Radio Frequencies

OscillatorFeedback loop

Oscillator

• As the output of the amplifier is fed to the input, feedback or oscillation occurs

Tuned Oscillator

Oscillator

• When properly tuned to a high enough frequency, the oscillator will produced radio frequencies

• Frequencies begin to take on the characteristics of radio frequencies (RF) at about 30,000 KHz

• RF can travel great distances, and can be modulated to carry information (audio & video)

RF

• Antennae are conductive rods that will easily radiate RF

• When the output of the oscillator is connected to an antenna, the electrons in the antenna begin to vibrate or oscillate at RF frequencies

• Waves of electromagnetic radiation will emanate from the antenna at those RF frequencies (+30KHz)

RF spectrum

• Very Low Frequencies – 3 – 30 KHz• Low Frequencies 30 – 300 KHz• Medium frequencies 300 KHz – 3 MHz• High frequencies 3 – 30 MHz• Very High frequencies 30 MHz – 300 MHz• Ultra High frequencies 300 MHz – 3 GHz• Super High frequencies 3 – 30 GHz• Extremely High frequencies 30 – 300 GHz

RF and beyond• As particles continue to accelerate, creating

waves of decreasing wavelengths, energy takes on other characteristics

• Infrared• Visible light – red, orange, yellow, green, blue,

indigo, and violet• Ultraviolet• X-rays• Gamma rays• Cosmic rays

Spectrum management

• AM radio (MF) – 535 – 1705 KHz• Channels are 10 KHz• Radio receivers tune to the center frequency

in the channel or carrier

565535 545 555

540 550 560

Spectrum management

88.0

88.1

• FM radio (VHF) – 88 – 108 MHz• Channels are 200 KHz• Radio receivers tune to the center frequency

in the channel or carrier

88.2

+/- 75 KHz deviation

Spectrum management

82.0

83.25 MHz video carrier

• TV (VHF and UHF)• Channels are 6 MHz• TV receivers tune to the center frequency in

the channel or video carrier• In this example: Channel 6

88.0(1.25 MHz above lower edge of channel) (Audio 4.5 MHz

+/- 25 KHz)

(30 KHz above lower edge of channel)

Spectrum management

• http://frrl.files.wordpress.com/2010/11/frequency-allo-chart.jpg

Calculating wavelength

Velocity Frequency

WL =

Velocity = speed of light = 300,000,000 meters per second

Calculating wavelength

300,000,000 Frequency

WL =

Calculating wavelength

300,000,000 102,500,000

WL =

WHIZ-FM – 102.5 MHz

Calculating wavelength

300,000,000 102,500,000

2.93 =

Radio wave is 2.93 meters from crest to crest

Calculating wavelength

300,000,000 102,500,000

2.93 =

Calculating wavelength

300,000,000 1,240,000

WL =

WHIZ-AM – 1240 KHz

Calculating wavelength

300,000,000 1,240,000

241.93 =

Radio wave is 241.93 meters from crest to crest

Calculating wavelength

• Higher frequencies = shorter wavelengths• In the highest bands of the usable spectrum,

wavelength are measured in nanometers or angstroms

• Wavelengths in the “microwave” bands are so short that atmospheric moisture affects transmission

Calculating wavelength

• These calculations are used to determine ideal antenna length

• In FM and TV, antennae use half-wave dipole construction

• The antenna is one-half the length of the wave, and the pole is cut in half

Half wave dipole

“Stacking” the elements forces waves toward horizon. This adds gain to the antenna.

Quarter-wave vertical

• In AM, the longer wavelengths dictate the use of quarter-wave vertical antennae

• The tower itself becomes the antenna• AM also uses a ground array to propagate the

ground waves

How waves behave

• HF and above (FM, TV, satellite, etc.) travel in direct waves, or line-of-sight

• Direct waves will not “bend” or pass through solid objects

• LF and MF frequencies travel in sky waves, which bounce off the ionosphere

• LF and MF frequencies travel in ground waves, which follow the curvature of the earth

Antenna location

• Best location for an FM or TV antenna is on the highest unobstructed hill, building, tower, peak

• Best location for an AM antenna is low marshy location

Antenna schematics

FM antenna AM antenna

Ionosphere

• A layer of the atmosphere where hydrogen atoms become “ionized”

• Ionization occurs when the hydrogen atoms become “charged” because they give up electrons

• Heating of the ionosphere by the sun causes the ionization

• The will determine the behavior of sky waves

Sky waves

• May be absorbed during the daylight hours• May pass through during the daylight hours• May be reflected at night when the

ionosphere cools

Sunspots

• Affect terrestrial communication, telecommunications, broadcasting, computers, other electronics

• Occur in 11 year cycles• Activity builds and subsides slowly

1990 2000 2010

Modulation