Early last month we released a new broadcast AM high pass filter product. The goal of the filter is to block out extremely strong broadcast AM signals (and other problematic LF/MF signals) in order to prevent an SDR from overloading. This is especially needed if you live close to AM towers.
Over on the Utility DX Forum files section, reviewer D. B. Gain has written an excellent review of our broadcast AM high pass filter (pdf), also explaining why and in what situations it might be needed. In the review he explains how broadcast AM propagation works, and how it can change from day to night. He also explains how devices with diode switches (used for switching RF circuits such as filter in and out electronically) can easily overload and contribute to IMD within the switches themselves. This is why a filter without any diode switches in front of it is usually the best solution for reducing strong RF energies.
In the review he then goes on to test the filter, showing some screenshots of the reduction is AM signal strength.
On his blog leander has added a post which shows how he has set up a icecast streaming solution together with an RTL-SDR dongle which is receiving live NOAA weather radio. The idea is to give a computer with no soundcard the ability to stream compressed NOAA weather audio over a network. To do this he uses ezstream, icecast2 and lame. Streaming like this is great if you only want to listen to a single radio channel, and want a low bandwidth solution. Something like rtl_tcp streams the entire raw IQ data across the network which can use huge amounts of bandwidth. Streaming only MP3 audio is significantly more efficient.
First the RTL-SDR is set up to receive NOAA weather audio with rtl_fm. The audio is output to stdin, which is then sent to lame for encoding and MP3 compression. Next ezstream is set up to stream the encoded MP3 data via icecast. Now any PC on the network can use VLC or a similar program to connect to the stream and listen in.
Over on the Thought Emporium YouTube channel the team have uploaded two videos that may be of interest to radio hobbyists. The first video shows a nice overview about receiving NOAA weather satellite images. They explain everything from scratch for complete novice, so the videos are great for almost anyone to watch and learn about radio and SDR concepts. The blurb of the first video reads:
Over the past 2 months, me and my friend Artem have been building antennas to receive signals from weather satellites as they pass overhead. This video chronicles our progress through this project and goes through some of the science involved in working with radio and receiving transmissions. We explore how dipoles work and how to build them, and how we built our final double cross antenna. We used an SDR (software defined radio) called a HackRF to do the work of interpreting the received signals and then decoded them with some special software. We pulled images from 4 satellites: NOAA 15, 18 and 19 as well as METEOR M2. The satellites broadcast immediately as they take the images and no images are stored, so we’re likely the only ones on earth with these images.
The second video is about building a radio telescope. Like the NOAA video, they explain all concepts in a simple and easy to understand way, so that anyone even without any radio knowledge can understand what the project is about. In the video they also show how they use a 3D printer to create a tracking mount which can point a satellite dish. They then use the dish to create a satellite heat map. The blurb reads:
Over the last 2 months me and my friend Artem (you met him in the last video) built our first radio telescope. It was built mostly out of off the shelf components, like a satellite dish and Ku band LNB, as well as some parts we 3d printed. When all was said and done we had a system that could not only take images of the sky in radio frequencies (in this case 10-12ghz), but could also be used to track satellites. With it, we were able to see the ring of satellites in geosynchronous orbit, over 35,000km away, This is only the first of what I suspect will be many more telescopes like this. Next time we’ll be building ones that are far larger and can see things like the hydrogen lines so we can image the milky way.
Albrecht writes that his software is a fork of the qt-dab codebase, with the development goal being to create an easy to use DAB/DAB+ software receiver. The software is still under heavy development, and Albrecht mentions that he is looking for fellow developers and testers to help improve the software and report any bugs. Albrecht writes:
I’m proud to introduce a new open source DAB/DAB+ reception application welle.io https://www.welle.io. welle.io is a fork of qt-dab http://github.com/JvanKatwijk/qt-dab (old dab-rpi and sdr-j-dab) with the goal to develop an easy to use DAB/DAB+ reception application. It supports high DPI and touch displays and it runs even on cheap computers like Raspberry Pi 2/3 and 100€ China Windows 10 tablets. As input devices welle.io supports rtlsdr and airspy.
