Category: Applications

GQRX-Ghostbox: Electronic Voice Phenomenon Paranormal Research Tool

With perfect Halloween timing, SDR enthusiast and ghost hunter Doug Haber has released his RTL-SDR compatible software called “gqrx-ghostbox”. This software supposedly turns your RTL-SDR into a electronic voice phenomenon (EVP) tool a.k.a a “Ghost Box”. Douglas explains what a Ghost Box is in the following blurb:

A ghost box is a device sometimes used by paranormal researchers to talk to spirits, the dead, disembodied entities, shape shifting lizard people, and other intra-dimensional fauna.

Some ghost boxes have electronics that give them distinct properties, and others are effectively radio scanners. This tool is of the radio scanning style.

Many examples of ghost box usage can be found on youtube. Generally, it involves asking questions and then listening for a response. Some people believe a medium or trance state is necessary in order for it to work. If you search for “ghost box” or “spirit box”, you will find information on different usage styles.

We’re not 100% sure if this is a late April fools joke, or a serious tool, but the code is real (it appears to just use GQRX to scan through frequencies), and at least these days when almost everything possible has already been tried with an RTL-SDR, this is something new!

ghostbox

FlightAware Release their Pro Stick Plus: An ADS-B Optimized RTL-SDR with LNA and 1090 MHz Filter Built in

Back in March of this year we posted about the release of the FlightAware “Pro Stick”. The Pro Stick is FlightAware’s ADS-B optimized RTL-SDR dongle. It uses a low noise figure LNA on the RF front end to reduce the system noise figure, thus improving the SNR at 1090 MHz. Because the added gain of the LNA can easily cause overload problems if there are other strong signals around, FlightAware recommend using one of their 1090 MHz ADS-B filters in front of the dongle to prevent overload.

FlightAware have just come out with the “Pro Stick Plus” which is the same as their Pro Stick, but now with the 1090 MHz filter built into the dongle itself. The Pro Stick Plus costs $20.95 USD on Amazon, which is a good deal cheaper than buying the standard Pro Stick ($16.95 USD) plus their ADS-B filter ($19.95 USD), which totals $36.90. Customers outside of the USA can purchase the Pro Stick Plus from seller WiFi Expert on eBay for $29.95 USD.

FlightAware.com is a company that specializes in live air travel tracking. Most of their data comes from volunteers running RTL-SDR ADS-B receivers.

The new Pro Stick Plus RTL-SDR based ADS-B Receiver from FlightAware.
The new Pro Stick Plus RTL-SDR based ADS-B Receiver from FlightAware.

Over on their forums and on Amazon, they announced the device and specs. They wrote:

FlightAware is excited to announce the next evolution of USB SDR sticks for ADS-B reception! The new Pro Stick Plus USB SDR builds on the popular Pro Stick by adding a built-in 1090 MHz bandpass filter. The built-in filter allows for increased performance and range of reception by 10-20% for installations where filtering is beneficial. Areas with moderate RF noise, as is typically experienced in most urban areas, generally benefit from filtering. By integrating the filter into the SDR stick, we are able to reduce the total cost by more than 40% when compared to buying a Pro Stick and an external filter.

Specifications:

  • Filter: 1,075 MHz to 1,105 MHz pass band with insertion loss of 2.3 dB; 30 dB attenuation on other frequencies
  • Amp: 19 dB Integrated Amplifier which can increase your ADS-B range 20-100% more compared to dongles from other vendors which can increase range 10-20% over a Pro Stick in environments where filtering is beneficial
  • Native SMA connector
  • Supported by PiAware
  • R820T2 RTL2832U chips
  • USB powered, 5V @ 300mA

Note that this dongle is only for ADS-B at 1090 MHz, and not for 978 MHz UAT signals, as the filter will cut that frequency out.

Back in April, we did a review of the original Pro Stick. We found its performance on ADS-B reception to be excellent, but only when a filter was used. The low NF LNA theoretically improves the SNR of ADS-B signals by about 7-8 dB, but in reality there is too much gain causing signal overload everywhere, thus making reception impossible without the filter. Rural environments may not need a filter, but in a typical urban or city environment strong FM/TV/GSM/etc signals are abundant and these signals easily overloaded the Pro Stick when no filtering was used. This new Pro Stick Plus dongle completely solves that problem at a low cost with its built in filter.

Remember that if you are using a run of coax cable between the LNA and RTL-SDR, then it is more optimal to use an external LNA, like the LNA4ALL. Only an external LNA mounted near the antenna can help overcome coax, connector, filter and other losses as well as reducing the system noise figure. The FlightAware dongles are the optimal solution when they are mounted as close to the antenna as possible. This is usually the case when running the FlightAware feeder software on a Raspberry Pi.

We hope to soon review the Pro Stick Plus, however we assume it will operate nearly identically to the Pro Stick + FlightAware ADS-B filter combination.

Setting up a GOES Weather Satellite Antenna System

Many people with an RTL-SDR have had fun receiving NOAA and METEOR low earth orbit (LEO) weather satellite images. However, a step up in difficulty is to try and receive the geostationary orbit (GEO) weather satellites like GOES. These satellites are locked to a fixed position in the sky meaning there is no need to do tracking, however since they are much further away than LEO satellites, they require a 1m+ satellite dish or high gain directional antenna to have a chance at receiving the weak signal. The GOES satellites transmit very nice high resolution full disk images of the earth, as well as lots of other weather data. For more information see this previous post where we showed devnulling’s GOES reception results, and this post where we showed @usa_satcom’s presentation on GOES and other satellites.

