ADX-S Kit Assembly Manual
CRKITS.COM
2023/8/13 V1.5: Formal Release with 7 band upgrade

Photo: Jack Liang, BG7IKK who achieved DX contact of over 18,000 km with his EFHW antenna
Change history:
2023/3/26 V1.0: Formal Release2023/3/29 V1.1: Formal Release with issue fixes
2023/4/2 V1.2: Formal Release with minor change
2023/4/29 V1.3: Formal Release with CAT and other minor change
2023/7/24 V1.4: Formal Release with modifications
2023/8/13 V1.5: Formal Release with 7 band upgradeContents
ADX-S Kit Assembly Manual ..........................................................................................................1
Contents ....................................................................................................................................2
Specifications............................................................................................................................3
Part List.....................................................................................................................................3
Theory of Operation..................................................................................................................5
Step by Step Kit Assembly........................................................................................................8
Step 1: Diodes .................................................................................................................10
Step 2: +12V Power ........................................................................................................12
Step 3: Arduino Nano Module and +5V and +3.3V Power.............................................13
Step 4: Power supply for CD2003...................................................................................15
Step 5: 5351 Module .......................................................................................................16
Step 6: LEDs and Buttons ...............................................................................................18
Step 7: TX Driver 74ACT244 .........................................................................................20
Step 8: Complete the TX.................................................................................................21
Step 9: Audio Jacks .........................................................................................................24
Step 10: CD2003 RX ......................................................................................................25
Step 11: LPF band filter board ........................................................................................31
Step 12: Box the ADX-S .................................................................................................33
Settings and Calibration ..........................................................................................................36
Use the ADX-S........................................................................................................................38
Open Source Code Modification and Update .........................................................................40
CAT Support ...........................................................................................................................41
Modifications ..........................................................................................................................42
From 4 to 7-Band Upgrade .....................................................................................................44
Further readings ......................................................................................................................45
Reference and Acknowledgement...........................................................................................45

The ADX (Arduino Digital Xcvr) is an open source Arduino based digital modes HF QRP
transceiver designed by Barb, WB2CBA, who is known as one of the designers of uSDX. The
ADX-S is a superhet modification by BD6CR. The receiver performance is much improved andthe design details are refined to become a kit good for beginners. The normal building time is 3
hours, and the minimum requirement for test instruments is a frequency counter or just yourcommercial ham radio transceiver. You can use ADX-S with WSJT-x or JTDX on PC or FT8CN
on your Android phone or tablet. For WSPR TX, you can also use WSPR TX Android App.

Specifications
Dimensions: 97 mm x 97 mm x 22 mm, not including the protruding parts
Weight: 150 grams, including one LPF band filter board
Power supply: 10-12V from DC IN Jack or 5V from USB Port
Receive current: about 60mA at 12V
Transmit current: about 600mA at 12V (lower on 15 and 10 meters)
Transmit RF output: about 3.5W at 12V, about 0.3W at 5V (about half on 15 and 10 meters)
Spurious suppression: about -45dBc
Modes supported: Digital modes including WSPR, JS8, FT4 and FT8 on Upper Side Band
Bands supported: 40, 20, 15 and 10 meter by plugging in each band filter board
Audio jacks: MIC (to MIC jack of sound card) and SPK (to PHONE or SPK jack of sound card)
USB port: Type C

Part List
Please follow the part list to do parts inventory first. Report missing parts to your seller.
The Main Board

The LPF Band Module

Theory of Operation
The Arduino Nano module (XA1) is the control center. Besides the handling of buttons, LEDs and5351 frequency generation module, it counts the incoming audio frequency and adds to the carrier
frequency to complete the FSK modulation. So, ADX-S transmits single signal instead of DSB
signals like D4D. The Arduino Nano does not process receiving signal, so it is purely analog. The
Arduino Nano also provides regulated 5V to the main board.

The 5351 module (U2) is controlled by the Arduino Nano module through the I2C interface. The
module can generate 3 different square wave signals from the S0 to S2 ports. The S0 is fortransmitting, the S1 is for receiving local oscillator, and the S2 is for receiving beat frequency. In
calibration mode, the S2 port outputs 1MHz signal for calibration at the test point CAL.

