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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
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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