Over on his blog and Twitter account (@lucasteske) Lucas Teske has been documenting his work in building a GOES receive system. The SDR he uses mostly is an Airspy, but recently he showed that our RTL-SDR Blog V3 dongle is also capable at receiving the GOES signal.

The nice thing about Lucas’ post is that he documents his entire journey, including the failures. For example after discovering that he couldn’t find a 1.2m offset satellite dish which was recommended by the experts on #hearsat (starchat), he went with an alternative 1.5m prime focus dish. Then after several failed attempts at using a helix antenna feed, he discovered that his problem was related to poor illumination of the dish, which meant that in effect only a small portion of the dish was actually being utilized by the helix. He then tried a “cantenna”, with a linear feed inside and that worked much better. Lucas also discovered that he was seeing huge amounts of noise from the GSM band at 1800 MHz. Adding a filter solved this problem. For the LNA he uses an LNA4ALL.

To position the antenna Lucas used the Satellite AR app on his phone. This app overlays the position of the satellite on the phone camera making it easy to point the satellite dish correctly. He also notes that to improve performance you should experiment with the linear feeds rotation, and the distance from the dish. His post of full of tips like this which is very useful for those trying to receive GOES for the first time.

In future posts Lucas hopes to show the demodulation and decoding process.

GOES received with the dish, LNA4ALL, filter and an Airspy.
GOES signals received with the dish, LNA4ALL, filter and an Airspy.

Wintelive: Tutorial and Updates to the Windows Telive TETRA Decoder Implementation

Earlier this month we posted about “cURLy bOi”’s release of his Windows port of telive. Telive is a popular TETRA decoder created by SQ5BPF which until recently only ran on Linux systems. TETRA is a digital voice radio system used in many countries other than the USA.

Now cURLy bOi has just updated his software adding new Windows GUI features and simplifying the install process. The software and text install instructions can be downloaded from his web server, and the code can be found on GitHub.

In order to show the new features and how to use the software cURLy bOi has also created a tutorial video up on YouTube, which is shown below.

https://www.youtube.com/watch?v=OTKn1UwYMBI

A Multi-Channel Coherent RTL-SDR Product: For Passive Radar, Direction Finding and More

Coherent-receiver.com is a company which is a customer of our RTL-SDR V3 dongle and they have been working on creating a multi-channel coherent receiver product based on the RTL-SDR. An RTL-SDR multi-channel coherent receiver is at its most basic, two or more RTL-SDR dongles (multi-channel) that are running from a single clock source (coherent). A multi-channel coherent receiver allows signal samples from two different antennas to be synchronized against time, allowing for all sorts of interesting applications such as passive radar and direction finding.

The team at coherent-receiver.com have used the new expansion headers on our V3 dongles to create their product. In their receivers they attach a control board which has a buffered 0.1 PPM TCXO (buffered so it can power multiple RTL-SDR’s). They also added an 8-bit register and I2C connection capabilities which allows for control of future add-on boards. The I2C capability is useful because it means that several RTL-SDR dongles can be controlled and tuned from the same control signal. More information on the registers and build of the receiver control board can be seen on their technical support page.

A ten channel RTL-SDR coherent receiver.
A ten channel RTL-SDR coherent receiver.
The Coherent Receiver block diagram.
The Coherent Receiver block diagram.

One example application of a multi-channel coherent receiver is passive radar. Coincidentally, we’ve just seen the release of new GUI based Passive Radar software by Dr. Daniel Michał Kamiński in yesterdays post. Passive radar works by listening for strong signals bouncing off airborne objects such as planes and meteors, and performing calculations on the signals being received by two antennas connected to the multi-channel coherent receiver.

A second example is direction finding experiments. By setting up several antennas connected to a multichannel coherent receiver calculations can be made to determine the direction a signal is coming from. An interesting example of direction finding with three coherent RTL-SDRs can be seen in this previous post. A third example application is pulsar detection which we have seen in this previous post

Coherent-receiver.com sent us a prototype unit that they made with four of our V3 dongles. In testing we found that the unit is solidly built and works perfectly. We tested it together with Dr. Kamiński’s passive radar software and it ran well, however we do not have the correct directional antennas required to actually use it as a passive radar yet. In the future we hope to obtain these antennas and test the coherent receiver and the software further.

Currently they do not have pricing for these models as it seems that they are first trying to gauge interest in the product. If you are interested in purchasing or learning more they suggest sending an email [email protected] It seems that they are also working on additional RTL-SDR ecosystem products such as filters, downconverters, antennas and LNAs.

We hope that the release of this product and Dr. Kamiński’s software will give a boost to the development of coherent multi-channel receivers as we have not seen much development in this area until recently.

SDRDue running on the coherent-receiver.com unit.
SDRDue running on the coherent-receiver.com unit.

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

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.

The SDRDue Passive Radar Software
The SDRDue Passive Radar Software

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.

The interactive waterfall.
The interactive waterfall.

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.

SCA GNU Radio Decoder
SCA GNU Radio Decoder