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Explore radio waves, frequencies, and band divisions. Learn about electromagnetic waves, wavelength calculations, Hertz units, and amplitude and phase properties.
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TECHNICIAN BANDS RADIO AND SIGNAL FUNDAMENTALS CHPT 2, THE ARRL HAM RADIO LICENSE MANUAL
Understanding Radio Waves • To understand BANDS you first must understand what FREQUENCIES are. • Why? Bands are Frequency divisions. • To understand FREQUENCIES you must have an understanding of RADIO WAVES.
Understanding Radio Waves • RADIO WAVES: • Signals that travel back and forth between radios, carrying voices, data, and morse code. • These radio waves travel at the speed of light (300,000,000 m/s). A radio wave begins its journey as an electrical signal in an antenna that constantly alternates direction. The rate at which the signal changes direction determines the signal’s frequency. The radio wave then travels away from the antenna into space, vibrating or oscillating at the same frequency as the electrical signal. • These radio waves are also known as: • ELECTROMAGNETIC WAVES
RADIO OR ELECTROMAGNETIC WAVES • What are electromagnetic waves? • Electromagnetic waves or EM waves are waves that are created as a result of vibrations between an electric field and a magnetic field. In other words, EM waves are composed of oscillating magnetic and electric fields.
The Electric Field is perpendicular to the Magnetic Field (and visa-versa). These are perpendicular to the Wave Direction of travel.
Wavelength is the physical length from one point of a wave to the same point on the next wave. WAVELENGTH • Usually measured in Meters
Formula for Wavelength (in Hz)
Example Wavelength Calculations (300,000,000 m/s) (in Hz) 300,000,000 meters 300,000,000 = 2.0627 meters = Wavelength = 145.440 MHz 145,440,000 Hz 300,000,000 Wavelength = = .6714 meters = 67.14 cm 446.780 MHz 300,000,000 = 166.67 meters Wavelength = 1.8 MHz
UNIT OF MEASUREMENT:HERTZ • The unit of measurement for frequency is called the Hertz, abbreviated as Hz. • One cycle per second is one hertz or 1 Hz. 60 cycles per second is 60 Hz.
FREQUENCY • As the signal oscillates, each complete back-and-forth sequence is called a cycle. • The number of cycles per second is the signals’ FREQUENCY.
AMPLITUDE • The Amplitude is the height of the wave. • Often this is related to Power.
AMPLITUDE The Amplitude is the height of the wave, and is often related to Power.
PHASE • Phase is not a property of just one RF signal, but instead involves the relationship between two or more signals that share the same frequency. The phase involves the relationship between the position of the amplitude crests and troughs of two waveforms. • Phase can be measured in distance, time, or degrees. If the peaks of two signals with the same frequency are in exact alignment at the same time, they are said to be in phase. Conversely, if the peaks of two signals with the same frequency are not in exact alignment at the same time, they are said to be out of phase.
PHASE The above graph shows two waves that are 90° out of phase
THE BAND PLAN RF SPECTRUM RANGES
US AMATEUR RADIO TECHNICIAN PRIVILEGES (Band plan for all Technicians)