We've decided to ask the community what sort of radio would be more popular for a ~$30 RX-only SDR. Note that thus far this is only a hypothetical SDR that does not yet have any designs. We are just feeling for what's most interesting to people and exploring for future ideas which may not even be feasible at this time.
As always with engineering, there is always a trade off. It is likely that any low cost SDR can only be wide band, with basic RF performance, narrowband with good RF performance, or expensive.
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Wider bandwidth: Currently the RTL-SDR allows you to see up to 3.2 MHz of spectrum live. Higher bandwidth (10 MHz or more) would mean seeing more of the spectrum at once without needing to retune, faster whole spectrum scans and the ability to receive wideband signals.
RF Performance: The RTL-SDR has an 8-bit ADC. While sufficient for many applications, in the presence of strong signals the ADC will saturate resulting in poor reception and signal overload. Higher end SDRs like the SDRplay, Airspy, LimeSDR etc use 12-bit or higher ADCs.
Frequency Range: The RTL-SDR V3 can tune from 500 kHz to 1.75 GHz. An expanded SDR could potentially tune up to 4 GHz or even higher.
If you're interested in other things, please comment on this post!
Software defined radio (SDR) is a relatively new technology that has impacted the world of radio technology in many ways. But beyond SDR, there are still some other very interesting radio technologies being worked on, such as "Atomic Radio" a.k.a "Quantum Radio".
Atomic radio is essentially an idea that makes use of how special "Rydberg" atoms can modulate a laser beam when radio waves pass through them. A photo diode is then used to optically detect the radio wave from the modulated laser. This way of receiving requires no traditional radio circuits like amplifiers, mixers, and of course no antenna, so in theory the radio signal could be received with significantly less noise and with the highest possible SNR.
If you're interested in learning more about Atomic Radio, Hackaday recently ran an excellent article where they describe the concept and science behind it in more depth. They also go into some recent studies where scientists showed that they were able to receive two signals at once, and mention how one paper describes an extremely wideband Atomic Radio that can receive from the C-Band to the Q-band (4 GHz to 50 GHz).
Hackaday's Article is a Great Introduction to Atomic Radio
The Signal ID Wiki (sigidwiki) is our sister site that we started a few years ago as a way to collect and catalog various types of signals that an SDR user might see and hear on the airwaves. The idea is that a user could search the database to learn about and identify unknown signals. Over time it has grown significantly, with now almost 400 known signals with both waterfall images and sound samples available in the database. Special thanks to lead admin Carl Colena for maintaining and playing a huge role in the databases' growth.
Artemis is an open source Windows/Linux/MacOS compatible application initially programmed by Marco Dalla Tiezza. It brings the sigidwiki website into an offline searchable database with an easy to use UI. Today version 3.0 was released to the public. The new version has been completely rewritten from scratch in Python, as the previous versions were written in BASIC (a now abandoned programming language). The new version has an improved UI, and paves the path for future improvements.
Marco notes that in the future they hope to add an Autocorrelation function, which might help users automatically identify certain types of repetitive signals simply by playing the raw audio into Artemis.
Note that in order to download the software you will need to sign up to their forum, which is free.
In this episode Corrosive from the SignalsEverywhere YouTube channel begins a series on reverse engineering an old 90's Barbie branded 2.4 GHz wireless camcorder toy, and using it for Amateur Radio TV. The camcorder toy consists of the wireless camera, and a base station that plugs into a TV.
After taking the camcorder apart Corrosive discovered a potentiometer on the PCB which allows the transmit frequency to be adjusted, and that the camera's CCD sensor can actually output composite video, possibly allowing for improved video quality. In addition he found the datasheet for the main FM demodulator chip on board the base station, and saw that it is designed to operate from 350 to 550 MHz. So he speculates that elsewhere in the circuit is a 2.4 GHz downconverter which may be useful for other projects too.
The Raspberry Pi is the most popular credit sized computing board in the world. It is commonly used as a low cost and portable computing platform for SDRs like the RTL-SDR. Today the Raspberry Pi 4 was released, bringing us a new US$35 single board computer with many improvements. Some of the main improvements that make the Pi 4 great for software defined radios are listed below:
CPU: The Pi 4 uses a Quad-Core Broadcom ARM A72 clocked at 1.5 GHz. This chip should be significantly faster compared to the older chip used on the Pi3B+ with performance now being similar to that of the Tinkerboard. This will be especially useful for CPU intensive SDR applications like the direction finding and passive radar software for our coherent 4-tuner RTL-SDR known as the KerberosSDR. It should also help allow OpenWebRX servers to serve more simultaneous users, allow graphical programs like GQRX to run smoother, and allow for higher sample rates on higher end SDRs.
GPU: The new faster GPU should help graphical SDR programs run smoother.
