this setting is enabled, QDX will refuse to go into transmit mode if the specified synthesis
frequency is outside the Japanese band limits as specified in the JARL bandplans document
https://www.jarl.org/English/6_Band_Plan/JapaneseAmateurBandplans20200421.pdf . This setting is useful for
Japanese license regulations compliance.

CAT timeout enable
When this setting is enabled, which it is by default, there is a timeout on Transmit; if the timeout
elapses and QDX does not receive a CAT command requesting it to switch back to Receive, thenit will automatically switch back to Receive.
This feature needs to be disabled if using VOX.

CAT timeout (sec)
The duration of the CAT command timeout (see above), in seconds.

QDX operating manual; firmware 1_08

19

PTT Port as Serial 3
Enabling this parameter changes the behaviour of the 3.5mm PTT jack on PCB Rev 3 and above.
This jack becomes an additional serial port.
This requires a HARDWARE change to remove and bypass the transistors driving the PTT
signals. The port is then a 3.3V logic (5V logic tolerant) serial port with configurable baud rate.
These changes are as described in the schematic below. Remove Q12 and Q13 completely, alongwith R5 and R42. Jumper between the gate and drain of each of the transistors.

Serial 1 terminal
Specifies the baud rate of serial terminal 1. To disable serial terminal 1, leave the parameter atzero.

Serial 2 terminal
Specifies the baud rate of serial terminal 2. To disable serial terminal 2, leave the parameter atzero.

Serial 3 terminal
Specifies the baud rate of serial terminal 3. To disable serial terminal 3, leave the parameter atzero. Serial terminal 3 can only be used if the “PTT Port as Serial 3” setting is set to ENABLE (seeabove).

Night mode
Some constructors have commented that the 3mm red status LED is excessively bright. One
solution would be to increase the resistance in series. This “Night mode” option provides an
QDX operating manual; firmware 1_0820

alternative, all-firmware solution. When enabled, the LED brightness is extremely dim (the GPIO
pin is configured as an input pin with internal pull-up resistor, which drives the LED very weakly).
The flashing etc of the LED is the same as normal, but just very dim.

TX shift threshold
Specifies the number of milliHz that the detected audio signal during transmit must change before
the Si5351A is reconfigured to transmit the new value. On Rev 3/3a PCBs this parameter should
be set to 500 to avoid the “pops” being inserted into the transmitted signal. On other PCB revisions
this parameter can be zero. For modes like FT8 it doesn’t make any difference. For modes suchas FST4W with very slow transmit cycles and very narrow tone spacing, this parameter should bedecreased or zero if possible.

Use of the additional serial ports
These additional three serial ports can all be used alongside the existing Virtual COM Serial port
and interchangeably with it. This can be useful if you want to access the configuration settings at
the same time as use the main Virtual COM serial port for CAT control by WSJT-X (etc) softwareon the host PC.
The ports are standard serial connections, with configurable baud rate. To use them with USB
requires a USB to Serial converter. One option is to use the USB to Serial converter onboard the
QRP Labs QLG2 GPS Receiver module.

The correct jumper
configuration on the
QLG2 board for thisis shown below;
then the RX and TX
signals areconnected at therow of 6 pads
labeled PH2 at thebottom of the board(to GND, TXD and
RXD).

QDX operating manual; firmware 1_08

21

Connection of serial ports 1 and 2 (and also 3 if you have a pre-Rev 3 PCB) requires soldering
wires directly to the microcontroller pins, a task to be undertaken with considerable care, to say
the least. The Rev 5 PCB has pin headers at the board edge for most of these connections and isvery easy.
The various possible connections are described in the following diagram:

You may note that firmware 1_05 and above also have the possibility of a monochromatic VGA
output and PS/2 keyboard connection. The VGA signal is generated directly on microcontroller
pins by firmware. It implements 800
x 600 pixel, 56fps SVGA mode. Due
to RAM constraints on the
microcontroller, it actually sends
each scanline twice, so effectively it
is 800 x 300 pixels. The code
implements an 80 x 25 character
sort-of-VT220 type of terminal feel,using a character font on a speciallydesigned 10 x 12 pixel font.
The classic “amber” type display
colouring is attained by driving red
and green monitor inputs in parallel(which would give yellow), then using
the monitor’s own colour adjustment
QDX operating manual; firmware 1_08

22

menu to reduce the green contribution to around 70-75% according to taste, which produces theamber-ish colour tone.
So there are FIVE possible serial terminals: the classic USB Virtual COM Serial connection, three
additional serial ports, and the built-in VGA and PS/2 interfaces for the bold.
If more than one terminal is connected, access to the various terminal applications is in mostcases limited to only one terminal; when adifferent terminal accesses a particularapplication, it goes red on other terminals to
indicate that it cannot be opened (on the
VT220 which is monochrome and so doesn’t
have “red”, disabled applications are enclosed
in parenthesis).
For fun, there’s also a secret “Easter egg” inthe code, which you can access by pressing
the M key at the main menu (on the PS/2
keyboard terminal only), which draws theMandelbrot set on the VGA output.

