Yesterday a reader wrote in to let us know about two comprehensive paperback books about radio signal identification that he’d found online. This reader thought the books would be relevant to RTL-SDR users wanting to know more about the vast number of signals available to them. The books are titled
Where each book is split into describing signals from VHF/UHF and HF respectively. More information on these books, and versions written in German can be found on the official book website. The author also has a book titled Signal Analysis for Radio Monitoring, which discusses techniques for analyzing unknown waveforms.
From the excerpts the book looks incredibly useful, so if our Radio Signal Identification Guide is not enough for you, we suggest trying a copy of these books.
Recently a reader wrote in to correct some mistakes regarding the Linrad software on our big list of RTL-SDR supported software post. Along with those corrections this reader also wanted us to know how much of a superior receiver he believes Linrad and the special Linrad RTL2832U E4000 drivers are.
The reader who wrote in wants to remain anonymous, but we will say that as far as we can tell he is not affiliated with the development of Linrad, and is simply a Linrad user and fan.
The first point the reader would like to make is about the Linrad RTL-SDR drivers special linearity mode.
[The Linrad drivers] main advantage for RTL E4000 based dongles isn’t the weak signal mode. It’s actually the linearity mode that provides significant dynamic range improvements over the existing osmocom drivers (http://www.sm5bsz.com/linuxdsp/hware/rtlsdr/rtlsdr.htm).
The author of Linrad, Leif, is very knowledgeable in both RF and SDR technology. It is extremely rare to be skilled in both. Leif submitted his modified RTL drivers to the osmocom team, but as best as I could tell, it became quite apparent the osmocom team does not have a firm grasp of the concept of dynamic range, and receiver performance metrics. Leif’s code was rejected for cosmetic reasons. It is a large shame, but highlights the extremely poor understanding the SDR community has of basic receiver performance metrics.
Shortly after the 4 minute mark, a strong signal is introduced into all four dongles. This signal is swept across so at times it is not present in the frequency span the dongles are listening to. Two of the dongles are E4000 based RTL SDRs, and naturally the Linrad one is using properly optimized settings. Notice how the properly optimized Linrad drivers show a nice calm spectrum, free form spurs, harmonics, images and other offending signals when the signal generator is introducing a signal several MHz away from the listening frequency span.
Notice how the osmocom dongles are essentially trashed, where nothing but the strongest of strong of signals could be heard, and even then it’s likely to have distortion. This is what happens in the real world. For most people, when they connect their RTL to an outdoor antenna, their receive performance is not limited by the noise figure of the dongle, but rather by its dynamic range. Leif is the _only_ SDR program author that fully understands this.
As well as the driver issue the reader also highlights some advanced features of the Linrad SDR program itself which are not present in most other similar software defined radio programs.
1) Proper I/Q calibration. Other programs at most only allow you to calibrate a SDR for a single part of the spectrum. This is not proper, because at a few kHz away, the I/Q balance will shift and the calibration will no longer be accurate. Linrad allows you to calibrate for many frequency intervals across the SDR’s bandwidth, resulting in a flat frequency response and true I/Q phase and amplitude balance calibration.
3) Linrad can multicast its output to multiple computers or directly to a single computer over the network. You can also run multiple instances of it on the same computer.
4) Linrad’s waterfall is effortlessly optimized to display signals ~10dB (or more) weaker than what you can hear. No other SDR program allows this “out of the box”. Some will achieve similar performance by adjusting various settings, but will require more averaging (slower water fall speed) to achieve a similar waterfall “visual” SNR as Linrad.
In short, if you want to listen to FM broadcast signals from 88-108 MHz, take your pick of SDR programs, it doesn’t matter when picking up a 50+ kW transmitter a few dozen kilometers away. If you want top performance, learn about DSP, RF, performance metrics, and so forth, there is only one suitable program: Linrad. Nothing else comes close.
D-STAR or (Digital Smart Technologies for Amateur Radio) is a Frequency Division Multiple Access (FDMA) Gaussian Minimum Shift Keying (GMSK) digital voice and data protocol used in amateur radio.
Up until recently it was possible to decode D-STAR headers using either DSD 1.6 or dstar.exe and an RTL-SDR, but it was not possible to decode voice. Now amateur radio hobbyist PU2VLW has brought to our attention that the latest DSD development version 1.7 is capable of decoding D-STAR audio (his post is in Portuguese so we suggest using Google translate). He shows a video of some example D-STAR decoding which we show at the end of this post.
DSD 1.7 can currently be downloaded as source from it’s GitHub respository. Instructions for installing DSD 1.7 on Linux can be found on the post by PU2VLW and the GitHub readme. PU2VLW built DSD 1.7 in Ubuntu 10.04, noting that newer versions of Ubuntu have removed OSS (Open Sound System) support which DSD requires. He then runs SDR# on a Windows PC, tuned to a D-STAR signal, and uses an audio out cable to connect the Windows PC’s audio out to the Ubuntu PC running DSD 1.7.
