Welle.io is a Windows/Linux/MacOS/Android/Raspberry Pi compatible DAB and DAB+ broadcast radio decoder which supports RTL-SDR dongles, as well as the Airspy and any dongle supported by SoapySDR. It is a touch screen friendly piece of software which is excellent for use on tablets, phones and perhaps on vehicle radio touch screens.
DAB stands for Digital Audio Broadcast and is a digital signal that is available in many countries outside of the USA. The signal contains digital broadcast radio stations, and is an alternative/replacement for standard broadcast FM.
Early last year we posted about Welle.io a couple of times, but now the software has reached maturity as version 1.0 has just been released. Author Albrech writes to us:
We fixed a lot of bugs again and added the translation to Hungarian, Norwegian, Italian and French.
Binary packages are available for Windows, Linux and Android (APK and Play store). The macOS support is possible via Homebrew and we now that welle.io runs also on a Rapsberry Pi 2 and newer.
For questions and support please feel free to use the new forum (https://forum.welle.io).
A Discone is a type of antenna that is designed to be resonant over a wide range of frequencies. Most antenna designs only really receive well on a few resonant frequencies, but a Discone is resonant over a much wider frequency range. This makes it a good partner for RTL-SDR and other SDR units as many SDRs tend to have wide tunable frequency ranges. With a wideband antenna like a Discone connected to an RTL-SDR one can scan over the almost entire tunable frequency range without needing to change antennas for each band. The drawbacks to a Discone however is that the antenna gain is not very high, and that it makes the SDR more susceptible to out of band interference. They also tend to be fairly expensive and difficult to build.
The Discone antenna is remarkable in that it is capable of receiving and transmitting over a wide range of frequencies with good matching. Because of this, it is a good match for SDR receivers such as the popular RTL-SDR sticks.
The only really tricking thing about making a discone is that the disc has to be balanced at the very top of the cone, which is mechanically awkward.
The two parts here allow the cone to be solidly clamped and provide an adequate base for the disk. There also two holes for bring the coax centre and braid out to the disc and cone. The base part has a socket at the bottom for 25mm (1 inch) plastic conduit for mounting
This antenna illustrated is designed for 400MHz and up, and as such transmits well on the 70cms amateur band, US and UK PMR channels and 23cms. It also receives aircraft ADS-B signals very well. I used .3mm plastic sheet for the cone and 2mm plastic for the disc, and then covered them with aluminium weatherproof tape. Be sure to check for continuity across the tape stripes.
The screenshot is of a calculator by VE3SQB which can be downloaded from http://www.ve3sqb.com/ if you want to make attenna's for other ranges.
A 3D Printed Discone
If you're interested in building wideband antenna there is also the planar disk antenna (pdf) which can be built out of pizza pans.
Wired.com has recently run a short article about Roland F5ZV's hobby of radiosonde hunting. A radiosonde is a small box containing electronic sensors that measure things like wind, temperature, humidity and also give out a GPS location. The radiosonde is carried into the upper atmosphere by a weather balloon, and these probes are usually launched twice a day in many locations around the world by meteorological agencies. The data is useful for weather forecasting and research.
The wired article discusses the hobby of radiosonde hunting, which is the sport of using radios to hunt and collect the radiosonde as it bursts and falls back to earth. He also writes how he was able to convince the Swiss Meteorological agency to allow him to attach a GoPro to a radiosonde which allowed him to capture some interesting images.
We'd like to remind readers that in many places in the world it is possible to receive and decode radiosonde data with an RTL-SDR, and we have a tutorial available here.
Thanks to user 'luma' on our forums for submitting his technique for managing multiple RTL-SDR dongles on a Linux system. The problem is that rtl_tcp tends to enumerate devices depending on the order they are plugged in. This can create problems like not knowing which dongle is connected to which antenna without physically checking. He writes:
I was looking to utilize a couple RTL dongles to monitor two ISM band frequencies commonly used in LoRa without buying an SDR with wide enough bandwidth to cover both ranges. I pretty quickly ran into issues with how SpyServer and rtl_tcp enumerate devices, which appears to be based mostly upon the order in which each device had been plugged in.
With some work, I think I've come upon a flexible and secure solution to handle an arbitrary number of dongles on one system while maintaining deterministic control of each device. This means I can label an individual dongle, connect it to the desired antenna, and then connect to that dongle on the assigned TCP port every time, without regard to the order in which things have been plugged in.
The rest of his post shows the steps which include creating an unprivileged service user, using rtl_eeprom to set device serial numbers and using a script that automatically runs on startup which will enumerate the dongles deterministically each time.
