Electricity, ElectronicsAnd

Ham Radio

“Kopertroniks”

ByNick Guydosh

4/12/07

Electricity Basics• Electricity: a stream of electrons flowing through a

wire• Similar to water flowing

through a hose– Water current– Pressure (pump) voltage (battery)– The hose wire

• Circuit: electricity flowing in a loop– Similar to the

cooling system in a car– The resistance of a device

(radiator) to the water is likea resistor in an electrical circuit

– The pump is like the battery

Electricity Basics• Two kinds of electricity:

– Alternating current (AC):electrons vibrate back and forth

• Example: generator or car alternator • Frequency: number of

vibrations (cycles)/sec

– Direct Current (DC):Electrons flow in one direction

• Example: battery

• How do we measure electricity?– Voltage: “volts” – Current: “amperes” or amps or A

Electrical Components• Components (symbols given):

– Voltage source – drives the electricity in circuitexample: a battery or generator.measured on volts

– Resistor: Resists the flow of currentmeasured in “Ohms” or

– Capacitor: stores electrical energy (electrons}measured in “farads”two plates

– Inductor: stores magnetic energy from the current.Measured in “henrys”a coil of wire

• Electrical quantities use numerical prefixes:– Ex: 2000 ohms = 2K or 2K, 1/1000 amp =1 milliamp or ma

DC AC

Ω

Ω

Circuits• A circuit is a network of “components” through

which electricity may flow.– For all practical purposes – all closed loops

• Example:

Resistive Circuits• Basic Law of electricity – “Ohms Law”

– Tells us how much current will flow in a resistor for some given amount of voltage across it. = IxR

– I = V/R

V = I x RI = V / RR = V / I

Three versions: Example: 2 D cell (V = 3 volts)R = 560 ohmsI = V/R =3/560 = 0.0054A = 5.4ma

Series/Parallel Circuits• Lets look ar how we can hook up two resistors

in a circuit:

Voltage division:

Current division:

Questions:How would the voltageand current split upif R1 = R2?

If you are measuringVoltage, how would youhook the meter probes?

Same question forCurrent.

A question

• Is it possible for a current to flow if the circuit is not physically connected in a loop?– For example a capacitor is just two plates separated by

space of an insulator:– Example 1: What happens when the switch is closed:

Current flows for a short timeAs the capacitor charges upTo full voltage V

A question

• What happens if we replace the DC voltage supply in the previous example with an AC source?

AC current flows will flow continuouslyas the capacitor continuously chargesand discharges;

I

Current though capacitor vs time

Basics of Radio• Lets switch gears to AC electricity

– Electrons are vibrating back & forth – as in the previous example.

– Their speed is constantly changing as it continually reverses direction.

– In other words, the electrons are accelerating and decelerating constantly.

• Fundamental principle:Whenever an electron (or charge) is accelerated it will radiate radio waves!

… principle of “electromagnetic radiation”could be microwaves or light waves if vibrations are fast enough – high frequencies.

Electromagnetic Propagation• Radio waves or any light waves, for that

matter, are made up of:

http://micro.magnet.fsu.edu/primer/java/polarizedlight/emwave/index.html

Electric field (red) – as from a charged up combMagnetic field (blue) – as from a magnet (or electromagnet)They are perpendicular to each other And vibrate & fly though empty space at 186,000 mi/sec

Radio Transmission• Just as AC current could “flow” though a

capacitor (charging & discharging):– High frequency currents could also flow into an antenna.– They produce radio waves (our basic principle)

Vibrating current

Vibrating current

Transmitter Cable to antenna

dipole antenna

Outgoing Radio waves

Radio Receiving• The process can be reversed!• Radio waves hitting an antenna will

induce high frequency currents in the antenna– they could be detected by a radio receiver.

Vibrating current

Receiver Cable from antenna

dipole antenna

incomingRadio waves

Combine the twoTogether & we have A Transceiver!

Sending Information On Radio Waves• OK – so we now could send and receive radio

signals – how do we get our voice on the air?

• If we convert voice waves (audio) toelectrical waves, the frequencieswould be less that 20,000 cycles per second (20 KHz).– This is much too low for creating efficient

radio waves.– We need frequencies of many millions of cycles per

second or higher – MHz to GHz.– So what do we do now?

• The answer is to “modulate” a high frequency “carrier” with our audio frequency (voice) signal

Modulation• It is not efficient to walk from NY to CA

so we us a carrier – an aircraft

• In radio we use a carrier signal is some high frequency, say 1290 Khz or 1,29 Mhz ( a local radio station)

• The audio signal causesthe amplitude of the carrierto vary as the value of thesignal varies.

vs

Note:

Note: frequency = speed of light / wavelength

Amplitude Modulation (AM)How its done:

Frequency Modulation (FM)

Less sensitive to noise

Typically used highercarrier frequencies

A Simulation of Modulation

Putting it together

Carrier RF amplifier

Transmit antenna

Radio waves

Receive antenna

Audio

Modulate

De-Modulate Audio amp audio

Lab Exercise #1 – series Circuit

Lab Exercise #1 – series Circuit - probe

Lab Exercise #2 – parallel Circuit

Lab Exercise #2 – parallel Circuit – probetotal current

Lab Exercise #2 – parallel Circuit – probecurrent in one parallel resistor