T3B

Radio waves: fields, speed and wavelength

A radio wave is a pair of fields moving at light speed, and its wavelength is just 300 ÷ frequency.

12 pool questions1 on the exam

Syllabus: Electromagnetic wave properties: wavelength vs frequency, nature and velocity of electromagnetic waves, relationship of wavelength and frequency; Electromagnetic Spectrum Definitions: UHF, VHF, HF

A radio wave is two fields, at right angles

A radio wave has two parts: an electric field and a magnetic field. They move together, 90° apart.

Red = electric field. Blue = magnetic field. Both are perpendicular to the direction of travel.

Polarization is just the direction of the electric field. Electric field up‑down → vertical polarization.

RememberTwo fields, at right angles. Polarization = direction of the electric field.

Every radio wave travels at the speed of light

In free space, all radio waves move at the speed of light: about 300,000,000 meters per second.

Frequency changes how fast the wave wiggles, never how fast it travels.

HF, VHF, microwaves, even visible light: same speed. Only the frequency and wavelength differ.

Higher frequency, shorter wavelength

Wavelength (λ) is the distance one full wave takes up. Since the speed is fixed, more wiggles per second means each wiggle is shorter.

Wavelength in metersλ = 300 ÷ f (MHz)

Top: more waves squeeze into the same space as frequency rises (schematic). Bottom: the real wavelength on a log scale.

Frequency146 MHz

Wavelength ≈ 300 ÷ f2.05meters

Nearest ham band2 m

Try 146 MHz: 300 ÷ 146 ≈ 2 meters. That's why it's the "2‑meter band". Bands are named by their wavelength.

RememberFrequency up → wavelength down. Divide 300 by the frequency in MHz.

HF, VHF and UHF: each is ×10 the last

Each named range spans one factor of ten. Frequency increases to the right.

Name	Range	Think
HF	3 – 30 MHz	High
VHF	30 – 300 MHz	Very high
UHF	300 – 3000 MHz	Ultra high

Memory hook3‑30, 30‑300, 300‑3000. Each step multiplies by 10, and the first digit stays 3.

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Compendium articles on the ideas in this lesson, beyond what the exam asks.

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Practise the 12 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".

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