The VGA terminal during development:

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23

4.5 Band configuration

The Band Configuration screen allows specification of all parameters that are handled per-band.
This screen is populated by default with the correct information to set QDX up for 5-band operation
on 80, 60, 40, 30 and 20m. However, if you wish to experiment with other bands (which will require
hardware modifications to Receiver Band Pass Filter and Transmitter Low Pass Filter component
values – for which you are on your own), then you may specify the other band parameters here.
There is space for 6 band configurations, which are arranged in columns in a table. You may movefrom one column to the next by using the left/right arrow keys. Use the up/down arrow keys tomove up and down the rows of each band specification column.
On a QDX-M only a single column is shown.
Note that for 160m, 630m and 2200m operation, the QDX uses a different technique to generate
90-degree quadrature oscillator signals on reception. For a period of 20ms the two clock signals
are set to a slightly different frequency (12.5Hz apart) such that after 20ms the clocks have exactly
90-degree phase shift; then they are set again to the exact same frequency, and the 90-degree
phase difference is maintained. To trigger this operation, the band name must be set to 160, 600,
630 or 2200.
Remember that the number of characters in each setting is limited. To change the parametersetting, you generally need to press the Delete key in order to delete the existing setting
characters, then enter new ones. The setting is stored in memory when you press the Enter key,or one of the arrow keys to move to a different cell of the table.
As usual, press Ctrl-Q to quit the Band Configuration utility.
An explanation of the items in the Band Configuration screen follows:

QDX operating manual; firmware 1_08

24Band name (m): The name of the band - this appears in all the other terminal applications suchas RF sweep, Transmitter test etc. to identify the set of settings corresponding to the band. The
name also determines certain behaviour, as follows.
For operation below 3MHz – which is given by 25MHz (ref freq) x 15 (minimum PLL multiplier)divided by 126 (maximum phase offset register value), Si5351A quadrature output on Clk0/Clk1
has to be generated by a different method. Setting the phase offset register equal to theMultiSynth divider does not work, because the phase offset register is only 7 bits. An alternative
method is used, as in the QCX-series transceiver operation on 160m. Specifically, when entering aband below 3MHz, two clocks are set to be initially in phase, but 12.5Hz apart. 20 milliseconds
later, they are set back to the same frequency; by this time they have drifted 90-degrees apart,which is the desired phase offset and is maintained during further frequency changes that affectonly the PLL multiplier.
This behaviour for bands under 3MHz is triggered by the Band name parameter being one of
2200, 630, 600 or 160. QDX operation therefore works for the bands 2200m, 630/600m and 160m.
Additionally, when the band name is within the set {2200, 630, 600, 160, 80, 60, 40, 30, 20} the
MultiSynth divider is fixed, according to this table:
Band name

MS Divider

2200

1280 and div-by-4

630

1280

600

1280

160

320

80

126

60

126

40

126

30

84

20

64

For any other band name, the MS divider is chosen to be the next even integer below 600 / Band
name. For example, for 21.078MHz operation, the divider would be 600 / 21.078 = 28.47 MHz,and the next even integer below that is 28. Therefore the divider 28 is used.
Audio gain (dB): 54 is the default and corresponds to the default value of 5,000 used in earlier
firmware versions in the main configuration screen. Valid values for the parameter are 0 to 99.
This makes it easy to choose a gain by band - which is often useful to get WSJT-X and JS8Call
perfectly happy on each band without needing to manually fiddle with gain adjustments whenchanging bands. WSJT-X and JS8Call documentation recommends when the band is empty, thesignal strength meter on the bottom left should be at about +30dB.
Frequency min.: When you command a new frequency via CAT (from WJST-X etc), this is thelower limit of this band definition.
Frequency center: The center frequency, which is the frequency of the vertical blue line seen in
the RF sweeps, the test frequency for AF sweeps, and is the frequency used by the Transmitter
Test screen. It doesn't have any other purpose and doesn't have to be the actual center (half way
between min and max).

QDX operating manual; firmware 1_08

25

Frequency max.: When you command a new frequency via CAT (from WSJT-X etc), this is theupper limit of this band definition .
Sweep start: the start frequency for the RF sweep screen. Note that the minimum measurable
frequency is 375 / MS Divider (see Band name section above, for details on MS Divider). If thesweep starts on an non-measurable frequency, the actual graph line will not start until ameasurable frequency occurs.
Sweep step: the step frequency for each point of the RF sweep plot screen. Similarly to the above(Sweep start), the maximum measurable frequency is 1150 / MS Divider and points above this are
not plotted on the graph.
BPF number (0-3): The Band Pass Frequency selection for this band.
LPF number (0-2): the Low Pass Frequency selection for this band.
PIN fwd bias (mA): Specifies the forward current, in mA, to be driven through each of the two PIN
diode switches either side of the Low Pass Filter during transmit. The adjustment range is 5 to
60mA. The default value is 30mA and should generally be left alone.
Transmit: Enabled or Disabled, to allow or prevent transmission on this band. Press the E key toenable, D key to disable.
TX PTT +5V: To enable or enable, for this band, whether +5V appears on the PTT connector"ring" connection during transmit. Press the E key to enable, D key to disable.
This output is designed to directly interface with the QCX-series 50W Power Amplifier with asimple stereo jack audio cable. Remember, the 50W PA is a SINGLE BAND amplifier so should
only be used on the QDX with a single band, unless you are going to build an external switched
Low Pass Filter. Also remember that the 50W QCX-series amplifier is designed for CW operationand not suitable for the high duty cycle of digital modes; therefore if you wish to use this with the
QDX transceiver, be sure to limit it to around 20-25W output power; this will be achieved by using
a 12V supply voltage to the 50W PA kit.
TX PTT grounded: To enable or disable, for this band, whether the PTT "tip" connection isgrounded during transmit. Press the E key to enable, D key to disable. This PTT output is suitablefor driving a typical grounded PTT type amplifier.
Please refer also to the hardware documentation (assembly manual) for more information on the
PTT connection, and the circuits driving it.
The PTT connector is a 3.5mm stereo jack connector. The “ring” connection can be configured asa +5V PTT output, suitable for switching the QCX-series 50W amplifier. The “ring” connection is
also used on the 50W PA so only a standard stereo audio jack cable is required. The “tip”
connection can be configured as a grounding PTT output for connection to most other amplifiers.
Both the +5V-going and grounded PTT outputs (‘ring” and “tip” connections respectively) are
MOSFET open-drain outputs (utilizing P-channel and N-channel type MOSFETs respectively).
Both outputs have a 470-ohm resistor in series to protect them against accidental damage forexample, shorts to ground.
RX PTT +5V: To enable or enable, for this band, whether +5V appears on the PTT connector"ring" connection during receive. Press the E key to enable, D key to disable. Generally for use
with an external PA, these settings should all be left DISABLED. However if you wish use the +5V
output for some auxiliary control purpose such as a relay for external switching of antennas, then
you can configure it to be active during Receive as well as transmit.

