This shows the elevation radiation pattern of a half-wave horizontal dipole antenna — how strongly it radiates at each elevation angle above the horizon — and, more importantly, why that pattern has the shape it does: it's produced by the direct wave from the antenna interfering with the wave reflected off the ground below it. The white pulsing sphere is the antenna itself, current oscillating along its length, viewed end-on from one tip of the wire looking straight down its axis.
Brighter arcs mean stronger signal in that direction — a lobe. Dimmer, darker arcs mean weaker signal — a null. This is the single most important thing to read on screen: follow the brightness outward in any direction and you're reading the antenna's actual gain in that direction.
Magenta —
the direct wave, radiating straight out from the antenna.
Cyan — the
wave reflected from the ground. Watch the small yellow dots
traveling outward along the ground line — each one marks the exact spot where an
expanding magenta (direct) wavefront reaches the earth. That's the bounce point;
the cyan reflected wave arcs are mathematically what a real reflection from that
point produces, everywhere above ground.
A solid ring marks a wave crest (peak); a dashed ring marks a trough (the opposite extreme). Both are equally strong when reinforcing — solid vs. dashed only tells you which part of the wave cycle you're looking at, not how strong it is. Strength is brightness alone.
These mark the directions where the direct and reflected waves are perfectly in phase — where they reinforce each other as strongly as physically possible. These are the true lobe directions, and you should see them running right through the brightest, most consistent arcs on screen.
Frequency sets the operating frequency (and therefore the wavelength). Height above ground is the dipole's physical height above the earth, expressed in wavelengths — this is the key variable that reshapes the whole pattern. Zoom just adjusts your viewing distance.
Drag the height slider and watch the lobes reshape in real time. At very low heights (around 1/8 to 1/4 λ), a significant amount of energy is directed at steep upward angles, with the pattern fairly broad and close to omnidirectional overhead — this is the NVIS effect (Near Vertical Incidence Skywave), useful for regional contacts where the signal needs to come back down from the ionosphere at a steep angle. As you raise the antenna, that broad high-angle lobe narrows and tilts down toward the horizon. At 0.5λ — a common, practical all-around height — you get one clean, well-formed lobe at a moderate angle (around 30°), a solid general-purpose compromise between local and long-distance coverage. Push the height higher, toward a full wavelength, and the main lobe keeps dropping toward the horizon (down toward 14° or lower) for the longest possible skip distance — though a second, higher-angle lobe also appears at those greater heights.