Category: Other

SOCORAD32: An ESP32 Based Walkie-Talkie with Data Communication

Over on Crowd Supply the SOCORAD32 project has been pre-announced for crowd funding in the future. The project is described as a "hackable, open source, ESP32 amateur radio board with walkie-talkie functionality and data communication". We note that this is not a software defined radio, rather it's a highly customizable software controlled radio.

Because it covers 400 - 470 MHz the device can be used without a license in the license free bands available in most countries. It's able to connect with a standard smartphone over Bluetooth, and can transmit and receive voice, supports voice encryption and compression, and can also transmit and receive SMS data. 

SOCORAD32, aka the ESP32Software Controlled Radio, is a professional-grade hackable walkie-talkie for amateur radio exploration, voice, and data communication using simple AT commands. Just add a speaker and a battery and you get a fully functional walkie-talkie radio. With the onboard dedicated Push To Talk (PTT) button, SOCORAD32 can be used straight out of the box without touching a single line of code!

Unlike using complicated SDR for amateur radio operation, SOCORAD32 is an amateur radio-tailored device that makes things simpler. Using uncomplicated AT commands, users can configure the audio volume, tone squelching, CTCSS, CDSS codes, etc. SOCORAD32’s frequency range covers the license-free bands for most countries.

SOCORAD32 also features all of the operations of a standard walkie-talkie. It employs a proprietary RF design featuring the RDA1846 IC. This is the same IC used in commercial walkie-talkies such as in Baofeng, Motorola and Hytera. Because of this, SOCORAD32 can communicate with commercial walkie-talkies with ease.

In addition to all of this, SOCORAD32 utilizes powerful ESP32 Bluetooth functionality. All SOCORAD32 settings can be adjusted via a connected mobile device using a serial Bluetooth app of any choice, while also being adjustable via the dedicated physical buttons. You can store as many channels as you would like in the onboard memory of the ESP32. SOCORAD32 can also communicate data, so you can explore the amateur radio frequencys for IoT or send texts. Texts can be read via the onboard OLED screen or via a Bluetooth connected mobile device.

Beyond communication SOCORAD32 is fully open source and hackable. For high level enthusiasts the RF module can be opened and tinkered with, allowing features like upgrading the power amplifier, among other adaptations.

Overall, SOCORAD32 makes it fun and interesting to explore the intricacies of amateur radio, portable two-way radio walkie-talkies, and long distance audio or data communications similar to LoRa. All done using easy to understand AT commands and the power of the ESP32 module.

SOCORAD32

Video Introduction to Scattering Parameters with Animated Examples

Thank you to Apostolos for sharing with us his educational video that introduces "scattering parameters" (aka S-Parameters), and how these parameters relate to antennas and RF networks. S-Parameters are a matrix of values that can be used to describe an electrical network. Apostolos' video explains these parameters in detail, giving good visual examples. Apostolos writes:

Here are the topics I cover:

  • What is a 'Network'?
  • Power Waves
  • Complex Impedance & Phase Angle
  • S-Matrix & S-Parameters
  • Reflection & Transmission Coefficients
  • Standing Waves
  • Example Networks
  • Designating S-Parameters
  • Reciprocity & Losslessness
  • Reflection Coefficient and VSWR
A Visual Introduction to Scattering Parameters

Nils Critiques the MH370 WSPR Aircraft Scatter Theory

For some time now there has been chatter about the possibility of using WSPR logs to help track the mysterious disappearance of flight MH370. WSPR or the "Weak Signal Propagation Reporter" is a protocol typically used on the HF bands by amateur radio operators. The properties of the protocol allow WSPR signals to be received almost globally despite using low transmit power.  Amateur radio operators use it for making contacts, or for checking HF radio propagation conditions. MH370 is a flight that infamously vanished without a trace back in 2014.

