Radio Hacks

1333 Articles

19 RTL-SDR Dongles Reviewed

September 5, 2017 by 44 Comments

Blogger [radioforeveryone] set out to look at 19 different RTL-SDR dongles for use in receiving ADS-B (that’s the system where airplanes determine their position and broadcast it). Not all of the 19 worked, but you can read the detailed review of the 14 that did.

Granted, you might not want to pick up ADS-B, but the relative performance of these inexpensive devices is still interesting. The tests used Raspberry PI 3s and a consistent antenna and preamp system. Since ADS-B is frequently sent, the tests were at least 20 hours in length. The only caveat: the tests were only done two at a time, so it is not fair to directly compare total results across days.

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Wearable Foxhunt Transmitter For Conventions

August 31, 2017 by 13 Comments

Amateur radio operator [KE4FOX] wanted to build his own 2M fox hunt transmitter for use at conventions. It would be contained in a 1020 Pelican micro case and attached to a person who would walk around transmitting a signal, leaving the hams to track down the fox. The project uses a DRA818 VHF/UHF transceiver plugged into a low-pass filter combined with a hardware DTMF decoder, all controlled by an ATmega328P and powered by a 11.2 mAh battery.

[KE4FOX] also etched his own PCB, using the PCB toner transfer method, folding a sheet of transfer paper around the board to align both layers. Then he etched the board using cupric chloride. When assembling the board he realized he had made a terrible error, assuming the transceiver module’s pins went in the top layer when in fact they should have gone in the bottom layer. He solved this by soldering in the module in upside down.

He dropped the project into the 1020 and installed an SMA antenna. After he assembled the project he found out that the level shifter he used on the Arduino’s 5 V data didn’t work as expected and it was stuck at a single frequency. Something to work on for V2!

We publish a large number of amateur radio posts here on Hackaday, including fox hunting with Raspberry Pi and how to make a TDOA directional antenna.

[thanks, that Kat!]

AI Watches You Sleep; Knows When You Dream

August 29, 2017 by 5 Comments

If you’ve never been a patient at a sleep laboratory, monitoring a person as they sleep is an involved process of wires, sensors, and discomfort. Seeking a better method, MIT researchers — led by [Dina Katabi] and in collaboration with Massachusetts General Hospital — have developed a device that can non-invasively identify the stages of sleep in a patient.

Approximately the size of a laptop and mounted on a wall near the patient, the device measures the minuscule changes in reflected low-power RF signals. The wireless signals are analyzed by a deep neural-network AI and predicts the various sleep stages — light, deep, and REM sleep — of the patient, negating the task of manually combing through the data. Despite the sensitivity of the device, it is able to filter out irrelevant motions and interference, focusing on the breathing and pulse of the patient.

What’s novel here isn’t so much the hardware as it is the processing methodology. The researchers use both convolutional and recurrent neural networks along with what they call an adversarial training regime:

Our training regime involves 3 players: the feature encoder (CNN-RNN), the sleep stage predictor, and the source discriminator. The encoder plays a cooperative game with the predictor to predict sleep stages, and a minimax game against the source discriminator. Our source discriminator deviates from the standard domain-adversarial discriminator in that it takes as input also the predicted distribution of sleep stages in addition to the encoded features. This dependence facilitates accounting for inherent correlations between stages and individuals, which cannot be removed without degrading the performance of the predictive task.

Anyone out there want to give this one a try at home? We’d love to see a HackRF and GNU Radio used to record RF data. The researchers compare the RF to WiFi so repurposing a 2.4 GHz radio to send out repeating uniformed transmissions is a good place to start. Dump it into TensorFlow and report back.

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Sorry US; Europeans Listen To Space With GRAVES

August 27, 2017 by 18 Comments

In Europe, the GRAVES radar station beams a signal on 143.050 MHz almost straight up to detect and track satellites and space junk. That means you will generally not hear any signal from the station. However, [DK8OK] shows how you can–if you are in Europe–listen for reflections from the powerful radar. The reflections can come from airplanes, meteors, or spacecraft. You can see a video from [way1888] showing the result of the recent Perseid meteor shower.

