The popular trunking decoding software Unitrunker now supports the RTL2832U R820T RTL-SDR directly in its new version. This means that extra SDR receiver software like SDR# is no longer required to use Unitrunker.
In a normal radio system, one company (or talkgroup) might use a single frequency for radio communications. However, this is very inefficient as the frequency may not be in use for the majority of the time. In a trunked radio system, a small set number of frequencies are shared between a large number of talkgroups. Each radio receives a special computer controlled control channel. The control channel determines a vacant frequency that a particular talkgroup should use. This helps to make radio frequency allocations more efficient.
Because a talkgroup might switch between various frequencies often, it can make listening to a conversation difficult for radio scanners. Unitrunker can be used to decode the control channel and follow a voice conversation as it hops across various frequencies. With two RTL-SDR dongles you can set up a trunking receiver station with just Unitrunker. What follows below is a tutorial on how to set this up.
The High Performance Software Defined Radio (HPSDR) project is an open source SDR project that aims to create a modular SDR for ham radio use. The idea is that users only need to include the specific HPSDR hardware that they need for their particular application.
Using his tool Richard was able to get seven R820T RTL-SDR dongles running simultaneously on an EKB311 Quad core ARM Cortex A9 based mini-pc using a USB 2.0 hub with a modified power supply to provide 5V@2A.
Over on Reddit, user cronek discovered by using his RTL-SDR that the microphone on his HP EliteBook 8460p laptop computer was continuously and unintentionally transmitting the audio from the built in microphone at 24 MHz in FM modulation. He found that the only requirement needed for the microphone to transmit was that the laptop needed to be turned on – even muting the microphone did nothing to stop the transmission.
I accidentally stumbled upon a signal in the 24MHz range, appearing to be 4 carriers. I tuned to it and heard silence, then someone came into my office and started talking and I could hear them speak. The signal appeared to be coming from my other laptop (not the one running the SDR) and was pretty weak (my antenna, the crappy one that comes with the dongle, stuck to a metal stapler was right next to the HP laptop).
This is of potential concern as as the US Military is apparently transitioning to this particular laptop. However, this may be an isolated incident, as in the thread cronek explains that other laptops he tested did not display this behavior.
A few days ago we posted a video by sm5bsz showing some comparisons between the E4000, R820T and FC0013 tuners, and also a comparison between the special linearity gain mode driver in Linrad and standard Osmocom driver in SDRSharp.
Now sm5bsz, programmer of Linrad and the special gain modes for the E4000 has done another test using only Linrad, which more fairly demonstrates the difference between the various tuners, and the effect of the special gain drivers in Linearity mode. He writes
In this video RTL2832 dongles are compared for sensitivity, spurs and intermodulation. The difference between the Linrad linearity mode and the original Osmocom gain setting is demonstrated as well as spurs in R820T and FC0013.
Which one to prefer depends on the local RF Environment and whether a selective filter is used between the antenna and the dongle.
Note: The Linrad vs SDRSharp video has been removed by the uploader.
Finally in this video, he also compares the standard Osmocom driver to the sensitivity mode available in the modified gain profile drivers. He writes
The sensitivity mode has very poor performance for signals far away from the passband, but it allows about 10 dB better dynamic range for interferences within the passband. Sensitivity mode is for usage with a selective preamplifier while the Osmocom gain mode is a reasonable compromise. The Linrad linearity gain mode is for use without filters in difficult RF Environments.
In this video YouTube user ek6rsc shows a timelapse of meteor reflection observations during the yearly Perseids meteor shower which occurred in 2013 during August 10-15. To do this he uses an R820T RTL-SDR tuned to 59.25 MHz, and the HROFFT software to do the recording.
Meteors entering the atmosphere can cause radio frequency reflections which may allow extremely distant radio signals to be received briefly. Reception of such a signal may be a good indicator that a meteor has fallen. A good informational guide on meteor scatter with the RTL-SDR can be found in this pdf file by Marcus Leech.
2013 Perseids Aug10-15 radio observations Meteor reflection 59.25Mhz