The theory proposed by aerospace engineer Richard Godfrey is to use logs of sent and received WSPR transmissions that may have intersected the potential flight path of MH370, and to look for potential reflections or 'scatter' in the signal from the metal aircraft hull. From the reflections an approximate track of the aircraft could be calculated much in the same way that bistatic over the horizon radar systems work.

While it is an exciting theory, it is unfortunately considered by most experts as highly unlikely to yield any suitable results with the main problems being WSPR transmission power too weak to detect reflections from an aircraft, and the effect of the ionosphere too difficult to account for. 

Over on his blog Nils Schiffhauer (DK8OK) has posted a thorough critique of the idea, explaining the theory, technical details and difficulties in depth, ultimately coming to the conclusion that the idea is based more in wishful thinking than in fact. Nils summarizes:

Time and again, there are news stories in the professional and popular press about the fact that log data from the WSPR data network can help locate aircraft. In particular, the effort is to determine the actual crash site of flight MH370. This effort essentially amounts to detecting "unusual" level jumps and frequency changes ("drift") in the archived WSPR log data and attributing them to reflections from specific aircraft ("aircraft scatter").

In a blog entry, Nils Schiffhauer, DK8OK, for the first time critically evaluates this theory. On the one hand, this is based on years of observation of aircraft scatter on shortwave as well as an investigation of about 30 Doppler tracks. The results of this complex analysis of more than 10,000 data in one example alone are sobering: The effects of aircraft scatter on the overall signal are almost always well below 0.3 dB.

To prove a correlation between level changes of the overall signal and aircraft scatter seems hardly possible on the basis of the WSPR data material. The reasons are manifold, but lie mainly in shortwave propagation, where level changes of 30 dB within a few seconds are the rule rather than the exception.

However, since the local and temporal state of the ionosphere is not known in previous investigations on the WSPR data material - it is recorded in parallel in professional OTH radar systems and calculated out of the received signal - level jumps can hardly be clearly assigned from the sum signal alone. This finding is supported by further arguments in the blog:
https://t1p.de/t5kr

Nils demonstrates aircraft scatter on China Radio International, a 500kW transmitter.

TechMinds: Testing Off-Grid LoRa Radio Mesh Text Messaging with Meshtastic

Low cost ESP32 based LoRa capable boards have been available from marketplaces like Aliexpress for some time now. They typically include features such as LoRa, WiFi or Bluetooth and GPS all on a PCB board with small screen and battery holder for mobile use. LoRa is a modern IoT communications protocol that is designed to be operated with low power, and in a networked mesh-way for extended range. One application of this hardware is to use it as a mesh based text messaging system, using the Meshtastic firmware. This might be useful for teams of hikers, pilots, or skiiers who operate in remote areas without cell phone reception.

In his latest video Matthew from the Tech Minds YouTube channel shows how to install and use the Meshtastic firmware on a TTGO board. He uses the alpha firmware which has a web app, allowing users to send text messages through a web based GUI that users can connect to locally via WiFi.

OFF-GRID LORA Radio Mesh Text Messaging - Meshtastic

GNU Radio Conference 2021 Talks Now Available on YouTube

The GNU Radio YouTube channel has recently finished uploading the talks from GRCon21, this years annual GNU Radio Conference. GNU Radio is an open source development toolkit for signals processing and is commonly used to build software demodulators and decoders for Software Defined Radios.

The GNU Radio conference talks are generally about cutting edge SDR research topics and the YouTube playlist contains 67 videos covering a gambit between what changes have been made in new releases of GNU Radio to presentations and demonstrations focusing on topics such as reverse engineering smart power meters and 5G cell detection among many others.

Some of the talks from this years conference that we found most interesting include:

GRCon21 - Keynote: Joe Gibbs Racing Team

FutureSDR: An Async SDR Framework Implemented in Rust

FutureSDR is an experimental open source SDR framework (similar to GNU Radio) that is being developed by Bastian Bloessl. The idea behind the framework is that it is implemented in Rust, which is a programming language that supports async (asynchronous) code. The end result to the user should be faster, more portable and lower latency digital signal processing (DSP) code. The framework is still in the early stages with there being very few DSP blocks available, but as per his blog new blocks are slowly being implemented by contributors. 

