Leif, the programmer of Linrad has uploaded a video on YouTube showing how to set up it’s waterfall for very high sensitivity reception of extremely weak signals. Linrad is an SDR GUI receiver software with a tough learning curve, but very advanced features. In the tutorial Leif uses an RTL-SDR dongle to receive a weak beacon at 144.412 MHz. He shows how to adjust the Linrad settings to produce a waterfall and FFT spectrum that it optimized for visualizing and tuning to very weak signals such as distant beacons.
Over on the SonicGoose.com blog, the author has recently created a tutorial showing how to use Modesdeco which is a multi platform command line ADS-B decoding software application. ADS-B stands for Automatic Dependent Surveillance Broadcast and is a signal broadcast by aircraft that can be used to track them like a radar.
Modesdeco is a command line ADS-B decoder quite similar in purpose to other software like dump1090, RTL1090 and ADSB#, however it has more available features built into it. The blog author writes about Modesdeco:
Want to feed BaseStation and PlanePotter at the same time? No problem. Want to add another data stream for Virtual Radar Server? No problem. Want statistics about the types of data being received? No problem. Want to run it on a variety of platforms, including Windows, Mac OS X, Linux, or the RaspberryPi? No problem.
The author’s tutorial goes over setting up the software on Windows and turning on some features like it’s web statistics interface, interactive map and how to feed data to another virtual radar application like Basestation. In the future the author plans to write a second tutorial showing how to use another feature which allows a user to combine the ADS-B feeds from various computers running Modesdeco.
Screenshot of the Modesdeco statistics web interface.
Over on YouTube user Mile Kokotov has uploaded a video showing his home made low loss helical bandpass filter for 145 MHz, but also tunable from 110 MHz to 160 MHz. Bandpass filters are useful for the RTL-SDR as often strong out of band signals can cause overload, causing poor reception. A bandpass filter blocks all signals outside of its pass band. A helical bandpass filter is simply a coiled wire enclosed in a conductive container that can be tuned with a variable capacitor made out of two plates.
In his video Mile shows the inner construction of his helical filter, explains the parts and shows what calculations he used for construction.
145 MHz Low Loss Bandpass Helical Filter by Mile Kokotov
With most low cost RTL-SDRs the provided 28.8 MHz local oscillator is of low quality and will often have a sizeable frequency offset and temperature drift. To fix this the oscillator can be replaced with a higher quality one.
Milan also writes how the Si535A has options for different drive currents and writes that by lowering the drive current from 8 mA to 2 mA the spurious signals found at multiples of 28.8 MHz in the RTL-SDR are reduced. He also writes the the Si535A also allows you to detune the frequency a bit which can help to tune around any spurious signals. This could be useful for example when using rtl_power as you could create a spurious free plot.
Using a Si5351A to replace the local oscillator on an RTL-SDR.
The script can easily be run by first editing the script to specify the frequency, dongle number, gain, PPM offset and destination folder. It can then be run by calling is with the start time, date, length and output file name. He also writes that you must be careful to not record for too long as long IQ files can use up a lot of disk space. To overcome this he uses a networked attached storage (NAS) device which is similar to an external hard drive.
Over on his blog /dev/thrash RTL-SDR experimenter Elia has been attempting to build an antenna to receive Global Positioning System (GPS) signals with his RTL-SDR. After doing some research he decided to build a Skew Planer Wheel antenna which he tuned for the GPS L1 frequency at 1575.42 MHz. A Skew Planar Wheel antenna is circularly polarized omnidirectional antenna which can be built out of wire. It is well suited to receiving signals from low earth orbiting (LEO) satellites such as the GPS satellites.
Elia later tested his antenna with a commercial GPS receiver circuit and was able to obtain a GPS fix.
Skew Planar Wheel Antenna on the RTL-SDR for receiving GPS.
Rtl_power is a command line program that can be used to create very wideband spectrum scans over a long period of time with an RTL-SDR. It comes with the official RTL-SDR release, but a more modern version can be downloaded from keenerds Windows builds.
Over the past few weeks programmer MichelinoK has been working on an Android app that allows the RTL-SDR to be listened to and controlled remotely. The app is called “Remote RTL_UDP” and allows you to control the parameters such as frequency, modulation type and gain settings on a remote rtl_udp server. It also allows you to store frequencies in a database and import frequencies from a SDR# database. The server can be run on a Raspberry Pi, Linux PC or any Linux device that is capable of running rtl_fm.
The post contains a full tutorial on the set up which involves the installation of ezstream and icecast for streaming audio as well as instructions for the installation of the modified version of rtl_fm called rtl_udp which allows remote control of the parameters via udp.
