The allure of tuning in to analog broadcasts remains timeless, even as we now wield devices capable of streaming high-definition films at our fingertips. Beyond the digital veil of cookies, contractual fine print, and service agreements, there lies a welcome respite for those seeking a reprieve from the virtual world’s subtleties. While some may find thrill in short-range transmissions, for enthusiasts like myself, the true excitement lies in successfully snatching signals from distant locations – hundreds of kilometers away – using traditional methods that require a deep comprehension of atmospheric conditions, antenna design, and electronic principles.
The hobby of using a variety of skills and knowledge to communicate with distant locations via radio signals is commonly referred to as amateur radio DXing. As we converse, advancements in digital signal processing enable the development of remarkably successful receiver electronics in a compact and affordable package, making it an unprecedentedly exciting era for DX enthusiasts. Among the most elite examples of high-performance electronics stands the flagship product, introduced by its creators in 2013 and subsequently refined numerous times since its inception.
The chip has been extremely profitable in automobile radios, largely owing to its low cost and exceptional audio consistency, but most notably due to its astonishingly high sensitivity and selectivity to radio signals. The TEF 6686 radio module is capable of receiving both FM and AM signals, with adjustable settings allowing it to accommodate diverse frequency band widths used across various global regions. The unit could also decode a broadcast station’s digital Radio Data System (RDS) feed, which currently supports real-time updates such as the title of a track currently playing.
The chip’s exceptional selectivity and sensitivity stem from the precise application of software-defined radio and advanced digital signal processing technologies, which enable it to effectively filter out adjacent frequencies. This feature allows for the reception of extremely faint signals that would otherwise be overwhelmed by nearby transmissions. The chip has proven irresistibly alluring to radio enthusiasts, drawing them in with features that exceed the standard offerings of an automotive radio. The device could potentially capture signals not just from the industrial broadcast bands, but also from the shortwave and long-wave frequency ranges. The chip potentially offers real-time signal-strength information.
The TEF 6686 chip is often embedded in a versatile module located at the top-left corner, which provides electromagnetic shielding and a convenient through-hole interface. The ESP32-based improvement board situated in the top middle portion effectively governs the module’s functionality and undertakes signal processing tasks. The user-friendly interface of the LCD display screen is easily navigated using intuitive buttons and a convenient rotary control located at the bottom left. James Provost
As a newly minted radio enthusiast in the Netherlands, my curiosity was piqued by the fervent reviews surrounding the TEF6686. During the COVID-19 pandemic’s widespread lockdowns in 2020, I initiated development of an openly sourced tuner capable of extracting the optimal performance from the chip for FM enthusiasts engaged in DXing activities. As I explored the vast online marketplace of AliExpress, my excitement surged upon stumbling upon the TEF6686 tuner modules, an innovative find that piqued my curiosity and sparked a desire to learn more. These bundles include a TEF6686 chip in a user-accessible configuration, suitable for through-hole soldering, as the TEF6686 is a surface-mount device, and feature radio-frequency shielding to minimize electromagnetic interference. These modules typically offer excellent value at a low cost, often available for around USD 25.
Within a short timeframe, I opted for a setup comprising two printed circuit boards interconnected via a ribbon cable. The principal board houses the TEF6686 module alongside the microcontroller, while the showcase board features a compact OLED display accompanied by switches and encoders controlling the radio’s functionality. After evaluating various versions of Arduino-compatible microcontrollers, I found that most had significant drawbacks, including slow performance and insufficient flash memory.
The microcontroller requires storage of flash memory to accommodate the firmware that controls the radio, which is downloaded to the TEF6686 after each boot-up, as well as storing various fonts for the display, diverse images, and a database of North American flight identifiers, including Canadian provinces and U.S. states? The states of this information, combined with diverse capabilities, enable consumers to instantly recognize the transmission signal and pinpoint the location of the transmitter they’re receiving from. After evaluating my options, I chose the module offering the required velocity and reminiscence capabilities. Although this choice could also be programmable using my preferred dot notation.
In early 2021, we released a preliminary model of the firmware and schematics for DIY enthusiasts. I had also been in contact with a Dutch webshop that still offered an older version of the radio for sale. By autumn 2021, I designed a novel model featuring an intuitive human-machine interface (HMI) display. With this show featuring an integrated processor, I can effectively delegate supplementary user interface responsibilities away from the ESP32. This enhancement substantially accelerated the radio’s performance, while also unlocking new graphical possibilities. This model includes an added Wi-Fi feature, enabling seamless connectivity to online sources such as XDR GTK, a user-friendly interface that streamlines PC control of the radio tuner, and RDS Spy, which real-time decodes RDS information into usable data. If you desire to build this model independently, you will need to commission custom printed circuit boards. The Gerber information, a comprehensive invoice of supplies, and innovative building ideas are readily accessible on. The soldering process, when completed in its entirety, is estimated to require around two hours.
While the show and controls are directly linked to the microcontroller using general-purpose input/output pins, the TEF6686 receiver chip is controlled via instructions transmitted over a serial I2C bus. The stereo audio signal is routed through separate amplifier stages, ultimately terminating at standard RCA audio connectors.James Provost
While some may not be inclined to invest in equipment, there’s still a viable option available. In the early stages of 2022, I received an unexpected message from Justin Peng, a dedicated Chinese language enthusiast and amateur inventor. He was eager to share his remarkable achievement: a portable prototype inspired by my original design. During that sweltering summer, the main differences stemmed from this innovative design of his. As the news of our open-source initiative spread, global interest surged, and amateur radio enthusiasts around the world eagerly adopted the FM receiver.
In 2023, I received an invitation from a Czech enthusiast to join his burgeoning community of like-minded individuals on a platform dedicated to collaborating and refining open-source software for amateur radio enthusiasts. We possess a diverse team consisting of a graphic designer, subject matter experts in RDS, skilled programmers, and a colleague from China who developed a model tailored for hardware designers seeking to create radios for the AliExpress marketplace. Together, we comprehensively scrutinized the code, introducing a more refined graphical interface, expanded connectivity options, language selection capabilities, and various upgrades to further optimize performance.
I am deeply thankful to this exceptional team for their tireless efforts in creating an open-source radio that has the potential to become the most outstanding and high-performing radio of its kind, ever. Will you take on the challenge and revive the thrill of discovering hidden gems, even for those who no longer make an effort to tune in to high-fidelity FM radio broadcasts?
