From Open Source Project ADX to Kit ADX-S
BD6CR @ CRKits.COMOriginal Design: WB2CBAModification and Kitting: BD6CRI 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 ADX – Arduino Digital Xcvr a few months
ago, I immediately ordered both ADX (through hole) and ADX UNO (surface mount) PCB
samples. I started building ADX UNO and put into a dental floss case and made a few contacts onpark bench. However, the soldering is too much for my eyesight. So, I turned back to 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 withthe 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 asuperhet SSB receiver with 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 share the great news with Barband he encouraged me to carry the flag to make it a kit, since my design D4D was his first digitalradio and he loved it.
You can refer to Barb’s page on ADX https://github.com/WB2CBA/ADX. My hardware
modification can be outlined in this schematic. I have added FL1, PFB455JR ceramic filter by
Murata and C25, a coupling capacitor from CLK2 of SI5351 module. The RX audio comes frompin 11 instead of pin 4.

I modified 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 easier to build.

Photo: Mr. Han, BH3RQW
I was a student of Computer Science, but never worked as a programmer. It was great fun tomodify the code to look concise and work efficiently. The freedom is on your side, you change thecode and even the way you operate the radio. For example, I changed the way to switch band
because it is not easy to press both buttons at the exactly same time. You can do it as well since thecode is open source.
About 3 dozens of 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 with more 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 withFT-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 aradio 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 enjoy the fun of building and operating the ADX-S!