Over on our forums poster hotpaw2 has released news about his new RTL-SDR app for iOS (iPhones/iPads). If we're not mistaken, this will be the first app that enables RTL-SDR usage on iOS. However, as iOS devices don't allow RTL-SDRs (or any arbitrary USB device) to connect directly to devices, you still need to use a Raspberry Pi or other network connected computing device as an rtl_tcp server. So the RTL-SDR does not plug directly into the iOS device. Currently he is looking for beta testers to help test a pre-release of the software. Hotpaw2 writes:
Hi. A first version of my iOS SDR app is nearing completion. So I'm interested finding a few users who would like to beta test a pre-release of the app, and provide some feedback. The beta test requirements are having a 64-bit iOS device (iPhone or iPad) running iOS 11.2.x or newer, having Apple's TestFlight app installed, having a Mac, PC, Raspberry Pi (or other Linux box) that already has rtl_tcp installed and ready to run. (And an RTL-SDR obviously.) The rtl_tcp server must be on a fast WiFi network reachable by your iOS device. Note that iOS TestFlight app distributions do have an expiration date.
iOS does not recognize arbitrary USB devices such as an RTL-SDR. This is even true when using Apple's Lightning Camera Connection kit to provide an iPhone with a wired USB port. So an adapter must be used. I use a headless Raspberry Pi 3 running rtl_tcp as the USB adapter to provide raw IQ samples from the RTL-SDR to the iOS app. A Raspberry Pi Zero W would also work. I then connect to the server either over WiFi, or via wired ethernet.
This iOS SDR app is fairly simple. I've been experimenting with developing low-level DSP code in Swift. So this SDR app was written from scratch in the Swift programming language. Because the app is targeted for the iOS App store, it uses none of the existing SDR C++ code base.
The app currently demodulates AM, N-FM, and mono W-FM. It also displays a spectrum and rudimentary waterfall, and allows one to swipe-to-tune. There are not a lot of controls, as screen real-estate on an iPhone is quite limited. But I can walk around the house and, from my iPhone, monitor if my RTL-SDR or AirSpy HF+ are picking up any interesting signals.
Source code to librtlsdr and rtl_tcp can be found in many repositories on github, but zero support for finding or installing such, and/or setting up your Raspberry Pi, will be provided by me.
Thanks to Andrey for writing in and showing us his Java based Meteor-M decoder for the RTL-SDR which he uses on a Raspberry Pi. The decoder is based on the meteor-m2-lrpt GNU Radio script and the meteor_decoder which he ported over to Java. Essentially what he's done is port over to Java a bunch of GNU Radio blocks as well as the meteor decoder. The ported Java blocks could also be useful for other projects that want to be cross platform or run without the need for GNU Radio to be installed.
In his blog post (blog post is in Russian, use Google Translate for English) Andrey explains his motivation for writing the software which was that the Windows work flow with SDR# and LRPTofflineDecoder is quite convoluted and cannot be run headless on a Raspberry Pi. He then goes on to explain the decoding algorithm, and some code optimizations that he used in Java to speed up the decoding. Andrey notes that his Java version is almost 2x slower compared to the GNU Radio version, but still fast enough for real time demodulation.
Meteor-M2 is a Russian weather satellite that operates in the 137 MHz weather satellite band. With an RTL-SDR and satellite antenna these images can be received. Running on a Raspberry Pi allows you to set up a permanent weather satellite station that will consistently download images as the satellite passes over.
Images received with Andry's Meteor-M software running on a Raspberry Pi.
Fosdem 2017 and 2018 were conferences on software development that occurred on 4 & 5 February 2017 and 3 & 4 February 2018. The conference features several software defined radio and RTL-SDR based talks which appear to have recently been uploaded to YouTube. Below we're posting some of our favorite SDR related talks, but the full video list can be found here, and here is the SDR playlist from Fosdem 2018.
(Yet another) passive RADAR using DVB-T receiver and SDR
by Jean-Michel Friedt @ FOSDEM 2018
In this presentation Jean-Michel shows a GNU Radio passive radar implementation utilizing two coherent RTL-SDR dongles. During the talk he demonstrates his results with RTL-SDR passive radar operating on planes, boats and cars.
(Yet another) passive RADAR using DVB-T receiver and SDR.
Intro to Open Source Radio Telescopes
by Martin Braun and Sue Ann Heatherly @ FOSDEM 2018
In this talk Martin and Sue discuss how amateur radio astronomy can be performed using lost cost software defined radio tools such as an RTL-SDR. They show how to receive solar flares and detect the 21cm hydrogen line and focus on showing how easy it can be to do these projects in a classroom environment.
Intro to Open Source Radio Telescopes
Claim Space, the Libre Way, using SDRs
by Manolis Surligas @ FOSDEM 2018
In this talk Manolis from the Libre Space Foundation and SatNOGs discusses how they use RTL-SDR's and other SDR's in their volunteer run network of satellite ground stations to create an online database of received satellite data.
