From idea to kit: Adam introduces the Arduino Digital Modes HF QRP Transceiver (ADX-S) kit

Many thanks to Adam (BD6CR) who shares the following guest post about his latest project:

From Open Source Project ADX to Kit ADX-S

by Adam (BD6CR)


Original Design: WB2CBA

Modification and Kitting: BD6CR

I knew Barb, WB2CBA from his uSDX design a few years ago and I introduced both DL2MAN and his designs in my blog. So, when I came across the ADX – Arduino Digital Xcvr a few months ago, I immediately ordered both the ADX (through hole) and the ADX UNO (surface mount) PCB samples.

I started building the ADX UNO and put it in a dental floss case and made a few contacts on park bench. However, the soldering is too much for my eyesight. So, I turned back to the ADX because I don’t need to solder any SMD parts, since both the M328P and SI5351 are module based. I could build the project in 3 hours and it worked the first time.

However, I felt unsatisfied with the strong BCI since the CD2003 radio receiver chip was connected as a direct conversion receiver. JE1RAV mentioned in his QP-7C modification project that he tried JA9TTT’s idea to build a superhet SSB receiver with the TA2003 or CD2003, so I tried and it worked very well. I have decided to name the new circuit as ADX-S, where S stands for Superhet.

I shared the great news with Barb and he encouraged me to carry the flag to make it a kit, since my design D4D was his first digital radio and he loved it.

You can refer to Barb’s page on ADX here.

My hardware modification can be outlined in this schematic. I have added an FL1, PFB455JR ceramic filter by Murata and a C25 coupling capacitor from CLK2 of SI5351 module. The RX audio comes from pin 11 instead of pin 4.

I modified it by cutting two traces on the ADX PCB and it looked ugly, so I redrew the PCB.

The top and bottom panels are redesigned to look better and be easier to build.

Photo: Mr. Han, BH3RQW

I was a student of Computer Science, but never worked as a programmer. It was great fun to modify the code to look concise and work efficiently. The freedom is on your side, you change the code and even the way you operate the radio. For example, I changed the way to switch bands because it is not easy to press both buttons at the exactly same time. You can do it as well since the code is open source.

About 3 dozen local hams built the kit and provided feedback to me. Overall they were happy. I made a few changes to the details and I hope you will build it with confidence.

It is easy to tell the difference between ADX-S and ADX in terms of RX performance because you can see much less BCI and weak signals are clearer in spectrum. Moreover, the comparison with FT-450 by a local ham friend surprised me. The SNR looks better, but the background noises remain at the same level.

RX Comparison by Mr. Qin, BD4AHS

Since the front end is not tuned, you will likely suffer very serious BCI if you live very near to a radio station. If it happens, I would recommend that you connect a Z-match or similar tuned ATU in between ADX-S and antenna.

My field operation at a park seems very promising. The only complaint is the size of the board – 97 mm by 97 mm seems still a bit bulky if you really like handy operation. The transmitter puts 3.5 watts on 20m or lower with high efficiency so you will have more hours of operation. You don’t have to worry about the potential interference to others since it is a single sideband signal and the spurious suppression is good enough.

Let’s wait for the report from reviewers and beta testers and allow me to write a kit assembly manual. Stay tuned and I hope you will soon enjoy the fun of building and operating the ADX-S!

Click here to view the ADX-S manual [PDF]. 

Update: VK3YE’s Video Review

Peter (VK3YE) recently posted this video review of the ADX-S:

Click here to view on YouTube.

13 thoughts on “From idea to kit: Adam introduces the Arduino Digital Modes HF QRP Transceiver (ADX-S) kit”

    1. I would love to, but I simply don’t have time at present to even build it. Thinking about doing it this summer, though for kicks.

      It’s a very cool little project!

      Are you considering it?


      1. I would if I didn’t already have a QDX. I wouldn’t mind building one though, so if you want one and don’t want to build it, I’m here for you…


        1. So funny. We’re kindred spirits. I find the building part to be the most fun part! I’d offer you the same service, OM!

      1. Alan, you might want to shoot Adam an email (his contact info is at the top of the post). I think orders are open for the kit!

  1. Cool idea. I’ve never done digital, but I’d like to. And this rig is right up my alley. Might have to bite.

    Thanks for the post!

  2. Has anyone tried putting an RF preamp in front of the CD2003? chip? I have a rather small antenna and I’m not sure the signal would be good enough for this transceiver. I bought 5 radio chips and will play around with them to see how they do. Then, if I can find some, I’ll incorporate the 455 KC resonator.

    A simple J310 cascode amp is what I’ll add.



  3. Hola gente linda.
    Digo así, gente linda, porque me encanta lo que están haciendo y compartiendo.
    Yo ántes hacía lo mismo y me divertía muchísimo también. Ahora ya no puedo.
    Les deseo lo mejor y muchos éxitos en sus proyectos. Solo tengo una duda que paso a plantearles… ¿Cuál es la razón por la que utilizan Arduino?
    ¿Comandos?, Ajustes de frecuencia y modos?
    Gracias por satisfacer mi curiosidad.

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