software-defined radio

123 Articles

The Cable Modem To SDR Transformation

October 10, 2020 by 5 Comments

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

September 30, 2020 by 45 Comments

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.

Continue reading “KiwiSDR Vs RaspberrySDR — A Tale Of Two SDRs” →

SDR Transmitting Gets The Power

August 29, 2020 by 28 Comments

Most hobby-grade software defined radio setups don’t transmit. Of the few that do, most of them put out anemic levels around one milliwatt or so. If you want to do something outside of the lab, you’ll need an amplifier and that’s what [Tech Minds] shows how to do in a recent video. (Embedded below.)

The video covers LimeSDR, HackRF, and the Pluto SDR, although the amplifiers should work with any transmitter. The SPF5189Z module is quite cheap and covers 50 MHz to 4 GHz, amplifying everything you throw at it. The downside is that it will amplify everything you throw at it, even parts of the signal you don’t want, such as spurs and harmonics.

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Virtual Software Defined Radio

August 7, 2020 by 5 Comments

Software defined radio or SDR has changed the radio landscape forever. But to use one you need to buy some kind of hardware right? Maybe not. As [Tech Minds] shows in a recent video there are plenty of SDRs publically available on the Internet. We know that isn’t news, but the video does cover several different methods of finding and using SDR receivers including many that run totally in the browser.

Of course, there are a lot of reasons you might want to borrow an alien radio receiver, even if you have your own hardware. Maybe you don’t have a great antenna or maybe you want to hear a signal — maybe even your own — from a different location.

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Stop Bad Laws Before They Start

July 25, 2020 by 88 Comments

With everything else going on this summer, you might be forgiven for not keeping abreast of new proposed regulatory frameworks, but if you’re interested in software-defined radio (SDR) or even reflashing your WiFi router, you should. Right now, there’s a proposal to essentially prevent you from flashing your own firmware/software to any product with a radio in it before the European Commission. This obviously matters to Europeans, but because manufacturers often build hardware to the strictest global requirements, it may impact everyone. What counts as radio equipment? Everything from WiFi routers to wearables, SDR dongles to shortwave radios.

The idea is to prevent rogue reconfigurable radios from talking over each other, and prevent consumers from bricking their routers and radios. Before SDR was the norm, and firmware was king, it was easy for regulators to test some hardware and make sure that it’s compliant, but now that anyone can re-flash firmware, how can they be sure that a radio is conformant? Prevent the user from running their own firmware, naturally. It’s pretty hard for Hackaday to get behind that approach.

The impact assessment sounds more like advertising copy for the proposed ruling than an honest assessment, but you should give it a read because it lets you know where the commission is coming from. Reassuring is that they mention open-source software development explicitly as a good to be preserved, but their “likely social impacts” include “increased security and safety” and they conclude that there are no negative environmental impacts. What do you do when the manufacturer no longer wants to support the device? I have plenty of gear that’s no longer supported by firmware updates that is both more secure and simply not in the landfill because of open-source firmware.

Similarly, “the increased capacity of the EU to autonomously secure its products is also likely to help the citizens to better protect their information-related rights” is from a bizarro world where you can trust Xiaomi’s home-automation firmware to not phone home, but can’t trust an open-source replacement.

Public comment is still open, and isn’t limited to European citizens. As mentioned above, it might affect you even if you’re not in the EU, so feel free to make your voice heard. You have until September, and you’ll be in some great company if you register your complaints. Indeed, reading through the public comments is quite heartening: Universities, researchers, and hackers alike have brought up reasons to steer clear of the proposed approach. We hope that the commission hears us.

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Software Defined Radio Academy Goes Virtual

July 8, 2020 by 4 Comments

They say every cloud has a silver lining. It’s hard to find a positive among all the bad news about the current global pandemic, but it has pushed more conferences and events to allow online participation either live or after the fact. A case in point: The Software Defined Radio Academy’s annual event is all on a YouTube channel so you can attend virtually.

Not all the videos are there yet, but the keynote along with some very technical talks about techniques ranging from FPGAs to spectrum monitoring and spectral correlation density — you can see that video, below. We presume you’ll eventually be able to watch all the presentations listed in the program.

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Tackling Trunked Radio With Software

June 16, 2020 by 12 Comments

For those starting to wade into radio as a hobby, one of the first real technical challenges is understanding trunked radio systems. On the surface, it seems straightforward: A control channel allows users to share a section of bandwidth rather than take up one complete channel, allowing for greater usage of the frequency range. In practice though it can be difficult to follow along, but now it’s slightly easier thanks to software defined radio.

This guide comes to us from [AndrewNohawk], who is located in San Francisco and is using his system to monitor police, fire, and EMS activity. These groups typically used trunked radio systems due to the large number of users. For listening in, nothing more than an RTL-SDR setup is needed, and the guide walks us through using this setup to find the control channels, the center frequency, and then identifying the “talk groups” for whichever organization you want to listen in on.

The guide goes into great detail, including lists of software needed to get a system like this started up, and since [AndrewNohawk] is a self-identified “radio noob” the guide is perfectly accessible to people who are new to radio and specifically new to trunked systems like these. Once you get the hang of it, it’s not too hard to scale up, either.