What This Simulation Shows
Radio waves behave very differently depending on their frequency. This
simulation visualises the three main propagation modes:
ground wave (follows Earth's surface, best at LF/MF),
sky wave (refracted by the ionosphere back to Earth,
enables long-range HF), and
line-of-sight (straight-line, dominates VHF and
above).
How to Use
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Switch Frequency Band to see how propagation mode
changes — HF enables sky-wave skip, VHF is line-of-sight only.
-
Adjust Elevation angle: lower angles favour
long-skip sky wave; higher angles may pass through or be absorbed.
-
Change F-layer height and density to simulate
day/night ionosphere conditions (F-layer descends at night and
density rises).
-
Enable Multi-hop to see how HF signals can bounce
multiple times and reach antipodal distances.
Did You Know?
The ionosphere is ionised by solar UV radiation. During daylight,
there are distinct D, E and F layers; at night the D and E layers
largely disappear and the F layer rises and strengthens — this is why
shortwave radio reception is dramatically better at night, a
phenomenon exploited for decades by broadcasters reaching audiences
thousands of kilometres away.
About Radio Wave Propagation
This simulation visualises how radio signals travel from a transmitter across a curved Earth, splitting the picture into ground wave, sky wave and line-of-sight modes. The ionosphere is modelled as reflecting E and F layers, and sky-wave skip is computed geometrically by treating the F-layer as a flat mirror, with skip distance equal to 2 × layer height ÷ tan(elevation angle).
You choose a frequency band (LF 300 kHz, MF 1 MHz, HF 10 MHz or VHF 100 MHz) and adjust the antenna elevation angle, transmit power, F-layer height and density, and E-layer height. The stats panel reports the F-layer critical frequency (foF2 ≈ 9 × density MHz) and the Maximum Usable Frequency, MUF = foF2 ÷ sin(elevation). This explains why HF amateur and shortwave broadcasting can span thousands of kilometres.
Frequently Asked Questions
What does this radio wave propagation simulation show?
It shows the three principal ways a radio signal can travel from a transmitter: a ground wave that hugs the Earth's surface, a sky wave refracted back by the ionosphere, and a straight line-of-sight path. You can toggle each mode and see how the dominant one changes with frequency band.
What is the difference between ground wave, sky wave and line-of-sight?
Ground wave follows the Earth's curvature and works best at low frequencies (LF and MF). Sky wave is bent back to the ground by the ionosphere, enabling long-range HF links. Line-of-sight is a direct straight path that dominates at VHF and above, limited by the radio horizon.
How is the sky-wave skip distance calculated here?
The model treats the F-layer as a flat reflecting mirror, so the single-hop skip distance is 2 × F-layer height ÷ tan(elevation angle). Lowering the elevation angle stretches the skip out to longer ranges, while raising the F-layer height also increases the distance covered in one hop.
What do the frequency band buttons change?
They set the transmit frequency to 300 kHz (LF), 1 MHz (MF), 10 MHz (HF) or 100 MHz (VHF). Lower bands favour ground wave and sky-wave reflection, whereas at 100 MHz the signal usually exceeds the Maximum Usable Frequency and punches straight through the ionosphere, leaving only line-of-sight.
What are the critical frequency and MUF in the stats panel?
The critical frequency (foF2) is the highest frequency the F-layer reflects at vertical incidence; here it is modelled as roughly 9 MHz times the layer density. The Maximum Usable Frequency is foF2 divided by the sine of the elevation angle, so lower-angle, longer-range paths can use higher frequencies than steep ones.
How do the elevation angle and power sliders affect propagation?
Elevation angle sets the take-off angle of the wave: low angles give long skips, high angles give short skips or pass-through. Transmit power scales the brightness and reach of the drawn rays, representing signal strength, but it does not change the geometry of where the skip lands.
Why does shortwave radio work better at night?
During the day, solar ultraviolet creates absorbing D and E layers and a lower, denser F region. At night the D and E layers largely vanish and the F layer rises and reorganises, reducing absorption. Raising the F-layer height and lowering its density in the simulation mimics this, lengthening night-time skips.
What is the skip zone or silent zone?
Between the edge of the ground-wave coverage and the point where the first sky-wave hop returns to Earth lies a ring where neither mode delivers a usable signal. This skip zone is marked in the simulation, and its size grows as the take-off angle is lowered and the skip distance increases.
What does the multi-hop mode demonstrate?
Enabling multi-hop shows the sky wave bouncing between the ionosphere and the ground several times. Each hop adds roughly the same skip distance, so a few hops can carry an HF signal many thousands of kilometres, which is how amateurs and broadcasters reach the far side of the planet.
How physically accurate is this model?
It is a simplified educational model. Real ionospheric refraction is gradual rather than a flat mirror reflection, and it ignores frequency-dependent absorption, multipath, Doppler and tilted layers. The trends it shows — skip distance versus angle, MUF versus density, and the LF-to-VHF mode shift — are correct, but exact distances should not be taken as operational predictions.