Bastian has created a presentation introducing the framework. It will only be interesting to programmers, and DSP coders, but it shows the possible software engineering improvements that we could see applied to SDR DSP code in the future. 

Features
An experimental asynchronous SDR runtime for heterogeneous architectures that is:

  • Extensible: custom buffers (supporting accelerators like GPUs and FPGAs) and custom schedulers (optimized for your application).
  • Asynchronous: solving long-standing issues around IO, blocking, and timers.
  • Portable: Linux, Windows, Mac, WASM, Android, and prime support for embedded platforms through a REST API and web-based GUIs.
  • Fast: SDR go brrr!

Overview
FutureSDR supports Blocks with synchronous or asynchronous implementations for stream-based or message-based data processing. Blocks can be combined to a Flowgraph and launched on a Runtime that is driven by a Scheduler. It includes:

  • Single and multi-threaded schedulers, including examples for application-specific implementations.
  • Portable GPU acceleration using the Vulkan API (supports Linux, Windows, Android, …).
  • User space DMA driver for Xilinx Zynq to interface FPGAs.

RasPad 3.0 Review: Building a Portable Raspberry Pi 4 Tablet with Built in RTL-SDR

The Raspad 3.0 is a portable tablet enclosure for the Raspberry Pi 4B. It comes with a high resolution 1280 x 800 10.1 inch touch LCD screen, built in speakers, built in battery and a plastic enclosure that houses the LCD driver board and Raspberry Pi. Accessible on the side of the enclosure are the USB, HDMI, ethernet and audio ports which connect via the LCD driver board. They also include an accelerometer shim which allows the screen to autorotate.

The Raspad 3.0 is available on Amazon USA for $259, or directly via their website for $219 with free worldwide shipping.

A few months ago SunFounder, the company behind the RasPad 3.0 reached out to us and asked if we wanted to review the product with a free sample. Normally we don't review products unrelated to SDR like this, but given the amount of RTL-SDR software available for the Raspberry Pi, and what appeared to be sufficient internal space, we were curious if there was a way to turn this into a portable RTL-SDR tablet...

The RasPad 3.0

Unboxing

A few weeks ago the Raspad 3.0 arrived, well packed and with all the advertised components. Note that the Raspad 3.0 does not come with a Raspberry Pi 4B, this is something you will need to provide on your own.

Inside was a mains power cable, 15V DC power brick, two HDMI jumpers, a USB jumper, accelerometer shim, SD card ribbon, small 5V fan, heatsinks for the Pi, screwdriver and mounting screws, a manual and the RasPad LCD screen itself.  

The Raspad 3.0 Box and Unboxing

Assembly

Assembly is straight forward. You unscrew the enclosure using the provided screw driver, insert the Pi 4B, screw it down, connect all the cables from the Pi to the LCD driver board and SD card slot, then reassemble. After inserting the Raspberry Pi 4B and attaching all the cables this is what the inside looks like.

Inside an assembled RasPad 3.0

Now we could have reassembled the enclosure here, but we wanted this to be a portable RTL-SDR tablet, with the RTL-SDR and an SMA antenna port built in. 

It turns out that the best way to fit in an RTL-SDR Blog V3 is to directly connect it to the spare USB port on the Pi. You might also consider using a micro style RTL-SDR which would fit more easily, but those do tend to get quite hot in a small package, and can be quite bad with internal noise. Also good shielding is probably quite critical in this application due to the dongles proximity with the LCD driver board which could be an RFI source.

The SMA side of the RTL-SDR Blog V3 rests nicely on top of the USB port of the LCD driver board providing some stability, and when the bottom lid is assembled there is plenty of clearance and no squashing.

