Akos from the SDR for Mariners blog has posted an article that highlights the effects of coaxial cable attenuation. Long runs of coaxial cable between the antenna and RTL-SDR can significantly attenuate signals. This means that strong signals at the antenna will become weak signals at the receiver. The solution to this is to either reduce the cable length or to use higher quality cable. A preamp like an LNA may also help to overcome long runs of coaxial cable. Akos’ article discusses these issues.
Results from Akos’ test on different lengths of coax cabling
There are now some custom RTL-SDR kits available from Chinese and Russian manufacturers. These kits are essentially the standard RTL-SDR laid out on a custom PCB with extra upconverter (or direct sampling) circuitry on board.
Over on YouTube user k2nccvids has posted a video showing how he was able to decode APRS signals and plot them on a map using APRSISCE32. APRSISCE32 is an advanced Automatic Packet Reporting System (APRS) decoder which has mapping capabilities and can also connect to the internet as an iGate. APRS is used by amateur radio hobbyists to send data like messages, announcements and also GPS coordinates.
Over on YouTube user taroz1461 shows real time GPS positioning done in software using a BladeRF. The BladeRF is a ~$400 software defined radio which similar specs to the HackRF and compared to the RTL-SDR is capable of receiving much larger bandwidths and transmitting.
On YouTube user 王康 has been working with his HackRF One to create a computer keyboard controlled interface for his remote control car. The HackRF is a ~$300 software defined radio similar to the RTL-SDR, but with transmit capabilities.
To control the car he wrote a GNU Radio program to generate a control signal that is transmitted by the HackRF and a GUI to listen to keyboard presses on the PC.
Over on YouTube Adam Alicajic has posted a video showing how much a bandpass filter at the front end of an RTL-SDR can significantly improve reception. He points out that it is a myth that modern software receivers do not need preselector filters at the front end for best performance.
He tests the RTL-SDR with and without a front end 2m triple helical bandpass filter on a CW beacon at around 144 MHz. With the filter on there is almost a 10dB improvement in signal reception.
The PAL/NTSC analogue TV viewer TVSharp has recently been updated to version 1.2. This new version features an updated GUI as well as automatic frequency correction and automatic position correction. This may correct some of the scrolling and slanting problems seen in previous versions.
Word of warning: Chrome recognizes the download as malicious, however I have downloaded the file using FireFox and scanned it with Microsoft Security Essentials which found it to be clean.
The VHF Data Link mode 2 (VDL2) is a new transmission mode used on aircraft for sending short messages, position data (similar to ADS-B) and also for allowing traffic controllers to communicate to pilots via text and data. VDL2 is intended to eventually replace the standard ACARS modes. It is found at 136.975 MHz.
Recently, a wiki page explaining how to decode VDL2 using MultiPSK, Planeplotter and the RTL-SDR has been put up. MultiPSK is a sophisticated software program that can decode a wide range of amateur radio digital signals as well as several professional modes like VDL2. To decode most professional modes like VDL2 however, the paid version of MultiPSK is required, but a 5 minute per use trial of VDL2 decoding can be used for testing. Newer versions of MultiPSK can now even directly connect to the RTL-SDR dongle.
The wiki page shows how to set up the RTL-SDR dongle on MultiPSK to receive VDL2 signals, and then shows how to connect it to PlanePlotter in order to plot the aircraft positions on a map.
