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 –Resistor: Resists the flow of current measured 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 R I = V / R R = V / I Three versions: Example: 2 D cell (V = 3 volts) R = 560 ohms I = V/R =3/560 = A = 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 voltage and current split up if R1 = R2? 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? AC current flows will flow continuously as the capacitor continuously charges and 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: 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

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 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 incoming Radio waves 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 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 causes the amplitude of the carrier to vary as the value of the signal varies. vs Note: 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 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 – probe total current

Lab Exercise #2 – parallel Circuit – probe current in one parallel resistor