HF Propagation Input Form
This page uses secant-law geometry, link budget loss, and normal distribution reliability estimates for an advanced HF propagation study.
Plotly Frequency Sweep
The graph shows how received power, SNR, and predicted availability change across the current HF window.
Example Data Table
These sample bands are evaluated using the current form values, so the table updates after every calculation.
| Band | Frequency (MHz) | Received Power (dBm) | SNR (dB) | Availability (%) | Status |
|---|---|---|---|---|---|
| 80 m | 3.5 | -90.23 | 12.77 | 0.03 | Outside window |
| 60 m | 5.3 | -84.10 | 18.90 | 3.26 | Outside window |
| 40 m | 7.1 | -82.09 | 20.91 | 15.02 | Outside window |
| 30 m | 10.1 | -81.36 | 21.64 | 56.51 | Marginal |
| 20 m | 14.2 | -81.86 | 21.14 | 70.34 | Good |
| 17 m | 18.1 | -82.72 | 20.28 | 4.77 | Outside window |
| 15 m | 21.2 | -83.44 | 19.56 | 0.35 | Outside window |
| 12 m | 24.9 | -84.30 | 18.70 | 0.00 | Outside window |
| 10 m | 28.4 | -85.06 | 17.94 | 0.00 | Outside window |
Formula Used
This estimator blends classic HF geometry with a statistical link model. It is designed for fast planning rather than measured ionogram replacement.
Adjusted foF2 = foF2 × solar factor × sunspot factor × geomagnetic factor × seasonal factor
Takeoff angle = arctan(2 × virtual height ÷ hop span)
MUF = adjusted foF2 × secant factor
FOT = 0.85 × MUF
LUF = base noise term + D layer absorption term + geomagnetic term + seasonal term
FSPL = 32.44 + 20 log10(distance in km) + 20 log10(frequency in MHz)
Received power = TX power(dBm) + TX gain + RX gain − total path loss
SNR = received power − noise floor
Availability = Normal CDF((link margin − frequency penalty) ÷ sigma)
Sigma is the fading spread term. It grows with higher sunspot activity, extra hops, and stronger geomagnetic disturbance.
How to Use This Calculator
- Enter path distance, hop count, and virtual height for your expected route.
- Set ionospheric values such as foF2, solar flux, sunspot number, season, and Kp.
- Fill the link budget fields for power, antenna gains, system loss, noise floor, and required SNR.
- Choose reliability and confidence values to control the statistical operating margin.
- Press the calculate button to display the result summary above the form, review the graph, and export the output.
Frequently Asked Questions
1. What does MUF mean here?
MUF is the maximum usable frequency predicted for the selected path geometry and adjusted ionospheric state. It marks the upper edge of the likely usable window.
2. Why is FOT lower than MUF?
FOT is set below MUF because operating slightly under the upper limit usually provides better stability. It leaves room for fading, uncertainty, and short term ionospheric variation.
3. What does LUF represent?
LUF is the lowest frequency likely to provide enough signal over the noise floor after absorption and system losses. It forms the lower edge of the working window.
4. Why can the path be marked closed?
A closed path means the estimated LUF rises above the estimated MUF. In practice, the lower usable edge overtakes the upper usable edge, leaving no stable window.
5. How does target reliability affect the result?
Higher reliability demands a larger statistical margin. That makes weak paths look less favorable and raises the performance standard for a band to be considered dependable.
6. Is this suitable for digital modes?
Yes. Enter the required SNR and fading margin that match your mode. Narrow digital modes often need different thresholds than voice or wideband data links.
7. Does more solar flux always help?
Not always. Higher flux can raise the upper frequency limit, but daytime absorption and noise may also increase. The useful result depends on both MUF growth and LUF movement.
8. Should I treat this as a precise forecast?
No. This is a planning calculator. Use it for quick decisions, then compare with real ionograms, measurements, or on air testing whenever accuracy matters.