# TechGen Week 3: Electricity, Components, and Circuits

This is the class outline for week 3 of the SCARS 2018 Technician / General Class.

## Week 3 Question Pool

Today’s class will concentrate on the above listed topics, and the question pools that you can download here:

## Electricity

 Quantity Description Symbol(s) Unit(s) Measured by: Current Flow of electrons I, i Amps Ammeter Voltage Electromotive force (EMF) that causes current flow V, v, E Volts Voltmeter
• Electrons: negative electrical charges
• Current generally flows through a conductor (e.g., wire) or component (e.g., light bulb, transistor)
• Conductors: metals (copper, aluminum, gold, silver), graphite, water (pure: poor; salty: fair)
• Voltage difference
• Earth is reference (“zero”): earth ground, ground potential,ground
• Chassis (car body, metal box) also referred to as ground
• Voltage can be negative (-) or positive (+); like charges repel, so:
• Negative voltage repels electrons
• Positive voltage attracts electrons

### Circuit

• Various components, usually connected by wire, copper trace on circuit board, chassis
• Parallel, serial circuits

### Water flow analogy

• pump analogous to voltage source
• pipe analogous to conductor
• gallons/minute, liters/second, etc. analogous to current
• water wheel, turbine, pipe constriction analogous to load (resistance, or impedance, etc.)

Note: voltage measured across battery (parallel); current measured inline (series)

## Multimeter Demo

Don’t measure current or resistance of battery

## Parallel and Series Circuits

• (A) same current through all components
• (B) same voltage across all components
• Open circuit: infinite resistance (“OFF”)
• Closed (short) circuit: zero resistance (Bad mojo!)

### Resistance

• resists, or impedes, current
• ohms, Ω (Greek upper case omega)
• measured with (gasp!) ohmmeter
• German physicist Georg Simon Ohm (mhos!)

## Ohm’s Law

• expresses relationship between voltage, current and resistance
• R = E/I
• I = E/R
• E = I x R

## Power

• rate energy is used (e.g., jogging requires 500 calories per hour)
• measured in watts (W), with a wattmeter
• Power = voltage times current (curent can be determined by knowing voltage and power; appliance labels)
• P = E x I
• E = P/I
• I = P/E

### Combining Ohm’s law and Laws’s law

• P = E x I, but E = I x R, so

P = I2R

• I = E/R, so

P = E2/R

## AC/DC

### AC:

• alternating current
• alternates polarity
• current flows one way, then the other
• household current in US is 60 Hz, 120 V AC

### DC:

• same polarity
• constant voltage
• car battery: 12 V, DC

## Components and Units

### Basic Components

• resistors
• capacitors
• inductors (coils)

### Resistors

• ohms, kilohms, megohms
• restricts current flow
• generates heat, or light (e.g., light bulb)
• variable resistors: potentiometers, or “pot”
• often marked with color code (red-violet-brown-gold: 270 ohms, tolerance 5%)

### Capacitors

• stores electric energy in electric field
• smooths out voltage changes
• schematically, two metal plates separated by insulator
• blocks DC
• AC: higher the frequency, lower the reactance (a kind of impedance)
• variable capacitors

### Inductors

• henrys, millihenrys, micro-henrys, nano-henrys
• stores electric energy in magnetic field
• smooths out current changes
• schematically, coil of wire
• passes DC
• AC: higher the frequency, higher the reactance
• coil may have iron or ferrite core to increase inductance

### Transformer

• two inductors in proximity, used to change voltage (and current)
• voltage change proportional to turns ratio

Schematic of a transformer.

Typical transformer.

Power-pole transformer.

## Reactance and Impedance

• resistor does not affect phase of current and voltage
• capacitor: current changes lead voltage changes
• inductor: voltage changes lead current changes
• inductive reactance: X, increases with frequency (low-pass filter)
• capacitive reactance: X, decreases with frequency (high-pass filter)

combination of resistance and reactance: impedance, Z

## Resonance

• at some frequency (resonant frequency), capacitive reactance and inductive reactance cancel
• impedance is minimum
• filter: passes some frequencies, blocks others
• tuned circuit is (narrow) band-pass filter

## Diodes, Transistors, and Integrated Circuits

• response depends on voltage, current and/or polarity
• silicon, germanium…
• “doped” with impurities to allow positive or negative charges to pass
• P-type, N-type
• PN junction allows more current flow in one direction than the other

