HFcast is a privacy-first offline-friendly HF propagation forecasting app for amateur radio operators. Absolutely free, no ads, no tracking of any kind.
Pick a place, pick a band, enter your radio settings and get a custom forecast for HF propagation.
When online, two features do reach out to the network with no identifying data of yours being sent out:
- Today's space weather (from NOAA)
- Recent ionosphere measurements (from GIRO)
Everything else:
- Runs on a de-Googled phone or your old tablet without any Google services
- Developed and tested on GrapheneOS
- Works fully offline by calculating conditions based on historical HF propagation records
- Nothing about your station, your position, or the path you're checking leaves the device
- No ads
- No account
- No sign-in
- No tracking
- No data collection
- No phoning home
- No annoying registration
- No mandatory tutorials
- No noisy email spam
- No push notifications
- No crapware
- No spyware
The forecast is based on the point-to-point propagation model NTIA/ITS has maintained for decades. Faithfully translated to Rust and running directly on the phone.
- When online, HFcast enters live ionospheric data into VOACAP's model to give you the most accurate up to date propagation map.
- When offline or looking at future times, HFcast uses VOACAP's monthly climatology estimate.
- Every day inside the same month gets the same base answer unless the sunspot number changes; HFcast can pull today's space weather to adjust that, but the underlying model is still telling you what's typical for a path like yours in a month like this one.
The model's numbers are corrected against real measured signals, and the correction data — what was measured, and where the model is weakest — is documented in docs/ and in the engine repository.
Start with the quick start — about 15 minutes on a machine that already has the toolchain — then the rest of the development guide if you're going to work on the code.
| Part | What it is |
|---|---|
| mobile/ | The application, for Android and the web |
| server/ | The prediction API, for builds that have no engine |
| docs/ | The guides |
The propagation engine itself lives in a separate repository, hfcast-engine — a Rust translation of VOACAP, tested cell by cell against the original Fortran.
Almost everything HFcast knows comes from other people's work. The same list, with links and full licence text, is in the app's About screen.
| What | Whose | Terms |
|---|---|---|
| VOACAP, the propagation model | NTIA/ITS, maintained by Greg Hand | US Government work, not subject to copyright protection in the US |
| voacapl, the Unix port this engine was translated from | J.A. Watson | CC0 |
| The ionospheric coefficient maps | CCIR Reports 322 and 340, published by ITU-R | published for implementers free from copyright assertions |
| The place list searched offline | NTIA/ITS, from the VOACAP distribution | US Government work |
| Coastlines and country borders | Natural Earth | public domain |
| Sunspot numbers and solar indices | NOAA Space Weather Prediction Center | US Government work |
| Measured ionosonde soundings | UMass Lowell Global Ionosphere Radio Observatory | used with attribution |
| Place search, when online | Open-Meteo | CC BY 4.0 |
| The aurora on the launch screen | NASA / Samantha Cristoforetti, ESA | public domain |
| IBM Plex Sans, the typeface | IBM | SIL Open Font License 1.1 |
Three of those are live services the app calls directly, with no key: NOAA and GIRO, at most once every 15 minutes each, and Open-Meteo, only when a searched place isn't in the built-in list.
The Institute for Telecommunication Sciences, NTIA, US Department of Commerce, developed VOACAP. NTIA/ITS and NOAA do not endorse HFcast and are not responsible for what it reports.