At a time after we all carry smartphones that may stream high-definition films into our palms, 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 folk like me although, a giant a part of the allure is the joys that comes from pulling in a sign from 1000’s of kilometers away—and doing it the time-honored approach: with an understanding of atmospheric situations, antennas, and electronics.
This pastime of utilizing different information and expertise to tug in very distant stations is named DXing. In the present day, digital sign processing makes it doable to place stupendously succesful receiver electronics into a cheap and really transportable bundle, 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 might be configured to accommodate the totally different bandwidths utilized by stations in numerous international locations. It will probably additionally decode a broadcast station’s digital RDS (Radio Data System) feed, which when current comprises constantly up to date info such because the title of a music at present enjoying.
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 will 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 info.
The TEF6686 chip might 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 lively radio newbie (PE5PVB) within the Netherlands, I grew to become intrigued by the enthusiastic evaluations I began seeing of the TEF6686. Through the COVID lockdown of 2020, I began designing a very open-source tuner that will 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 bundle, 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 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 primary board, which comprises 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 numerous variations of Arduino-compatible microcontrollers, and located that the majority have been all too gradual and had inadequate flash reminiscence.
The microcontroller wants a number of flash as a result of it should retailer not solely all of the firmware that operates the radio, which is distributed to the TEF6686 after each boot up, however it additionally should retailer the totally different fonts for the show, numerous 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 right away 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 released on GitHub an preliminary model of the firmware and schematics for different DIYers. I additionally was involved with a DIY Webshop within the Netherlands, Team AmateurRadioShop.nl, which nonetheless sells a kit 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 likewise opened up some new graphical potentialities. On this model I additionally added Wi-Fi, which allows connection to on-line sources equivalent to XDR GTK, a consumer interface that permits for high-quality pc management of the radio tuner, and RDS Spy, which decodes the RDS information into usable info in actual time. If you wish to construct this model your self, you’ll need to have your individual printed circuit boards made up. However Gerber recordsdata, a invoice of supplies, and building ideas can be found on my Web site at www.pe5pvb.nl. Soldering it collectively will take about 2 hours.
The show and controls are straight linked 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 straightforward RCA audio sockets.James Provost
For many who don’t really feel like making a equipment, there’s an choice 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 season, the primary variations primarily based on this design of his appeared on AliExpress. Within the months after that, curiosity in my open-source undertaking 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 bettering software program for this radio. On this staff 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 utterly reviewed the code and added a smoother graphical design, extra connectivity, selectable languages, and different enhancements.
I’m very grateful to this staff for all their laborious work to make this open-source radio maybe the highest-performing radio of its sort, ever. I hope you’ll strive it out, and even for those who 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 subject as “The Final SDR Receiver.”