The CD2003 (U1) is a compatible Chinese model of Toshiba TA2003, which is a mature AM/FM
radio receiver chip. It uses ceramic filters instead of IF transformers as the IF filter. The original
design of ADX uses the mixer stage for direct conversion receiver, while ADX-S adds a ceramic
filter and injects beat frequency to make a simple superhet receiver thanks to the design ideas from
JA9TTT. The PFB455JR filter by Murata is a 2-element ceramic filter to provide better selectivity
although the bandwidth is wider than 3kHz. The receiver front end is not tuned considering themultiple band design, so it is recommended to add a tuned ATU like Z-match tuner in between the
ADX-S and antenna to somehow reject the strong BCI if necessary. A simple Z-match tuner canbe made by two variable capacitors and a toroid, see https://www.qsl.net/g3vgr/zmatch.html. The
following hand drawing schematic shows the receiver side modification from the ADX.

The transmitter of the ADX-S is the same as the original ADX design. The CLK0 from the5351module (U2) is amplified by the driver stage of 74ACT244 (U3), fed to the final class E
amplifier stage of 3 BS170 in parallel, filtered by the LPF band module (U4), and finally fed to theantenna through J1. The T/R switching is implemented by firstly switching CLK0 or
CLK1+CLK2 outputs, and also switching by the RXSW line.

The ADX-S keeps the same 5 LEDs and 3 buttons like ADX. Among them, 4 LEDs are indicating
both band (B1-B4) and mode (WSPR, JS8, FT4 and FT8). The band is shown by blinking at thepower on period, while the mode is shown by a solid LED on. By switching the mode, you also
switch the frequency based on the fixed frequency table. The TX LED is on in both TX andBAND setting statuses. In normal working mode, TX button will enable manual transmitting,while in calibration or BAND setting mode, it is used to confirm and save the current setting. The
major difference of ADX-S from ADX is the band switching way. Now you only can switch bandby pressing and holding the BAND button at power on, instead of holding two buttons in normal
working mode.

Step by Step Kit AssemblyLet’s start to build the kit. It is a kit of all though-hole components, so it is much easier for youreyes. It is recommended you use a fine tipped soldering iron since the pads are not very big. You
will need to supply solder wire by yourself. 0.8mm diameter, 63% Sn and 37% Pb with flux is
recommended.

The kit comes in a plastic container. In the container, you will see main PCB, top cover PCB andbottom cover PCB, a bag of parts for main board, and a bag of parts for 4 LPF band filters andaudio cables.

Let’s start with the main board. For the complete schematic and BOM, please download from
Files section of our group. If you are not yet a member, please subscribe first.
https://groups.io/g/crkits/files/ADX-S
Here are the current PCB photos. Check the date for revisions.

Step 1: Diodes
Bend the leads of diodes like this. From left to right: D9 – 1N5817, D10 – 1N4756A, D6-D8 –1N4148.

Populate D6-D8 as shown. The diodes have polarity so never swap the two leads.

Bend the leads so they will not drop after you turn the PCB for soldering. If your soldering station
supports temperature adjustment, you can adjust to 350C. It is good for both the leaded or
lead-free solder wire. Solder about 3 seconds for each pad. Don’t solder too long time.

Trim the extra leads using a wire cutter.

Populate D9 and solder. Never swap the two leads

Populate D10 and solder. Never swap the two leads.

Step 2: +12V PowerThe photo shows C18 – 10uF. The long lead goes to the pad with + marking. Never swap theleads.

Likewise for C24 – 100uF. Solder C18, C19-100nF, C20-100nF, and C24.

Now let’s do a test to make sure the 12V does exist on VIN pin of XA1 – Arduino Nano module.
Use the DVM for voltage measurement of about 12V. The red probe goes to the VIN pad, while
the black probe goes to ground pad of the BNC connector. Plug in the 12V power supply (center
positive) and measure. Looks good so far.

Step 3: Arduino Nano Module and +5V and +3.3V PowerThe XA1 - Arduino Nano Module serves as the +5V and +3.3V power supply for the main board,
so we will measure them after soldering the Nano module.
Use the pin headers to solder the Nano module on the main board. Populate both 15-pin headers,shorter lead side on the top.

Plug in the Nano module. Make sure the USB port is at the main board edge. Watch out the holes
in the four corners. Solder all 30 pins.