QDX operating manual; firmware 1_08

26

RX PTT grounded: To enable or disable, for this band, whether the PTT "tip" connection isgrounded during receive. Press the E key to enable, D key to disable. Generally for use with an
external PA, these settings should all be left DISABLED. However if you wish use the grounded
output for some auxiliary control purpose such as a relay for external switching of antennas, then
you can configure it to be active during Receive as well as transmit.

4.6 Audio filter sweep
QDX contains its own internal signal generator, which can be used to sweep the audio passbandof the receiver, checking the audio response and the unwanted sideband cancellation.
Connect a dummy load for best results.
On entering the application, a sweep automatically commences. The percentage completion of thefrequency sweep is indicated in the bottom right corner of the screen.
The sweep starts at 100 Hz (injected signal is 100 Hz higher than the “USB Dial Frequency”, thenproceeds in 50 Hz steps up to and including 3850 Hz. The RF frequencies (“USB Dial Frequency”)
used for bands are defined in the Band Configuration screen of the QDX. For example, for 80, 40,
30 and 20m are 3.573, 7.074, 10.136 and 14.074 MHz respectively. The vertical axis shows audio
decibel (dB) level. The offset is arbitrary. Gridlines axis are displayed in blue. Vertical gridlines are
every 20dB, and horizontal axis gridlines every 1000 Hz. Gridline labels are displayed in blue; theminimum and maximum audio level (in dB) displayed in white, and the maximum audio sweep
value also displayed in white.
The chart contains two lines, the line of yellow asterisks is the Upper Sideband (USB) and the redline is Lower Sideband (LSB). In the default demodulation mode (USB), we expect to see theyellow line nice and flat between the filter cut-off points 150 Hz to 3.2 kHz. The red line is theunwanted sideband and we expect to see it around 60dB below the wanted sideband.
The – and + keys can be pressed to move down and up to adjacent bands defined in the Band
Configuration screen. Generally the result should not differ much from one band to the next.

QDX operating manual; firmware 1_08

27

4.7 RF filter sweep
QDX contains its own internal signal generator, which can be used to sweep the receiver input
Band Pass Filters, checking its response and center frequency. Though the difference inperformance is small, the perfectionist may wish to adjust (by squeezing turns) the Band Pass
Filter inductor L12 to optimize the center frequencies of the filters.
Connect a dummy load for best results.
On entering the application, a sweep automatically commences. The percentage completion of thefrequency sweep is indicated in the bottom right corner of the screen.
The center frequency and sweep width are defaulted appropriately per band, to show several MHz
of frequency sweep cleanly, and are not adjustable. The vertical axis shows audio decibel (dB)level. The offset is arbitrary. Gridlines axis are displayed in blue. Vertical gridlines are every 20dB,
and horizontal axis gridlines as appropriate to the band. Gridline labels are displayed in blue; theminimum and maximum audio level (in dB) displayed in white.
A vertical line is shown at the position corresponding to the default operating frequency in thecurrent band. Ideally the peak of the response (line of yellow asterisks) should coincide with thecenter frequency of the band. The filters are not very very sharp so the performance degradation
by being slightly off frequency is not severe. In the example screenshot (40m), the center
frequency is incorrectly somewhat below the 40m operating frequency.
The – and + keys can be pressed to move down and up to adjacent bands as defined in the Bandconfiguration screen.
Pressing the R key re-runs the sweep on the existing band.

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28

4.8 Input analysis
The Input analysis application is one of the most interesting screens in the QDX Terminal
application suite. It shows a “waterfall” which scrolls upward, with the measured audio frequency
shown as a yellow block in each row, with its horizontal position determined by its frequency. The
scroll rate, and the screen width, are adjustable. The application can be used for checking theaccuracy of the frequency analysis (for example when changing configuration parameters“Minimum cycles” and “Minimum samples” at various incoming audio frequencies).

Keyboard controls
During operation, the following keyboard buttons may be pressed to control the operation of thewaterfall:
CTRL-Q:

Quit the input analysis application

Right arrow:

Increase the screen width (higher number of Hz per horizontal division)

Left arrow:

Decrease the screen width (lower number of Hz per horizontal division)

Up arrow:

Scroll faster (shorter time interval per vertical division)

Down arrow:

Scroll slower (longer time interval per vertical division)Space bar:

Pause or un-pause the display; when paused the top right corner text shows“PAUSED” in inverted yellow text

. (dot):Change the colour of the background gridlines. The default colour is blue. Eachtime the dot is pressed, the colour changes; it cycles through: Blue, Magenta,
Cyan, White, Red, Green, Yellow and then blue again.

