HackRF Opera Cake Released: A Rapid RF Switching Board

Back in 2016 Michael Ossmann, founder of Great Scott Gadgets and creator of the HackRF released schematics for 'Opera Cake', a rapid RF switching add on board for the HackRF. We also saw back in a January 2018 post how Opera Cake was capable of being used as the switching hardware for Pseudo-Doppler direction finding. Up until now Opera Cake has only been available as a schematic, for advanced hackers who could produce and build the board themselves.

Earlier this week Opera Cake was released for sale via various resellers in the US, UK and EU. The pricing from the US reseller is US$190.

Opera Cake is an antenna switching add-on board for HackRF One that is configured with command-line software either manually, or for automated port switching based on frequency or time. It has two primary ports, each connected to any of eight secondary ports, and is optimized for use as a pair of 1x4 switches or as a single 1x8 switch. Its recommended frequency range is 1 MHz to 4 GHz.

When HackRF One is used to transmit, Opera Cake can automatically route its output to the appropriate transmit antennas, as well as any external filters, amplifiers, etc. No changes are needed to the existing SDR software, but full control from the host is available.

Opera Cake also enhances the HackRF One’s use as a spectrum analyzer. Antenna switching works with the existing hackrf_sweep feature, which can sweep the whole tuning range in less than a second. Automatic switching mid-sweep enables the use of multiple antennas when sweeping a wide frequency range.

Opera Cake connected to multiple antennas
Opera Cake connected to multiple antennas
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Quick Demo of our KrakenSDR Network Mapping Direction Finding Software (Alpha)

The KrakenSDR is our 5-channel coherent radio based on RTL-SDRs, and it can be used for applications like radio direction finding and passive radar. We successfully crowd funded the device on Crowd Supply back in November 2021.

Over the past year we've been working on a networked mapping system for KrakenSDRs that will allow distributed units to contribute radio direction finding bearing data to a central server. This allows for multiple fixed KrakenSDR sites to combine live bearings, allowing for near instantaneous localization of transmission sources.

We are close to releasing an alpha version of this software for KrakenSDR and KerberosSDR customers to test, and will have news about signups within the next few weeks. For now it will be restricted to three networked units per user.

In the future we plan to add (reasonably priced) advanced features like support for more units, history rewind, multi-channel layering, remote KrakenSDR management, object tracking, ID differentiation, and recording and playback of mp3 sound bites based on tracked location. 

Below is a simple timelapse demo of the system tracking a weather balloon from a single station. Because it's only a single station, the red estimation dot can be ignored. The yellow dot indicates the actual GPS location of the weather balloon. Once the weather improves we'll be setting up a distributed two-station test.

One interesting thing to note is how the KrakenSDR tracks the balloon accurately, until the elevation angle between the antenna and balloon goes above 45 degrees which happens when the balloon rises higher and comes too close to the station. At this angle the antenna array can no longer track the balloon correctly. Once the balloon falls to a lower altitude and the elevation from the antenna is less than 45 degrees accurate tracking resumes.

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A WebUSB Based RTL-SDR Aircraft ADS-B Decoder

Over on GitHub @devdevcharlie has uploaded open source Javascript code for creating an ADS-B Aircraft Radar system entirely within a web browser. The code makes use of the Web USB API, which enables USB devices like RTL-SDR dongles to connect directly to the code running in the web browser.

In her blog post, Charlie explains her code in greater detail, noting that it draws inspiration from AirplaneJS and rtlsdr.js. She explains how the Web USB API works, how to process the raw ADS-B data, and what her final setup looks like.

A demo site that you can use to directly connect to your RTL-SDR is available here.

In the past we've seen other WebUSB projects, like "aprs-sdr" which creates an APRS repeater system using a HackRF.

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A Broad Overview About HF on the RTL-SDR Blog V3

Over on YouTube, Tom the Dilettante has uploaded a video demonstrating how to receive HF signals with an RTL-SDR Blog V3 running in direct sampling mode. This is something already known to most RTL-SDR fans, but on the RTL-SDR V3 we have built in a direct sampling circuit that enables reception below 24 MHz with a simple settings change in software.

In the past and with other dongle brands, enabling direct sampling required hardware mods involving directly soldering a wire antenna to very small pins or pads. Direct sampling is not a high performance mode for HF, but in many situations it can be good enough for casual listening. 