Turn the main board and solder all the leads of the pin headers. Don’t need to trim the extra leads.

Now it is test time. Plug in the 12V power supply (center positive) and measure the voltage on the+ pad of C1 – 100uF with the red probe. 4.93V falls well in the tolerance range of 5V regulator on
the Nano module. Don’t short circuit in this step, or the regulator will be damaged and it is very
difficult to desolder the Nano module.

Measure 3.3V at the left pin of R1 – 1M. Looks good. Don’t short circuit in this step, or the
regulator will be damaged and it is very difficult to desolder the Nano module.

Step 4: Power supply for CD2003
The LC filter on the power supply line is necessary for an analog device like CD2003 receiverchip. The photo shows the L1 – 1uH and L2 – 100uH fixed inductors.

Solder L2, C13-10uF, C1, C16-100uF, C2, C14, C15-100nF. Beware of the polarity of C1, C13
and C16.

You can plug in the 12V power supply (center positive) again and test on pin 15 of U1-CD2003 to
make sure the +5V power supply for CD2003 exist.

Step 5: 5351 Module
Let’s identify color codes of the blue resistors, and pick 2 pcs 10K resistors for this step.

Populate R16, R17-10K as close to the PCB as possible and solder. The 5351 module has a 8-pin
header but it only needs 7 pins, so you will need to trim 1 pin first, and plug in the 7-pin header,again, shorter lead side on the top.

Plug in the 5351 module on the pin header and solder. The chip on the module might be a Chinesecompatible chip with Silicon Labs SI5351, but it works just fine.

Turn the main board and solder the pin headers. Again, don’t need to trim the extra leads.

Let’s proceed to the next step then we can perform test for this module.

Step 6: LEDs and Buttons
Populate all the 1K resistors R5-R9 and R13 and solder.

Populate all the 10K resistors R3, R4, R10, R11, R15 and solder.

The long lead of the red LED goes to the + marking pad of D1.

Populate D1 as close to the PCB as possible and solder.

Populate D2-D5 and SW1-SW3 as close to the PCB as possible and solder.

Now press and hold the SW2-DOWN(CAL) button and plug the power supply until you see bothB1 and B4 LEDs are on. Now you can probe on the test point CAL using a frequency counter orother test instruments like an oscilloscope to see if you can get a 1MHz square wave. Please note,you should clip on the ground first before you probe on the CAL test point. You can perform
coarse calibration here if the frequency has big tolerance. Press SW1-UP(BAND) or
SW2-DOWN(CAL) several times to get 1MHz as close as possible, then press SW3-TX to savethe setting. Please note, the frequency counter on oscilloscope might not be very accurate, andsome frequency counters might need higher amplitude to be able to read something.

Step 7: TX Driver 74ACT244
Populate C22, C23-100nF, and U3-74ACT244 and solder. It is recommended you use a socket.
The new chip comes with the leads not very vertical. You can carefully hold the chip with both
hands and press on a table to make them vertical, so you can easily plug into the socket. Don’t
bend the pins one by one.

Now let’s do a radiation TX test. Turn the board and power on. Use a probe of DVM to touch thecenter pin of Q3-BS170 as a radiation antenna.

Press SW3-TX button to transmit, the nearby receiver will hear a quite strong signal. It is S9 plus
60dB on my TS-590 transceiver. I tuned to 14.074MHz because I have identified from the LED
that the band is 20m and mode is FT8.

Step 8: Complete the TX
Identify the color codes of the rest 4 resistors. R1-1M, R2-4.7K, R12-2.7K, and R14-100R.
Populate them and solder.

Populate Q1-Q3 – BS170 and solder all the leads but the center leads. Don’t touch the leads withyour hands as they are static sensitive.

Make sure your solder iron is well grounded. If not, you can unplug the power of your solder ironand solder the 3 center leads.
Suppose you already have the LPF band filter board ready. It is recommended you plug in the pinheader sockets on the LPF band filter board first to make sure they are matched.

Plug the pin header sockets to the main board and solder.

Populate J1-BNC in place and solder. Please make sure it is not floating as it sets the height
limitation of the board.