QDX operating manual; firmware 1_08

29

Display elements
This annotated screenshot illustrates the various elements on the display.

The display elements on the top row are:•

80Hz: Total 80-column screen width, in Hz. In this case an 80 Hz wide screen means eachblock is a 1 Hz Waterfall bucket•/10Hz: Hz per horizontal division. There are always 8 horizontal divisions on the screen.
This parameter displays the number of Hz per division.

•

160ms: the update rate of the screen, or put another way, time per horizontal scroll row.

•

/2s: The time per vertical division of the screen (distance between the horizontal blue dot
grid lines)•

FT8: The mode matching this update rate; various popular modes coded and when an
update rate matches a mode, the mode name is written here. See below for the list of
supported update rates.

•

1510: Center frequency of the waterfall•

1512.35: The most recent frequency measurement
NO SIGNAL: displayed at the top right when no audio signal is detected
PAUSED: displayed at the top right when the screen is paused by the space bar

NOTE: At very fast update rates, which are useful for displaying some features, the screen update
is too slow to display all the information and still be capable of updating fast enough. Therefore
information is dropped. At 20ms per row (50 row updates per second) the only text on the display
is “20ms” in the top left corner; the grid lines are still displayed. At 10ms (100 row updates per
QDX operating manual; firmware 1_08

30

second), even the grid lines are dropped; only “10ms” is written in the top left corner, and theyellow block drawn for the measured frequency.

Update rates:
The available update rates (selected by the up/down arrow keys) are chosen to match various
popular modes. For example, the symbol duration for FT8 is 160 ms. So “FT8” is written next tothe vertical division rate, on the top row of the display.
Updaterate (ms)verticalDiv (s)Matching Comment
mode

10

1

Only display “10ms” in top left

20

1

Only display gridlines and “20ms” in top left

40

1

80

1

160

2

FT8

227

2

JT4

361

5

JT65

576

5

JT9

683

5

WSPR

Horizontal size (Hz):The available horizontal screen size (selected by the left/right arrow keys) are chosen to cleanly fit
the 80 columns display width.
Screenwidth (Hz)Horizontal
Div (Hz)

12

1.5

20

2.5

40

0.5

80

1

160

2

320

4

QDX operating manual; firmware 1_08

31

Demonstration of sliding frequency changes

A fun and useful demonstration of the capabilities of QDX and the Input Analysis application, is toinvestigate the FT8 tone change transition. We know according to the WSJT-X documentation thatto avoid splatter onto adjacent frequencies, WSJT-X makes a smooth transition between one tone
symbol and the next. It’s nice to be able to check this using the Input Analysis screen.
Here the screen width is 80Hz so each horizontal column is a 1 Hz bucket. The FT8 symbolchange event is 2 tones (a frequency change of 12.5 Hz since the FT8 tone spacing is 6.25 Hz.
The scroll rate is sped up the fastest rate, 10 ms per horizontal row (100 frequency measurements
per second).
We see clearly that at the moment the FT8 tone changes, the measured frequency smoothly
changes in the expected way from one tone to the next.
Note that an even smoother transition could be made, by setting the “Minimum samples”
parameter to 240 samples – this would result in slightly lower accuracy measurement but asmoother transition in tones.
We’re talking here about tradeoffs in different aspects of performance; either way the performanceis excellent and QDX keeps up with the changes in input frequency! So this is a nice confirmationof the excellent performance characteristics of QDX.
Pressing the M key during input analysis, is another “Easter egg” trick that enables a slightly
different mode of operation. In this mode, a window opens in the top left of the display, and scrolls
the last 8 CAT commands and CAT command responses. The screen scrolling pauses until the
QDX operating manual; firmware 1_08

32

QDX is in transmit mode (actual audio being received). This mode is really only useful when using
a second terminal, or the VGA + PS/2 keyboard terminal, in addition to the normal USB Virtual
COM connection being used for CAT control by the host PC software (WSJT-X etc).
This photograph of my VGA monitor was taken during this mode, during a 20m JS8 QSO with
Timo OH8XAT.

4.9 Image sweep
QDX implements a conversion to baseband, sampling quadrature I and Q channels at 48ksps to a
24-bit stereo ADC then the rest of the receiver is done in Digital Signal Processing in the
microcontroller – a Software Defined Radio (SDR). The SDR implements a superhet with 12kHz
IF. Like any superhet, this means that there is an image response on the other side of the IF
frequency. In this case, that means the image response is 24kHz down the band. The amount of
the image rejection depends on:•

Amplitude balance between the I and Q channels•

Any phase error in the 90-degree quadrature relationship

In QDX to date, no attempt is made to compensate for these errors. The image rejection has beenfound to be adequate without it.
In order to be able to visualize and measure the image rejection, firmware 1_05 introduced the“Image sweep” screen, which sets the VFO to the band center frequency as defined in the Band
QDX operating manual; firmware 1_08

33

Configuration screen, then sweeps the signal generator input from -30.5kHz (below) to +7kHz(above). An example of the resulting sweep is shown below:

You may get better or worse image rejection than this (depending on your particular combinationof component tolerances).
However if you have a significantly worse image rejection then it is time to start debugging yourunit; most likely is a problem in the area of the trifilar transformer. Faults such as incorrect wiring(wires in the wrong holes), a broken wire, shorts between wires, etc., can all cause this.
Another cause of poor image rejection, if you have a Rev 3a board, can be the C41 via short fault.
Please refer to the Rev 3a Assembly manual for details of how to resolve this fault, if you have notdone so already.
In this annotated image,the four audio
responses are
identified; all four
appear in the receivers
audio passband. Wheneverything is correct,
the three unwanted
ones (the lower
sideband and the USB/
LSB at the image
frequency) are at amuch lower signal level
than the wanted inchannel USB reception.

