Category: Other

Creating a Software Defined Radio from Tiny Tapeout Chips

Tiny Tapeout is a project that allows anyone to design and fabricate custom open ASIC silicon at a low cost by combining hundreds of projects from different people on the same chip. Each design on the the chip is freely available to use by others.

Over on Hackster.io, we've seen a post where Sylvain Munaut used two of these Tiny Tapeout chips to create a software defined radio.

On the Tiny Tapeout 6 chip, Sylvain discovered that Tiny Tapeout customer Carsten Wulff had implemented an 8-bit ADC on the chip. Then, on the Tiny Tapeout 7 chip, Sylvain found that Kolos Koblász had implemented an RF mixer. So, he decided to combine the two Tiny Tapeout chips together to build a software defined radio.

The entire build consists of the two Tiny Tapeout chips, a Glasgow Interface Explorer (USB interface), and a GNU Radio flowgraph to demodulate and display the signals received.

In his YouTube video, Sylvain demonstrates the software defined radio in action, showing that it has 2 MHz of bandwidth and is capable of receiving FM signals.

SDR with custom silicon ! Combining TinyTapeout projects.

Using an EFR32 IoT Microcontroller Transceiver as an SDR

Thank you to Joshua R. for writing in and sharing some links on how an EFR32 microcontroller can be used as a software-defined radio. The EFR32 is a microcontroller designed for IoT applications such as Zigbee, Z-Wave, Thread, Bluetooth. Of interest to us is that the EFR32 has a special mode that allows for the demodulator/modulators to be switched off and instead allowing for raw IQ data to be transferred from the chip.

An example of the EFR32 being used as an SDR has been provided by OH2EAT/tejeez and can be found in this write-up and in his 'geckokapula' GitHub repo. This MIT-licenced repo provides hardware schematics and software for creating a full handheld FM, AM, USB, LSB, and CW receiver with FM, CW, USB, and LSB transmit capabilities. It also supports a 12 kHz waterfall display. The tuning range is nearly 13.2 MHz to 2.9 GHz, but there are some gaps.

This Knowledge Article by Silicon Labs also explains the SDR mode of the EFR32.

This is an interesting low-cost chip, but the limiting factor appears to be the small bandwidth.

An EFR32 SDR by Tejeez/OH2EAT
An EFR32 SDR by Tejeez/OH2EAT

SignalSurge – An open source bandpass filter with selectable LNA for the VHF and UHF bands

Thank you to Rodrigo Freire for writing to us and sharing his project called 'SignalSurge'. The SignalSurge project started when Rodrigo discovered that adding an RTL-SDR Blog FM Bandstop filter to his Yaesu FT-991A significantly improved his reception in the 2-meter band.

An FM bandstop filter can improve reception by reducing the power of strong broadcast FM signals, which can overload the front end of radios, causing the desensitization of signals on other bands.

This finding led Rodrigo to design SignalSurge, a bandpass filter for VHF and UHF bands, with a selectable LNA. The design includes selectable 2m and 70cm bandpass filters, a selectable 15dB LNA, automatic LNA shutdown when the radio is transmitting, and ESD protection. A 50W relay gives the ability to select between filters and switch the LNA in or out.

The design is entirely open source and available on the SignalSurge GitHub.

SignalSurge Schematic
SignalSurge Schematic

Creating an SDR from a TEF6686 Car Radio FM/AM Chip

A recent IEEE Spectrum article details how hobbyist PE5PVB has repurposed an NXP TEF6686 automotive FM/AM tuner chip into a software-defined radio with a tuning range of 65 MHz - 108 MHz and 144 kHz - 27 MHz.

PE5PVB developed custom open-source firmware for TEF6686 dev boards, allowing them to tune beyond their original design frequency range. He then went on to develop a version that included a screen. Eventually, the Chinese manufacturers caught on to the potential of the design and are now producing a full handheld version that is available on Aliexpress at a current sale price of US$61.26.

Reviews of the product are all positive, and it appears to be one of the best choices for a portable handheld DXing radio.

A TEF6686 based SDR available on Aliexpress.
A TEF6686 based SDR available on Aliexpress.

Hackaday Supercon 2024: Microcontrollers Are Just Radios in Disguise

Thank you to RTL-SDR.COM reader David for letting us know about an excellent talk from Charles Lohr (@cnlohr) at the 2024 Hackaday Supercon about turning microcontrollers into radios by abusing their output GPIOs to create RF generators.

This talk explores ways to leverage every cycle of underpowered microcontrollers to get them doing the work of parts ten times their price, including operations normally done with dedicated radio hardware.

This is a concept we have seen quite often before in projects like RPiTX and Osmo-FL2K which turns a Raspberry Pi and cheap VGA adapter respectively, into an arbitrary RF signal transmitter with no transmit components required.

