REFERENCE // TOOL
HF Propagation
Estimate usable HF bands and NVIS conditions for the day.
Real-Time Propagation Tools
HF propagation depends on ionospheric conditions that change constantly. Use these tools for actual predictions:
prop.kc2g.com - MUF/foF2 Maps
Real-time ionospheric data from global ionosonde network. Shows actual MUF and critical frequency (foF2).
VOACAP Online - Full Propagation Prediction
Industry-standard HF prediction using ITU-R P.533 methodology. Point-to-point circuit analysis.
HamQSL Solar Data
Current solar flux index (SFI), K-index, A-index, and band condition assessments.
Australian Space Weather - HF Systems
Official ionospheric maps and NVIS frequency support data.
Understanding HF Propagation
Key Concepts
| foF2 | Critical frequency of F2 layer. The highest frequency reflected straight up. For NVIS, operate below this value. |
| MUF | Maximum Usable Frequency. Calculated as: MUF = foF2 × M(3000)F2 where M-factor ~3 for typical F2 paths. |
| FOT | Frequency of Optimum Transmission. Use FOT = 0.85 × MUF for reliable communications. |
| NVIS | Near Vertical Incidence Skywave. Coverage 35-650 km. Requires frequency below foF2. Typically 2-10 MHz. |
Solar Flux Index (SFI) Guidelines
| SFI Range | Conditions | Higher Bands (20m+) |
|---|---|---|
| < 70 | Poor | Marginal - stick to 40m and below |
| 70-100 | Fair to Average | 20m possible during day |
| 100-150 | Good | 20m/17m reliable |
| > 150 | Excellent | 15m/12m/10m open |
Source: Electronics Notes - Solar Indices
K-Index (Geomagnetic Activity)
| K-Index | Conditions | Effect on HF |
|---|---|---|
| 0-1 | Quiet | Best conditions |
| 2 | Unsettled | Good conditions |
| 3-4 | Active | Degraded, especially polar paths |
| 5+ | Storm | Poor to blackout conditions |
Source: 4X4XM Propagation Guide
FreeDV DATAC Modes for Reticulum
| Mode | Speed | Required SNR | Bandwidth | Use When |
|---|---|---|---|---|
| DATAC1 | 122.5 bytes/sec | 5 dB | 1.7 kHz | Good conditions, strong signals |
| DATAC3 | 40 bytes/sec | 0 dB | 500 Hz | Fair conditions, interference |
| DATAC4 | 11 bytes/sec | -4 dB | 250 Hz | Poor conditions, weak signals |
PAPR Warning
FreeDV DATAC modes have high peak-to-average power ratio (~10dB). Set transmitter power conservatively and monitor ALC - it should barely move.
Transmission Times (with ~67 byte Reticulum overhead)
| Message Size | DATAC1 | DATAC3 | DATAC4 |
|---|---|---|---|
| 50 chars (~117 bytes) | ~1.0 sec | ~2.9 sec | ~10.6 sec |
| 100 chars (~167 bytes) | ~1.4 sec | ~4.2 sec | ~15.2 sec |
| 200 chars (~267 bytes) | ~2.2 sec | ~6.7 sec | ~24.3 sec |
Official References
- Reticulum Manual - Official documentation
- FreeDV Project - Digital voice and data modes
- freedvtnc2 - FreeDV TNC for Reticulum HF
- ITU-R P.533 - HF propagation prediction method (official standard)
- International Reference Ionosphere - IRI model used by propagation tools
Licensing Requirement
HF amateur bands require appropriate license. Users must understand and comply with their regulatory environment. This tool is for educational purposes only.