In his video Tom demonstrates HF reception with the RTL-SDR Blog V3 and an MLA-30 active loop antenna. This is a cheap loop antenna available on Aliexpress that works very well for the price.

Listen Around the World - No Internet Required (HF & Shortwave on RTL SDR)

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Radio Jove Spectrograph Hardware and Software

NASA's Radio Jove is a project that enables students and amateur scientists from around the world to observe and analyze the HF radio emissions from Jupiter, our Sun and our galaxy using easy to construct HF radio telescopes that receive spectrographs from 16-24 MHz. The project has existed for more than two decades, and these days the telescope builds mostly make use of low cost software defined radios.

In a presentation for the Society of Amateur Radio Astronomers (SARA) Richard Flagg & Jim Sky talk about what sort of hardware is used these days for the Radio Jove project. They note that SDRs like the Softrock, Funcube Dongle Pro+, SDR-IQ, SDR-14, RTL-SDR, and RASDR have been used. They go on to discuss some of the spectrograph logging software that is used with the project as well.

The presentation slides in PDF form can be found here.

Richard Flagg & Jim Sky: Radio Jove Spectrograph Hardware and Software (RJ10/11)

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SDRSharp Big Guide Book Updated to V5.3

Paolo Romani (IZ1MLL) has recently released version 5.3 of his SDRSharp PDF Guide. The book is available for download on the Airspy downloads page, just scroll down to the title "SDR# Big Book" and choose your language.

As before the document is a detailed guide about how to use SDRSharp (SDR#), which is the software provided by Airspy. While intended for Airspy devices, SDRSharp also supports a number of third party SDRs, including the RTL-SDR, and it is the software we recommend starting with when using an RTL-SDR.

Paolo writes:

Youssef Touil hasn't rested for a moment and the SDR# releases have been moving forward in leaps and bounds with new Denoisers (NINR), CCC, Audio/Baseband records and the new menu features.

I also had to re-update my Big Book PDF to v5.3 as a result!!

I have also implemented the SpyServer section a lot in multi OS and a chapter "Ideas and Suggestions" with two paragraphs: SDR & MacOS and the other using SDR# with two multiple monitors.

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Detecting Starlink Satellites with a Portable Raspberry Pi + RTL-SDR

Over on his YouTube channel "saveitforparts" has in the past created a portable homemade 'tricorder' which was a boxed up Raspberry Pi with multiple sensors including an RTL-SDR. One new application he's found for the tricorder is the ability to detect the beacons from Starlink satellites using the RTL-SDR and an LNB.

Starlink beacons typically transmit at around 11.325 GHz, so to receive them with an RTL-SDR a downconverter and antenna such as an LNB is required.

In the video he demonstrates the hardware in use, and shows some of the beacons being received on the spectrum, via the tricorders built in LCD screen.

Detecting Starlink Satellites With DIY Tricorder

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SatDump ReWork Release with Significant Feature and GUI Updates

SatDump is a popular piece of software that can be used with RTL-SDRs and other software defined radios for decoding images from a wide array of weather imaging satellites including GOES, GK-2A, NOAA HRPT, FengYun, Electro-L and Meteor M2 LRPT + HRPT, and many others (note: there is no APT support at the moment, but it is planned for the future). It is compatible with Windows, Linux and even has an Android APK available.

Recently author @aang23 has updated the software, noting that he's done an almost full rewrite, including major updates to the GUI. The SatDump blog post goes into greater detail about he updates, but as a summary some of the biggest updates include:

  • A reworking and tidy up of the GUI with improved FFT view
  • A viewer which allows you to view output image products, and create RGB composites
  • A projection tool on the viewer, allowing you to project images onto OpenStreetMap.
  • Upgrades to the plugins system, allowing developers to more easily add support for new satellites / missions and SDRs.
  • The addition of 'products' metadata, allowing users to separate raw channel data
  • The addition of demodulators like DVB-S2, GOES-R GRB, HimawariCast, DVB-S
  • Support for additional SDRs like BladeRF, SDRplay RSP Duo, PlutoSDR and MiriSDRs.
  • Updates to the CLI interface
  • Updated less buggy Android App
SatDump new Live Decoding / Recorder Interface
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