Now you have done the assembly of the TX portion. Before the TX test, please make sure the LPF
band filter module and the band setting of Nano is matched. If not, please press and hold
SW1-UP(BAND) button and power on so you can adjust. To adjust the band, you can pressSW1-UP(BAND) or SW2-DOWN(CAL). Remember the default setting is B1 – 40, B2 – 20, B3 –15, B4 – 10. Press SW3-TX to confirm the band setting. Now let’s connect the TX to a RF power
meter or a spectrum analyzer if you have. Make sure you have proper 50 ohm load for the TX. In
my case, I have a -45dB power attenuator inserted between the TX under test and the spectrum
analyzer, so I can measure the RF output and spurious by pressing the SW3-TX button. It looks
good that the RF output is 3.13W and the spurious is -50dBc or so. The RF output varies with thevoltage of the power supply. If your spectrum analyzer reads 35dBm or around, it equals to 3W oraround on a 50 ohm load. Please double check if your overall current is around 600mA.

Step 9: Audio Jacks
Populate C3, C6-100nF, C4, C5-10nF, C7-1uF, CON1-TO SPK and CON2-TO MIC, and solder.

Use an audio signal generator like Sonic Tools App on iPhone to inject audio to CON1-TO SPK
jack. Turn the volume to MAX and it should trigger TX, and the TX LED should be on. When you
perform this test, please make sure the 50 ohm load is still connected to J1-BNC.

Step 10: CD2003 RX
The photo shows C11-560pF, 620pF or 680pF and C25-5.1pF. They look quite similar.

The photo shows the center pin of Q4-BS170 to make sure it is safe from static.

The photo shows the marking of FL1 is facing CD2003.

Populate all the parts L1-1uH, Q4-BS170, FL1-PFB455JR, U1-CD2003, C8,C9,C10,C21-100nF,
C12,C17-10nF, C11-560pF or 620pF or 680pF, and C25-5.1pF and solder to complete thesoldering of the main board.

And the solder side.

Now you can put on the top cover and fasten the screws. Put on the caps of the switches. Red for
SW3-TX.

And put on the bottom cover and fasten with M3x5 standoffs.

Check out the stack of the sandwich and the standoffs to make sure they are right. If you identify
the risks of potential short circuit, please correct them before you apply power supply.

Now, the main board assembly is completed.

Step 11: LPF band filter board
Let’s take 20m LPF band filter board as an example. You have parts like this. For 10 and 15
meters, you will have yellow toroids instead of red.

Wind the toroids based on the BOM, and prepare the pin headers and capacitor leads. The black
toroid has 12 turns, and the red toroids have 10 turns and 7 turns. Remove the enamels of thewires ends before soldering. Some people use sandpapers. Wire length: 1.5 cm per turn plus 5 cm.
For 12 turns, the length is 23 cm.

It is recommended you use the sockets on the main board as support. Populate the parts correctly
and solder. Always remember, C7-100nF is near to the black toroid, and the red toroid with moreturns is in the middle of 3 toroids. Some schematic and BOM of the original design ADX does notmatch the PCB very well, so please double check the ADX-S BOM.

Use a marker pen or label to mark the LPF band filter board.

The completed 20m LPF band filter board looks like this.

Step 12: Box the ADX-S
If your plastic container looks still nice after shipping, you can consider using it as the chassis,
although the sandwich PCBs look great too. If your container is broken, please don’t hate us as it
is not even included in the BOM.
Align the BNC hole location and mark it with a dot. The belt line of the container defines theupper limit of the BNC hole. It is recommended you install the ADX-S boards upside down so you
can easily swap the LPF band filter board.

Drill a small hole, enlarge it gradually so you can protrude the BNC connector. The electric drill
sold by IKEA for screw fastening will do the job here.

Press the board down so you can get correct locations for audio jacks, power supply jack and USB
port on container sides, or the buttons will lift the board. Now mark the locations.

You can mark the USB port location with a short line, drill two holes, enlarge them and join them.
The finished chassis looks like this.

Settings and Calibration
There are two settings: BAND setting and MODE setting. Please note, BAND setting is a designchange from the original design ADX.
Before any TX, please make sure the LPF band filter module and the band setting of Nano ismatched. To adjust the BAND setting, please press and hold SW1-UP(BAND) button and poweron. After LED flashes are done, you can press SW1-UP(BAND) or SW2-DOWN(CAL) to adjust.
Remember the default setting is Band1 – 40, Band2 – 20, Band3 – 15, Band4 – 10. Press SW3-TX
to confirm the band setting.

