Tagged: rtl-sdr

Video Demonstrating Hydrogen Line Detection with an RTL-SDR and WiFi Dish

Back in January 2020 we posted a tutorial showing how it's possible to detect and measure the galactic Hydrogen line using a simple 2.4 GHz WiFi dish, RTL-SDR Blog V3 and a filtered LNA. Since then many people have used the same setup with great results.

Over on YouTube user stoppi who is one such person who is using the same steps from our tutorial, and he has uploaded a video showing his setup and results. If you're thinking of getting started with Hydrogen Line reception, his video slide show tutorial would be a good complimentary overview to go along with our text tutorial.

Detection of the galactic hydrogen - the 21 cm radiation - Wasserstoffstrahlung der Milchstrasse

TechMinds: Receiving and Decoding Packets from the GreenCube Cubesat Digipeater

GreenCube is a CubeSat by the Sapienza University of Rome, and it is designed to demonstrate an autonomous biological laboratory for cultivating plants onboard a CubeSat.

While this is an interesting mission in itself, for amateur radio operators there is another interesting facet to the satellite. Unlike most CubeSats which are launched in Low Earth Orbit (LEO), GreenCube was launched higher in Medium Earth Orbit (MEO) which provides a larger radio reception footprint over the earth. The satellite also contains a digital repeater (digipeater) at 435.310 MHz, which allows amateur radio operators to transmit digital radio packets up, and have the satellite repeat the packet back over a wide area footprint on earth. 

Over on his latest video, Matt, from the TechMinds YouTube channel shows us how to receive and decode the packets from the GreenCube digipeater. In his demonstration Matt uses an SDRPlay RSPdx as the receiver, SDR++ as the receiver software, SoundModem as the packet decoder, GreenCube Terminal for displaying the messages, and GPredict for tracking the satellite and compensating for the doppler effect. He also notes that while a directional antenna on a motorized tracker is recommended, he was able to still receive packets with his omnidirectional terrestrial antennas without much issue.

RECEIVING AND DECODING GREENCUBE CUBESAT

Building an OpenWebRX Server with an RTL-SDR Blog V3 for HF Monitoring

Thank you to Ramadhan (YD1RUH) who has put together a brief set of commands showing how to quickly get setup with OpenWebRX and an RTL-SDR Blog V3. OpenWebRX is a web based SDR program that allows users to use their SDR over a network or internet connector. It is compatible with several SDRs including the RTL-SDR.

 The installation is based on Ubuntu, and uses docker for the install. He also shows how to set up the OpenWebRX configuration file so that it will use the Q-branch direct sampling mode in RTL-SDR Blog V3 dongles for HF reception.

A demonstration of the result can be seen on Ramadhan's public OpenWebRX page. You can select between the various enabled HF bands in the lower left.

OpenWebRX HF reception running on an RTL-SDR Blog V3 dongle.

RFinder P10 – An Android Tablet with a built in Two Way Radio and RTL-SDR

Recently we came across a company called RFinder / AndroidDMR who are a shop selling custom made two way radios and Android Tablets with built in radio hardware. One of their new tablets that is currently in pre-order is being advertised with a built in RTL-SDR. The preorder status notes that they should be shipping within less than a months time.

The "RFinder Android Radio 10 Inch Tablet - 136-174mhz, 400-490mhz DMR/FM - Embedded RTL-SDR" is able to be pre-ordered for $1,499.95 USD + shipping. It is a ruggedized 10 inch Android tablet with a built in two way 4W VHF/UHF DMR/RF radio as well as an additional built in RTL-SDR. In terms of computing hardware, it comes with an Octa-Core 2.3 GHz CPU, 4GB RAM, 64GB ROM, and it supports cellular connectivity.

In their manual they share the following slide showing the built in RTL-SDR running the RF Analyzer Android app.

Various reviews of the RFinder P10 have been showing up on YouTube. Here is one review by Ham Radio 2.0 where the RFinder P10 is demonstrated at the Huntsville Hamfest.

New RFinder P10 Tablet with Dual Band DMR and RTL-SDR Receiver - Huntsville Hamfest

Decoding the Mexican Seismic Alert System (SASMEX Alerta sísmica)

Back in 2015 we posted about the dsame software, which is a decoder for the American Emergency Alert System (EAS) which is encoded with the SAME (Specific Area Message Encoding) protocol. EAS transmits on the NOAA weather frequency. 

Recently programmer Sam submitted news about his fork of dsame which adds the ability to decode the Mexican SASMEX (Sistema de Alerta Sísmica Mexicano) alert system. SASMEX is a system developed by the Mexican Government which can detect earthquakes and rapidly activate a warning siren across the country, allowing an early warning for people to prepare for an incoming earthquake.

