Category: Applications

Vela Pulsar Glitch Detected with RTL-SDR Based Radio Telescope

On February 1st 2019 the HawkRAO amateur radio telescope detected a "glitch" during it's observations of the Vela Pulsar. A pulsar is a rotating neutron star that emits a beam of electromagnetic radiation. If this beam points towards the earth, it can then be observed with a large dish or directional antenna and a radio, like the RTL-SDR. The Vela pulsar is the strongest one in our sky, making it one of the easiest for amateur radio astronomers to receive.

Pulsars are known to have very accurate rotational periods which can be measured by the radio pulse period. However, every now and then some pulsars can "glitch", resulting in the rotational period suddenly increasing. Glitches can't be predicted, but Vela is one of the most commonly observed glitching pulsars.

The HawkRAO amateur radio telescope run by Steve Olney is based in NSW, Australia and consists of a 2 x 2 array of 42-element cross Yagi antennas. The antennas feed into three LNAs and then an RTL-SDR radio receiver. He has been observing the Vela pulsar for 20 months.

His observations indicate that Vela glitched and spun up by 2.5PPM at 14:09 UTC on Feb 1, 2019. He claims that this glitch detection is a first for amateur radio astronomy as far as he is aware.

If you're interested in Pulsar detection, check out a few of our previous posts on the topic.

The HawkRAO Amateur Radio Telescope Vela Glitch Detection
The HawkRAO Amateur Radio Telescope Vela Glitch Detection (Blue graph on the right indicates the glitch detection)

RSGB Talk – The Farnham WebSDR: DC to Microwaves on your Smartphone

Over on YouTube the Radio Society of Great Britain (RSGB) has uploaded a talk by Noel Matthews (G8GTZ) titled "The Farnham WebSDR: DC to Microwaves on your smartphone". The Farnham WebSDR runs 8 (soon to be 10) RTL-SDR dongles in order to cover multiple bands from DC to 2 GHz.

If you're interested in their talks, the RSGB also recently uploaded several other amateur radio related talks from their 2018 convention to their YouTube channel.

This presentation gives an overview of the Farnham WebSDR (http://farnham-sdr.com/) which currently covers the LF bands through to 10GHz. The presentation describes the system architecture and antennas currently used on each band and how the team has used RTL dongle receivers, available for under £10, to give good RF performance on all bands from DC to 10GHz. There is a demonstration of the SDR in use on both PC and smartphone.

RSGB 2018 Convention lecture - The Farnham WebSDR: DC to Microwaves on your smartphone

RTLion: The Multipurpose RTL-SDR Framework

Redditor [K3PWN] has recently released his project called “RTLion”. RTLion is a software framework for RTL-SDR dongles that currently supports various features such as a power spectrum plot and frequency scanning. The software can run on a Raspberry Pi 3 and all features are intended to be accessed via an easy to use web browser interface, or via an Android app. The software can also be run with Docker, making it useful for IoT applications.

RTLion project can be described as a framework due to the implementation of various features other than the frequency scanner. The common structure of the project is appropriate for adding new features too. RTLion Framework has a Flask–SocketIO based Web interface which houses it’s features there. Web interface preferred to the command line interface for facilitating the usage and supporting remote operations. Matplotlib used for creating graphs, more specifically pylabpsd(Power Spectral Density) method mostly used for converting the complex samples (stored in a numpy array) to FFT graphs.

Main purpose of the RTLion Framework is creating a framework for RTL2832 based DVB-T receivers and supporting various features such as spectral density visualizing and frequency scanning remotely. These features are provided on the Web interface and accessible via the RTLion server or the RTLion Android App for RTL-SDR & IoT applications.

RTLion - IoT RTL-SDR

All of his code is open source and available on Github. Currently he’s looking for feedback on improving the framework and we are interested to see where this project may lead in the future.

Decoding EMWIN Weather Information VHF Rebroadcasts with an RTL-SDR

EMWIN is an acronym for Emergency Managers Weather Information Network, and is a service for emergency managers that provides weather forecasts, warnings, graphics and other information in real time. EMWIN is broadcast from geostationary NOAA GOES satellites, and if you have a GOES SDR receiver setup it is possible to receive and decode EMWIN data.

However, if you don't want to set up a GOES receiver, KD9IXX writes on his blog how he investigated EMWIN and found that 24/7 dedicated EMWIN VHF repeaters are common around the US. Having found an EMWIN repeater in his area at 163.37 MHz he used the TrueTTY decoder and was able to successfully decode the 1200 baud 8-bit ASCII encoded signal and receive weather text information. He notes that VHF EMWIN is an excellent source of non-internet based weather data that could be useful to anyone requiring weather data in emergency circumstances.

EMWIN VHF Repeater Decoded with TrueTTY
EMWIN VHF Repeater Decoded with TrueTTY

LimeSDR Angle of Arrival Experiments at 145 MHz

Two J-Poles used in LimeSDR Angle of Arrival Experiments.
Two J-Poles used in LimeSDR Angle of Arrival Experiments.

Together with some Spanish amateur radio operators, Daniel Estevez performed an experiment with the goal of detecting the angle of arrival of meteor reflections coming from the GRAVES radar at 143.05 MHz.

