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Calcimator

HF Propagation Calculator

Estimate Maximum Usable Frequency (MUF), optimum frequency, and hop count from solar flux index, time, distance, and season.

Inputs

km

Results

Max Usable Frequency (MUF)

14.17 MHz

Optimum Frequency (FOT)

12.05 MHz

Lowest Usable Freq (LUF)4.72 MHz
Critical Frequency (foF2)14.13 MHz
Hops Needed2
Total Hop Loss16 dB
Max Single Hop3,956 km
Sec(θ) Factor1
Recommended Band20m (14 MHz) or 17m (18 MHz)
How to Use This Calculator
  1. Enter the current Solar Flux Index (SFI) from WWV, DX bulletins, or propagation websites.
  2. Set the UTC time, path distance to your target (km), and current season.
  3. Review the Maximum Usable Frequency (MUF), Optimum Working Frequency (FOT), and LUF.
  4. Select frequencies at or below the FOT for reliable propagation on this path.
  5. Account for foF2 critical frequency and estimated number of ionospheric hops needed.

How the result changes with Time (UTC)

Time (UTC)Max Usable Frequency (MUF)Optimum Frequency (FOT)
2.34.96 MHz4.22 MHz
8.059.96 MHz8.46 MHz
1514.67 MHz12.47 MHz
218.61 MHz7.32 MHz

What each input means

Solar Flux Index (SFI)
10.7cm solar flux index (65-80 = low, 100-150 = moderate, 200+ = high solar activity)
Time (UTC)
Time of day in UTC (local noon ≈ peak ionization)
Target Distance
Distance to target station in kilometers
Season
1=Winter, 2=Spring, 3=Summer, 4=Fall

How this is calculated

Formula

MUF = foF2 × sec(θ); FOT = 0.85 × MUF

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Solar Flux Index (SFI) = 120, Time (UTC) = 12, Target Distance = 5000, Season = 1 = 4 input(s) provided
  2. Calculate Max Usable Frequency
    Max Usable Frequency = m
    14.17 = 14.17
  3. Calculate Optimum Frequency
    Optimum Frequency = m
    12.05 = 12.05
  4. Calculate Lowest Usable Freq
    Lowest Usable Freq = m
    4.72 = 4.72
  5. Calculate Critical Frequency
    Critical Frequency
    14.13 = 14.13

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.

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