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Old 01-18-2008, 03:54 PM
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Seldom Seen Seldom Seen is offline
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Location: Highlands Ranch
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Notes on the T4 section - Radio and Electronic Fundamentals


Units of electrical quantities

current - measured in amperes (A)

power - measured in watts (W)

voltage - measured in volts (V)

resistance - measured in ohms (Ω)

frequency - measured in Hertz (Hz)

wavelength - measured in meters (m)

Metric prefixes

mega- (M) 1,000,000

kilo- (k) 1,000

milli- (m) 1/1,000

micro- (μ) 1/1,000,000

Current

- the flow of electrons in a circuit

- direct current (DC): flows in one direction only

- alternating current (AC): flows back and forth in alternating directions

- conductors (metals, acids, bases) allow charge to flow easily through them

- insulators (wood, glass, plastic) do not allow charges to flow easily

- measured using an ammeter

Resistance

- electrical friction due to electrons' collisions with atoms inside the conductor

Voltage

- electrical pressure that pushes the electrons through a circuit

- auto batteries provide 12 volts

- measured using a voltmeter

-also called EMF (electromotive force) or electrical potential difference

Frequency

- the number of times per second that an AC current switches direction, or, the number of complete radio waves

produced by a radio per second

- voice frequencies: sounds from 30-3000 Hz

- audio frequencies: frequencies from 20-20,000 Hz

- radio frequencies: frequencies above 20,000 Hz

- 6 meter band: frequencies from 50-54 MHz

- 2 meter band: frequencies from 144-148 MHz

- 70 cm band: frequencies from 420-450 MHz

Wavelength

- length of one complete radio wave

- often "bands" are referred to by their wavelengths

Relationship between frequency, wavelength, and the speed of a wave:

- speed = frequency wavelength

-equation: c = f λ

c = speed

f = frequency

λ = wavelength

- radio waves move at the speed of light: c = 300,000,00 m/s or 3 x 10 (to the 8th) m/s

- as the frequency of a radio wave increases, its wavelength decreases (and vice-versa)

Electrical devices

- receiver: converts radio waves to sound waves

- transmitter: converts sound waves to radio waves

- transceiver: combined receiver and transmitter

- power supply: converts AC from wall outlet to DC for radio

- amplifier: increase power put out by radio

- battery: provides DC voltage

- single battery is called a "cell"

- lithium-ion batteries have the longest lives

- nickel-cadmium batteries provide 1.2 volts each

- carbon-zinc batteries: non-rechargable

- to keep rechargeable batteries stored for emergencies…

…check them periodically

…recharge every 6 months

…keep cool and dry

- draw current from a battery slowly to help it last longer

Ohm's law: the relationship between current, voltage, and resistance

- equation: E = I x R

E = voltage

I = current

R = resistance

Power equation relating power, voltage, and current

- equation: P = E x I

P = power

E = voltage

I = current

Last edited by Seldom Seen; 01-26-2008 at 03:24 AM.
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