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Amateur Radio Licensure Week 5: Advanced Electronics Seth Price, N3MRA New Mexico Institute of Mining and Technology February 28, 2016 Transformers • Transformers contain a primary winding and a secondary winding: – Primary Winding: Connected to the source of energy (power supply) – Secondary Winding: Connected to the load Transformer Voltage • Windings can be used to scale voltage: 𝑉𝑝 𝑁𝑝 = 𝑉𝑠 𝑁𝑠 – Ex: a 120V input into a 2250 turn primary coil produces 26.7V output onto a 500 turn secondary coil Other Instances of Inductance • Solenoid – Often used to open physical devices • Toroid – ferrite core helps: • Achieve high inductances • Contain magnetic field And can be tailored to a specific frequency range Notes on Inductance • In the case of a transformer, we like mutual inductance (coupling) • If we have two solenoids, we might not want them coupled – In this case, it is best to have them positioned perpendicular to each other Diodes (PN Junction) • Semiconductor device – Anode and cathode • Non-linear resistance • Conduct in only one direction • “Knee” or “turn on” voltage – Silicon: 0.6-0.7V – Germanium: 0.3V – Light Emitting Diode (LED): 1.7V IV Curve for Diodes https://learn.sparkfun.com/tutorials/diodes/real-diode-characteristics Diode vs. Sine Wave http://www.duncansonelectric.com/blog/wpcontent/uploads/2009/08/23-half-waverectifier-1024x368.gif Rectification • Means for converting an AC signal into a DC signal • Half Wave – Only half (180 degrees) of each cycle is rectified • Full Wave – Each cycle is completely rectified (360 degrees) – If not filtered, this appears as a pulse train of DC signals at twice the frequency of the input! • Rectifier should be rated: – Minimum Peak-Inverse-Voltage should be twice that of the normal peak output voltage of the supply Transistors • Semiconductor device (3 layers) • Uses – Voltage or current signal to control current flow (switch) – Amplifiers (Gain controls amplification) • Something Types of Transistors • BJT: Bipolar Junction Transistor • FET: Field Effect Transistor • JFET: Junction Field Effect Transistor • MOSFET: Metal Oxide Semiconductor FET BJT • Three terminals: Base, Emitter and Collector http://it.tdklambda.com/content/glossary/1285220540 22990000_BJT%20image.png FET • Three terminals: Source, Gate and Drain http://www.angelfire.com/planet/funwithtran sistors/images/FIG-4-21.gif Transformers • Two parallel inductors can induce a current in each other – This is called “mutual inductance” • No electron passes between the two inductors Power Supplies • Convert 120VAC to 13.8V DC or some other output voltage • Functionally, they have a – Transformer for stepping the voltage down – A diode bridge to produce full-wave rectification – An electrolytic capacitor to smooth output voltage Power Supplies Ground Loop • To avoid ground loops, make sure all ground connections are connected to a single point – Symptom: reports of a “hum” in your transmitted signal Lightning Safety • The biggest reason for having lightning protection is to reduce fire hazards! • To protect your station: – Disconnect antenna cables – Unplug AC cords – Stop using equipment and move to another room • Don’t climb a tower during a lightning storm Oscilloscope • Measures complex waveforms – V or I against time – Contains amplifiers for vertical and horizontal channels • Useful for checking: – CW waveform – Radio Frequency (RF) envelope of output signal, through attenuator and vertical channel Voltage (RMS) • An AC signal dissipates the same power as a DC signal at VRMS. 𝑉𝑅𝑀𝑆 = 0.707𝑉𝑝 • Something • Something Circuit Construction • Rosin core solder is the best for radio construction • Cold solder joints = bad connection – Grainy or dull surface • We’ll do some soldering tonight! References • • • • • • • • http://www.isomatic.co.uk/images/smtraf-11.jpg http://www.electricityforum.com/images/electrical-transformer-design.jpg http://www.societyofrobots.com/actuators_solenoids.shtml http://www.kitsandparts.com/howtowindtoroidswithoutpain.php http://archive.evaluationengineering.com/archive/articles/1105/1105rf_p ower.asp http://et.nmsu.edu/~etti/fall96/communications/db/db.html http://wpcontent.answers.com/wikipedia/commons/thumb/c/cc/Bode_Lo w-Pass.PNG/350px-Bode_Low-Pass.PNG http://www.epanorama.net/documents/groundloop/basics.html