MODE setting can be made during normal working mode. The LED shows the current MODE,
from left to right: WSPR, JS8, FT4 and FT8. You also change frequency when you change MODE.
The combination of the BAND and MODE setting defines the carrier frequency. For example,
20m band and FT8 mode defines the carrier frequency 14.074MHz. The frequency table in thefirmware is as follows.
(kHz)

40 meter

20 meter

15 meter

10 meter

WSPR

7038.614095.621094.6

28124.6

JS8

7078

14078

21078

28078

FT4

7047.5

14080

21140

28180

FT8

7074

14074

21074

28074

The necessary calibration is the frequency calibration. The oscillating frequency of the 25MHz
crystal on the 5351 module has tolerance, so you can press and hold SW2-DOWN(CAL) buttonand power on to enter the calibration mode in which both B1 and B4 LEDs are lit. You need to
wait for at least 2 minutes to warm up. The standard calibration method is that you probe the test
point CAL with a frequency counter of 1Hz resolution, press SW1-UP(BAND) or
SW2-DOWN(CAL) to adjust to as close to 1MHz as possible, then press SW3-TX to save thesetting. You can exit the calibration mode only by recycling the power.
If you don’t have a frequency counter, you can consider a commercial ham radio transceiver withfrequency accuracy. It is advised to choose 10 meter band to perform the frequency calibration, so
the frequency of the lower bands will be accurate automatically. Let’s say we choose FT8 mode on
10 meter band, so you can tune to 28074kHz USB to monitor. Please make sure you have inserted
10 meter LPF band filter module, and set band correctly. Connect a 50 ohm dummy load of atleast 5 watts or a resonant antenna to the BNC connector. Press SW3-TX button, and you shouldhear a tone of about 1kHz. Use an audio spectrum analyzer app, like Sonic Tools for iPhone, tomeasure the frequency of the tone. If you use an audio cable, you can download fromhttp://www.qsl.net/zl1an/Software/Spectrum3.zip and run on PC. Enter the calibration mode at
power up, and adjust 10 steps in one direction, press SW3-TX to save the setting, recycle thepower and redo the frequency measurement. You will need a few steps to calibrate the frequency
to accurate, so you will hear exact 1kHz tone.

If you have access to the tinySA, you can use the signal generator function to inject 28075kHz,-85dBm together with a fixed attenuator (-30 or -40dB) in between, and monitor the receiverspectrum of ADX-S with WSJT-x or JTDX. Do the calibration at power up, until you see spectrum
like this.

If you have access to the nanoVNA, you can carefully adjust the LPF band filter module, so theRF output is maximized and the harmonics are minimized. The default is not bad, so it is optional
only for the experienced builders.

Use the ADX-S
You can change band by inserting the correct LPF band module to ADX-S first, then setting by the
BAND button at power on. It is critical to insert the LPF band module in the correct orientation,
especially when the bottom cover is not yet installed, or the board could get damaged. The
capacitors on the LPF band module should be on the outer side of the main board. After properly
inserting the band module, you will need to press and hold the BAND button and power on, wait
for a while until you see the current band setting, switch the band by UP or DOWN key, andconfirm the setting by TX button.
Please power the ADX-S with 10-12V. The maximum is 3 Li-Ion battery in series or 12.6V. The
RF output is in QRP range. It draws about 400-600mA. QRP power is good for JS8, FT4 and FT8,
but not quite good for WSPR, as the heat generated by transmitter might cause too much
frequency drift.
You can switch to QRPP range by powering by the USB port at 5V. Never power by both 12V andUSB ports, or the Arduino Nano module will get damaged. The output is about 1/10 of the QRP
power. Less heat is generated in QRPP and much more stable for WSPR. Some people also use
QRPP to pursue more challenging DX communication and it is a lot of fun.

