Download Electricity, Electronics and Ham Radio

Electricity, Electronics
And
Ham Radio
“Kopertroniks”
By
Nick 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 like
a 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 circuit
example: a battery or generator.
measured on volts
DC
AC
– Resistor: Resists the flow of current
measured in “Ohms” or Ω
– 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 Ω or 2K, 1/1000 amp =1 milliamp or ma
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
Three versions:
V=IxR
I=V/R
R=V/I
Example:
2 D cell (V = 3 volts)
R = 560 ohms
I = V/R =3/560 = 0.0054A = 5.4ma
Series/Parallel Circuits
• Lets look ar how we can hook up two resistors
in a circuit:
Questions:
How would the voltage
and current split up
if R1 = R2?
Voltage division:
Current division:
If you are measuring
Voltage, how would you
hook the meter probes?
Same question for
Current.
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 time
As the capacitor charges up
To full voltage V
A question
• What happens if we replace the DC voltage
supply in the previous example with an AC
source?
I
AC current flows will flow continuously
as the capacitor continuously charges
and discharges;
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:
Electric field (red) – as from a charged up comb
Magnetic 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
http://micro.magnet.fsu.edu/primer/java/polarizedlight/emwave/index.html
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
Outgoing
Radio waves
dipole antenna
Vibrating current
Transmitter
Cable to antenna
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.
incoming
Radio waves
dipole antenna
Vibrating current
Receiver
Cable from antenna
Combine the two
Together & 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) to
electrical waves, the frequencies
would 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
vs
• In radio we use a carrier signal is some high
frequency, say 1290 Khz or 1,29 Mhz ( a local
radio station)
Note:
• The audio signal causes
the amplitude of the carrier
to vary as the value of the
signal varies.
Note: frequency = speed of light / wavelength
Amplitude Modulation (AM)
How its done:
Frequency Modulation (FM)
Less sensitive to noise
Typically used higher
carrier frequencies
A Simulation of Modulation
Putting it together
Receive antenna
Transmit antenna
Modulate
Radio waves
Audio
De-Modulate
Carrier
RF amplifier
Audio amp audio
Lab Exercise #1 – series Circuit
Lab Exercise #1 – series Circuit - probe
Lab Exercise #2 – parallel Circuit
Lab Exercise #2 – parallel Circuit – probe
total current
Lab Exercise #2 – parallel Circuit – probe
current in one parallel resistor