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34

4.10 CAT command test
The CAT command test application is a simple screen which allows you to test CAT commands.
An annoying thing about typing CAT commands directly into a terminal emulator when QDX is in
the normal operating mode, is that you cannot see the command you are typing, nor can you edit it
if you made mistakes.
Here in this simple application, you can type the command (or commands) you wish to send to
QDX in the yellow area of the bottom row. If you forget the trailing semicolon, the application adds
one automatically for you. Then simply the command is shown in yellow in the left column, and thecommand result in yellow in the right column. When the screen is full, it will scroll automatically.
Naturally unrecognized CAT commands simply return an error ? as per the CAT specification.

Cat command set
QDX implements a subset of the Kenwood TS-480/TS-440 CAT command set which is an oldstandard, but contains all the necessary commands for WSJT-X and other software to be able tocontrol QDX, and is old enough that it is widely supported by most software packages.
Additionally QDX provides an extended set of CAT commands Q0, Q1, Q2 and so on until QB.
These commands allow a host program to set and get all of the parameters in the QDX
configuration screen. Except for the default start-up operating frequency, all of these commands
have effect only for the current operating session, they are not stored in EEPROM. If you need topermanently store the configuration parameters in EEPROM please use the Terminal
Configuration screen. These commands could be useful for example, if you wish to provide aparticular start-up script of CAT commands in your PC software to configure your QDX a certainway.

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35

The following lists the commands and responses in alphabetical order:
AG: Get/Set AF Gain
Set: Sets the audio gain. The actual gain setting is the supplied gain in dB. So for example
command AG21; will set the gain to 21dB, in the currently active band. Note that the gain canalso be set in the Terminal Band Configuration application.
Get: Returns the audio gain in dB.
C2: Get/Set Signal Generator frequency
Set: Sets the Si5351A Clk2 output frequency (the signal generator).
Get: Gets the frequency of Si5351A Clk2 (the signal generator)
FA: Get/Set VFO A
Set:

Sets VFO A value. Example: FA7030000; sets VFO A to 7.030MHz

Get:

Returns the VFO A contents as an 11-digit number. Example: “FA;” returns “FA00007030000;”

FB: Get/Set VFO B
Set:

Sets VFO B value. Example: FB7016000; sets VFO B to 7.016MHz

Get:

Returns the VFO B contents as an 11-digit number. Example: “FB;” returns “FA00007016000;”

FR: Get/Set Receive VFO Mode
Set:

Set VFO Mode: 0, 1, 2 correspond to VFO A, VFO B or Split respectively. This is the case forboth the FR and FT commands (which are nominally Receive and Transmit VFOs) because in
the QDX the VFO mode use does not correspond exactly to TS-480.

Get:

Get Receive VFO Mode: 0 means VFO A is used for receive (could be due to VFO mode
being VFO A, or VFO Mode being Split); 1 means VFO B is being used for receive (must be
VFO Mode B).

FT: Get/Set Transmit VFO Mode
Set:

Set VFO Mode: 0, 1, 2 correspond to VFO A, VFO B or Split respectively. This is the case forboth the FR and FT commands (which are nominally Receive and Transmit VFOs) because in
the QDX the VFO mode use does not correspond exactly to TS-480.

Get:

Get Transmit VFO Mode: 0 means VFO A is used for transmit (must be VFO Mode A); 1
means VFO B is being used for transmit (could be due to VFO mode being VFO B, or VFO
Mode being Split)

FW: Get filter bandwidth
Get:

Always returns 3200 meaning, 3200Hz (the QDX’s filter bandwidth).

ID: Get radio ID
Get:

Always returns 020 (Kenwood TS-480)

QDX operating manual; firmware 1_08

36

IF: Get transceiver information (TS-480 format).
Get:

Returns a composite information string containing the state of the transceiver, as follows(excluding command ID and ; terminator character):
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•

11-digit operating frequency (VFO A or B, according to the VFO mode setting and transmit/
receive state
5 spaces
5-digit RIT frequency, as +/-9999Hz e.g. RIT up 200Hz returns “+0200” in this field
RIT status: 0 = RIT OFF, 1 = RIT ON
XIT status: always 0 because QDX has no XIT
Memory channel bank number: always 0
Memory channel number: always 00
Transceiver status: 0 = RX, 1 = TX
Operating mode: returns 1 for LSB, or 2 for USB (the normal mode for digi)
Receive VFO: 0 = VFO A, 1 = VFO B
Scan status: always 0
Split: 0 = Simplex operation (VFO mode A or VFO mode B), 1 = Split
Tone: always 0
Tone number: always 0Space character

MD: Get/Set operating mode
Set:

Set to 1 to set Lower Sideband (LSB) or any other value to set Upper Sideband (USB)

Get:

Returns 2 (USB) if the mode is Upper Sideband (USB) which is the normal mode. Returns 1 if
the mode is Lower Sideband (LSB).

