Today's video from Corrosive on the SignalsEverywhere YouTube channel discusses Bias Tee's. He explains what they're used for, and how to enable them on various SDRs. In particular he shows how to use the software to enable the bias tee on our RTL-SDR Blog V3 dongles. A bias tee allows you to power antenna side devices like low noise amplifiers by putting DC voltage on the coaxial cable.
The RTL-SDR Blog V3 dongle has a built in software selectable bias tee. By default it is turned off, and can easily be turned on by running some simple software. Instructions are available on the V3 users guide at www.rtl-sdr.com/V3.
The Raspberry Pi is the most popular credit sized computing board in the world. It is commonly used as a low cost and portable computing platform for SDRs like the RTL-SDR. Today the Raspberry Pi 4 was released, bringing us a new US$35 single board computer with many improvements. Some of the main improvements that make the Pi 4 great for software defined radios are listed below:
CPU: The Pi 4 uses a Quad-Core Broadcom ARM A72 clocked at 1.5 GHz. This chip should be significantly faster compared to the older chip used on the Pi3B+ with performance now being similar to that of the Tinkerboard. This will be especially useful for CPU intensive SDR applications like the direction finding and passive radar software for our coherent 4-tuner RTL-SDR known as the KerberosSDR. It should also help allow OpenWebRX servers to serve more simultaneous users, allow graphical programs like GQRX to run smoother, and allow for higher sample rates on higher end SDRs.
GPU: The new faster GPU should help graphical SDR programs run smoother.
RAM: The Pi 4 comes with three RAM options, either 1GB, 2GB or 4GB of RAM. The versions with more RAM will be great for memory intensive applications such as GNU Radio (and compiling GNU Radio). It will also allow more programs to run in the background, and perhaps combined with the improved CPU speed allow for multiple SDRs to be used on demanding tasks.
Networking: The Pi 4 finally support Gigabit Ethernet which will be very useful to people using the board as an SDR server over the internet.
USB: There are now two USB 3.0 ports available which means that USB 3.0 SDRs like the LimeSDR could in theory be used at higher sample rates on the Pi 4.
There are also many other improvements such as dual 4K HDMI ports, a USB-C power supply port and faster SD card transfers.
Raspberry Pi 4 Improvements
It is not yet known if the very useful Raspberry Pi specific software known as RPiTX will continue to function on the new Pi 4. RPiTX is software that turns Raspberry Pi units into fully functional RF transmitters without the need for any additional transmitting hardware - just attach an antenna wire to a GPIO pin. It works by modulating the GPIO pin in such a way to create almost any type of RF transmission. RPiTX only functions on the specific proprietary Broadcom CPU chips that the Raspberry Pi's use. The Pi 4 does continue to use a Broadcom CPU, so we are hopeful.
The new changes bring the Raspberry Pi up to speed with rivals like the Tinkerboard, but at a lower price and with a much better amount of software and OS support provided. The boards currently cost $35 for the 1GB version, $45 for the 2GB version and $55 for the 4GB version. They are sold via local resellers which can be found on the official Pi 4 product page.
A while back we posted about flight tracking company RadarBox.com who had launched their 1090 MHz ADS-B optimized RTL-SDR. Like other ADS-B optimized RTL-SDR's, the dongle contains a 1090 MHz filter and a low noise amplifier that reduces the noise figure, resulting in better SNR, and thus more planes spotted at further distances.
We spoke with RadarBox and asked if they could provide a low cost RTL-SDR + Antenna bundle for us. That bundle is now available in our store for $49.95 + shipping. Shipping takes about 2-3 weeks and costs between $10 - $25 depending on your country. Shipping costs will automatically added to the cart on checkout (please ignore other shipping options and choose free shipping unless you have other items in the cart). Please note that due to the larger size this will be shipped in a cylindrical package from a separate Chinese warehouse, and tracking info will come a few days later in a separate email.
The bundle includes:
1x RadarBox ADS-B 1090 MHz SMA Outdoor Antenna with mounting brackets
1x RadarBox ADS-B Optimized 1090 MHz RTL-SDR
The antenna has 7 dBi gain, 50 (+-5) Ohm impedance, and is made from fiberglass and aluminum. It is fully waterproof and outdoor rated. This is a great set at a great price to get started tracking planes with ADS-B.
To purchase, please click the Add to Cart button below or visit our store at www.rtl-sdr.com/store. Please note we only have limited stock of this product! NOTE: The first shipment of this product will be on July 2nd.