Update: See this post for installing DSD 1.7 on Windows.
Decodificando Dados e Voz da tecnologia D-STAR sem utilizar DV Dongle
CTCSS is an acronym for Continuous Tone-Coded Squelch System and is a system that is used in shared two way radio systems. It is common for a single radio channel to be shared over a number of user groups for frequency use efficiency. CTCSS uses a special tone to identify each group of users, and this tone is used to prevent a group hearing radio chatter from another group sharing the channel.
The antenna was created by F5ANN, and he used his active antenna together with an RTL-SDR dongle, the RTL1090 ADS-B decoding software and PlanePlotter, and was able to receive 194 simultaneous aircraft signals with a message rate of 556 messages a second at distances of up to 250 nm.
This antenna can now be bought from the 1090mhz.com webstore, and is available with or without LNA. The LNA will help if you need long runs of coaxial cable between the antenna and RTL-SDR.
Smart meters are meters that monitor electricity usage and wirelessly transmit consumption data to the electricity company. They are a part of the “smart grid”, and allow for better electricity control and usage reporting.
Douglas recently wrote in to us to let us know about his work on RTLAMR, an RTL-SDR based Automatic Meter Reader (AMR) decoder. Currently Douglas has tested the decoder on his local Itron C1SR smart meters, but notes that it should work on any meter using the common AMR protocol known as Electronic Receiver Transmitter (ERT).
There are now dozens of software defined radio packages that support the ultra cheap RTL-SDR. On this page we will attempt to list, categorize and provide a brief overview of each software program. We categorize the programs into general purpose software, single purpose software, research software and software compatible with audio piping.
If you know of a program that is missing please leave a comment in the comments section at the bottom of the page.
SDR# (pronounced "SDR Sharp") is the most popular free RTL-SDR compatible software in use at the moment. It is relatively simple to use compared to other SDR software and has a simple set up procedure. We have a full overview of the installation procedure on our Quick Start Page. SDR# is designed to be use with the $199 Airspy SDR, but works just fine with the RTL-SDR.
SDR# is a simple to use program that also has some advanced features. It has a useful modular plugin type architecture, and many plugins have already been developed by third party developers. The basic SDR# download without any third party plugins includes a standard FFT display and waterfall, a frequency manager, recording plugin and a digital noise reduction plugin. SDR# also decodes RDS signals from broadcast FM.
HDSDR is based on the old WinRAD SDR program. HDSDR supports the RTL-SDR through use of an ExtIO.dll module. To install HDSDR, download the program from the link on the main HDSDR page, then to use the RTL-SDR you will need to download the ExtIO_RTL2832.dll file an place it into the HDSDR folder. When opening HDSDR, select the newly copied ExtIO_RTL2832.dll. The other dlls that come with HDSDR will not work with the RTL-SDR, even though they have RTL-SDR in their filename. The official installation instructions can be found here.
Along with a FFT display and waterfall, HDSDR has some extra advanced features. Users will also find an Audio FFT and waterfall display on the bottom of the screen. The output audio can also be bandpass filtered by dragging the filter borders on the display. Bandpass filtering the audio can really help clean up a noisy signal. The audio processing also supports placing of notch filters either manually or automatically. There are also noise reduction and noise blanker features and an automatic frequency centering algorithm which will automatically center the signal, so you don't need to click exactly in the center of a signal. Traditional ham radio users will also enjoy the S-units signal strength meter and the built in frequency manager.
SDR-RADIO.COM V2 and the newer V3 is a popular SDR program with many advanced features. As such is it a fair amount more difficult to learn and use compared to SDR# and HDSDR. Be sure you install version 2 and not V1.5 as only V2 has RTL-SDR support.
Once sdr-radio is installed, to get it working with the RTL-SDR you will need to compile or download three .dll files (SDRSourceRTL2832U.dll, rtlsdr.dll and libusb-1.0.dll) and place them into the sdr-radio folder. To compile your own dlls see the instructions here, otherwise download the dlls directly from the bottom of this link. If the dlls were placed in the correct folder you will be able to add your RTL-SDR as a receiver by clicking on the +Definitions button, and then finding and adding the RTL SDR (USB) option under the search drop down menu.
Like HDSDR, not only does sdr-radio have a RF FFT signal and waterfall display, but also an optional audio spectrum FFT and waterfall display. Built in are also several DSP features like a noise blanker, noise reduction filter, notch filter and squelch options. The EMNS noise reduction filter is particularly good at automatically cleaning up and clarifying voice signals.
To add to the feature list, sdr-radio also has built in PSK, RTTY and RDS decoders, and also comes with a satellite tracker. Furthermore, sdr-radio V2 (not V3 yet) has an excellent remote server which will allow you to easily set up and connect to a remote RTL-SDR server over a network or the internet. Finally, sdr-radio is capable of listening to up to 6 signals in the same chunk of visible spectrum at a time.
