Remoticon Video: Learning The Basics Of Software-Defined Radio (SDR)

Have you dipped your toe into the SDR ocean? While hacker software-defined radio has been a hot topic for years now, it can be a little daunting to try it out for the first time. Here’s your change to get your legs under you with the SDR overview workshop presented by Josh Conway during the 2020 Hackaday Remoticon.

Josh’s presentation starts with a straightforward definition of SDR before moving to an overview of the hardware and software that’s out there. Hardware designs for radios can be quite simple to build, but they’ll be limited to a single protocol — for instance, an FM radio can’t listen in on 433 Mhz wireless doorbell. SDR breaks out of that by moving to a piece of radio hardware that can be reconfigured to work with protocols merely by making changes to the software that controls it. This makes the radio hardware more expensive, but also means you can listen (and sometimes transmit) to a wide range of devices like that wireless doorbell or automotive tire pressure sensors, but also radio-based infrastructure like airplane transponders and weather satellites.

This is the quickstart you want since it explains  a lot of topis at just the right depth. The hardware overview covers RTL-SDR, ADALM-PLUTO, HackRF, KerberosSDR, and BladeRF (which we just featured over the weekend used on the WiFi procotol). For software, Josh recaps GQRX, SDR#, SDRAngel, ShinySDR, Universal Radio Hacker, Inspectrum, SigDigger, RPITX, GnuRadio Companion, and REDHAWK. He also takes us through a wide swath of the antenna types that are out there before turning to questions from the workshop attendees.

If SDR is still absent in your toolbox, now’s a great time to give it another look. Once you’ve made it through the ‘hello world’ stage, there’s plenty to explore like those awesome RF Emissions testing tricks we as in another Remoticon talk.

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Doing WiFi With Software Defined Radio

Software defined radio lets RF hardware take on a broad spectrum of tasks, all based on how that hardware is utilized in code. The bladeRF 2.0 micro xA9 is one such device, packing a fat FPGA with plenty of room for signal processing chains on board. As a demonstration of its abilities, [Robert Ghilduta] set about writing a software-defined WiFi implementation for the platform.

The work is known as bladeRF-wiphy, as it implements the PHY, or physical layer of the WiFi connection, in the 7-layer OSI networking model. Modulation and demodulation of the WiFi signal is all handled onboard the Cyclone V FPGA, with the decoded 802.11 WiFI packets handed over to the Linux mac80211 module which handles the MAC level, or medium access control. Thanks to the capability baked into mac80211, the system can act as either an access point or an individual station depending on the task at hand.

[Robert] does a great job of explaining the why and the how of implementing WiFi modulation on an FPGA, as well as some basics of modem development in both software and hardware. It’s dense stuff, so for those new to the field of software defined radio, consider taking some classes to get yourself up to speed!

Fox Hunting With Software-Defined Radio

Fox hunting, or direction finding, is a favorite pastime in the ham radio community where radio operators attempt to triangulate the position of a radio transmission. While it may have required a large amount of expensive equipment in the past, like most ham radio operations the advent of software-defined radio (SDR) has helped revolutionize this aspect of the hobby as well. [Aaron] shows us how to make use of SDR for direction finding using his custom SDR-based Linux distribution called DragonOS.

We have mentioned DragonOS before, but every iteration seems to add new features. This time it includes implementation of a software package called DF-Aggregator. The software (from [ckoval7]), along with the rest of DragonOS, is loaded onto a set of (typically at least three) networked Raspberry Pis. The networked computers can communicate information about the radio waves they receive, and make direction finding another capable feature found in this distribution.

[Aaron] has a few videos showing the process of setting this up and using it, and all of the software is available for attempting something like this on your own. While the future of ham radio as a hobby does remain in doubt, projects like this which bring classic ham activities to the SDR realm really go a long way to reviving it.

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Learning SDR And DSP Hack Chat

Join us on Wednesday, November 11th at noon Pacific for Learning SDR and DSP Hack Chat with Marc Lichtman!

“Revolution” is a term thrown about with a lot less care than it probably should be, especially in fields like electronics. It’s understandable, though — the changes to society that have resulted from the “Transistor Revolution” or the “PC Revolution” or more recently, the “AI Revolution” have been transformative, often for good and sometimes for ill. The common thread, though, is that once these revolutions came about, nothing was ever the same afterward.

Such is the case with software-defined radio (SDR) and digital signal processing (DSP). These two related fields may not seem as transformative as some of the other electronic revolutions, but when you think about it, they really have transformed the world of radio communications. SDR means that complex radio transmitters and receivers, no longer have to be implemented strictly in hardware as a collection of filters, mixers, detectors, and amplifiers; instead, they can be reduced to a series of algorithms running on a computer.

