Software Defined Radio Academy 2023 Conference Talks

Videos of talks from the Software Defined Radio Academy 2023 (SDRA23) conference have recently been uploaded to YouTube. SDRA23 was held during the HAMRadio World Fair in Friedrichshafen, Germany during June 2023.

The talks appear to be slowly releasing on YouTube and currently about eight talks have been released with more to follow. Make sure you subscribe to their YouTube channel to be notified when more talks are released.

Some currently released talks of interest include:

  • Andreas Spiess, HB9BLA: SDR-A Keynote. SDR: What is next ?
  • Laurence Barker, G8NJJ: Completion of the Saturn SDR
  • G3ZIL & G4HZX: Propagation path analysis on HF, using SDR and FST4W
  • Rob Robinett, AI6VN: Creating a LCHP FST4W/WSPR beacon using RFzero or QPR Labs QDX
  • Gerhard Häring, DK6RH: Selfmade Portable HF-TRX with Hermeslite2 and Rasp Pi
SDRA'23 - 01 - Welcome & Introduction

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Manuel Tests the RTL-SDR Blog V4 on SDRuno

In one of his latest YouTube videos, Manuel Lausmann has been testing the RTL-SDR Blog V4 on SDRuno. SDRuno is the official software for SDRplay RSP devices, however, they provide an ExtIO interface which allows it to be used with an SDR that has an ExtIO driver.

The RTL-SDR Blog V4 recently got an ExtIO driver via hayguen's latest ExtIO release at https://github.com/hayguen/ExtIO_RTL/releases.

In the video Manuel shows how to download and copy over the ExtIO dll, and how to select it in SDRuno. He then goes on to show it in action receiving some HF signals. Note that Manuel's video is narrated in German, but you can use YouTubes auto-caption and auto-translate features to get English subtitles.

RTLSDR Blog V4 mit SDRUNO

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Raspberry Pi 4 USB Bug Experienced with RTL-SDRs now Fixed with Kernel Update

Thank you to Michael B for letting us know about recent fixes to the Raspberry Pi kernel which affect RTL-SDR users. If you've been experiencing error "rtlsdr_read_reg failed with -7" when running RTL-SDR software on Raspberry Pi 4's running a Linux kernel with version 6.1 or higher, a Raspberry Pi kernel fix has been pushed which should fix the problem.

This problem "rtlsdr_read_reg failed with -7" appears to occur after having closed any program that uses an RTL-SDR, and then reopening it.

This doesn't seem to have been an issue for the older 5.12 and 4.19 kernels where this issue was previously fixed, but Raspberry Pi recently moved to the 6.1 kernel in May 2023 where the issue came back. Raspbian releases after this date may have been problematic.

The official Raspbian should eventually update, but if you've been experiencing this issue, you could try update your kernel now using:

sudo apt install rpi-update
sudo rpi-update

Alternatively according to Michael, kernel version 6.6.y should also have this problem fixed:

sudo rpi-update rpi-6.6.y

Note that updating the kernel could break other software, so doing this is at your own risk.

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Wok-The-Hydrogen: A Low Cost Wok Based Hydrogen Line Radio Telescope

In addition to the last Hydrogen Line radio astronomy post from a few minutes ago, we've also recently seen a post on Hackaday about a research paper (PDF) that describes a Hydrogen Line Radio Telescope made from a cooking Wok, LNA and RTL-SDR dongle.

In the paper Leo W.H. Fung et al of Hong Kong University of Science and Technology uses a 61cm cooking Wok with a custom made dipole feed at the calculated focal point. A filtered LNA sits after the feed, and is connected to an RTL-SDR Blog V3 dongle enclosed within a metal cookie box for additional shielding.

The results show that the Hydrogen Line was indeed detected, and measurements of the galactic rotational velocity were possible.

Again we note that we will soon by crowdfunding for a product called the 'Discovery Dish' that will be fairly similar in size and shape. It is designed for receiving L-band weather satellites, but can also be used as a Hydrogen Line telescope too.

The Wok Hydrogen Line Telescope Setup
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TechMinds: Demonstrating OpenWebRX Plus

In one of his videos from a few days ago Matt from the Tech Minds YouTube channel tests out OpenWebRX+, an unofficial fork of OpenWebRX. OpenWebRX is open source software which enables users to put software defined radios like RTL-SDRs on the internet, allowing people from all over the world to access the receiver if desired, or just letting yourself access it remotely if you want to keep it private.