Using a software-defined radio receiver, [DK8OK] tunes slightly off frequency and waits for reflections to appear in the waterfall. In addition to observing the signal, it is possible to process the audio to create more details.

Why is there a giant vertical radar transmitter in the middle of France? The transmitter uses a phased array to send a signal over a 45-degree swath of the sky at a time. It makes six total steps every 19.2 seconds. A receiver several hundred miles away listens for reflections.

Even the moon reflects the signal when it is in the radar’s path. If you are interested in a moon bounce, you may be able to build a station to hear the reflections without being in Europe.

Of course, if you can transmit yourself, you might want to bounce your own signal off airplanes. If you want to do it old school, you could emulate [Zoltán Bay].

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Sniff Your Local LoRa Packets

August 22, 2017 by 15 Comments

As the LoRa low-bandwidth networking technology in license-free spectrum has gained traction on the wave of IoT frenzy, LoRa networks have started to appear in all sorts of unexpected places. Sometimes they are open networks such as The Things Network, other times they are commercially available networks, and then, of course, there are entirely private LoRa installations.

If you are interested in using LoRa on a particular site, it’s an interesting exercise to find out what LoRa traffic already exists, and to that end [Joe Broxson] has put together a useful little device. Hardware wise it’s an Adafruit Cortex M0 Feather with onboard LoRa module, paired with a TFT FeatherWing for display, and software wise it scans a set of available frequencies and posts any packets it finds to the scrolling display. It also has the neat feature of logging packets in detail to an SD card for later analysis. The whole is enclosed in a 3D printed case from an Adafruit design and makes for a very attractive self-contained unit.

We’ve featured quite a few LoRa projects here, including this one with a Raspberry Pi Compute module in a remote display. Of more relevance in a LoRa testing sense though is this look at LoRa range testing.

ESP8266 Based Internet Radio Receiver Is Packed With Features

August 22, 2017 by 36 Comments

Have a beautiful antique radio that’s beyond repair? This ESP8266 based Internet radio by [Edzelf] would be an excellent starting point to get it running again, as an alternative to a Raspberry-Pi based design. The basic premise is straightforward: an ESP8266 handles the connection to an Internet radio station of your choice, and a VS1053 codec module decodes the stream to produce an audio signal (which will require some form of amplification afterwards).

Besides the excellent documentation (PDF warning), where this firmware really shines is the sheer number of features that have been added. It includes a web interface that allows you to select an arbitrary station as well as cycle through presets, adjust volume, bass, and treble.

 

If you prefer physical controls, it supports buttons and dials. If you’re in the mood for something more Internet of Things, it can be controlled by the MQTT protocol as well. It even supports a color TFT screen by default, although this reduces the number of pins that can be used for button input.

The firmware also supports playing arbitrary .mp3 files hosted on a server. Given the low parts count and the wealth of options for controlling the device, we could see this device making its way into doorbells, practical jokes, and small museum exhibits.

To see it in action, check out the video below:

[Thanks JeeCee]

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Don’t Miss Watching This Solar Eclipse High Altitude Balloon Online

August 20, 2017 by 8 Comments

[Dan Julio] let us know about an exciting project that he and his team are working on at the Solid State Depot Makerspace in Boulder: the Solar Eclipse High Altitude Balloon. Weighing in at 1 kg and bristling with a variety of cameras, the balloon aims to catch whatever images are able to be had during the solar eclipse. The balloon’s position should be trackable on the web during its flight, and some downloaded images should be available as well. Links for all of that are available from the project’s page.

High altitude balloons are getting more common as a platform for gathering data and doing experiments; an embedded data recorder for balloons was even an entry for the 2016 Hackaday Prize.

If all goes well and the balloon is able to be recovered, better images and video will follow. If not, then at least a post-mortem of what the team thinks went wrong will be posted. Launch time in Wyoming is approximately 10:40 am Mountain Time (UTC -07:00) Mountain Daylight Time (UTC -06:00) on Aug 21 2017, so set your alarm!