In his talk Charles Lohr takes this concept further, showing how almost any microcontroller like an ATTiny85, ESP8266, CH32v203, and ESP32-S2 can be turned into a transmitter. In the talk, Charles shows how he used the I2S bus on an ESP8266 to transmit NTSC color video to a TV and transmit LoRa via his LoLRa software. He then notes that he was able to use the ESP32-S2 to transmit LoRa over 2.5 miles away.

Finally, Charles shows how the CH32v203 microcontroller can also be used as a receiver. With some code he wrote he is able to display the received signal on an FFT computed directly on the CH32v203, and even have a web interface to tune to specific frequencies and playback AM audio.

Hackaday Supercon 2024 - Microcontrollers Are Just Radios in Disguise - Charles Lohr

CNLohr's own YouTube video on the topic is also an excellent overview.

How far can I broadcast LoRa packets WITHOUT a radio? - LoLRa

NickStick Design Releases the RF PowerSnitch USB-C Version

Recently Majodi from NickStick Design wrote in and wanted to share with us some updates to the 'NickStick RF PowerSnitch' which we previously posted about in 2021. The PowerSnitch is a device that can be used to gain a quick insight into RF power levels. This is useful to help prevent exposing your expensive and sensitive RF equipment, like an SDR or VNA, to excessive power levels that could destroy it.

The device uses three LEDs to tell you the power level. Green means you have a safe power level, caution is yellow and danger is red. Yellow is set to around 0 dBm.

The RF PowerSnitch is available on Tindie or lectronz for US$29.50.

In a recent re-release, they replaced the micro USB port with a USB-C power port. They write:

Today, NickStick Design, an electronics design company for Makers, is excited to announce the launch of the RF Power Snitch USB-C, the newest version of its popular RF Power Snitch device. This updated model replaces the micro-USB port of the
original with a USB-C port, making it more versatile and future-proof for today’s connectivity needs.

“Our original RF Power Snitch saved many VNA devices from destructive power levels” Majodi of NickStick Design said. “With the RF Power Snitch USB-C, we’re excited to provide users with an upgrade which aligns with modern connectivity standards.

Over the years many more products in the RF domain became accessible to radio enthusiasts. RF Power Snitch is a valuable companion tool for checking the potentially destructive power of the signals one would want to feed to their equipment. Because, although tools like the TinySA, NanoVNA or SDR devices are extremely affordable today, for a maker it is still an investment worth protecting.

That’s why our goal was to develop a low-cost companion device that can help makers and experimenters (especially beginners) in the RF domain to gain insight in the power levels of a signal before hooking things up to their valuable test equipment. As an extra to this we also made it possible to attach an MCU for doing power readings and plotting.

Website: https://powersnitch.nickstick.nl

The RF PowerSnitch by NickStick Design
The RF PowerSnitch by NickStick Design

Videos from the Software Defined Radio Academy 2024 Conference Now On YouTube

Videos of talks from the Software Defined Radio Academy 2024 (SDRA'24) conference have recently been uploaded to YouTube. SDRA'24 was hosted primarily as an online conference but was also held physically at the German Friedrichshafen HAMRADIO conference in June 2024.

The talks are slowly being released on YouTube with eight talks released so far on their SDRA'24 playlist. Make sure you subscribe to their YouTube channel to be notified when more talks are released.

Some of the talks of interest that are released include:

  • FobosSDR by RigExpert
  • CW Bandwidth Optimization
  • DMR Tier III base station - TRX in software defined radio
  • High Res Propagation Measurements

You can find the titles of talks of videos that haven't been released yet on the SDRA'24 programme page. Some interesting yet to be released talks include:

  • High Resolution Propagation Measurements Using a WSPRSONDE-8 beacon and a RX888 SDR
  • GNU Radio Project Update
SDRA'24 - 01 - Welcome and Introduction

WarDragon: Real-Time Drone Remote ID Tracking with Snifflee, TAR1090 and ATAK

Over on YouTube Aaron, creator of DragonOS and the WarDragon kit has uploaded a video showing how he was able to detect drone Remote ID with a Bluetooth dongle and plot it on a TAK map. Remote ID is an RF system regulated in many countries that broadcasts drone information, including GPS position, often over Bluetooth Long Range or Wi-Fi. Note that the Bluetooth dongle is not an SDR, but this story may still be interesting for many readers.

The setup uses Sniffle, which is an open-source Bluetooth sniffer program for TI CC1352/CC26x2 based Bluetooth hardware. Sniffle passes sniffed data packets into SniffleToTak which is open-source software that relays the drone ID packets into a TAK server, which can then be viewed in TAK software like ATAK.

Aaron tests the setup with his DJI drone flying nearby, and shows that the drone is successfully detected and plotted on the TAK map. He also plots the positions of nearby aircraft received via a second ADS-B receiver to show that drones and aircraft can be plotted on the same map.

WarDragon Enhancing Drone Remote ID Real-Time Tracking + ADS-B w/ ATAK (TAR1090, Sniffle) Part 3