At a time once we all carry smartphones that may stream high-definition films into our arms, the romance of listening to old-school analog broadcast radio however endures. For some it’s a break from the cookies, contracts, and phrases of service that lurk behind each on-line exercise. For people like me although, an enormous a part of the allure is the fun that comes from pulling in a sign from 1000’s of kilometers away—and doing it the time-honored means: with an understanding of atmospheric circumstances, antennas, and electronics.
This pastime of utilizing diversified information and expertise to tug in very distant stations is known as DXing. At the moment, digital sign processing makes it doable to place stupendously succesful receiver electronics into a cost-effective and really transportable package deal, so there’s by no means been a greater time to be a DXer. And amongst these high-performance electronics, there’s arguably no higher instance than the TEF6686 chip, launched in 2013 by NXP Semiconductors and revised a number of occasions since then.
The chip has been very profitable in automobile radios, partly due to its low price and excessive audio constancy, however particularly due to its astoundingly excessive sensitivity and selectivity to radio indicators. The TEF6686 can obtain each FM and AM, and will be configured to accommodate the totally different bandwidths utilized by stations in several nations. It will probably additionally decode a broadcast station’s digital RDS (Radio Information System) feed, which when current accommodates repeatedly up to date data such because the title of a track at present taking part in.
The chip’s excessive selectivity and sensitivity outcomes from its adept use of software-defined-radio and digital-signal-processing (DSP) applied sciences to filter out adjoining frequencies. This allows reception of very weak indicators that may in any other case be drowned out by close by broadcasts. The chip has confirmed irresistible to radio lovers, attracted by options of the chip that go far past what is required by a automobile radio. It will probably obtain not simply the industrial broadcast bands, but additionally the shortwave and long-wave bands. The chip may also present instantaneous signal-strength data.
The TEF6686 chip will be present in a helpful module [top left] that gives electromagnetic shielding and a through-hole interface. An ESP32-based improvement board [top middle] controls the module and performs sign processing. An LCD display shows the consumer interface, which is managed utilizing buttons and rotary controls [bottom left]. James Provost
As an energetic radio beginner (PE5PVB) within the Netherlands, I turned intrigued by the enthusiastic evaluations I began seeing of the TEF6686. Through the COVID lockdown of 2020, I began designing a totally open-source tuner that may wring the best doable efficiency out of the chip for FM DXers. My enthusiasm grew when I discovered TEF6686 tuner modules on AliExpress. These comprise a TEF6686 chip in a DIY-friendly package deal, appropriate for through-hole soldering (the TEF6686 itself is a surface-mounted chip), and with radio-frequency shielding to assist reduce interference. These modules are low-cost—they’ll typically be discovered for round US $25.
I quickly settled on a configuration consisting of two printed circuit boards linked by ribbon cable. There’s a major board, which accommodates the TEF6686 module and the microcontroller, and a show board, with a small OLED show and the switches and encoders that management the radio. I evaluated varied variations of Arduino-compatible microcontrollers, and located that the majority have been all too gradual and had inadequate flash reminiscence.
The microcontroller wants a variety of flash as a result of it should retailer not solely all of the firmware that operates the radio, which is shipped to the TEF6686 after each boot up, but it surely additionally should retailer the totally different fonts for the show, varied photos, in addition to a database of North American name indicators and of Canadian provinces and U.S. states (this data, coupled with different capabilities, allows the consumer to instantly see the decision signal and state the place the transmitter they’re receiving is positioned). Finally I settled on a variant of the ESP32 module, that had the velocity and reminiscence capability I wanted, however that also may very well be programmed utilizing the favored Arduino IDE.
In early 2021, I launched on GitHub an preliminary model of the firmware and schematics for different DIYers. I additionally was involved with a DIY Webshop within the Netherlands, Staff AmateurRadioShop.nl, which nonetheless sells a package of an earlier model of the radio. Within the fall of 2021, I created a second model with a so-called human-machine interface (HMI) show fromNextion. This show has a built-in processor, so I may hand off extra user-interface duties from the ESP32. This sped up the radio significantly, and in addition opened up some new graphical prospects. On this model I additionally added Wi-Fi, which allows connection to on-line assets similar to XDR GTK, a consumer interface that enables for nice pc management of the radio tuner, and RDS Spy, which decodes the RDS information into usable data in actual time. If you wish to construct this model your self, you’ll need to have your personal printed circuit boards made up. However Gerber information, a invoice of supplies, and development suggestions can be found on my Web page at www.pe5pvb.nl. Soldering it collectively will take about 2 hours.
The show and controls are immediately linked to the microcontroller utilizing general-purpose enter/output pins, whereas the TEF6686 receiver chip is managed by way of instructions despatched over a serial I2C interface. The left and proper channels are amplified and handed to straightforward RCA audio sockets.James Provost
For many who don’t really feel like making a package, there’s an possibility for you, too. Early in 2022, a Chinese language hobbyist, Justin Peng, contacted me to say he had constructed a transportable model out of my design. That summer season, the primary variations based mostly on this design of his appeared on AliExpress. Within the months after that, curiosity in my open-source venture exploded, and the radio was adopted by FM DXers worldwide.
In 2023, I used to be contacted by a Czech hobbyist, Marek Farkaš, who invited me to a gaggle he was establishing on the Discord social platform with different hobbyists dedicated to engaged on and enhancing software program for this radio. On this crew we now have a graphic designer, some people who’re specialists in RDS, others who’re very expert programers, and a Chinese language fellow who wrote a model appropriate to be used by {hardware} designers seeking to make a radio for the AliExpress market. Collectively, we fully reviewed the code and added a smoother graphical design, extra connectivity, selectable languages, and different enhancements.
I’m very grateful to this crew for all their arduous work to make this open-source radio maybe the highest-performing radio of its variety, ever. I hope you’ll strive it out, and even in the event you don’t spend your time attempting to find distant stations, rediscover the enjoyment of high-quality FM radio broadcasting!
This text seems within the December 2024 print difficulty as “The Final SDR Receiver.”