Twenty-three years of amateur SDR, and where AetherSDR picks up.
Almost every software-defined radio console an amateur can run today traces back to one C# codebase that FlexRadio released under the GPL in 2003. This is what happened to it — which branches forked, which ones went quiet, and which are still being written.
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A software defined radio for the masses
Gerald Youngblood publishes a four-part series in ARRL’s QEX between July 2002 and March 2003. Part four announces the SDR-1000 as a semi-assembled board set, with the software to be released in open-source form.
AC5OG · Gerald Youngblood -
DttSP becomes the DSP core
Frank Brickle and Bob McGwier write the C signal-processing engine that sits underneath PowerSDR and release it under the GPL. Every console on this page inherits its architecture, directly or by way of a rewrite.
AB2KT · Frank BrickleN4HY · Bob McGwier -
SDR-1000 and PowerSDR ship under GPLv2
A headless box that converts RF to an 11 kHz I/Q pair over a parallel port, with everything else done in software. The GPL release is the single most consequential decision in this history — it is why the rest of the page exists.
FlexRadio Systems -
The HPSDR group forms
Phil Covington’s FPGA project merges with the XYLO effort by Phil Harman and Bill Tracey. The result is a modular open-hardware bus — Atlas, Ozy, Mercury, Penelope — built around direct conversion from DC to 55 MHz.
N8VB · Phil CovingtonVK6APH · Phil HarmanKD5TFD · Bill Tracey -
PowerSDR is ported to HPSDR hardware
Bill Tracey and Doug Wigley adapt FlexRadio’s GPL console to drive Mercury, Penelope, Ozy and Metis. The branch becomes OpenHPSDR PowerSDR mRX PS. From this point the two codebases evolve separately.
KD5TFD · Bill TraceyW5WC · Doug Wigley -
TAPR funds Mercury development
TAPR agrees to fund the Mercury receiver proposal in March and continues underwriting OpenHPSDR hardware from then on, distributing boards as kits and assembled units.
TAPR -
Apache Labs ships the ANAN-10
The Hermes board collapses Mercury, Metis and Penelope onto one PCB with Ethernet. Apache Labs wraps it in a chassis with a PA and filters. The ANAN-100 and ANAN-100D follow in March 2013, the latter built on the dual-ADC Angelia board.
M0KHZ · Kevin WheatleyApache Labs -
FlexRadio closes the source, and opens the API
The FLEX-6000 series is shown at Dayton with a direct-sampling architecture that moves DSP into the radio. SmartSDR is written from scratch as closed source and no code crosses between the two families again — but the same move opens something up. With the DSP inside the radio, a console is no longer a signal-processing engine; it is a control surface over the network, and FlexRadio documents that surface in full. A versioned command protocol, VITA-49 streaming for spectrum, waterfall and audio, and FlexLib published as a reference implementation. Slices, panadapters, meters, profiles, the ATU, DAX and remote access are all reachable from outside, so a client written from nothing can reach parity rather than approximate it. That depth is why AetherSDR could start from an empty file instead of a fork.
FlexRadio Systems -
First FLEX-6700 units ship
General release begins in June. SmartSDR v1.1 later that year doubles panadapters and slice receivers to eight on the 6700.
FlexRadio Systems -
PowerSDR 2.7.2 — FlexRadio’s last release
The final upstream build for the FLEX-1500, 3000 and 5000. The source stays available under GPLv2, which keeps the legacy line alive long after the company stops working on it.
FlexRadio Systems -
WDSP replaces DttSP
Warren Pratt rewrites the DSP layer as a new GPL library with separate receive and transmit chains. It becomes the shared engine under every non-FlexRadio console that follows — Thetis, piHPSDR, linHPSDR, deskHPSDR.
NR0V · Warren Pratt -
PureSignal wins the ARRL Technical Innovation Award
Adaptive predistortion implemented in WDSP pushes IMD3 on the ANAN line to around −50 dB — cleaner than a class-A transmitter while keeping class-AB efficiency.