The sirens appear to be activated wirelessly through the same frequencies that weather and EAS use, and so the signal can be monitored with an RTL-SDR or other SDR. When an active signal is present, the forked dsame software will decode the alert. The alert could then be used to activate a local siren or display.

How the SASMEX System Works (Credit: http://www.cires.org.mx/sasmex_n.php)

A Satellite Listening Journey

On his Medium.com blog, Mohsen Tahmasebi has posted an article about his journey into listening to satellites which started with his acquisition of an RTL-SDR Blog V3 dongle. The article begins by explaining his motivations for receiving satellites and how difficult hobbies like this are to get into in his home country of Iran. Despite the challenges he tasted success when he was able to receive NOAA APT signals on his second attempt using the included portable dipole antenna in a V-dipole configuration. Shortly after Mohsen was also able to receive Meteor-M2 LRPT.

Mohsen then built a more permanent V-dipole out of copper rods and optimized his antenna using NEC simulation software, finding that adding a reflector significantly improved reception. He then moved on to building a slightly more complex Turnstile antenna, which yielded even better results and allowed him to explore CubeSats at 435 MHz and contribute to SatNOGS. Finally, Mohsen ordered a Bullseye LNB and using a homemade bias tee, he received the QO-100 amateur radio transponder.

Overall, Mohsen's journey demonstrates that there is a lot of fun and learning available from internationally available satellites even in a country where equipment is hard to come by.

Mohsen's First Permanent V-Dipole for NOAA APT Reception

Combining ADS-B and VDL2 Data on PlanePlotter

Aircraft transmit multiple types of radio signals, including ADS-B and VDL2. ADS-B (Automatic Dependent Surveillance-Broadcast) is an air traffic surveillance technology that enables aircraft to broadcast their GPS position and other data. VDL2 (VHF Data Link Mode 2) is a digital VHF signal, allowing pilots to exchange text information with ground controllers and/or airline ground support. VDL2 is not designed to provide real-time positional data like ADS-B; however, positional information is often broadcast, and the VHF signals can propagate over longer distances.

Giuseppe (IT9YBG) was curious to see if he could receive and plot both signals together on a map using PlanePlotter. His setup consists of a Raspberry Pi 3 running with RTL-SDR Blog V3 dongles and a Windows PC running another RTL-SDR. The dumpvdl2 software is used to receive the VHF VDL2 signals, and RTL1090 is used for receiving ADS-B signals. Both output data to PlanePlotter, where the VDL2 messages can be read.

He also added the "Flight controls on RTL 1090XHSI" software, which allows users to view a simulation of an aircraft cockpit, using real-time ADS-B data from the RTL-SDR.

VDL2 positional data displayed on PlanePlotter

A Portable RTL-SDR and Raspberry Pi Based ADS-B Alarm for Drone Pilots

Pilots of RC planes and drones need to be aware of the area they are flying in, to make sure that they stay well out of the path of manned aircraft. However, this can sometimes be difficult with aircraft like police helicopters that could rapidly show up anywhere. Drones typically do not have ADS-B transmitters due to size/weight and price, but it is still possible for drone pilots to use ADS-B receivers to make their flying safer.

Over on YouTube user xjet has come up with a solution involving the use of a portable ADS-B alarm for drone pilots. The ADS-B receiver consists of a 3D printed enclosure containing a Raspberry Pi Zero 2W, LCD screen and an RTL-SDR dongle connected to an ADS-B whip antenna. xjet notes that when his code and 3D enclosure are finalized, he will release the design for free as open source over on http://www.rcmodelreviews.com.

The idea behind the ADS-B alarm appears to be that drone pilots will receive an alarm when they are within the vicinity of an aircraft. Assuming the drone is not too far away from the pilot (as rules specify drones must be flown within visible distance) the alarm being next to the drone pilot should be sufficient. xjet notes that we cannot rely on live ADS-B aggregation websites like FlightRadar24 due to their censorship of certain aircraft like police, military and some private jets, or due to possible lack of coverage, so a local receiver will be a better solution.

After more than two years of development and testing the ADSB alarm for RC plane and drone flyers is almost ready to go. I will be posting the full build details including an SD-Card image, source code, wiring diagrams and STL/DWG files for the case to the RCModelReviews website in the next week or so. This is a totally open-source project which I give freely to the hobby community so as to increase the levels of safety associated with our activities.

It is through the use of this technology that we can show how taking practical steps towards ensuring safety is every bit as important (if not more so) than blindly following regulations written by those who have probably never even flown an RC plane or drone themselves.

This changes everything (I'm not kidding!)