RAM: The Pi 4 comes with three RAM options, either 1GB, 2GB or 4GB of RAM. The versions with more RAM will be great for memory intensive applications such as GNU Radio (and compiling GNU Radio). It will also allow more programs to run in the background, and perhaps combined with the improved CPU speed allow for multiple SDRs to be used on demanding tasks.
Networking: The Pi 4 finally support Gigabit Ethernet which will be very useful to people using the board as an SDR server over the internet.
USB: There are now two USB 3.0 ports available which means that USB 3.0 SDRs like the LimeSDR could in theory be used at higher sample rates on the Pi 4.
There are also many other improvements such as dual 4K HDMI ports, a USB-C power supply port and faster SD card transfers.
Raspberry Pi 4 Improvements
It is not yet known if the very useful Raspberry Pi specific software known as RPiTX will continue to function on the new Pi 4. RPiTX is software that turns Raspberry Pi units into fully functional RF transmitters without the need for any additional transmitting hardware - just attach an antenna wire to a GPIO pin. It works by modulating the GPIO pin in such a way to create almost any type of RF transmission. RPiTX only functions on the specific proprietary Broadcom CPU chips that the Raspberry Pi's use. The Pi 4 does continue to use a Broadcom CPU, so we are hopeful.
The new changes bring the Raspberry Pi up to speed with rivals like the Tinkerboard, but at a lower price and with a much better amount of software and OS support provided. The boards currently cost $35 for the 1GB version, $45 for the 2GB version and $55 for the 4GB version. They are sold via local resellers which can be found on the official Pi 4 product page.
Over on YouTube Curious Droid has uploaded an interesting video that attempts to explain the purpose of the HAARP transmitter project. The High Frequency Active Auroral Research Program (HAARP) is an ionospheric research program based in Alaska. It consists of a high power transmitter and antenna array which is used to excite a portion of the atmosphere in order to study the ionosphere and investigate methods of affecting radio communications. Recently HAARP was also used in an art project called "Ghosts in the Air Glow" which saw HAARP used to transmit several audio art pieces.
HAARP has also been a popular target of conspiracy theorists who believe that the transmitter must have some sort of sinister purpose. Curious Droid's video explains the purpose and science behind HAARP elegantly, hopefully dispelling any conspiracy theories.
He also explains where some of the conspiracy theories may have originated from. The original idea that HAARP was based on was a patent claiming the ability of Ionospheric heating to disrupt communications, take down missiles & satellites, affect weather, scan the earth and even affect brains. However, a project with such abilities would require ridiculous levels of electrical power and land space for the antennas, making it very unrealistic.
Hanselminutes is a weekly podcast that aims to promote fresh technology and fresh voices to software developers. Last Friday they interviewed Ben Hilburn who is the project lead and president of the GNU Radio Foundation and Director of Engineering at DeepSig Inc who are working on combining deep learning with the signal processing. In the podcast Ben talks briefly about a broad range of topics like spectrum scarcity issues, different SDR hardware, basic SDR fundamental concepts, multipath, GPS, RF security, analogue vs digital and more. It is aimed at technical people who know little about SDR and radio.
EPISODE SUMMARY
Ben Hilburn is the Director of Engineering at DeepSig Inc., which is commercializing the fundamental research behind deep learning applied to wireless communications and signal processing. He also runs GNU Radio, the most widely used open-source signal processing toolkit in the world, serving as Project Lead and President of The GNU Radio Foundation. Ben talks to Scott about why Software Defined Radio is magical and they talk about how SDR can be used to teach STEM and solve interesting engineering problems.
EPISODE NOTES
Ben Hilburn is the Director of Engineering at DeepSig Inc., which is commercializing the fundamental research behind deep learning applied to wireless communications and signal processing. He also runs GNU Radio, the most widely used open-source signal processing toolkit in the world, serving as Project Lead and President of The GNU Radio Foundation. Ben talks to Scott about why Software Defined Radio is magical and they talk about how SDR can be used to teach STEM and solve interesting engineering problems.
If the math behind software defined radio and digital signal processing (DSP) concepts does your head in, the RSGB has a short document that explains core DSP concepts without any math. If you're just looking for an overview of what terms like sampling, nyquist, aliasing, number of bits, undersampling, digital filters and fast fourier transform mean, then this short article is a great start.
This article, based on a presentation first given at the 2017 RSGB Convention, is intended for the amateur radio exam tutors to help with teaching the new Software Defined Radio (SDR) material in Syllabus 2019. It goes slightly beyond the syllabus requirements and is designed to give a basic background into Digital Signal Processing (DSP), enabling Tutors to answer some questions that trainees may ask, and to help tutors develop their own knowledge. Links to suggested further reading are given for those who might want to know more.
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