Because ADX-S has built in VOX code, only two audio cables are required to operate. One audio
cable is connected between the jack marked TO MIC or MIC on the ADX-S and the MIC jack on
your sound card. The other audio cable is connected between the jack marked TO SPK or SPK on
the ADX-S and the PHONE or SPEAKER jack on your sound card. If you swap them, you will
see strange lines on the spectrum and the audio output cannot trigger transmitter. The ADX-S
prefers higher audio input level, and you don’t have to worry about over modulation. If theADX-S audio output is too low for your sound card, you can adjust the MIC gain if your system
supports. Take WSJT-x as example, you need to set Radio as None, PTT method as VOX. In themain window, you need to manually choose the correct band, frequency and mode, for correct
logging purpose.

In setting window, choose Radio as None, PTT method as VOX, and click OK to confirm

In main window, manually choose band the mode to display the correct working frequency. For
example, if you choose WSPR and 20m band, the frequency will be 14.095600 and it is the sameas the setting of the ADX-S firmware
To make a successful QSO, you will need to calibrate time and frequency. Type time.is in yourbrowser to make sure your computer time is accurate (1 sec accuracy is fine). Frequency
calibration is recommended before you put the ADX-S in actual QSO. Since the power level is
QRP, you can start with calling a strong station, at least -5dB SNR. Later, you can try to callweaker stations. It is not difficult to achieve DX contacts if you have a full sized antenna.
If your receiver suffers from strong broadcast interference, you can try a tuned antenna likemagnet loop antenna or add a Z-match ATU in between the ADX-S and the antenna. If it does not
help, you can temporarily add a fixed attenuator, say -20dB, in between the ADX-S and theantenna to see if it helps. If it does help, you can consider permanently modifying the receiver
front end to add the attenuator, and add a switch to enable or disable it.

Open Source Code Modification and Update
The Arduino code ADX_S_Vx.ino is open source, so you can modify and compile by yourself.
Normally the Arduino Nano module is pre-programmed and the B1-B4 setting is 40, 20, 15 and10m bands. If you wish to browse the code and customize your own, you will need to download
the Arduino IDE from https://www.arduino.cc/en/software
Remove the 12V power supply first, then connect the Arduino Nano module to the USB port ofyour computer by your TypeC USB cable. The board can be powered by your USB port. You will
choose Arduino Nano in board manager of the Arduino IDE, choose the correct port like COM5,
then choose ATmega328P(Old Bootloader) in processor if your Nano module is blue. Afterloading the code to the Arduino IDE, you can compile and upload the code to the Nano module. If
you get an error message saying the 5351 library is missing, you will need to load the library
Si5351Arduino-master through menu Sketch – Include Library – Add .ZIP Library. You need todownload both the source code and library file in the same place to avoid compatibility issues.

Since the ceramic filter has tolerance on bandwidth and center frequency, it is better that you finetune your own beat frequency, so you can get higher SNR and less interference. In order to do so,
you do a search in the source code and you will find two different beat frequencies. One is 464570,
the other is 447430. For now, 447430 is only for 20 meter band. Adjust them at 500-1kHz step andcompare with the default setting, so you will get the best value for your kit. This is the fun part ofthe open source kit. Optional Modification: If you have a 3pF capacitor, you can replace the
5.1pF and tune to get the best. Normally, the beat frequencies for 3pF should be closer to 455kHz.

CAT Support
CAT is the abbreviation of Computer Aided Tuning. With this function, the PC software can
automatically tune the radio. Although the shipping firmware in the Arduino module might notdirectly support CAT, you can re-program V1.2 firmware or later (Download the source code fromhttps://groups.io/g/crkits/files/ADX-S) to try CAT. The CAT commands support is limited, but itshould work with WSJT-x or JTDX. The implementation of CAT is well considered. The ADX-S
will stay in the original normal mode if CAT commands are not received. Once CAT commands
are received, the ADX-S will turn on both B2 and B3 LED’s to indicate CAT mode. Now, thebuttons are disabled and you can only control by CAT unless you recycle the power.
The firmware detects the CAT frequency and compares with the band set manually. If they are
different band, it can receive but cannot transmit. This is a newly added protection to the finals.
Again, never power by both 12V and USB ports, or the Arduino Nano module will get damaged.
Since USB port is always in use in CAT mode, either you can live with QRPP with USB 5V, or
you can consider cutting a PCB trace so you can power by both 12V and USB ports and transmit
at 3-5W QRP level.