Q0: Get/Set TCXO reference frequency
Set:

Set TCXO reference frequency. Only values between 24999000 and 25001000 are allowed.
The setting is for the current operating session only and is not written to EEPROM.

Get:

Get TCXO reference frequency.

Q1: Get/Set Sideband
Set:

Set sideband; 1 sets Lower Sideband (LSB), any other value sets Upper Sideband (USB). The
setting is for the current operating session only and is not written to EEPROM.

Get:

Get sideband; 0 = USB, 1 = LSB

Q2: Get/Set default operating frequency
Set:

Set default operating frequency. The value IS written to EEPROM.

Get:

Get default operating frequency.

Q3: Get/Set VOX Enable
Set:

Set VOX enable: 1 enables VOX, 0 disables VOX. The setting is for the current operating
session only and is not written to EEPROM.

Get:

Get VOX enable; 1 = Enabled, 0 = Disabled

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Q4: Get/Set TX Rise Threshold
Set:

Set TX Rise Threshold, which should be a percentage number between 0 and 99 (seedescription elsewhere in this manual). The default setting of 80 is normally appropriate. The
setting is for the current operating session only and is not written to EEPROM.

Get:

Get TX Rise Threshold value

Q5: Get/Set TX Fall Threshold
Set:

Set TX Fall Threshold, which should be a percentage number between 0 and 99 (seedescription elsewhere in this manual). The default setting of 60 is normally appropriate. The
setting is for the current operating session only and is not written to EEPROM.

Get:

Get TX Fall Threshold value

Q6: Get/Set Cycle Min parameter
Set:

Set Cycle Min parameter (see description elsewhere in this manual). The setting is for thecurrent operating session only and is not written to EEPROM.

Get:

Get Cycle Min parameter value

Q7: Get/Set Sample Min parameter
Set:

Set Sample Min parameter (see description elsewhere in this manual). The setting is for thecurrent operating session only and is not written to EEPROM.

Get:

Get Sample Min parameter value

Q8: Get/Set Discard parameter
Set:

Set Discard parameter (see description elsewhere in this manual). The setting is for thecurrent operating session only and is not written to EEPROM.

Get:

Get Discard parameter value

Q9: Get/Set IQ Mode
Set:

Set IQ Mode: 1 enables IQ Mode, 0 disables IQ Mode. In IQ Mode, the raw I & Q samples
from the ADC are streamed directly to the USB Sound card. The setting is for the current
operating session only and is not written to EEPROM.

Get:

Get IQ Mode; 1 = Enabled, 0 = Disabled

QA: Get/Set Japanese Band Limits mode
Set:

Set Japanese Band Limits mode: 1 enables Japanese band limits, 0 disables Japanese band
limits. In Japanese Band Limits mode, QDX cannot transmit outside the allowed Japaneseband limits. The setting is for the current operating session only and is not written to EEPROM.

Get:

Get Japanese Band Limits mode; 1 = Enabled, 0 = Disabled

QB: Get/Set CAT timeout enable mode
Set:

Set CAT timeout enable. 1 enables CAT timeout, 0 disables CAT timeout. When enabled, if intransmit mode, if there is no CAT command for a specified timeout, QDX automatically returns
to receive mode.

Get:

Get CAT timeout enable mode; 1 = Enabled, 0 = Disabled
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38

QC: Get/Set CAT timeout
Set:

Set CAT timeout. Specifies the CAT timeout in seconds.

Get:

Get CAT timeout. Returns the CAT timeout in seconds

QD: Get/Set PTT Port as Serial 3 mode
Set:

Set PTT Port as Serial 3 mode. 1 enables PTT Port as Serial 3 mode, 0 disables PTT Port as
Serial 3 mode. When enabled, the PTT port functions as Serial port 3, not as a PTT port. Thisrequires a hardware modification (see elsewhere in this manual).

Get:

Get PTT Port as Serial 3 mode; 1 = Enabled, 0 = Disabled

QE: Get/Set VGA PS/2 terminal mode
Set:

Set VGA PS/2 terminal mode. 1 enables VGA PS/2 terminal mode, 0 disables VGA PS/2
terminal mode. When enabled, QDX outputs VGA and enables its PS/2 keyboard interface,providing an additional terminal session on the QDX. This requires hardware connections (seeelsewhere in this manual).

Get:

Get VGA PS/2 terminal mode; 1 = Enabled, 0 = Disabled

QF: Get/Set Serial 1 terminal
Set:

Set Serial 1 baud rate

Get:

Get Serial 1 baud rate

QG: Get/Set Serial 2 terminal
Set:

Set Serial 2 baud rate

Get:

Get Serial 2 baud rate

QH: Get/Set Serial 3 terminal
Set:

Set Serial 3 baud rate

Get:

Get Serial 3 baud rate

QI: Get/Set Night mode
Set:

Set Night mode. 1 enables Night mode, 0 disables Night mode. When enabled, the brightnessof the 3mm red front panel status LED is very greatly reduced.

