Exploring Electricity and Radio Basics

1. Electricity, Electronics And Ham Radio “Kopertroniks” By Nick Guydosh 4/12/07

2. Electricity Basics • Electricity: a stream of electrons flowing through a wire • Similar to water flowingthrough a hose • Water  current • Pressure (pump)  voltage (battery) • The hose  wire • Circuit: electricity flowing in a loop • Similar to thecooling 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

3. Electricity Basics • Two kinds of electricity: • Alternating current (AC):electrons vibrate back and forth • Example: generator or car alternator • Frequency: number ofvibrations (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

4. 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

5. Circuits • A circuit is a network of “components” through which electricity may flow. • For all practical purposes – all closed loops • Example:

6. 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 = I x R 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

7. 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: If you are measuring Voltage, how would you hook the meter probes? Same question for Current. Current division:

8. 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

9. 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

10. 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.

11. 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

12. 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) Outgoing Radio waves Vibrating current dipole antenna Vibrating current Cable to antenna Transmitter

13. 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 Combine the two Together & we have A Transceiver! dipole antenna Vibrating current Cable from antenna Receiver

14. 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 efficientradio 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

15. Modulation • It is not efficient to walk from NY to CAso 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

16. Amplitude Modulation (AM) How its done:

17. Frequency Modulation (FM) Less sensitive to noise Typically used higher carrier frequencies

18. A Simulation of Modulation

19. Putting it together Receive antenna Transmit antenna Modulate Radio waves De-Modulate Audio amp audio Audio Carrier RF amplifier

20. Lab Exercise #1 – series Circuit

21. Lab Exercise #1 – series Circuit - probe

22. Lab Exercise #2 – parallel Circuit

23. Lab Exercise #2 – parallel Circuit – probetotal current

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