The SatNOGS project aims to provide low cost satellite ground stations (where one critical component is currently an RTL-SDR dongle) along with free networking software in order to create a crowd sourced satellite coverage network. The SatNOGS project was also the grand prize winner of the 2014 Hackaday prize which saw them take away almost $200k US dollars of prize money.
Recently the SatNOGS team announced the release of their new satellite database which can be used to look up satellite transmitter information such as downlink frequencies. It is described as “an effort to create an hollistic, unified, global transmitter database for all satellite transmitters”. The database is open to everyone and requires contributions in order to grow.
A new piece of software called ham2mon by programmer Louis Brown (KD4HSO) has been released. This is a GNU Radio Linux based program that can be used with an RTL-SDR or other SDR that is compatible with GrOsmoSDR to demodulate and record narrow band FM audio from N channels (as many channels as your CPU can handle) within the current bandwidth. Although it is command line based, it comes with a simple Curses command line based GUI.
He writes that in future versions he hopes to incorporate gr-dsd to be able to demodulate and record P25 digital audio as well.
The ham2mon Curses GUI.
Louis has also uploaded a video to YouTube showing the software in action.
Parabolic microphones allow listeners to clearly hear sounds from far away. They are often used by bird call enthusiasts and also probably by spies. A parabolic microphone works by using a dish to concentrate distant sound onto an amplified microphone and they have been commercially available since the 60’s as demonstrated by this old Radioshack ad.
An old parabolic micrphone advertised in a radioshack catalogue from the ’60’s
Usually, the listener uses a pair of headphones directly tethered to the parabolic microphone and walks around with the dish in hand. However, this week electronics hobbyist Mario Fillipi wrote in to RTL-SDR.com to let us know about his project in which he created a wirelessly operated parabolic microphone.
To do this Mario connected a wireless FM transmitter to the headphone output of his home made parabolic mic, mounted the dish on a tripod, and then used his RTL-SDR to receive the FM transmission and demodulate the remote sounds. Of course reception can be done with any suitable radio, but the RTL-SDR provides the advantage of being able to easily manage, record and analyze the received audio.
The parabolic microphone with FM transmitter
Mario used his wireless parabolic microphone to record the sounds of finches in a bird house that was about 70 feet (21 meters) away. Then he writes that in HDSDR he was able to analyze the finches calls in the audio spectrum waterfall. He noticed that the calls were in the 2300 – 6000 Hz audio range and that each call’s “imprint” or audio signature was very similar and could be easily recognized. You can listen to the finches calls that were recorded by the RTL-SDR in the audio file below.
Looking at the Finch calls’ “imprints” in the audio spectrum waterfall in HDSDR
Mario writes that this can be done with any commercially available parabolic microphone, but if you want to know how to build your own wireless parabolic microphone then check out Make magazine’s article on Mario’s work. The article shows in detail how to build a parabolic microphone out of a squirrel baffle (a bowl shaped piece of plastic that prevents squirrels from eating bird feed), a Velleman Super Stereo Ear kit (microphone + amplifier kitset) and a standard wireless FM transmitter. Mario writes that the audio range of his home made parabolic mic is about 100 feet (30 meters). A video from Make magazine showing Mario’s home made parabolic mic is shown below.
Over on YouTube user MrCircuitMatt has uploaded a video where he explains the concepts of FM deviation, modulation index and sidebands using an RTL-SDR dongle as the receiver, and a function generator connected to a Kenwood TM-D700 transceiver as the transmitter.
In the video he transmits a modulated signal and uses a GNU Radio flowgraph to demonstrate and visualize what happens when the modulation frequency is changed. Later in the video he moves to pen and paper to explain the theory behind the results he saw.
HB9UF: FM deviation, modulation index and sidebands with an RTL SDR dongle
Over on YouTube a talk about decoding water and electricity usage meters with an RTL-SDR has been uploaded from the 2015 Camp++ conference in Hungary. The presenter, Stef writes:
Budapest public utilities started to roll out some new metering devices for water and heating (at least in my block). The plumbers who should install these could not tell me about the privacy protections considered, as I was a bit worried about the things leaking information over radio-waves, so I built a radio and reversed the messages.
The talk shows how the presenter was able to reverse engineer the FSK wireless protocol of his heating meter with help from some patent information that he found on the web. Using a GNU Radio flow graph that he created he was able to extract information such as total energy consumption and temperature readings.
Being a security themed conference, the presenter also discusses some of the security risks associated with wireless meters such as whether or not the meter can be used to detect if someone is currently at home.
The BA5SBA direct sampling kit is a kitset PCB that combines with a standard (included) RTL-SDR dongle in order to enable the direct sampling mod. The direct sampling mod is a hardware modification that can be applied to any RTL-SDR dongle in order to enable HF reception capabilities. The BA5SBA kit improves upon some of the problems with the direct sampling mod by adding additional features such as a low pass filter to block broadcast FM interference, a matching transformer to better match the RTL2832U’s input impedance, extra power supply filtering, SMA connectors for HF and VHF/UHF (UV), an aluminium case and a bias tee.
The BA5SBA direct sampling RTL-SDR can be bought as a kit that requires hand assembly for about $30 USD or as a fully assembled product for about $50 USD. It is usually listed on Amazon and eBay as a “100KHz-1.7GHz full band UV HF RTL-SDR USB Tuner Receiver/ R820T+8232 Ham Radio”
Recently, RTL-SDR.com reader Simon (MW0SGD) bought one of these kits and discovered that the English instructions were very rare and hard to come by. We’ve decided to post these English instructions here for any future buyers who may search for them as this post should show up on Google. Simon also notes that “most of the instructions on the internet wind the inductors on a 5mm former. This says to use a 3mm one, which I did and it works ok.”
Recently RTL-SDR.com reader Slaven Krilic wrote in to use to announce his project called MNM4SDR which stands for Monitoring Network Manager for RTL-SDR. The software allows you to set up a remote Raspberry PI embedded computer with an RTL-SDR dongle attached and access it remotely through a Windows PC GUI.
Unlike other server software such as rtl_tcp, raw IQ data is not sent over the network. Instead audio is first compressed in lossless FLAC or OGG formats. This allows you to use much slower network or internet connections. The software also allows you to collected RF scans over a large bandwidth in a similar way to rtl_power.
The software works over an SSH connection and requires that you have RTL-SDR and VLC set up on your Rasperry Pi first.
Rtl_power is a tool that allows you to create wide band signal strength heat maps over a long length of time. It works by very quickly hopping across the spectrum, capturing the RTL-SDR bandwidth of about 2 MHz at a time, and then displaying it on a heat map. This is useful for seeing what frequencies are active and at what times.