Get:

Get Night mode; 1 = Enabled, 0 = Disabled

QJ: Get/Set TX shift threshold
Set:

Set TX shift threshold (see explanation in Configuration screen description section of thismanual)Get:

Get TX shift threshold

RD: Set negative RIT offset amount
Set:

Sets negative (down) RIT; for example “RD-200;” sets the RIT to -200Hz

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39

RT: Get RIT status
Get:

Returns RIT status: 0 = RIT off, 1 = RIT on

RU: Set positive RIT offset amount
Set:

Sets positive (up) RIT; for example “RD150;” sets the RIT to 150Hz

RX: Set the radio into Receive mode immediately
Set:

Command RX; immediately puts the radio into receive mode. It is equivalent to TQ0;

SP: Get/Set Split mode
Set:

Sets Split mode: 0 = OFF, 1 = ON. For example “SP1;” switches QDX to split mode

Get:

Returns the Split state: 0 = OFF, 1 = ON.

TQ: Get/Set transmit state
Set:

Sets transmit state: 0 = RX, 1 = TX. For example “TQ1;” switches QDX to transmit mode

Get:

Returns the transmit state: 0 = RX, 1 = TX.

TX: Set the radio into Transmit mode immediately
Set:

Command TX; immediately puts the radio into transmit mode. It is equivalent to TQ1;

VN: Returns firmware version
Get:

Returns the firmware version. For example, VN; command returns VN1_05;

4.11 CAT monitor
The CAT command monitor is a very plain blank screen, whose only purpose is to scroll incoming
CAT commands from the CAT host, and the QDX responses. You will only be able to use thisscreen if you have multiple serial ports connected – one (typically the main USB Virtual COM port)
to the PC host and one to a terminal (or terminal emulator on a PC, via a USB-Serial converter),running the CAT monitor terminal application.

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4.12 Log file
This application is very useful for debugging CAT problems. The log file is stored in the EEPROM
chip. The EEPROM chip capacity is 8 KB (Kilobytes) or 8,192 characters. However theconfiguration parameters also reside in EEPROM, so the available space for the log file is a little
less: 8,064 characters, to be precise! When the log file is full, no further characters are written to it.

On opening the Log file application, the existing contents of the log file are displayed. When thescreen is full, it will scroll automatically; you can use the scroll bar of the window to see text thathas scrolled off the top of the screen if you wish. The current logging status is displayed in yellow
in the bottom right corner. In this example, the status is “ALL” which means that all events arebeing logged.
The available keyboard commands are:
CTRL-Q:
C:
A:
E:
N:

Quit the log file application screen (logging remains active, if enabled)
Clear the log fileLog all events
Log only error events
No logging at all (logging is switched off)

In the log file, each event is written as one line. There are several times of log file entry:•

Errors have the line prefix “ERR:”•

CAT commands are shown (semicolon terminated) followed by the command result, if any.
An unrecognized or invalid CAT command would be prefixed by the error code “ERR: “.

•Radio state changes are indicated by the item being changed, followed by the new value.

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Various examples from the screenshot above:

VFO.A 1840000
FA00001840000;
ERR: Band

sets the VFO A frequency to 1.84 MHz
CAT command from WSJT-X MHz
Error message “Band”

In this example, a CAT command was received from WSJT-X, to set the QDX to frequency 1.84
MHz. The CAT command is “FA00001840000;” - Note that the entries in the log file are not quite inchronological order, since the VFO update event is printed BEFORE the CAT command event; thereason for this is that the CAT evaluation must be completed in totality before the CAT commandlog event takes place, because only then do we know if the CAT command was successful. The
final entry is an error message “Band” because 1.84 MHz is in the 160m band and this is not oneof the bands currently supported by QDX.

VFO.A 7074000
FA00007074000;
Band 40m

sets the VFO A frequency to 7.074 MHz
CAT command from WSJT-X MHz
Sets the band to 40m

The operator then realizes his error setting QDX to 160m in the WSJT-X drop-down and chooses
40m instead; this time the CAT command successfully sets frequency and band.

IF; IF00007074000+00000000003000000 ;Here the “IF;” or Information request CAT command is received from WSJT-X and QDX replies
with the CAT information string in the prescribed format.
For reasons known only to itself, WSJT-X likes to ask for the information screen multiple times inquick succession even though the result is the same.

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The complete list of log events is as follows:
Event

Explanation

Example Comment

Power upOccurs every
power up

Start
Shows the start event and version number
1_00_001

Set VFOVFO frequencychangeVFO.A
7074000

BandchangeBand is set to a
new valueBand 40m An error is generated for bands not supported.

TX

Radio switchedto Transmit

TX

Can be either by CAT command or by VOXRXRadio switched
to ReceiveRX

Can be either by CAT command or by VOX

VFO
Mode

VFO mode set
to A, B, or Split

Split ON/ CAT Split on/off
OFFcommand SP

VFO A is set to 7.074 MHz. VFO B is also available

VFO Mode An error is generated for any attempt other than A, B
Aor Split
Split ON

Clk2

Signal generator
frequency is set

Clk2
7075000

Gain

Set audio gain

Gain 25

RIT Down

RIT down CAT
command

RIT DN
500

RIT Up

RIT up CAT
command

RIT UP
500

CAT

Every CAT
commandIF;

Audio gain is set by the AG; CAT command

Every CAT command generates a log entry event

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43

4.13 Transmitter test
The Transmitter Test terminal application is useful for verifying correct operation of yourtransceiver, and making output power measurements into a dummy load, directly from the terminal
rather than needing to use WSJT-X’s “Tune” button.
The following keys are used in the Transmitter test application:+

increases the band-decreases the bandpEnable PTT (Highlights in YELLOW)t

Enable PTT and transmit (highlights in RED)

Ctrl-Q

Quit

The Transmitter test application respects the enable/disable band switches in the Configuration
application. So for example, if you have disabled 80m transmit operation, and you have selected
the band 80m, then pressing the t key to transmit, has no effect.
The frequency chosen for the transmission is just the default FT8 frequency for the selected band.