### Diode

• PN
• allows current flow in one direction
• heavy-duty diode: rectifier, converts AC into pulsating DC
• has anode and cathode
• diode across tuned circuit, hooked up to an antenna: “crystal” radio
• LED: light-emitting diode

## Transistors

• can control large voltage with small voltage (gain)
• amplifiers, switches
• two common types:
• BJT: bipolar junction transistors
• PNP, NPN
• base, emitter, collector
• FET: field-effect transistors
• FET: field-effect transistors
• conducting path or channel of N- or P-type material
• ends of channel form the source and drain electrodes
• gate electrode controls current flow through channel

## Integrated Circuits

• IC, or “chip”
• many components in a single solid-state device

## Protective Components

• fuses, circuit breakers, surge protectors, UPSs, lightning arrestors
• protect equipment

## Circuit Gatekeepers

• switches, relays
• open and close circuits
• number of poles and throws
• e.g., SPST is simplest switch

## Schematics and Component Symbols

### Oscillators and amplifiers

• oscillator produces steady signal at one frequency
• driver is a stable, low-level amplifier
• power amplifier further amplifies signal

### Filters

• pass certain frequencies
• attenuate other frequencies
• passive filter: tuned circuit, capacitors and inductors
• active filter: electronic curcuts that selectively amplify certain frequencies
• high-pass, low-pass, band-pass, notch

### Modulators

• discussed earlier, puts information (voice, data, morse code, etc.) onto carrier
• on-off, AM, FM, SSB, phase-modulation…

### Mixers

• result is sum and difference of the frequencies
• Example:
• radio receives bands at 3.5 MHz, 7.0 MHz, 14.0 MHz, 21.0 MHz, 28.0 MHz
• mix 3.5 MHz signal with 7.0 MHz => difference of 3.5 MHz
• mix 10.5 MHz signal with 14.0 MHz => difference of 3.5 MHz
• mix 17.5 MHz signal with 21.0 MHz => difference of 3.5 MHz
• mix 24.5 MHz signal with 28.0 MHz => difference of 3.5 MHz
• mixing makes multi-band receiver easy to implement

### Demodulators

• opposite of a modulator
• extracts information (voice, data, morse code, etc.) from RF signal
• detectors (for AM: envelope detector)
• product detectors (for SSB, CW)
• frequency discriminators (for FM)

### Transverters

• uses superheterodyne principle of mixing frequencies
• converts entire transceiver to operate on a different band
• Example:
• There are few 220 MHz-band SSB and CW radios
• transverter can allow transceiver for 10-meter band (28 MHz – part of every HF rig) to operate on 220 MHz band

T7A01 (C)
What is the function of a product detector?
A. Detect phase modulated signals
B. Demodulate FM signals
C. Detect CW and SSB signals
D. Combine speech and RF signals

T7A02 (C)
What type of receiver is shown in Figure T6?
A. Direct conversion
B. Super-regenerative
C. Single-conversion superheterodyne
D. Dual-conversion superheterodyne

T7A03 (C)
What is the function of a mixer in a superheterodyne receiver?
A. To reject signals outside of the desired passband
B. To combine signals from several stations together
C. To shift the incoming signal to an intermediate frequency
D. To connect the receiver with an auxiliary device, such as a TNC

T7A04 (D)
What circuit is pictured in Figure T7, if block 1 is a frequency discriminator?

T7A05 (D)
What is the function of block 1 if figure T4 is a simple CW transmitter?
A. Reactance modulator
B. Product detector
C. Low-pass filter
D. Oscillator

T7A06 (C)
What device takes the output of a low-powered 28 MHz SSB exciter and
produces a 222 MHz output signal?
A. High-pass filter
B. Low-pass filter
C. Transverter
D. Phase converter

T7A07 (B)
If figure T5 represents a transceiver in which block 1 is the transmitter
portion and block 3 is the receiver portion, what is the function of block 2?
A. A balanced modulator
C. A power amplifier
D. A high-pass filter

T7A08 (C)
Which of the following circuits combines a speech signal and an RF carrier?
A. Beat frequency oscillator
B. Discriminator
C. Modulator
D. Noise blanker

T7A09 (B)
Which of the following devices is most useful for VHF weak-signal communication?
A. A quarter-wave vertical antenna
B. A multi-mode VHF transceiver
C. An omni-directional antenna
D. A mobile VHF FM transceiver