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

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: V –Germanium: 0.3V –Light Emitting Diode (LED): 1.7V

IV Curve for Diodes

Diode vs. Sine Wave content/uploads/2009/08/23-half-wave- rectifier-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 lambda.com/content/glossary/ _BJT%20image.png

FET Three terminals: Source, Gate and Drain 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)

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 ower.asp w-Pass.PNG/350px-Bode_Low-Pass.PNG