At a time after we all carry smartphones that may stream high-definition films into our arms, the romance of listening to old-school analog broadcast radio nonetheless 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 appeal is the joys that comes from pulling in a sign from hundreds of kilometers away—and doing it the time-honored approach: with an understanding of atmospheric situations, antennas, and electronics.
This pastime of utilizing diversified data and abilities to drag in very distant stations is named DXing. At this time, digital sign processing makes it potential to place stupendously succesful receiver electronics into a cost-effective and really moveable 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 value and excessive audio constancy, however particularly due to its astoundingly excessive sensitivity and selectivity to radio alerts. The TEF6686 can obtain each FM and AM, and will be configured to accommodate the totally different bandwidths utilized by stations in several international locations. It may possibly 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 music at the moment 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 permits reception of very weak alerts that might in any other case be drowned out by close by broadcasts. The chip has confirmed irresistible to radio fans, attracted by options of the chip that go far past what is required by a automobile radio. It may possibly 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 growth board [top middle] controls the module and performs sign processing. An LCD display shows the person interface, which is managed utilizing buttons and rotary controls [bottom left]. James Provost
As an lively radio newbie (PE5PVB) within the Netherlands, I grew to become intrigued by the enthusiastic evaluations I began seeing of the TEF6686. In the course of the COVID lockdown of 2020, I began designing a very open-source tuner that might wring the very best potential 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 decrease interference. These modules are low cost—they’ll usually be discovered for round US $25.
I quickly settled on a configuration consisting of two printed circuit boards related by ribbon cable. There’s a foremost 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 had been all too gradual and had inadequate flash reminiscence.
The microcontroller wants numerous 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 photographs, in addition to a database of North American name indicators and of Canadian provinces and U.S. states (this information, coupled with different capabilities, allows the person to right away see the decision signal and state the place the transmitter they’re receiving is situated). Ultimately 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 might hand off extra user-interface duties from the ESP32. This sped up the radio significantly, and in addition opened up some new graphical potentialities. On this model I additionally added Wi-Fi, which allows connection to on-line assets corresponding to XDR GTK, a person interface that permits for superb laptop management of the radio tuner, and RDS Spy, which decodes the RDS knowledge 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 recordsdata, a invoice of supplies, and development ideas 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 related to the microcontroller utilizing general-purpose enter/output pins, whereas the TEF6686 receiver chip is managed through instructions despatched over a serial I2C interface. The left and proper channels are amplified and handed to plain 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 conveyable model out of my design. That summer time, the primary variations primarily based on this design of his appeared on AliExpress. Within the months after that, curiosity in my open-source mission 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 bunch he was establishing on the Discord social platform with different hobbyists dedicated to engaged on and enhancing software program for this radio. On this group we now have a graphic designer, some of us 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 trying 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 group for all their onerous 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 when you don’t spend your time trying to find distant stations, rediscover the enjoyment of high-quality FM radio broadcasting!
This text seems within the December 2024 print concern as “The Final SDR Receiver.”