OpenWebRX+ adds several additional decoders and features on top of the official version. In the video Matt demonstrates OpenWebRX+ running on a Raspberry Pi 4, with an SDRPlay RSPdx. He demonstrates the web GUI in action and shows decoding examples of the various decoders that OpenWebRX+ comes with.

OpenWebRX Plus - The ULTIMATE Web SDR Application

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TechMinds: Using a Software Defined Radio as a Radio Telescope

Back in 2020 we released a tutorial about how to use a 2.4 GHz WiFi Grid Dish antenna as a radio telescope which can detect and measure the Hydrogen line emissions in our Milky Way galaxy.

Recently matt from the TechMinds channel has uploaded a video showing this same project but using the NooElec mesh antenna that has been slightly modified for improved performance on 1.7G and 1.4G.

In his video Matt sets up a drift sky scan, where the rotation of the earth drifts the Milky Way through the beamwidth of the dish. Matt uses Stellarium to virtually visualize the live sky map, SDR# and the IF average plugin to average the spectrum, and an Airspy software defined radio.

We note that we will soon be crowdfunding for our 'Discovery Dish', which we believe will be a superior solution for detecting and measuring the Hydrogen Line on a budget.

Using Software Defined Radio As A Radio Telescope

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Demonstrating the FM Capture Effect – Why Aircraft use AM

Over on his YouTube channel Tall Paul Tech has uploaded a video that demonstrates the FM (frequency modulation) capture effect. Apart from the costs and difficult logistics to change from AM to FM worldwide, the FM capture effect may be one additional reason as to why aircraft still choose to use AM modulation for communications instead of FM.

The FM capture effect is a phenomenon that occurs when two FM transmitters transmit on the same frequency at the same time. What will happen with FM is that the stronger of the two transmissions will be the only one heard, with the weaker one totally muted. This is in contrast to AM where both signals can be heard, albeit garbled like two people talking at the same time.

With aircraft this is important as for example if some aircraft accidentally leaves a blank transmission open, another aircraft can still transmit on top of the blank transmission and still be heard. Or allowing air traffic control to hear if multiple aircraft are trying to transmit at once, and handle communications appropriately based on urgency. The disadvantage is that without the capture effect, AM is more prone to interference from interference and atmospheric noise like lightning.  

In his demonstration Paul uses two HackRF's with their clocks linked and an RTL-SDR to simulate two transmitters and a receiver.

Demonstrating FM Capture Effect

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Chris Reviews the RTL-SDR Blog V4 on the HF Bands

Thank you to Chris (NNN0BOC) for writing up a glowing review of the RTL-SDR Blog V4. In the review Chris covers the enhancements that the VB4 brings to the HF bands, the driver replacement, and tests it out on various signals such as STANAG S4285, HF FAX, HFDL, GMDSS, MilSpec 141A ALE and various SWL bands. In his tests he uses SDR-Console V3, of which there is now a beta version that has built in support for the RTL-SDR Blog V4 (scroll down the page to find the V3.3 beta download).

Chris makes note that the RTL-SDR Blog V4 does not have the Nyquist aliasing problem that occurs in the RTL-SDR Blog V3 and other RTL-SDRs that enable HF reception through direct sampling. Nyquist aliasing on the RTL-SDR means that signals will be folded around 14.4 MHz. So for example a real signal at 8 MHz would also show up on 14.4 + (14.8 - 8) = 20.8 MHz and vice versa. The lack of Nyquist aliasing makes for a much cleaner spectrum.

Chris summarizes with the following:

I must admit I spent _a lot_ of time just looking at the beauty of HF with the V4, watching all the crazy goings-on, the weird sweepers and random signals popping up and disapearing.

I didn't run into any dynamic range issues or stability issues stemming from the V4, I wondered if I would have to perhaps place the RTL SDR AMBC Filter in line to suppress the many AMBC signals always present, never had a prob. The 120+ foot horizontal loop antenna feeding the V4 only has a 30MHz lowpass filter in line to hinder any rf that impinges upon it.

For such an inexpensive and tiny device, and free-to-use software, the capabilities are really kinda amazing. I now want an RTL SDR embedded into a cheap phone to use as a spectrum display on non-sdr HF receivers!

The V4 seems to atone for some of the sins of the V3, especially on HF with specific regard to Nyquist aliasing, have no fear tuning above 14.4MHz dear friends, this thing won't be making aliases unless you are overloading it.

At this time I can't think of a better value for the money when shopping for an SDR to use with a pc or phone in the sub - $50 price range.

We note that the RTL-SDR Blog V4 dongle only is currently in stock on our store from our international shipping warehouse, and the V4 dongle + antenna set will be in stock in about a weeks time.

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