Tagged: rtl-sdr

October 17, 2016

SDRDue: New Software for Passive Radar with Two Coherent RTL-SDR Dongles

UPDATE March 2019: Daniel's site has gone down, but the downloads are still available here.

Dr. Daniel Michał Kamiński, author of two SDR# plugins has recently released a new passive radar program for the RTL-SDR called "SDRDue". Passive radar is a technique that makes use of signals from strong distant transmitters. The idea is that these signals can be reflected off the fuselage of aircraft or other flying objects, and the reflection can be observed by a passive radar receiver. By correlating data from two receivers and two antennas, more accurate positional data can be obtained.

For passive radar to work properly the receivers should be coherent, meaning that they run from the same clock and have synchronized samples. The RTL-SDR can be made coherent by connecting two dongles to a single clock source.

The software runs on multi-threaded C# code, and uses Microsoft XNA 4.0 for the graphical operations. It also supports GPU parallel calculations if you have OpenCL and an AMD graphics card.

Please note that we attempted to run the program, but it would not even open on our PC. We've contacted the author to ask if there is any known problems. If anyone gets it running please report back in the comments section of this post. EDIT: Daniel has updated the software and it appears to be functioning normally now. You will need to install it into a SDR# folder, and run SDR# first with both dongles before the software will recognise the dongles in SDRDue. We also had better luck with using the rtlsdr.dll_ file, rather than the default rtlsdr.dll file. Just delete the original rtlsdr.dll and rename rtlsdr.dll_ to rtlsdr.dll.

For more information on passive radar we recommend looking at this previous post where we showed the work of Juha Vierinen who used RTL-SDR's to build a passive radar.

October 13, 2016

Outernet Weather Updates Now Coming Down

A few days ago we reported that the Outernet L-band satellite service had just upgraded their software to make it available for receiving APRS and weather updates. Back then it wasn’t clear what the weather updates would entail. Today weather updates starting being transmitted. They are using NOAA data and displaying it on a live weather app (which can also be viewed online here).

The app can be used to view weather data such as wind vectors, temperatures, relative humidity, total precipitable water, total cloud water, mean sea level pressure and ocean currents. Outernet writes that the global weather data will be updated via their satellite system once per day, and that each update also provides 24h, 48h and 72h predictions.

We also see that grib files for mariners are now coming in as well as several Wikipedia articles and regular APRS broadcasts from the ISS.

It looks like the Outernet service is becoming more and more useful over time. If you are interested in receiving Outernet with an RTL-SDR see our tutorial post here.

October 13, 2016

New SDR# Plugin: Radio-Sky Spectrograph Data Stream

Edit: If you downloaded an older version of the plugin please note that it has now been updated. The update fixes some stability issues which would previously hang SDR#. The updated .dll file can be downloaded directly from https://goo.gl/0dPzOL.

Radio-Sky Spectrograph is a radio astronomy software program which is often used together with the RTL-SDR or other similar SDRs. It is best explained by the author:

Radio-Sky Spectrograph displays a waterfall spectrum. It is not so different from other programs that produce these displays except that it saves the spectra at a manageable data rate and provides channel widths that are consistent with many natural radio signal bandwidths. For terrestrial , solar flare, Jupiter decametric, or emission/absorption observations you might want to use RSS.

Usually to interface an RTL-SDR with Radio-Sky Specrtograph a program called RTL-Bridge is used. However, now SDR# plugin programmer Alan Duffy has created a new plugin that allows SDR# to interface with Radio-Sky Spectrograph via a network stream. This allows it to work with any SDR that is supported by SDR# plugins. Alan Duffy writes:

I wrote the plugin after becoming interested in amateur radio astronomy. The plugin allows you to use any of the software defined radios supported by SDR# to feed the Radio-Sky Spectrograph program with wide-band data. The plugin shows the frequency, bandwidth, and FFT resolution and has a user selected "Number of Channels" that are sent to the spectrograph program with an allowable range of 100 to 500. This number can only be edited when the data stream is not enabled. Also if certain key parameters change, such as the frequency or decimation, the network stream will stop as the spectrograph would no longer be capturing the same data. If this happens, simply click the start button on client side software (i.e. Radio-Sky Spectrograph). As long as the Enable box is checked on the server side, the plugin will listen for a connection and start transmitting data after RSS makes a new request for data.

We note that the software might also be useful for simply capturing a long term waterfall for finding active frequencies or looking for meteor scatter or aircraft scatter echoes.

October 12, 2016

Software for creating an Interactive RTL_POWER Visualization

RTL-SDR.com reader Dominic Chen recently wrote in to let us know about a new piece of software he’s created. The software is called d3-waterfall, and is an interactive web based waterfall display. It takes CSV data from the commonly used rtl_power software and produces an interactive labelled waterfall which can be viewed in a web browser. rtl_power is a program that allows RTL-SDRs to produce signal power scans over an arbitrarily wide swath of bandwidth, by quickly hopping between ~2 MHz chunks of live bandwidth.

Dominics software is built using “d3.js” and HTML5. The waterfall axes are automatically labelled, there are multiple color schemes and there is pan/zoom support. The main feature is that it is mouse interactive, so when you mouse over a frequency it shows what the signal is. The default signal frequency data is taken directly from our sister site sigidwiki.com, so it may not be accurate for your particular area. But the labels are editable, so it can be customized.

