March 15, 2018

Welle.io DAB Decoder updated to Version 1.0

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).

Vote

March 15, 2018

A Discone Antenna Made from 3D Printed Parts and Aluminum Tape

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.

However now over on Thingiverse, mkarliner (aka Mike) has a remedy for the difficulty in building a Discone with his 3D printable Discone design. To construct it you simply need the 3D printed parts, some .3mm and 2mm plastic sheets, a 25mm plastic conduit and some aluminium tape. Mike's design works from 400 MHz and up, but the design could be easily enlarged for better performance on the lower frequencies. He writes:

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.

If you're interested in building wideband antenna there is also the planar disk antenna (pdf) which can be built out of pizza pans.

Tweet1

Reddit17

Vote

18 Shares

March 14, 2018

Wired Article about Radiosonde (Weather Balloon) Hunting

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.

Radiosonde in flight captured by a GoPro camera.

Vote

March 14, 2018

Measuring the Noise Figure of Airspy and HackRF SDRs in Real Time

The Noise Figure (NF) is an important metric for low noise amplifiers and SDRs. It's a measure of how much components in the signal chain degrade the SNR of a signal, so a low noise figure metric indicates a more sensitive receiver. The Noise Figure of a radio system is almost entirely determined by the very first amplifier in the signal chain (the one closest to the antenna), which is why it can be very beneficial to have a low NF LNA placed right at the antenna

Over on his blog Rowetel has been attempting to measure the noise figure of his HackRF and Airspy, and also with the SDRs connected to an LNA. He's managed to come up with a method for measuring the noise figure of these devices in real time. The method involves using a GNU Octave script that he created and a calibrated signal generator.

It’s a GNU Octave script called nf_from_stdio.m that accepts a sample stream from stdio. It assumes the signal contains a sine wave test tone from a calibrated signal generator, and noise from the receiver under test. By sampling the test tone it can establish the gain of the receiver, and by sampling the noise spectrum an estimate of the noise power.

As expected, Rowetel found that the overall noise figure was significantly reduced with the LNA in place, with the Airspy's measuring a noise figure of 1.7/2.2 dB, and the HackRF measuring at 3.4 dB. Without the LNA in place, the Airspy's had a noise figure of 7/7.9 dB, whilst the HackRF measured at 11.1 dB.

Some very interesting sources of noise figure degradation were discovered during Rowetel's tests. For example the Airspy measured a NF 1 dB worse when used on a different USB port, and using a USB extension cable with ferrites helped too. He also found that lose connectors could make the NF a few dB's worse, and even the position of the SDR and other equipment on his desk had an effect.

Vote

March 14, 2018

Hackaday’s LimeSDR Mini Review

Over on Hackaday author Jenny List has today posted a review of the LimeSDR Mini. The LimeSDR Mini is a US$139 TX/RX capable SDR that was successfully crowd funded and has recently begun shipping to initial backers. In the review Jenny goes over the specs and differences between the Mini and standard LimeSDR. She then goes on to test it in GQRX, receiving a DAB digital radio signal, and creating a simple replay attack and FM transmitter in GNU Radio.

If you're interested in the differences between an RTL-SDR and a slightly higher level yet still budget friendly SDR then this review is a good overview. If you are interested, we also did a brief unboxing and initial thoughts review of the LimeSDR Mini which is available here.

Vote

March 12, 2018

Enumerating Multiple RTL-SDR Dongles Deterministically for rtl_tcp in Linux

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.

Vote

March 12, 2018

Real Time Passive Radar Running Native on the ADALM-PLUTO ARM CPU

The ADALM-Pluto (aka PlutoSDR) is a US$149 TX/RX capable SDR that we have posted about several times in the past. It has a tuning range from 70 MHz to 6000 MHz with a bandwidth of up to 56 MHz (with software hack applied). One additional useful feature on the PlutoSDR is it's built in ARM CPU, which can be used to run programs on board the SDR itself.

Over on his blog Mike has shown how he implemented simple passive radar code on the PlutoSDR's ARM processor. This means that no PC or other hardware is required to process the data, the entire script can be run via a SSH connection to the PlutoSDR. Mike doesn't seem to have shared his script anywhere, but one of his previous posts explains the process. The script creates the video in real time on board the PlutoSDR's ARM CPU, which is then streamed via ffplay to a PC with a screen. On his second post Mike shows some extra videos of passive radar working with FM Broadcast and DVB-T signals.

Passive radar is a radio technique allows you to detect and track RF reflective objects such as aircraft using strong signals from already existing transmission towers, such as broadcast FM or DVB-T signals.

Vote

March 12, 2018

Viewing Drone Signals with HackRF being used as a Wideband Spectrum Analyzer

Over on his YouTube channel user Andy Clarke has uploaded a video where he demonstrates his HackRF being used as a wideband spectrum analyzer with the HackRF Spectrum Analyzer software. About a year ago the HackRF team released a new firmware update which enabled the HackRF to be able to sweep through the frequency spectrum at a rate of up to 8 GHz per second. This allowed the HackRF to be used as a wideband spectrum analyzer which is able to display an arbitrarily large swath of spectrum. Shortly after the firmware update spectrum analyzer program by 'pavsa' was released on GitHub.

In the video Andy demonstrates the HackRF being used to view the WiFi band and show a 2.4 GHz WiFi connection between a drone and it's controller. He also shows it working with a handheld radio and the uplink of his mobile phone. Andy hopes to use the HackRF to avoid losing his drones due to interference.

Software Defined Spectrum Analyser - Hack RF

Watch this video on YouTube

Vote