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Diodes, Transistors and Tubes Silicon Semiconductors Doped Semiconductors P-N Junction Extra holes combine with extra electrons to form depletion zone Forward Bias Diode conducts only when it is forward-biased. Reverse Bias Diodes • let current flow in only one direction. Diodes • Diode conducts only when it is forward-biased. • Electrons flow from cathode to anode (ie NOT the direction of the arrow) • demodulation is one important application for diodes in recovering info from transmitted signals (more about that in the modulation and transmitters session) • What else might be a use of a diode? Rectification • Diode use: rectification, ie changing alternating current (AC) to pulsating direct current (DC) • Diode lets through current only in one direction, so if an alternating current is applied to the anode of a diode the cathode would have a pulsating direct current. • What other diodes are used in power supplies? Zener diodes • current can flow in reverse biased direction, but only if it is over a certain voltage, the breakdown voltage • Zener diodes work in the forward biased direction as a normal diode would, but they also allow current to flow in the reverse way when the voltage is above the breakdown voltage, and their breakdown voltage is precisely known. • used as voltage regulators, ie to regulate or maintain a constant voltage • What other kind of diodes? LED - light emitting diode • Semiconductor device that glows different colours depending on chemical composition Amplification or Gain • What is amplification? • Amplification increases voltage, current, and/or power • “Amplification” is equivalent to “gain” • Amplification is opposite of attenuation or loss, and an amplifier doesn’t have loss (since the exam talks about that a lot) • A circuit designed to increase the level of its input signal is called an amplifier • To increase the level of - very weak radio signals, use RF amplifier - very weak signals from a microphone, use an audio amplifier • What sort of device might be used? Transistors Bipolar Transistors • Transistors can be of PNP or NPN type • A transistor can amplify a small signal using low voltages. (tubes can amplify but need high voltages, but tube not option in exam) • A basic semiconductor amplifying device is the transistor (exam throws tubes in there, but they are not semiconductors) • The three leads are base, collector emitter • One example bipolar transistor would be a “general purpose audio NPN device” • A transistor can be destroyed by excessive heat. Field Effect Transistors Field Effect Transistors • Two basic types are N and P channel • functions are: – gate controls the conductance of the channel – source is where charge carriers enter the channel – drain is where charge carriers leave channel • The field-effect transistor is the semiconductor with the characteristics most similar to a triode vacuum tube. • To reduce current, increase reverse-bias voltage. Triode Vacuum Tube • Electrons released from cathode via thermionic emission • Electrons flow to positively charged anode • Negative voltage on grid repels electrons, decreases flow • Positive charge on grid attracts electrons, increases flow Triode Vacuum Tube • Inside the envelope is a vacuum. • Feature common to both transistors and tubes is that they can amplify signals. • A triode vacuum tube might be used because instead of a transistor because it may be able to handle higher power. • Can amplify a small signal but must use high voltages (transistor doesn’t need high voltages) • Parts – highest positive potential – plate – cylinder of wire mesh – grid (one grid!) – element furthest from plate is – filament • Cathode emits electrons • Most similar to a Field Effect Transistor Equivalencies • The exam has a bunch of “closest” comparisons Distortion • If an amplifier becomes non-linear, the output would become distorted (there are other kinds of distortion…) The End Schedule Date Topic Instructor Feb 20 - 9 AM Chapter 2: Basic Theory Rob Striemer (VE4SHS) Feb-20 Chapter 3: Ohm’s Law & Power Rob Striemer Feb-20 Chapter 4: Inductors & Capacitors Rob Striemer Feb 20 - 1 PM Chap. 1: Introduction to Amateur Radio Dylan Fijal (VA4DFJ) Feb-20 Chapter 12: Q codes, phonetics, emerg comms, etc. Dylan Fijal Feb-20 Chapter 17: Regulations, Towers, etc. Dylan Fijal Feb 27 - 9 AM Chapter 5: Wavelength, Frequency and Bands Collin Stanners (VE4CST) Feb 27 - 9 AM Chapter 6: Propagation Collin Stanners Feb 27 - 9 AM Ch. 7: Transmission Lines Collin Stanners Feb 27 - 1 PM Ch. 10: Power Supplies Peter Toth (VE4TTH) Feb 27 - 1 PM Chapter 11: Setting up an Amateur Radio Station Peter Toth Feb 27 - 1 PM Chapter 12: Operating an Amateur Radio Station Peter Toth March 5 - 9 AM Chapter 8: Antennas Tina Tenbergen (VA4THN) Mar-05 Chapter 8: Antennas Tina Tenbergen Mar-05 Chapter 9: Diodes, Transistors and Tubes Tina Tenbergen March 5 - 1 PM Chapter 13: Modulation and Transmitters Jim Townsend (VE4CY) Mar-05 Chapter 14: Receivers Jim Townsend Mar-05 Practice Exam March 12 – 9 AM Chapter 15: Radio Frequency Interference Bob Jacobs (VE4RCJ) Mar-12 Chapter 16: Safety Bob Jacobs Mar-12 Review March 12 - 1 PM Review & Practice Exam Rob Striemer March 19 – 9 AM Industry Canada Final Exam 9:00 AM Adam Romanchuk March 19 – 11 AM 11:00 AM - workshop: How to get started, tips, etc.