January 25, 2018

Pseudo-Doppler Direction Finding with a HackRF and Opera Cake

Last week we posted about Micheal Ossmann and Schuyler St. Leger's talk on Pseudo-Doppler direction finding with the HackRF. The talk was streamed live from Schmoocon 18, but there doesn't seem to be an recorded version of the talk available as of yet. However, Hackaday have written up a decent summary of their talk.

In their direction finding experiments they use the 'Opera Cake' add-on board for the HackRF, which is essentially an antenna switcher board. It allows you to connect multiple antennas to it, and choose which antenna you want to listen to. By connecting several of the same type of antennas to the Opera Cake and spacing them out in a square, pseudo-doppler measurements can be taken by quickly switching between each antenna. During the presentation they were able to demonstrate their setup by finding the direction of the microphone used in the talk.

If/when the talk is released for viewing we will be sure to post it on the blog for those who are interested.

Schyler's Poster on Pseudo Doppler from GNU Radio Con 17.

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January 25, 2018

TETRA Decoder Plugin for SDR# Now Available

Back in 2016 cURLy bOi released a Windows port of the Linux based "Telive" TETRA decoder. Now the latest development in TETRA decoders is that a TETRA decoder plugin for the SDR# software has been released. This makes setting up a TETRA decoder significantly simpler than before.

The plugin doesn't seem to be officially released anywhere, but we did find it thanks to @aborgnino's tweets on Twitter, and he found it on a Russian language radio scanner forum. The plugin is available as a direct download zip from here, but we suggest browsing to the last few posts in the forum thread to find the latest version.

Installing the plugin is a little more difficult that usual, as you first need to install MSYS2 which is a compatibility layer for Linux programs. The full installation instructions are included in the README.TXT in the zip file. One clarification from us: you need to copy the files in the msys_root/usr/bin folder from the zip file into the /usr/bin folder that is in your MSYS2 installation directory.

We tested the plugin and found it to work well without any problems. With the plugin turned on you just need to simply tune to a TETRA signal in WFM mode, and you will instantly be decoding the audio.

TETRA is a type of digital voice and trunked radio communications system that stands for “Terrestrial Trunked Radio”. It is used heavily in many parts of the world, except for the USA. If you have unencrypted TETRA signals available in your area then you can listen in on them with an appropriate SDR like an RTL-SDR and decoder software like the aforementioned plugin.

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January 23, 2018

Designing an Ultra Wideband Vivaldi Antenna

The LimeSDR mini is able to receive over a huge frequency range (10 MHz - 3.5 GHz), so having recently bought one "hexandflex" wanted to build an ultra wideband antenna to go along with it. On his three part blog post hexandflex introduces us to various ultra wideband antennas, introduces us to and shows us how to design and build a Vivaldi ultra wideband antenna, and measures the performance of the Vivaldi that he built.

The Vivaldi is a fairly well known ultra wideband antenna that is directional. It is fairly easy to build out of a PCB board, but requires some careful design considerations to work well. In the second post hexandflex goes over all the design considerations that he put into his Vivaldi incliding the feed design, substrate choice and additional improvements like adding corrugations and crafting the geometry for a lens effect.

The results show that the antenna works well as a directional antenna above 1.7 GHz, and begins to work more like a standard dipole below 1.7 GHz. Directional gain is greater than 5dB above 1.7 GHz, and becomes negative below 1 GHz. Although hexandflex notes that the gain below 1 GHz is still reasonable, and probably still better than any untuned monopole.

Hexandflex has put up a small number of Vivaldi antennas that he's produced up for sale on Tindie for US$18. Currently he has a limited batch of units to sell, but notes that he may run additional batches if they are popular.

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January 23, 2018

Reverse Engineering Weather Station RF Signals with an RTL-SDR

Johannes Smit wanted to be able to view the live data from his SWR WH2303 weather station and send it to a database. Whilst the weather data acquisition software that he paid for worked well, he thought that there must be a cheaper and more fun way to grab the data. But unfortunately the manufacturers would not respond to his request for the RF protocol specifications. So Johannes decided to reverse engineer the protocol using his RTL-SDR instead.

Johannes has submitted to us a document that very nicely details his every step taken when reverse engineering the weather station (Google docs document). He starts by confirming the signal frequency in GQRX, and then attempting to see is the rtl_433 could already recognise the signal. Whilst rtl_433 saw something, it was unable to decode the packet properly.

Next he fired up Universal Radio Hacker (URH) and captured a sample of the weather station signal. Using URH he was able to determine the modulation type (FSK) and the bit length parameter (150us). Johannes' next step was to open the weather station, find the RF chip, look up the RF chip information on the web and find the spec sheet. From the spec sheet and internet forum searches he was able to determine the properties of the packet including the sync word and preamble. With this data he was able to determine the packet structure.

Finally he captured a packet and recorded the exact data shown on the weather station at the time of the packet. With this he was able to search the binary data string for the data shown on the weather station, indicating the location of a particular piece of data within the string.

Johannes' tutorial shows just how powerful tools like Universal Radio Hacker can be, and his tutorial is an excellent start for those looking at reverse engineering any of their own local RF protocols.