WSJT-x or JTDX radio settings: Kenwood TS-2000, Correct Serial Port, Baud Rate 115200, CAT,
others are default. Press Test CAT to confirm it is working. You still need audio to trigger TX, so
Test PTT should not work.
Known frequency sync issue: You might see the red background in frequency display area to showout of sync at the beginning. You can switch MODE and switch back to sync.
If the CAT is disconnected when you transmit, it might be RFI and you can consider using someferrite cores on the USB cable, or move away from the antenna.
Normally, you don’t need to calibrate the frequency again after re-programming the Arduino.

Modifications
It is recommended that you apply the following receiver modifications to improve decoding whilebuilding. You can also do it after your assembly. The benefit of the modifications: Add a button controlled fixed attenuator in the RX front end
 Enable AGC of CD2003
 Reduce the amplitude of BFO and change firmware settings to improve the RX sensitivity
 You can also listen to AM broadcast in CAT mode (high impedance headphone is required)
The part list for the modification:
 2 pcs 1N4007 diode 1 pcs 10uF capacitor
 1 pcs red LED (3mm and 5mm are both okay)

The red LED will reduce the amplitude of CLK2 (BFO) and also indicate the existence of CLK2
(BFO). The 10uF will enable AGC of CD2003. The 1N4007 in place of R13 is used as anattenuator in the RX front end.

The 1k resistor is originally used for R13. Once you press both UP and DOWN buttons, thefirmware will toggle D5 pin and it will act as a switch for ATT.
You will need to update firmware to V1.2RX or later to enable all the features. Download thefirmware from https://groups.io/g/crkits/files/ADX-S and update by Arduino IDE (see above)
How to use:
SW1 (UP)

SW2 (DOWN)

SW3 (TX)

Both SW1 andSW2Normal Mode

Mode change

Mode change

TX

ATT toggle

CAT Mode

-5kHz

+5kHz

AM mode toggle(See the red LED
added in thismod to tell if the
BFO is on or off)

ATT toggle

You will need to add your AM broadcast frequencies into the frequency list of your WSJT-x.

From 4 to 7-Band Upgrade
The standard 4 bands are 40, 20, 15 and 10m. Now we are offering an upgrade kit to add 30, 17
and 12m. The firmware needs to be updated to V1.3 or higher. In the new firmware, you need to
add the receiver modification as well, as explained in the previous chapter, or the receiversensitivity will be degraded. Fortunately, the upgrade kit will include the modification parts.
The frequency table in the firmware is updated as follows.
(kHz)

40 m

30 m

20 m

17 m

15 m

12 m

10 m

WSPR

7038.610138.7

14095.6

18104.621094.6

24924.6

28124.6

JS8

7078

10130

14078

18104

21078

24922

28078

FT4

7047.5

10140

14080

18104

21140

24919

28180

FT8

7074

10136

14074

18100

21074

24915

28074

The blinking LEDs at power up represent bands like this.
B1 – 40m No change
B1&B2 – 30m New
B2 – 20m No change
B2&B3 – 17m New
B3 – 15m No change
B3&B4 – 12m New
B4 – 10m No change
The BOM of the band filters are updated as follows.

Further readings
This document will be updated in the folder, together with other documents like schematic, part
list and source code. If you are not yet a member, please subscribe first.
https://groups.io/g/crkits/files/ADX-S
or, scan this QR code with your cell phone.

Reference and Acknowledgement
Barb, WB2CBA
https://antrak.org.tr/blog/adx-arduino-digital-transceiver/https://github.com/WB2CBA/ADX
Burkhard Kainka, DK7JD
https://www.elektronik-labor.de/HF/FT8QRP.html
http://elektronik-labor.de/HF/SDRtxFSK2.html
JE1RAV
https://github.com/je1rav/QP-7C
JA9TTT
https://ja9ttt.blogspot.com/2018/07/short-wave-radio-design-2.html
QRPGUYS
https://qrpguys.com/qrpguys-digital-fsk-transceiver-iii
Jason Mildrum, NT7S
https://github.com/etherkit/Si5351ArduinoPeter Parker, VK3YE
https://www.youtube.com/watch?v=FGH0kUvkqX0
BD4AHS, BG7IKK, BH3RQW, BD6EC, BG7IBQ, BD8TE, BG8NSK, BA7MPY, BI4TMT,
BA1RB and more…