An example of a previous scan can be seen on Dominic’s website (note that this is a 65mb link so be careful if you are data restricted). The software can be downloaded from its GitHub page.

October 11, 2016

L-Band Setup with Mini LNA4ALL and Mini Patch Antenna

Over on his YouTube channel Adam 9A4QV has uploaded a new video showing reception of L-band signals with a bias tee powered LNA4ALL and a small patch antenna. The video seems to show a new miniature bias tee powered LNA4ALL device that Adam might be working on. The LNA4ALL is a low noise amplifier that works well with our bias tee capable RTL-SDR dongles.

The patch antenna is made out of a single piece of PCB board which was made by etching out the patch pattern with masking tape. While the patch antenna is not optimal, and tested indoors, Adam is still able to receive some AERO signals.

Later in the video he compares the PCB patch against a GPS patch antenna which gets no reception. He also compares the results when two LNA4ALL’s are used in series. Using two LNA’s improves reception slightly.

L band mini setup

Watch this video on YouTube

October 11, 2016

Experimenting with Broadcast FM RDS (TMC, RT+) and SCA Audio

A typical broadcast FM station can sometimes contain “hidden” subcarriers embedded within the main signal. The subcarriers contain data or audio services.

An example of a data subcarrier hidden within broadcast FM is the “Traffic Message Channel” (TMC). The TMC contains traffic data, and is used on GPS devices that advertise as having live traffic capabilities. TMC data is encrypted so that it can be sold, but is very easily broken. Another data service is RDS-RT+ data which transmits song information, for radios that can display it.

An example of a voice subcarrier (SCA/ACS) might be niche radio stations, such as ethnic stations, elevator music, music for doctors offices etc. Usually a specialized radio is required to receive a SCA channel. In a previous post we showed how a user was able to receive SCA on Windows.

Over on his blog Gough Lui has been investigating the broadcast FM subcarriers in his home town of Sydney, Australia. In his post he looks at TMC, RDS-RT+ and SCA subcarriers and explains a bit about what they are and how they work. He also goes on to receive and decode the subcarriers with an RTL-SDR, gr-rds and GNU Radio. While Gough doesn’t bother to decrypt the TMC service, he can still see when an event occurs and what the even was. Without decryption he just doesn’t know where the location on the event is. For SCA he wrote a GNU Radio program to extract the audio subcarrier and was able to decode audio from a local Indian station for migrants.

October 10, 2016

Identifying Transmitters with CTCSS Fingerprinting

Oona Räisänen is a RF hacker and enthusiast who has in the past brought us posts about decoding burger pagers in restaurants, decoding wireless bus signs and FM-RDS with SDR’s like the RTL-SDR. This time she has written an interesting post that shows how she can “fingerprint” radio transmitters by analysing their CTCSS transmissions. CTCSS is short for “Continuous Tone-Coded Squelch System” and is a low frequency tone added on to some transmissions used in handheld radio systems shared by several distinct groups. The CTCSS tone prevents users of a shared system from having to listen to other users talking if they are not part of the same group with the same CTCSS tone frequency. CTCSS provides no means for actually individually identifying a radio.

Oona wanted to see if she could fingerprint and thus identify individual radios by their CTCSS tone by looking at identifying features such as small variances in CTCSS tone power and frequency. The idea is that each radio will have minute differences in the exact tone and power produced by the CTCSS circuitry, due to differences in the crystal oscillators and component tolerances. Oona used an RTL-SDR to record CTCSS data from a conversation on a local handheld radio network. Then by plotting the frequency vs power data on a heatmap graph she was able to find 8 different clusters of points, which potentially identifies 8 individual handheld radios.

Frequency vs power heatmap identifying 8 different radios.

With the individual radios identifiable by their cluster centers, each cluster can be assigned a name. Now each subsequent transmission can be compared to each cluster center, and assigned to the closest matching cluster, thus matching a new unknown transmission with a known radio. This makes it easier for someone listening in with no context to follow a conversation.

Assign names to each radio. — Assign names to each radio/cluster center.

October 10, 2016

Outernet rxOS Version 3 Released: Automatic Decompression, APRS, NOAA Weather Data, News Updates

Outernet is a new L-band satellite services which aims to be a “library in the sky”. Their satellite signal can be received from almost anywhere in the world, and they aim to constantly transmit data like news, weather updates, books, images/videos and other data files. The service is free and can be received with an RTL-SDR, LNA and patch antenna. We have a full tutorial on receiving their service available here.

The “rxOS” decoder, file management system and web interface GUI has recently been updated to version 3.0. This new version has several new features:

Downloaded files are automatically decompressed after downloading, so they can be viewed directly in the Outernet web interface.
An hourly transmission of APRS data which comes from the repeater on board the international space station. APRS messages can now be relayed across the world via the ISS and Outernet.
This Monday they will begin transmitting NOAA weather data (we are unsure if this entails images or text data yet)
Soon they should begin transmitting news data too.

More details on the update can be found on their forum post. To update the service on a CHIP or Pi 3, download the .pkg file from the links on the forum and choose this file in the Update Firmware section of the Outernet settings menu.

An example of some received APRS messages from the Outernet.