Ionosphere-High Frequency Radio Wave Reflection

Schematic diagram showing the propagation of high-frequency (shortwave) radio waves by reflection off the ionosphere

Specific ionization conditions vary greatly between day (left) and night (right), causing radio waves to reflect off different layers of the ionosphere or transmit through them, depending upon their frequency and their angle of transmission. Under certain conditions of location, ionization, frequency, and angle, multiple “skips,” or reflections between ionosphere and Earth, are possible. At night, with no intervening layers of the ionosphere present, reflection off the F layer can yield extremely long transmission ranges.

High-frequency (HF) radio is in the 100- to 10-metre wavelength band, extending from 3 megahertz to 30 megahertz. Much of the HF band is allocated to mobile and fixed voice communication services requiring transmission bandwidths of less than 12 kilohertz. International (shortwave radio) broadcasting also is conducted in the HF band; it is allocated to seven narrow bands between 5.9 megahertz and 26.1 megahertz.

THE RST SYSTEM

Readability

1–Unreadable
2–Barely readable, occasional words distinguishable.
3–Readable with considerable difficulty.
4–Readable with practically no difficulty.
5–Perfectly readable.

Strength (Signal strength can be read from the S meter when receiving.)

1–Faint signals, barely perceptible.
2–Very weak signals.
3–Weak signals.
4–Fair signals.
5–Fairly good signals.
6–Good signals.
7–Moderately strong signals.
8–Strong signals.
9–Extremely strong signals.

Tone

1–Sixty cycle ac or less, very rough and broad.
2–Very rough ac, very harsh and broad.
3–Rough ac tone, rectified but not filtered.
4–Rough note, some trace of filtering.
5–Filtered rectified ac but strongly ripple-modulated.
6–Filtered tone, definite trace of ripple modulation.
7–Near pure tone, trace of ripple modulation.
8–Near perfect tone, slight trace of modulation.
9–Perfect tone, no trace of ripple or modulation of any kind.

Signal reports are exchanged when Amateur Radio operators contact each other.
For Morse code (CW) communications, all three are used. A very good signal report would be 599.
For voice communications, only readability and strength are used. A very good signal report would be 59.