Finding the correct direction to point a satellite for TV reception can be difficult without the right equipment. YouTube user MegaOscarVideos shows us in the video below how he uses an RTL-SDR to accurately aim his satellite for TV reception.
He uses a TV satellite dish with an LNB connected to a bias-T circuit as the receiver, which is then connected to the RTL-SDR. As the satellite is moved he looks for the direction at which the signal level in SDR# increases the most.
Amateur radio hobbyist LA3ZA shows an image on his blog showing how busy the 70cm ISM band can be in his area in Norway. He uses a roof mounted 1.7 m long vertical antenna with 7.2dBi gain in the 70 cm band. Each signal burst may come from a remote car key, weather monitor, electricity monitor, or other telemetry device. Some of these signals may be decodeable with rtl_433.
Back in November we posted about Oona’s work with decoding radio controlled bus stop display signs using her RTL-SDR. Oona has given a talk at the Chaos Communication Congress about her work on decoding FM-RDS and the bus stop displays. The talk is now available on YouTube.
How I discovered mysterious hidden signals on a public radio channel and eventually found out their meaning through hardware hacking, reverse engineering and little cryptanalysis.
A story about my experiences with FM-RDS (Radio Data System), a digital subcarrier embedded in FM broadcast transmissions, and also cryptanalysis of the weakly encrypted TMC traffic messages contained therein. I originally found about the existence of such transmissions in a roundabout way, by using a spectrum analyzer program to examine intermodulation distortion in my radioâs Line Out audio. As it turned out, the inaudibly quiet distortion, probably caused by the radioâs stereo demuxer circuitry, contained all the information needed to decode all RDS data present in the transmission. I will demonstrate the journey I took and give a short introduction to how the data is actually encoded. Live acquisition of local RDS data depending on signal conditions in the premises.
As a bonus, I’m introducing yet another little-known FM subcarrier called DARC, and my recent reverse engineering of the bus stop display radio protocol used in Helsinki.
Satellites in Low Earth Orbit have tons of nifty signals, but they move quickly though the sky and are difficult to track with fine accuracy. This lecture describes a remotely operable satellite tracking system that the author built from a Navy-surplus Inmarsat dish in Southern Appalachia.
The entire system is controlled through a Postgres database, fed by various daemons spread across multiple machines. So when I click on a satellite on my laptop or cellphone, it runs “UPDATE target SET name=’Voyager 1′;” and the motor daemon then begins to track the new target while the prediction daemon maintains accurate estimates of its position in the sky. Additional daemons take spectral prints or software-defined radio recordings of the targeted object for later review.
Update: This post is now very old. The latest version of DSD+ can now to found at www.dsdplus.com.
Over on Reddit we've seen mention of an upgraded Digital Speech Decoder (DSD) program, named DSD+. The original DSD is a program that can be used in conjuction with a SDR receiving program such as SDR#, and an audio piping program like VBCable to decode digital speech, such as P25 and DMR/MOTOTRBO.
DSD+ claims to have improved decoding and audio quality capabilities. An audio sample from a weak P25 sample can be found here for DSD+, and for comparison here for the old DSD.
To run DSD+. you will need to place an MP3 encoder file lame_enc.dll into the same folder as the dsd.exe executable. This file is not included with DSD+ due to licencing. For Windows, lame_enc.dll can be downloaded from http://lame1.buanzo.com.ar/#lamewindl (Mega Mirror). Download the ZIP option, and then copy the dll file into the same folder as DSD+.
If you don't know how to use DSD, see our tutorial on using DSD here, and if desired simply use DSD+ instead of the original DSD. (Note cygwin is not required for DSD+)
Gough shows how he was able to receive and decode the data from an Aldi weather station device and a wireless doorbell transmitter. He also was able to modify the rtl_433 code slightly to produce a CSV log file of the temperatures that were received and decoded from the weather station.
After checking for local causes of interference and finding nothing, they decided that the interferer must be coming from further away. To find the location of the jamming signal they did some radio direction finding. This involved driving around with Yagi and magnetic loop antennas and RTL-SDR and USRP N200 SDRs and then measuring the signal strength at various points.
For the software they used a custom GNURadio block which calculated the power spectra using the FFTW C library, and averaged the results to disk. They then post processed the data to calculated the RFI power, and correlated the data with GPS coordinates recorded on his phone.
After all the data was processed, they discovered that the interference originated from an FM radio tower which had a faulty FSK telemetry link. They notified the engineer responsible who then replaced the link and the interference disappeared.