Add to cartRadarBox Bundle: Includes 1x Outdoor ADS-B Antenna, 1x ADS-B Optimized RTL-SDR
On his latest video Corrosive from the SignalsEverywhere YouTube channel discusses Inmarsat LES EGC and AERO ACARS decoding. Inmarsat is a satellite provider that has multiple geosynchronous satellites that can be received from almost anywhere in the world at around 1.5 GHz with an RTL-SDR and appropriate antenna + LNA. Inmarsat EGC and AERO are two channels on Inmarsat satellites that can easily be decoded.
The Enhanced Group Call (EGC) messages typically contain text information such as search and rescue (SAR) and coast guard messages as well as news, weather and incident reports. AERO messages on the other hand are a form of satellite ACARS, and typically contain short messages from aircraft. More interestingly with a bit of work compiling audio decoders, it is also possible to listen in to AERO C-Channel conversations, which is an emergency phone call service available on some aircraft.
In his video Corrosive gives an overview and demonstration of EGC and AERO reception.
Thank you to Shreyas Ubale for submitting his blog post about reverse engineering a wireless doorbell, and then performing a replay attack. Shreyas had purchased a wireless doorbell set containing one button transmitter and two bell receivers. However, his situation required two transmitters, one for visitors at the door, and one to be used by family within his house.
In order to create a second transmitter he decided to reverse engineer the doorbells wireless signal, and use that information to create an Arduino based transmitter. His process involves first using an RTL-SDR to determine the transmission frequency, then using the rtl_433 software to capture the raw waveform which he then analyzes manually using Audacity. Once the binary string, length and pulse width is known he is able to program an Arduino connected to a 433 MHz transmitter to replicate the signal.
In future posts Shreyas hopes to explore other ways to transmit the signal, and eventually design a simple but configurable 433 MHz push button that supports RF, WiFi, and can support the IFTTT web service.
If you're interested, check out some of our previous posts that highlight many other successful reverse engineering experiments with RF devices and SDR.
Doorbell Signal Analysis in Audacity. Captured with an RTL-SDR.
Over on our forums user qrp has released a modified ExtIO that allows the direct sampling mode to work correctly in SDRUno. SDRUno is SDRplay's official software for their RSP line of software defined radios, but SDRUno can also work with ExtIO input dlls which allow other SDRs like the RTL-SDR to be used.
The commonly found RTL-SDR ExtIO however doesn't seem to work properly with direct sampling mode in SDRUno, so HF on RTL-SDR Blog V3 or other direct sampling modified RTL-SDR dongles is inaccessible. The new ExtIO fixes the direct sampling problem, and also enables a Remove DC algorithm to remove that center spike, which isn't an option in SDRUno.
To use the ExtIO simply extract the ExtIO_RTLSDR_u8.dll and rtlsdr.dll files from the zip file into a folder on your PC. Then from the Start Menu find the SDRUno (EXTIO) shortcut and run it. When it asks you, select the ExtIO_RTLSDR_u8.dll file. Note that you will probably need to use the older v1.22 SDRUno version as V1.31 doesn't appear to have an ExtIO version.
Over on YouTube OLHZN High Altitude Balloons has posted a very entertaining video showing how to use an RTL-SDR and small grid dish antenna to track and recover a fallen weather balloon and its radiosonde. OLHZN writes:
The US National Weather Service (#NWS) launches over 200 weather balloons everyday carrying an LMS-6 #radiosonde / rawinsonde made by Lockheed Martin to an altitude of over 100,000 ft. and you can track & follow the flights from home and even find the landing site and pick them up! This is a fun #DIY project that you can do yourself from home and I'll show you how to do it here along with some tips so you can go find yourself a weather balloon & radiosonde!
How to track & recover a NWS weather balloon & radiosonde 🎈🎈 Ham Radio DIY
This week on the SignalsEverywhere YouTube channel, host Corrosive gives us a tutorial on common modulations that you'll see on your software defined radio. His tutorial covers Amplitude Modulation (AM), Frequency Modulation (FM), Single Side Band (SSB) and Conintuous Wave (CW) modulations. In the video he shows what they look like and how to select the correct mode and bandwidth settings in SDR#. Corrosive uses an Airspy in the video, but the same concepts are valid for any SDR, like the RTL-SDR.
If you're new to SDR then this is a great introductory video to watch and learn from.
AM FM SSB and CW | Common Modulation You'll See on SDR