The binary packet data in Universal Radio Hacker.

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January 22, 2018

Echoes: An RTL-SDR Tool for Meteor Scatter Detection

Thanks to "gmbertani" for letting us know about his recently released RTL-SDR compatible software called "Echoes". Echoes is a Windows, Linux and Raspberry Pi/Arch compatible tool that can be used together with an RTL-SDR and appropriate antenna to monitor for meteor scatter detections.

Meteor scatter works by receiving a distant but powerful transmitter via signal reflections off the trails of ionized air that meteors leave behind when they enter the atmosphere. Normally the transmitter would be too far away to receive, but if its able to bounce off the ionized trail in the sky it can reach far over the horizon to your receiver. Typically powerful broadcast FM radio stations, analog TV, and radar signals at around 140 MHz are used. By listening to these signal blips it can be possible to estimate the number of meteors falling.

Below we paste the official description and feature list of Echoes, and at the end is a video demonstrating Echoes in action:

Echoes it's a radio spectral analysis software for RTL-SDR devices, designed for meteor scattering purposes.

Echoes doesn't demodulate neither decode any human-made signal. Its main goal is to analyze and record the total power of natural signals and generate screenshots and tabular data (CSV, GNUplot) output in presence of particular peaks in a selected narrow range of frequencies. Since there is no demodulation, there is no provision for audio listening, except for a notify sound when an event has been recorded.

Features

Captures waterfall spectra as PNG screenshots and statistics data files.

Optionally generates GNUplot data files

Multiple instances can manage separate dongles plugged in the same computer

Three operating modes: continuos (records data only), periodic (captures data and screenshot every X seconds) and automatic (record data and screeshot each time a customizable (S-N) treshold is exceeded)

HTML report production

Installers ready for Windows7++ and RPMs / SRPMs for Linux

xz binary package for Raspberry PI / Arch distro

It can run headless, recording GNUplot and statistic data only

perseidi 2017

Watch this video on YouTube

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January 22, 2018

Tom’s Radio Room Tests and Reviews the RTL-SDR Blog Multipurpose Dipole Kit

Over on his YouTube channel Tom Stiles (hamrad88) has been experimenting with and reviewing our multipurpose dipole kit. Tom is a ham radio YouTuber who runs a show that produces content often, so we encourage you to subcribe to his channel if you're interested. Tom reviewed our dipole kit over a series of 5 videos which we link here [1: Discussing the product], [2: Unboxing], [3: First ADS-B Tests], [4: Second ADS-B Tests], [5: Third ADS-B Tests]. We post have embedded video 2 and 5 below.

In his testing Tom finds that using the antenna in the vertical orientation improves ADS-B performance. This is expected as ADS-B signals are vertically polarized, and so the antenna should be too. By using the included suction cup mount Tom is able to get the antenna attached to his window which improves reception by getting the antenna as close to the outdoors as possible. This is an expected use case for the antenna, and it's good to see that good results are being had!

If you're interested in the set please see our store at www.rtl-sdr.com/store, or use the links provided in Tom's videos. We also have a tutorial and use case demonstrations for our dipole kit available at www.rtl-sdr.com/DIPOLE.

TRRS #1384 - RTL-SDR.COM Portable Antenna - Parts

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TRRS #1388 - RTL-SDR.COM Antenna Testing Pt 3

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January 22, 2018

Using a Raspberry Pi 3 and RTL-SDR as a 40m FT8/JT65/JT9 Monitor

Over on YouTube user radio innovation has uploaded a brief screen capture showing his Raspberry Pi 3 and RTL-SDR dongle being used as an always-on monitor for low transmit power based signals such as FT8, JT65 and JT9. These signals are transmitted by ham radio enthusiasts for the purpose of making contacts, and determining propagation conditions. This is a good application for an RTL-SDR and Raspberry Pi 3 as it enables cheap monitoring of these signals without the need to tie up a full sized ham radio.

To do this "radio innovation" runs Linrad on the Raspberry Pi, which is a program like GQRX that interfaces with the RTL-SDR dongle. Then the WSJTx software is used to decode the signals. He writes:

Remote Desktop screencapture of my Raspberry Pi3 monitor receiver on 40m amateurradio band with WSJTx and decoding FT8,JT65 and JT9. Receiver hardware is RTL-SDR(tcxo) + simple converter and homemade bandpass filter.

SDR software is LINRAD by SM5BSZ.

RasperryPi3 OS is Ubuntu Mate 16.04.

Watch this video on YouTube

Update: We now have a tutorial on creating a similar set up available on a new post.

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January 19, 2018

Schmoocon 18: Live Stream of Micheal Ossmann and Schuyler St. Leger on Psuedo-Doppler begins in 15 minutes

Micheal Ossmann @michaelossmann (famous for creating the HackRF SDR and various other projects) and Schuyler St. Leger @DocProfSky (a very talented young man) will soon be presenting their "Pseudo-Doppler Redux" talk at the Schmoocon 2018 conference at 3:30pm EST. The talk is available for all to watch live on Livestream.

Michael Ossmann and Schuyler St. Leger demonstrate their new take on Pseudo-Doppler direction finding techniques, using SDR to enhance direction finding capabilities.

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