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44

4.14 Factory reset
Selecting Factory reset at the main terminal menu, then answering the question “Are you sure?”
with “Y”, results in the EEPROM configuration resetting to the factory default state, including
restoring the TCXO reference frequency to 25000000 and erasing the log file (if any). Pressing
any other key cancels the factory reset.

4.15 Update firmware
Puts QDX into the QFU Bootloader mode, for firmware update. Please refer to the section of thismanual describing the firmware update procedure.

4.16 Exit terminal
As mentioned previously, exit terminal returns QDX to normal operating mode, processing
incoming CAT commands as usual. The terminal should also be disconnected (or closed) so as tofree up the serial port for use by WSJT-X or whatever software you are using – remember that
only one PC software application can use the serial port at a time.

5. Troubleshooting Transmit issues
A common problem is that you think you’re transmitting in WSJT-X (for example), but QDX is notproducing any audio. The 3mm red Status LED on the QDX front panel can be used to debug
these issues efficiently. The Status LED flashes during transmit, once, twice or thrice, with the
LED on for 0.1 seconds and off for 0.1 seconds between flashes; the sequence is repeated every
1 second. Observe what the LED is doing when you think you are transmitting, and diagnose thefault as below.

No flashes
If the LED does not flash at all when you try to transmit from your host PC application, then you
may not have set up your Virtual COM Port setting correctly in the host PC application (forexample, WSJT-X). Normally it is recommended to use CAT control to enable PTT, not VOX.
When it wishes to switch from transmit to receive (or vice versa) the PC will issue CAT commands
over the Virutal COM Port serial interface, telling QDX to switch to transmit. This will only work if
the serial port has been correctly set to the port QDX is on, and if you have selected the correct
CAT rig (for example, Kenwood TS-440). VOX is not recommended, but if you have enabled VOX
PTT rather than CAT, and QDX does not transmit, it means the sound is not reaching QDX (seethe 1-flash and 2-flashes diagnostics below).

1 flash:In this case, the host program on the PC has activated the PTT (Push To Talk) by the appropriate
CAT command, switching QDX into transmit mode; however, no audio is being received from thePC over the USB cable link. This is normally because you have not selected QDX as the audio
output device in your PC software settings e.g. WSJT-X. Refer to the configuration section earlier

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45

in this manual. The fault could also arise if the output volume is zero, which could be due to theaudio output channel being muted somewhere in your PC audio settings.

2 flashes:
QDX is receiving audio from your PC. But the volume is insufficient to trigger the key-down(transmit) action. Remember that there is a “Rise Threshold” setting in the QDX Configuration
terminal application, which defaults to 80% of maximum value. If the amplitude of the audio
sinewave coming from the PC is less than 80%, key-down will never be triggered.
It is therefore highly recommended to set the audio output level of the PC to 100%. Unfortunately
this simple recommendation can be the cause of great confusion. The exact places to set thevolume varies also depending on the operating system (Windows, Linux, Mac). But in principle
there are THREE places on the PC that all affect the output channel volume, and all three need to
be set to 100%:
1. The output volume of the software application itself, for example the “Pwr” slider in thebottom right area of the WSJT-X screen; these should always be left at maximum.
2. The output device corresponding to QDX must be set at 100% also. In Linux Sound
Manager (XUbuntu 18.04 example shown), the Output Devices tab for QDX should have its
slider set to 100% as per the example below. Don’t set it to more than 100%!

3. The “Master Volume” control of the PC should also be set to 100%. There is such a setting
in both Windows and Linux (and most likely Mac too). In Linux, clicking the loudspeaker
icon at the bottom right of the screen shows which audio device is being used for thedefault sound output; selecting QDX will show you the master volume level, and it needs tobe set to 100% (not more, not less). There’s a similar thing on Windows OS.

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3 flashes
If the status LED shows a slow pulsation, a 1Hz (once per second) cycle, where the LED current ismodulated with a 1Hz sinewave, this means that QDX is being correctly commanded to go totransmit mode (the host application activates the PTT CAT command), QDX is detecting andmeasuring the audio from the PC, and furthermore, the audio is of sufficient level to activate the
QDX transmit.
If you are STILL not getting power output then this indicates a hardware problem, either with QDX,
or with the connections to your power meter.
QDX transmitter hardware problems are often the result of failure to properly remove the enamel
from the enameled copper wire on the toroids and/or binocular core, resulting in no electricalconnection.

6. Resources

For updates and tips relating to this kit please visit the QRP Labs QDX kit page http://qrplabs.com/qdx
For any questions regarding the assembly and operation of this kit please join the QRP
Labs group, see http://qrp-labs.com/group for details

7. Document Revision History
1_03 23-Dec-2021

First version, for firmware 1_03

1_04 20-Jul-2022

Firmware 1_04 changes

1_05 30-Sep-2022

Firmware 1_05 changes

1_05a 30-Sep-2022

Added notes in section 4.5 about the Band name parameter operationin determining behaviour below 3MHz and the RF Sweep limits.

1.06

12-Dec-2022

Firmware 1_06 changes

1.08

17-Jan-2022

Firmware 1_08 changes

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