The GRAVES radar at 143.05 MHz is often used by amateur radio astronomers as a way to detect the echos of meteors entering the atmosphere. The basic idea is that meteors leave behind a trail of ionized air which is reflective to RF energy. This RF reflective air can reflect the signal from the powerful GRAVES space radar in France, allowing the radar signal to be briefly received from far away. Detecting the angle of arrival from these reflections could help determine where the meteor entered the atmosphere.

Their experiments used a pair of J-Pole antennas and a LimeSDR receiver. The LimeSDR has two channels and can receive the signal coherently from both channels. The phase difference in the received signals from the two antennas can then be measured, and the angle of arrival calculated.

In their testing the first tested with 145 MHz amateur radio satellites. Unfortunately due to the low elevation of the antennas and multipath from terrain obstructions an angle could not be calculated. In a second experiment they tried receiving terrestrial APRS signals. With APRS they were successful and were able to determine the angle of arrival from multiple stations. Unfortunately for GRAVES meteor echoes they were not entirely successful, citing multipath issues due to houses, and the need for a clear view of the horizon.

We note that it may be possible to perform similar experiments with our KerberosSDR coherent RTL-SDR unit.

A Raspberry Pi and RTL-SDR Based Boombox

Thank you to Walter P. for writing in and sharing with us his conversion of an old analog boombox into a fully functional wideband software defined radio based on an RTL-SDR dongle and upconverter.

Walters Ghettoblaster RTL-SDR Radio
Walters Boombox RTL-SDR Radio

Inside the boombox Walter stripped away the analog circuitry and replaced it with a new LCD screen, Raspberry Pi, RTL-SDR, upconverter and an audio amplifier. Four rotary switches on top of the radio are used to control the frequency, demod mode and volume, and there is also a numerical keypad which can be used to enter the frequency directly. 5V and HF antenna connectors have been added to the side, as well as an upconverter enable switch on top. Walter also added a Spyserver mode to the software, which allows you to connect to the radio over WiFi with SDR#, although he notes that using the integrated Pi WiFi module seems to introduce noise on the speakers.

If you're interested in building a similar device, Walter has provided the full Python code and installation instructions for his build.

Edit 09 May 19: It was pointed out that the word "ghettoblaster" could be considered offensive in some cultures. We have changed the word in our article to "boombox" and apologize for any unintended offence.

RaspBRadio - A Raspberry Pi and RTL-SDR Based Boombox

KerberosSDR Direction Finding with Android App Demo and Tutorial

Over on our YouTube channel we've uploaded a short video that gives a tutorial and demo of the KerberosSDR being used as an RF direction finding system in a car. If you weren't aware, KerberosSDR is our recently released 4x Coherent RTL-SDR which can be used for tasks such as direction finding and passive radar. KerberosSDR was successfully crowdfunded over on Indiegogo, and we have recently completed shipments to all backers. Currently we are taking discounted pre-orders for a second production batch on Indiegogo.

In the video we use a Raspberry Pi 3 B+ running the KerberosSDR image as the computing hardware. The Pi 3 is connected to a high capacity battery pack. It is important to use a high quality battery pack that can output 3A continuously as this is required for the Raspberry Pi 3 B+ to run without  throttling. The battery pack we used has multiple outputs so we also power the KerberosSDR with it.

Once powered up we connect to the KerberosPi WiFi hotspot, and then browse to the web interface page. We then tune the KerberosSDR to a TETRA signal at 858 MHz, perform sample and phase calibration, set the decimation and FIR filtering, and then enable the direction finding algorithm. At this point we enter the Android app and begin direction finding and logging our data.

After driving for a few minutes we stop and check the logfile and find that the majority of the bearing lines point in one direction. With this info, a drive in the direction of the bearing points to gather more data is performed. Once additional data was gathered we open the log file up again, and see where all the bearing lines cross. Where they cross indicates the location of the 858 MHz transmitter. The heatmap data also gives us a second confirmation that the transmitter is located where we think.

NOTE: Some of the features shown in the video like the heatmap, confidence settings and plot length settings are not yet released in the current version of the app. They will be released next week.

Full instruction on using the KerberosSDR are available at rtl-sdr.com/ksdr.

KerberosSDR Direction Finding With Android App Demo and Tutorial

SingalsEverywhere: Running OpenWebRX on a PlutoSDR with PlutoWEB Firmware

Over on YouTube Corrosive from the SignalsEverywhere channel has uploaded a new video that shows how to install the the PlutoWEB Firmware on a PlutoSDR, which allows OpenWebRX to run directly on the PlutoSDR itself. OpenWebRX is a SDR streaming platform that enables people to connect to the SDR remotely over the internet. Multiple users can access the SDR at the same time as well. Many public OpenWebRX servers running on KiwiSDRs can be found at sdr.hu as the KiwiSDR uses it by default.

The PlutoSDR is a low cost (typically priced anywhere between $99 - $149 depending on sales) RX/TX capable SDR with up to 56 MHz of bandwidth and 70 MHz to 6 GHz frequency range. It also has an onboard FPGA and ARM Cortex-A9 CPU which can be used to run programs on the PlutoSDR itself.

Corrosive's video shows us how to install PlutoWEB which is an unofficial firmware package for the PlutoSDR. It comes preinstalled with many programs such as OpenWebRX and dump1090. He then shows how to set up OpenWebRX and then shows a demo of it in action.

OpenWebRX via PlutoSDR using PlutoWEB Firmware