Radio Frequencies

Oscillator Feedback 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

Spectrum management FM radio (VHF) – 88 – 108 MHz Channels are 200 KHz Radio receivers tune to the center frequency in the channel or carrier /- 75 KHz deviation

Spectrum management 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 (1.25 MHz above lower edge of channel) (Audio 4.5 MHz +/- 25 KHz) (30 KHz above lower edge of channel)

Spectrum management ency-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, ,500,000 WL = WHIZ-FM – MHz

Calculating wavelength 300,000, ,500, = Radio wave is 2.93 meters from crest to crest

Calculating wavelength 300,000, ,500, =

Calculating wavelength 300,000,000 1,240,000 WL = WHIZ-AM – 1240 KHz

Calculating wavelength 300,000,000 1,240, = Radio wave is 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

Modulation