Below the Noise Floor
Below the Noise Floor is a self-education project turned podcast. One licensed amateur radio operator learning HF radio and AetherSDR from the ground up - the bands, the waterfall, the voice chain, the digital modes, the antennas - and sharing the process. These episodes are mostly AI-generated content built around real curiosity and real equipment. If you are new to HF or new to software-defined radio and want something that starts from zero and builds methodically, this might be exactly what you were looking for.
Below the Noise Floor
Below the Noise Floor — Episode 2: Getting Started with AetherSDR
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Last episode, I talked about what HF radio is and why skywave propagation is one of the more remarkable things physics has given us. I mentioned Ether SDR near the end as the software we were going to spend some time with. This episode is where we actually start. Before anything else, a quick note on what Ether SDR is and is not. Ether SDR is a client application for Flex Radio Systems Transceivers. It speaks the Smart SDR protocol, the same protocol that Flex Radio's own Windows software uses, which means it connects directly to your radio over the network and gives you full control of it. Spectrum display, waterfall, transmit and receive, filters, modes, tuner control, all of it. It was built specifically because Flex Radio's official software has historically been Windows only, and a lot of operators run Linux or Mac OS or just do not want to maintain a Windows machine solely to run their radio. Ether SDR changes that. It is free and open source, licensed under the GPL V3, built with QT6 and C and actively developed. The project is the work of a single developer who goes by 109876 on GitHub. It is not affiliated with Flex Radio Systems. It is an independent community project, and as of version 26.5.1, which is the current release as of this recording and the first release the developer has called Stable and 1.0 equivalent, it is in remarkably good shape for something that started as a personal project. I will put links to the software in the show notes. The GitHub repository is at github.com 109876 AetherSDR, and the latest release is always at GitHub.com 109876 AetherSDR releases latest. There is also a home page at ethersdr.com. If you are listening to this episode months or years after it was recorded, the release page is where you want to go. That will always have the current version. Now, platforms. Ether SDR runs on Linux, Mac OS, and Windows. Linux is the primary supported platform. That is where the project started and where most of the testing happens. Mac OS and Windows builds are provided as what the developer calls a courtesy, which in practice means they work well, but Linux is where you will find the most active community attention. On Linux, Ether SDR is distributed as an app image. If you have not used app images before, the concept is simple. It is a single self-contained file that includes everything the application needs to run, packaged together so you do not have to worry about dependencies or package managers or system libraries. You download one file, you make it executable, you run it. That is the entire install process. There is also an ARM build for Raspberry Pi and other ARM-based Linux machines. If you are running a Pi 4 or Pi 5 or an ARM laptop like a Pinebook, the ARM app image works the same way. Single file, market executable, run it. On macOS, Ether SDR is distributed as a universal DMG, a disk image that works on both Apple Silicon machines, the M1 and later chips, and on Intel Macs via Rosetta. The DMG is signed and notarized, which means Mac OS will not complain about it being from an unidentified developer. You download the DMG, open it, drag Ether SDR to your applications folder, and you are done. Standard Mac application install. On Windows, there are two options. There is an installer, a setup wizard that creates a start menu shortcut, and an uninstaller, the way most Windows software works. And there is a portable zip. A folder you extract wherever you want and run directly, no install needed. The portable zip is useful if you want to run it without administrator rights or without touching the registry. For most people, the installer is the simpler choice. So to summarize the install on each platform, Linux is one file, market executable, run it. ARM Linux is the same. Mac OS is download, drag to applications, open. Windows is run the installer, or extract the Zype, and run the executable inside. Let me walk through what first launch actually looks like. When you start Ether SDR for the first time, one of the first things it does is look for flex radio transceivers on your local network. This is called auto discovery, and it works because flex radio radios broadcast their presence on the local network using a protocol called Smart Discovery. If your radio and your computer are on the same network, EtherSDR will find the radio automatically. You do not have to know its IP address. You do not have to configure anything. The radio announces itself and Ether SDR listens. When the radio appears in the list, you click on it and Ether SDR connects. At that point, you will see the main interface come up, the pan adapter, which is the spectrum display showing signal strength across a range of frequencies, and below it the waterfall, which is the scrolling color map we talked about last episode. Strong signals show as bright colors, yellows and whites, weak signals show as faint traces in blues and greens. The baseline noise floor of the band shows as a relatively consistent color across the whole display. For most people, that moment of first connection is the payoff. You have a radio. You have software running on your platform of choice, and suddenly you can see the entire band. Every signal that is present on that slice of the spectrum is visible at once. If there is activity on 20 meters, and there almost always is during daylight hours, during the current part of the solar cycle, you will see it. From there, tuning is straightforward. You click on a signal in the waterfall or pan adapter and the receive frequency moves to that point. The mode controls are along the interface. USB for upper sideband, which is the standard voice mode on the HF bands above 10 MHz, LSB for lower sideband used below that, CW for Morse code, AM, FM, and digital modes. The filter controls let you narrow or widen the receive bandwidth. The AGC automatic gain control manages how the receiver handles strong signals automatically. If you want to transmit, the PTT button is there, as are the microphone controls, Vox, and compression settings. Before you transmit for the first time, you will want to make sure your audio input is configured correctly in the settings and that your power level is set appropriately for your antenna and the band you are on. But that is for a later episode. This one is about getting connected and seeing that waterfall for the first time. There are a few things worth knowing going in. Ether SDR currently targets Smart SDR protocol version 1.4.0000, validated against firmware version 4.2.18 on the Flex Radio 8600. Earlier version 4 firmware works. Version 3 firmware is not supported. If you are running an older radio on V3 firmware, you will need to update it before Ether SDR will connect. The Flex Radio 6000 Series and 8600 are the primary supported hardware. The Aurora, which is the newer model in the Flex Radio line, works as well. One more thing for anyone who has a tuner Genius XL in their station. Ether SDR has explicit support for it. The tuner appears in the interface, and you can control it directly from the software. That was one of the things I specifically needed to confirm before committing to the software for my own setup, and it checked that box. The developer has also recently added support for the PowerGenius XL amplifier for those running that hardware. That is the core of the setup. Download the appropriate binary for your platform from the releases page. On Linux, mark the App Image Executable with ChmodPoilex and run it. On Mac OS, drag to applications and open. On Windows, run the installer. Let Ether SDR find your radio on the network. Click Connect. Watch the waterfall come up. Next episode, we are going to go deeper on what you are actually seeing in that waterfall and how to start making sense of it. What different signal types look like, how to spot the digital mode traffic that has become the dominant activity on HF in the last decade, and how to start using the band activity as a real time propagation tool. The show notes for this episode have direct links to the Ether SDR homepage, the GitHub repository, and the releases page. I will keep those updated as new versions come out. The current version, as of this recording, is 26.5.1. This is below the noise floor.