Go-based FM stereo transmitter with RDS, Windows-first and cross-platform

Jan Svabenik 3678b43427 feat: wire full DSP chain into offline generator with FM IQ output mode		vor 1 Monat
cmd	feat: add output-rate override and stronger offline wav tests	vor 1 Monat
docs	feat: report source label in dry-run summaries	vor 1 Monat
examples	Add output backend abstractions	vor 1 Monat
internal	feat: wire full DSP chain into offline generator with FM IQ output mode	vor 1 Monat
scripts	docs: define pre-v1 release posture	vor 1 Monat
.gitignore	docs: bootstrap fm rds transmitter project plan	vor 1 Monat
CHANGELOG.md	docs: define pre-v1 release posture	vor 1 Monat
PROJECT_PLAN.md	docs: switch plan to windows-first and soapy-first	vor 1 Monat
README.md	docs: polish public project readme	vor 1 Monat
RELEASE.md	docs: define pre-v1 release posture	vor 1 Monat
go.mod	feat: add pre-emphasis, MPX limiter and FM IQ modulation DSP blocks	vor 1 Monat

README.md

fm-rds-tx

Go-based FM stereo transmitter project with RDS.

Status

This repository is currently at a pre-v1, no-hardware-tested milestone.

What works today:

JSON configuration loading and validation
small HTTP control/status surface
dry-run generation for no-hardware inspection
offline IQ/composite-style file generation
simulated transmit path through a Soapy-oriented backend abstraction
automated no-hardware tests and smoke checks

What does not work yet:

real SDR hardware transmission
full RDS group framing / CRC / standards-grade correctness
real live audio ingest pipeline
production-ready broadcast chain processing

Project goal

Build a Go-based UKW/FM stereo transmitter with RDS that starts on Windows but is designed to stay cross-platform.

Design direction:

Windows-first bring-up
cross-platform architecture
CPU-first implementation
optional CUDA later where it actually helps
SoapySDR-oriented backend strategy for flexibility

Legal note

This project is intended only for lawful use within the relevant license and regulatory constraints. RF output, deviation, filtering, spurious emissions, harmonics, and actual transmitted power must be validated on real hardware with proper measurement equipment. Software controls are not a substitute for RF compliance work.

Quickstart

Print effective config

go run ./cmd/fmrtx -print-config

Dry-run (JSON summary, no hardware)

go run ./cmd/fmrtx --dry-run --dry-output build/dryrun/frame.json

Simulated transmit path (main CLI, no hardware)

go run ./cmd/fmrtx --simulate-tx --simulate-output build/sim/simulated-soapy.iqf32 --simulate-duration 250ms

Offline generator

go run ./cmd/offline -duration 500ms -output build/offline/composite.iqf32

Full local check

powershell -ExecutionPolicy Bypass -File scripts/check.ps1

Repository layout

cmd/
  fmrtx/      main CLI
  offline/    offline no-hardware generator
internal/
  app/        simulated transmit path wiring
  audio/      sample/frame helpers
  config/     config schema + validation
  control/    HTTP control/status handlers
  dryrun/     JSON no-hardware summaries
  dsp/        DSP helpers
  mpx/        MPX combiner primitives
  offline/    deterministic offline composite generation
  output/     backend abstractions + file/dummy sinks
  platform/   Soapy-oriented backend abstraction
  rds/        basic RDS encoder scaffolding
  stereo/     stereo encoder primitives
examples/
  soapy_simulated/
docs/
scripts/

Current release posture

Recommended current milestone tag:

v0.3.0-pre

Next priorities

real audio ingest path
stronger RDS implementation
tighter end-to-end regression coverage
real SoapySDR backend integration
first true v1.0 criteria review after those pieces exist