Claim Space, the Libre Way, using SDRs
Receiving Wireless Mobile Traffic Lights
by Bastian Bloessl @ FOSDEM 2017
Wireless mobile traffic lights are often used to secure construction sites when roads are partially blocked. Some day, when a pair of them was placed close to our home, I set off to explore how they are working. In this talk, I will describe how I used a cheap RTL-SDR together with GQRX, Inspectrum, and GNU Radio to reverse engineer the modulation and frame format of different types of wireless traffic lights. With some patience, I could also make some sense out of the bits. In particular, I was able to extract the signal state and display it in a web interface, mirroring the traffic light. A closer look at the frame format and the apparent absence of any authentication might leave one with a bit of a worrying impression regarding the security of those systems.
The R820T2 is the main tuner chip used in most RTL-SDR dongles. Several months ago Rafael Micro ceased regular production of their R820T2 chip, and the older R820T has also been discontinued for some time too.
However, Rafael are still producing new quality R820T2 chips for factories if they make very large bulk orders. Since it is one Chinese manufacturer producing all of RTL-SDR.com V3, NooElec, FlightAware and most generically branded dongles, the volume restriction is not a problem for them as long as the RTL-SDR is still in demand. So most dongles using R820T2 RTL-SDRs should be able to continue business as usual for the forseeable future. But we have also recently seen that a lot of generically branded RTL-SDR dongles presumably produced at other factories have started to ship with the less desirable FC0012/13 tuner chips instead.
The R820T chip is already 8 years old, and the R820T2 has been around for the last two years. The R820T2 was a slight improvement on the R820T, due to a higher quality manufacturing process used to produce it. The change in manufacturing process resulted in mostly higher yields, less chip-to-chip variance, better sensitivity, reduced L-band heat VCO lock issues, and wider filters.
Recently the Youssef from the Airspy team announced the likely early retirement of their Airspy Mini and R2 line of products(see update below, Airspy Mini/R2 production will continue) These are SDRs that used the R820T2 tuner chip combined with a 12-bit ADC, allowing for significantly better performance compared to an RTL-SDR. It seems that they were able to acquire R820T2 chips from a distributor, but the stock proved to be very low yield. Possibly once discontinued a lot of low quality chips were dumped onto the distributors for final sale. They write:
I have some bad news. Rafael Micro officially discontinued the R820T2 since a few months. This is the tuner we use in the Airspy R2 and Airspy Mini.
We tried to secure an extra batch from Rafael (even at a higher price) but the quality of the silicon of the samples we received wasn't very good and most units didn't pass our automated QA tests. Sacrificing the performance is out of question. The alternatives proposed by Rafael are not pin compatible and require both a significant hardware redesign and new tuner control code - and this is a large investment with very little guarantees on the final result.
I can say this has been one of the longest running designs that resisted the new silicon tuner SDR's popping in and out while setting a standard for performance and price.
For now, our distributors are running out of R2/Mini's very quickly and, until a final solution is found or a new replacement is designed, there won't be any new batches out.
I was checking my notes for alternatives to the current Airspy R2/Mini design and wondered if consulting the community would give some constructive input. As the market is already crowded with low cost receivers and transceivers, but yet Icom manages to sell a 4 figures SDR, I was thinking of making something that is as open as possible for extensions and work good enough for the most demanding operators and pro's, all while being affordable.
The idea is to replace the R820T2 tuner with one of its latest high performance siblings, then replace the old LPC4370 with the brand new i.MX RT1020. This MCU can be interfaced with a good ADC and has enough processing power for oversampling and decimation through the Cortex M7 core, which will bring the final resolution higher. The general goals:
Better RX performance than the general purpose low cost silicon transceivers
12 bit RX at 10MHz bw and up to 16bit at narrow band
Coverage from 30 MHz to 1.8 GHz or more
Switched pre-selectors
Open source
Same form factor as the Airspy HF+ (same box actually)
Leverage the RF manufacturing and testing capability developed at Itead Studio
Affordable
UPDATE (May/2018): The Airspy team have managed to acquire a new batch of good R820T2 chips, so production of the R820T2 based Airspies can continue as per usual.
So in conclusion there is no need to panic buy R820T2 RTL-SDRs as production will continue as per normal for the forseeable future as the RTL-SDR demand is high enough for factories to make large bulk orders of new R820T2 chips. Even if the R820T2 is fully discontinued, there are alternative tuners with the same performance that we can switch to after a minor redesign.
Note that we're currently out of stock of RTL-SDR V3's on Amazon and low in stock on our store but this is not related to R820T2, but rather simply shipping delays. We should be fully back in stock within a few weeks.