Next we drilled a hole on the rear wall of the bottom half of the enclosure for the SMA female port, and tightened the SMA connector down with a nut. In the future we'll be upgrading this to a long barrel style SMA female connector, as a regular SMA female connector is a bit short. Then a short well shielded SS405 coax cable was used to connect to the RTL-SDR dongle.

RasPad 3.0 with RTL-SDR Blog V3 Inside
Raspad 3.0 with SMA port hacked in

ProTip: Do take care to remember to remove the SD card when disassembling the RasPad! If you don't you'll end up with the SDcard slot getting ripped from it's ground traces. This happened to us, but we were able to easily solder it back on. There is a sticker on the backside of the enclosure warning about this.

Software & Testing

SunFounder provide a custom Raspbian distribution designed specially for the RasPad. However, we decided to instead install the DragonOS Pi64 Distro which is an Ubuntu distribution for the Raspberry Pi 4B that has many built in SDR programs. We burnt the image to a SD card, inserted it on the side, plugged the Raspad in to the power connector, and held the power button down for a few seconds to turn it on. Despite a few initial error messages saying it cannot enable the USB ports, everything eventually booted just fine.

We then plugged in a cable going to one of our multipurpose dipole antennas mounted just outside the office window, and tested both SDR++ and GQRX. In both cases we were immediately able to connect to the RTL-SDR and receive signals with signal strength equivalent to that received by our desktop PC, indicating that LCD interference was not a problem.

The resolution of the screen is high enough and images and text are clear. The screen is also decently bright, and brightness can be adjusted using the buttons on the side.

RasPad 3.0 with built in RTL-SDR running SDR++ and GQRX

DragonOS Tablet Compatibility Issues & Fixes

As DragonOS is not designed for a tablet setup, there were a few bugs. It should be noted however that these issues are not a reflection on the Raspad hardware, as obviously the official Raspad OS will not have these issues as it's designed specifically for tablet use.

We initially had no sound in SDR++ from the built in speakers. After some troubleshooting we managed to get sound by disabling the headphone jack in the audio mixer settings, which appears to be the default output in DragonOS. To do this, click on the speaker icon on the bottom right task bar and click on Mixer. Then go to the Configuration tab and uncheck the second Built-in Audio entry. Close it, and open SDR++.

Disabling the headphone jack to get the built in speakers working.

In DragonOS the touch screen works fine, although it is difficult to click on small buttons. There is no onscreen keyboard available by default. We couldn't find a way to enable a tablet mode in DragonOS, so instead opted to install an onscreen keyboard called 'onboard' via 'sudo apt install onboard'. The accelerometer is also not enabled in DragonOS. We did not attempt to fix this as we have no need for screen rotation.

Interference

LCD screens are well known to be sources of RF interference, and putting an SDR in close proximity to one could result in the spectrum being very noisy. However, without an antenna connected we did not notice any interference across the spectrum from the LCD screen. It appears that the LCD RFI noise levels are not too bad, and the shielding on the RTL-SDR Blog V3 and the coax jumper cable is good enough to prevent any being received. When an antenna with a few meters of coax was connected (such as a magwhip or our portable dipole) we also didn't notice any LCD interference. 

However, when a SMA telescopic antenna was connected directly to the SMA port we did start noticing the telltale spikes across the spectrum that are typically generated from LCD screens. If the magwhip or dipole was also moved within 2-3cm of the LCD screen, we also saw these interference spikes appear.

LCD Screen interference appears with a telescopic whip connected directly to the SMA port.

So it would be recommended to use a magwhip or dipole that has a coax run that can sit a few centimeters away from the screen. This limits the handheld ability of the RasPad a little, but you'd probably want a magwhip, dipole or other antenna over a directly connected telescopic whip for better reception anyway. 