NR0V · Warren Pratt -
Thetis begins
HPSDR’s next-generation firmware introduces an entirely new radio-to-PC protocol that PowerSDR cannot speak, and gigabit Ethernet becomes mandatory. Doug Wigley leads a new console for it. Later versions speak both protocols.
W5WC · Doug Wigley -
KE9NS forks PowerSDR 2.7.2
Darrin Kohn picks up the abandoned legacy branch on New Year’s Day and adds cluster spotting on the panadapter, callsign decoding in the waterfall, band stacking and much else. It is still the best software for a FLEX-5000.
KE9NS · Darrin Kohn -
piHPSDR takes the codebase native
John Melton writes a client in C on his own Linux and Android port of WDSP, breaking the dependency on Windows and .NET. Christoph van Wüllen later takes over as maintainer and his fork becomes the mainline.
G0ORX · John MeltonDL1YCF · Christoph van Wüllen -
MW0LGE starts working on Thetis
Richard Samphire begins contributing, and over the following years his fork becomes the de facto mainline — multi-panadapter rendering, TCI, the voice keyer and a long run of releases through v2.10.
MW0LGE · Richard Samphire -
Hermes-Lite 2 wins the ARRL Technical Innovation Award
Steve Haynal’s low-cost open transceiver puts protocol 1 in reach of anyone, and the native-C clients are what make it usable across Linux and macOS.
Steve HaynalN2ADR · Jim AhlstromM5EVT · Matthew -
The canonical Thetis repository goes quiet
TAPR’s upstream stops at v2.10.0.0. Development continues only in the MW0LGE fork.
TAPR -
ANAN-G2 arrives on the SATURN board
A large FPGA rated around 930 GMAC/s with a Raspberry Pi compute module on board, derived from the 7000DLE mk2 RF chain. For the first time the radio can run its own console.
G8NJJ · Laurence BarkerN1GP · Rick Koch -
SmartSDR moves to a subscription
From v4.0, bug fixes stay free under SmartSDR Basic while new features require an annual SmartSDR+ licence. FlexRadio’s stated reasoning is that fourteen years of major-version upgrades produced only two paid releases.
FlexRadio Systems -
AetherSDR starts from an empty file
First commit lands on 12 March — a root commit with no history behind it. A native Qt6 and C++20 console written clean-room against FlexRadio’s published VITA-49 and SmartSDR APIs. No PowerSDR ancestry, no Thetis ancestry.
KK7GWY · Jeremy Fielder -
Thetis is archived
Richard Samphire archives the repository. The reasons are entirely technical: the codebase still depends on .NET Framework 4.8, rendering runs on SharpDX which is itself archived, and multiple receive slices would need a full display-engine rewrite. Final release v2.10.3.15 ships in May.
MW0LGE · Richard Samphire -
Apache Labs funds piHPSDR
Apache Labs forms an in-house software team whose first stated mission is assisting DL1YCF with piHPSDR, plus companion tooling and continued support for the 7000DLE and 8000DLE. After twenty years, the OpenHPSDR side finally has paid engineers.
Apache LabsDL1YCF · Christoph van Wüllen -
Where AetherSDR sits
Native on Linux, macOS and Windows, driving the FLEX-6000 and 8000 series and Aurora. More than 15,000 downloads and over 40 contributors, on a monthly CalVer release cadence. Nothing above the AetherSDR lane is a dependency — it is a parallel start, written for this decade rather than inherited from the last one. Where it goes next runs the other way. The split this page traces is an accident of hardware and protocol history rather than anything operators asked for, and the intent is to close it inside the client: native support for the Metis- and Thetis-derived radios alongside the FLEX families, so one console speaks both branches. The three things that ended Thetis — a .NET Framework dependency, a rendering stack archived underneath it, and multiple receive slices needing a display engine it never got — are already solved here. Same console, same habits, whichever branch your radio came down.
GPL-3.0aethersdr.com
Lane colours mark independent codebases, not companies. A dashed fork means no shared source.