Currently daily Windows binary builds are available over on the projects GitHub. For Linux and Raspberry Pi users you’ll need to compile the code from source, but in the future he plans to provide Ubuntu snaps.
We gave the welle.io software a brief test and it ran as expected. There is an automatic channel scan feature which scans through all the possible DAB channels and an advanced mode for seeing technical information such as the frequency, SNR and error rates. The software also has a nice touchscreen friendly GUI which automatically downloads and displays the DAB/DAB+ program guide information.
UnoSDR is a simple, modern, intuitive interface, small and fast PC-based DSP application for Software Defined Radio (SDR). It’s written in C++ and Qt Quick cross-platform framework. Typical applications are Shortwave listening, Ham Radio, Radio Astronomy and Spectrum analysis.
UnoSDR supports both the RTL-SDR and soundcard based SDRs. With the RTL-SDR UnoSDR must be run via an rtl_tcp server. The software is for the Windows platform, but it seems that there is also an Android version, although this may not yet support the RTL-SDR as we could not get it to connect to our rtl_tcp server.
We tested the Windows version and it ran well despite a few glitches with trying to get the software to connect. There is also a bit of a delay when tuning due to the use of rtl_tcp, and the delays that using a network stream entail even when connected to the localhost. Also we only saw support for AM, USB, LSB and WFM modes. The other modes may be added later as the software still appears to be in development.
The free versions of both decoders only decode the EGC broadcast messages which contain SafetyNET messages. These include messages like weather reports, shipping lane activity and hazards such as submarine cables and oil rig movements, pirate activity, refugee ship reports, missing ship reports, and military exercise warnings.
The paid version can decode the other non-broadcast private LES STD-C channels. LES STD-C channels typically contain email like messages sent to and from ships. Mostly it’s company messages about the ship route plans, cargo discussions, repair/fault discussions, ship performance information and weather reports etc. Sometimes small files are also downloaded. Each Inmarsat satellite contains about 7 LES channels each run by a different telecommunications company, so one may be of interest to you.
The paid version of the Tekmanoid decoder also has a nice feature for visualizing the SafetyNET EGC messages. Every now and then an alert containing coordinates and an area is sent out. Usually it is something like a distress alert from an EPIRB or the search area for a missing vessel. The decoder generates an HTML file that displays these areas on a map, alongside the text message.
The author of the Tekamnoid software allowed us to test his new paid version for free. We ran the software using signal from an Outernet patch antenna and LNA. An RTL-SDR V3 + SDR# was used as the receiver, and the audio was piped to the Tekmanoid decoder with VB-Cable. Decoding was almost flawless on both LES and EGC STD-C channels. In a previous recent update the Tekmanoid decoder was updated for improved decoding performance, and now in our opinion it is almost or just as good as the inmarsatdecoder.com software.
If you are interested in learning more about decoding Inmarsat STD-C we have a tutorial available here. LES channels for the Inmarsat satellite in operation over your geographic location can be found on UHF-Satcom’s website.
Remember that LES STD-C messages are not publicly broadcast, so in some countries it may not be legal to receive them. Most countries will have a law that says you can receive and decode the data, but you may not act upon or use to your advantage any information from the messages.
The new software requires a different DVB-T driver app to be installed first, which is also provided by Martin. This is because the RTL-SDR needs to be operated in a mode different to the way that the SDR drivers use it in. Martin has also open sourced his Android DVB-T driver and it is available on GitHub.
Aerial TV is currently free on the Google Play store, but looks like it may eventually have some in-app purchases. Also, it is currently marked as ‘Unreleased’ on Google Play, which is essentially a beta version, so you might expect there to be some bugs.
Over on YouTube use radiosification has uploaded a video showing the Windows TETRA decoder ‘wintelive’ in action. Wintelive is a Windows port of the popular RTL-SDR compatible Linux based ‘telive’ TETRA decoder. Back in October 2016 we posted about its release and we have a tutorial for telive and the RTL-SDR available here.