Battery Life

We tested a worst case scenario, with the RasPad running the RTL-SDR and SDR++ continuously at the brightest screen setting. With this test the battery lasted 2 hours and 10 minutes from a full charge. Presumably if the screen was dimmed and turned off for some periods of time, it would easily last 3-4 hours.

Portability

The total weight of the Raspad including our mods is just under 1 kg (2.2 lbs). About double the weight of a modern tablet, but still light enough to be easily carried.

Other Notes

The small 5V fan provided in the kit is unfortunately a bit noisy, and it's cooling ability is seems limited. We've seen these small fans on other Raspberry Pi cooling accessories and found that they are next to useless at cooling. It would be good to see a slightly larger and quieter fan, or perhaps a better passive cooling heatsink.

The power brick output is 15V, 2A. Ideally we would be able to charge the RasPad via a car/boat 12V connection as well. We're awaiting a response to see if this is possible. Update: Unfortunately 12V seems to be a no-go, quoting SunFounder "the 12v supply may cause the Raspad to fail to charge, as the minimum is 15v".

Conclusion

The RasPad 3.0 in our opinion overall a good product. It allows you to easily go portable with your Raspberry Pi 4. While it was designed for other projects, there was just enough hackability left in it for us to fit a RTL-SDR Blog V3 and antenna port into the enclosure, yielding us a clean and portable SDR solution.

With at least 2 hours of battery life when running an RTL-SDR and software, we can easily see this being taken out in the field for spectrum analysis, decoding with rtl_433, or for portable listening to the airband, trunking etc. However, some customization of DragonOS or the RaspadOS is going to be needed to get the most out of the touchscreen.

There are also alternative LCD screen products designed for the Raspberry Pi where you sit the Raspberry Pi on the back of the screen. But it's unclear if there would be enough space inside to fit an RTL-SDR, and not to mention the lack of a battery. We also previously reviewed the Elecrow CrowPi which is somewhat similar, but a lot more clunky if you're just after a pick up and go portable SDR tablet solution. There are also higher end higher priced laptop style enclosure products for the Pi, like the Pi-Top but we're unsure if they're likely to fit the RTL-SDR internally this easily.

Disclaimer: We do not receive any compensation for this review apart from a free Raspad 3.0.

We also recently came across this review from German YouTuber Manuel Lausmann who installed and ran SDR++ on the Raspad with an SDRplay RSP SDR. 

SDR ++ mit dem RASPAD 3 -Raspberry PI 4-

SDR Talks from the SDRMakerspace Online Presentation

Thank you to Robert for letting us know about these videos from the "ESA ARTES SDR MakerSpace Presentations" from September 6-8, 2021 which are now available on YouTube. 

Libre Space Foundation ( Greece) and the Institute of Reconfigurable & Embedded Digital Systems(REDS) of the Haute Ecole d’Ingénierie et de Gestion du Canton de Vaud – HEIG-VD (Switzerland) have been implementing a number of smaller projects as part of an Software Defined Radio MakerSpace of the European Space Agency.

This activity is part of the ARTES programme of ESA that supports innovation in satellite communications.

The findings were presented in three 2-hour slots in the afternoon at 15:00 CEST (for which you are requested to register separately) on Mon 6, Tue 7 and Wed 8 September 2021.

  • Monday 6 Sep was focused on the evaluation of various SDR boards and FPGA tools chains. High-rate direct sampling by SDR’s and SDR on Android will also be presented.
  • Tuesday 7 Sep was dedicated to building blocks that have been implemented as open source developments for Gnuradio, such as gr-leo, gr-ccsds, gr-soapy etc.
  • Wednesday 8 Sep was mainly about the combination of SDR and AI/ML to do signal detection and classification. In addition, an SDR testbed and spectrum monitoring will be presented.

The talks cover various SDR topics related to satellite observing. Some talks we were interested in are highlighted below, but the full list can be found on the SDRMakerspace website, or the SDRMakerspace playlist on the Libre Space Foundation YouTube channel.

SDRMakerspace - SDR on mobile