See Satellites with a Simple Radio Telescope

Have you got a spare Dish Network antenna lying about? They’re not too hard to come by, either curbside on bulk waste day or perhaps even on Freecycle. If you can lay hands on one, you might want to try this fun radio telescope build.

Now, don’t expect much from [Justin]’s minimalist build. After all, you’ll be starting with a rather small dish and an LNB for the Ku band, so you won’t be doing serious radio astronomy. In fact, the BOM doesn’t include a fancy receiver  – just a hacked satellite finder. The idea is to just get a reading of the relative “brightness” of a radio source without trying to demodulate the signal. To that end, the signal driving the piezo buzzer in the sat finder is fed into an Arduino through a preamp. The Arduino also controls stepper motors for the dish’s azimuth and elevation control, which lets it sweep the sky and build up a map of signal intensity. The result is a clear band of bright spots representing the geosynchronous satellites visible from [Justin]’s location in Brazil.

Modifications are definitely on the docket for [Justin], including better equipment that will allow him to image the galactic center. There may be some pointers for him in our coverage of a tiny SDR-based radio telescope, or from this custom receiver that can listen to Jupiter.

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Backscatter Your Own FM Pirate Radio Station

If you live in a city, you’re constantly swimming in a thick soup of radio-frequency energy. FM radio stations put out hundreds of kilowatts each into the air. Students at the University of Washington, [Anran Wang] and [Vikram Iyer], asked themselves if they could harness this background radiation to transmit their own FM radio station, if only locally. The answer was an amazing yes.

The trailer video, embedded below, demos a couple of potential applications, but the paper (PDF) has more detail for the interested. Basically, they turn on and off an absorbing antenna at a frequency that’s picked so that it modulates a strong FM signal up to another adjacent channel. Frequency-modulating this backscatter carrier frequency adds audio (or data) to the product station.

One of the cooler tricks that they pull off with this system is to inject a second (stereo) channel into a mono FM station. Since FM radio is broadcast as a mono signal, with a left-minus-right signal sent alongside, they can make a two-channel stereo station by recreating the stereo pilot carrier and then adding in their own difference channel. Pretty slick. Of course, they could send data using this technique as well.

Why do this? A small radio station using backscatter doesn’t have to spend its power budget on the carrier. Instead, the device can operate on microwatts. Granted, it’s only for a few feet in any given direction, but the station broadcasts to existing FM radios, rather than requiring the purchase of an RFID reader or similar device. It’s a great hack that piggybacks on existing infrastructure in two ways. If this seems vaguely familiar, here’s a similar idea out of the very same lab that’s pulling off essentially the same trick indoors with WiFi signals.

So who’s up for local reflected pirate radio stations?

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Using SDR to Take Control of Your Home Security System

[Dan Englender] was working on implementing a home automation and security system, and while his house was teeming with sensors, they used a proprietary protocol which was not supported by the open source system he was trying to implement. The problem with home automation and security systems is the lack of standardization – or rather, the large number of (often incompatible) standards used to ensure consumers get tied in to one specific system. He has shared the result of his efforts at getting the two to talk to each other via his project decode345.

The result enabled him to receive signals from Honeywell’s 5800 series of wireless products and interface them with OpenHAB — a vendor and technology agnostic open source automation software. OpenHAB offers “bindings” that allow a wide variety of systems and hardware to be integrated. Unfortunately for [Dan], this exhaustive list does not yet include support for the (not very popular) 345MHz protocol used by the Honeywell 5800 system, hence his project. Continue reading “Using SDR to Take Control of Your Home Security System”

GSM Sniffing on a Budget with Multi-RTL

If you want to eavesdrop on GSM phone conversations or data, it pays to have deep pockets, because you’re going to need to listen to a wide frequency range. Or, you can just use two cheap RTL-SDR units and some clever syncing software. [Piotr Krysik] presented his work on budget GSM hacking at Camp++ in August 2016, and the video of the presentation just came online now (embedded below). The punchline is a method of listening to both the uplink and downlink channels for a pittance.

[Piotr] knows his GSM phone tech, studying it by day and hacking on a GnuRadio GSM decoder by night. His presentation bears this out, and is a great overview of GSM hacking from 2007 to the present. The impetus for Multi-RTL comes out of this work as well. Although it was possible to hack into a cheap phone or use a single RTL-SDR to receive GSM signals, eavesdropping on both the uplink and downlink channels was still out of reach, because it required more bandwidth than the cheap RTL-SDR had. More like the bandwidth of two cheap RTL-SDR modules.

Getting two RTL-SDR modules to operate in phase is as easy as desoldering a crystal from one and slaving it to the other. Aligning the two absolutely in time required a very sweet hack. It turns out that the absolute timing is retained after a frequency switch, so both RTL-SDRs switch to the same channel, lock together on a single signal, and then switch back off, one to the uplink frequency and the other to the downlink. Multi-RTL is a GnuRadio source that takes care of this for you. Bam! Hundreds or thousands of dollar’s worth of gear replaced by commodity hardware you can buy anywhere for less than a fancy dinner. That’s a great hack, and a great presentation.
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SDR and Node.js Remote-Controlled Monster Drift

Most old-school remote controlled cars broadcast their controls on 27 MHz. Some software-defined radio (SDR) units will go that low. The rest, as we hardware folks like to say, is a simple matter of coding.

So kudos to [watson] for actually doing the coding. His monster drift project starts with the basics — sine and cosine waves of the right frequency — and combines them in just the right durations to spit out to an SDR, in this case a HackRF. Watch the smile on his face as he hits the enter key and the car pulls off an epic office-table 180 (video embedded below).

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Raspberry Pi SDR

[Chris D] noticed that the excellent software defined radio (SDR) software gqrx will run on the Raspberry Pi now. So he married a Raspberry Pi 3, a touchscreen, an RTL-SDR dongle, and an upconverter to make a very nice receiver setup. You can see the receiver in action below.

The video is a little light on build details, but there is a shot of the setup with the pieces labeled, and you should be able to figure it out from there. Of course, gqrx works with lots of different SDR devices so you might have to make adjustments depending on what you use (for example, many of the supported dongles won’t need the upconverter that [Chris] uses).

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Ice, Ice, Radio Uses FPGA

Building a software defined radio (SDR) involves many trades offs. But one of the most fundamental is should you use an FPGA or a CPU to do the processing. Of course, if you are piping data to a PC, the answer is probably a CPU. But if you are doing the whole system, it is a vexing choice. The FPGA can handle lots of data all at one time but is somewhat more difficult to develop and modify. CPUs using software are flexible–especially for coding user interfaces, networking connections, and the like) but don’t always have enough horsepower to cope with signal processing tasks (and, yes, it depends on the CPU).

[Eric Brombaugh] sidestepped that trade off. He used a board with both an ARM processor and an ICE FPGA at the heart of his SDR design. He uses three custom boards: one is the CPU/FPGA board, another is a 10-bit converter that can sample at 40 MSPS (sufficient to decode to 20 MHz), and an I2S DAC to produce audio. Each board has its own page linked from the main project.

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