Teamed with DSP, SDR has resulted in massive shifts in the RF field, with powerful, high-bandwidth radio links being built into devices almost as an afterthought. But the concepts can be difficult to wrap one’s head around, at least when digging beyond the basics and really trying to learn how SDR and DSP work. Thankfully, Dr. Marc Lichtman, an Adjunct Professor at the University of Maryland, literally wrote the book on the subject. “PySDR: A Guide to SDR and DSP using Python” is a fantastic introduction to SDR and DSP that’s geared toward those looking to learn how to put SDR and DSP to work in practical systems. Dr. Lichtman will stop by the Hack Chat to talk about his textbook, to answer your questions on how best to learn about SDR and DSP, and to discuss what the next steps are once you conquer the basics.

join-hack-chatOur Hack Chats are live community events in the Hackaday.io Hack Chat group messaging. This week we’ll be sitting down on Wednesday, November 11 at 12:00 PM Pacific time. If time zones baffle you as much as us, we have a handy time zone converter.

Click that speech bubble to the right, and you’ll be taken directly to the Hack Chat group on Hackaday.io. You don’t have to wait until Wednesday; join whenever you want and you can see what the community is talking about.

[Banner image credit: Dsimic, CC BY-SA 4.0, via Wikimedia Commons]

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Easy-SDR Gets Updates

Back in 2018, we covered [Igor’s] Easy-SDR project that aimed to provide open hardware extensions for the chap RTL-SDR receivers. If you haven’t been there for a while, it’s worth a look as there have been many recent updates. According to the author’s Reddit post:

  1. Most of the devices are now prepared for installation in a metal case measuring 80 x 50 x 20 millimeters.
  2. There’s a completely redesigned LNA design. Now, Bias Tee powered amplifiers are housed in a 50 x 25 x 25mm metal case and have N-type connectors.
  3. There’s an added amplifier based on the PGA-103 microcircuit.
  4. Added is the ability to install filters in final amplifiers (a separate printed circuit board, depending on the filter used).
  5. A new device – SPDT antenna switch for receiving antennas.
  6. The upconverter has been redesigned. Added intermediate buffer stage between the crystal generator and mixer.
  7. RF lines in all devices were recalculated to correspond to the characteristic wave impedance of 50 Ohm.
  8. Reduced size of PI attenuator PCB.

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The Cable Modem To SDR Transformation

What do you do with an old cable modem in a closet? If you are [stdw] you reverse engineer it and turn it into a software-defined radio. The modem in question was a Motorola MB7220. After looking at a similar project using a different modem, it seemed like it should be doable.

Cracking open the case revealed two likely UART ports, one of which was active. The output from that UART provided a lot of info. The chip was a Broadcom BCM3383 which is a MIPS processor. It had eCos as an operating system. However, the bootloader eventually disables the UART, so there wasn’t much more investigation possible via the serial terminal.

The next step was to dump the flash memory. That required a little solder surgery to prevent the board from starting while the flash chip had power. It appeared that some key credentials and configuration data were present, but they were really backups. After doing a factory reset to remove the backups, the right data was apparent.

After some lengthy exploration, the diagnostic that builds a spectrum display gave up its data. At first, the data was just a small sample of what was really required, but it did show a local FM station as a spectrum. Eventually, the data loss rate was down to about 12% when streaming which is not great, but good enough. You can hear an audio clip of the reception. Not exactly crystal-clear quality, but not bad.

Of course, no one will use this for an FM radio. But it is a fascinating view into how far you can hack into a device like this if you have some skills and patience. There must be something about quarantine that is making people hack old gear, as we just recently saw a similar Netgear hack. Even cheap games aren’t safe.

KiwiSDR Vs RaspberrySDR — A Tale Of Two SDRs

Once you move away from the usual software defined radio (SDR) dongles, you have only a few choices unless you want to drop some serious cash. One common hobby-grade SDR is the KiwiSDR. This popular unit runs Linux and can receive up to 30 MHz. The platform uses a dedicated A/D converter, an FPGA, and BeagleBone computer. Success of course breeds imitators, and especially when you have an open source design like the Kiwi, you are going to find similar devices with possibly different end goals. That’s how the RaspberrySDR came to be. This is a very similar unit to the KiwiSDR but it uses a Raspberry Pi, along with a handful of other differences. What’s different? [KA7OEI] tells us in a recent blog post.

Other than the obvious difference of the computer and all that it entails, the RaspberrySDR has a higher speed A/D (125 MHz vs 66 MHz) and 16-bits of resolution instead of the Kiwi’s 14 bits. This combines to give the Raspberry a wider receive range (up to 60 MHz) and — in theory — better performance in terms of dynamic range and distortion.

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