Transcript Document

Chapter 4
Components and Circuits
Electrical Review
• Current is the flow of electrons and is measured
in amperes or amps (A) with an ammeter.
• Voltage is the potential that moves electrons and
is measured in volts (V) with a voltmeter.
• Resistance is the opposition to current flow and
is measured in ohms (Ω) with a ohmmeter.
• Power is the energy use (or generation) per unit
time and is measured in watts (W).
• Ohm’s Law (E = voltage, I = current, R =
resistance)
E  IR
• Power (P = power)
2
E
P  IE  I R 
R
2
• Metric Prefixes
–
–
–
–
–
–
milli (m) = 1/1,000 = 10-3
kilo (k) = 1,000 = 103
mega (M) = 1,000,000 = 106
Micro (μ) = 1/1,000,000 = 10-6
nano (n) = 1/1,000,000,000 = 10-9
pico (p) = 1/1,000,000,000,000 = 10-12
• Examples:
– Calculate the resistance that would draw 10 mA with
an applied voltage of 15 V.
– Calculate the power dissipated by a 200 Ω resistor
with a current of 1.5 A flowing through it.
– Calculate the voltage drop across the above resistor.
AC and DC Waveforms
• Direct current (DC) flows in one direction.
The voltage maintains the same polarity.
• Alternating current (AC) reverses direction.
The voltage polarity changes regularly.
– AC is represented by a sine wave (1 cycle or
wavelength is shown)






•  f  c , where λ is the wavelength (meters,
m), f is the frequency (Hertz, Hz), and c is
the speed of light (3×108 m/sec)
• Examples
– Calculate the wavelength of 29.6 MHz signal.
– Calculate the frequency of a 75 meter signal.
Decibels
• A bel is logarithmic unit expression the
ratio of a quantity such as power or sound
intensity. A bel is a large unit so the
decibel (dB) is used. Deci is the metric
prefix for 1/10, so a decibel is one tenth of
a bel.
 P 
 V2 
 V
dB  10 log10 
 10 log10  2   20 log10 

 Pref 
 Vref 
 Vref





 P 
dBm  10 log10 

 1 mW 



• Examples
– Calculate the gain in dB of an amplifier that
amplifies a 1 W signal to a 20 W signal.
– Calculate the power in dBm of a 10 W signal.
– Calculate the dB ratio that represents a
doubling of the power.
– Calculate the fraction of the original
transmitter power that gets to an antenna with
2 dB of loss in the coax running to the
antenna.
AC Power
• An AC signal varies over the course of a
cycle from zero to a positive peak, back to
zero, then a negative peak and back to
zero again.
• For a given DC voltage in a circuit that is
dissipating a given power, the equivalent
AC voltage with same power dissipation is
called the RMS (root mean square)
voltage.
VRMS  0.707  VPeak
VPeak  Peak
 0.707 
2
VPeak  1.414  VRMS
VPeak  Peak  2.828  VRMS
• Examples
– Calculate the RMS voltage for VPeak = 120 V
– Calculate the VPeak-Peak when VRMS = 12 V.
• Peak Envelope Power (PEP) is the
average power over over one RF cycle at
the peak of the signal’s (audio) envelope.
• Peak Envelope Voltage (PEV) is one half the
peak to peak voltage.
• For an AC signal, power, voltage, and current
are related by the same equations as DC, but
using PEP power, VRMS and IRMS.
• The average power in an umodulated AM signal
is the PEP power. Key down average power in
CW is also PEP power.
• Examples
– If an oscilloscope measures a 150 VP-P voltage across
a 50 Ω load, calculate the PEP power.
– What is the RMS voltage across a 50 Ω load
dissipating 100 W PEP?
Basic Components
• Electrical components are described by
the following;
– Nominal value (for example 75 Ω resistor)
– Tolerance describes a range over which the
manufacturer specifies the component value
(for example +/-5%).
– Temperature coefficient is the gives the
components variation with temperature.
– Power/voltage/current rating is a maximum
rating that the component can handle without
overheating or shorting out.
• Resistors
• Thermistors are resistors with a calibrated
change in resistance with temperature and
can be used a temperature sensor.
• Inductors store energy in a magnetic field
created when a current flows through
them.
• Inductors resist a change in current flow
and therefore will act like a low pass filter.
• Inductors have inductance. The unit of
inductance is the Henry (H).
• Inductors can filter high frequencies out of a
power supply’s output. They are called filter
chokes.
• Wirewound resistors have a parasitic inductance
which limits their use at radio frequencies. Use
carbon, or metal oxide resistors at radio
frequencies.
• An iron core in an inductor increases the
inductance over an equivalent air wound
inductor.
• The core material in an inductor can saturate at
high frequencies. The core material has an
optimized frequency range.
• Mutual inductance is the transfer of
magnetic energy between two inductors.
It is used to advantage in transformers. In
radio circuits, mutual inductance is not
desirable and can be avoided by placing
inductors are right angles to each other or
using toroidal cores.
• Capacitors are constructed from two
parallel metal plates and store energy in
the electric field between the plates. An
applied voltage establishes the electric
field.
• Capacitors are defined by their
capacitance, which is measured in Farads
(F).
• The metal plates of a capacitor have a
dielectric insulating material between
them. The dielectric can be air, mylar, or
other insulating materials.
• Inductors, which have parallel
windings can have a parasitic
capacitance.
• Capacitors can have parasitic
inductance. The leads can have
parasitic inductance also.
• Ceramic capacitors are low cost
and usable through VHF and
UHF (with some parasitic lead
inductance).
• Electrolytic capacitors are used in
power supplies for filtering.
Series and Parallel Circuits
• Kirchoff’s Voltage Law (KVL) – The voltages
around a circuit must add up to the applied
voltage.
• Kirchoff’s Current Law (KCL) – The total current
entering a junction must equal the sum of the
currents leaving the junction.
• For two resistors in parallel, you can use
the simpler formula;
REQU
R1  R2

R1  R2
• The same formula will work for capacitors
in series and inductors in parallel.
• Examples
– Calculate the equivalent resistance of three
150 Ω resistors in parallel.
• Examples (continued)
– Calculate the equivalent inductance of a 30
mH and 25 mH inductor in series.
– Calculate the equivalent capacitance of a 20
μF, 50 μF, and a 35 μF capacitor in series
– Calculate the equivalent resistance of a 500
pF and 1000 pF capacitor in parallel.
• Transformers use mutual inductance
between two inductors to transform AC
voltages. Power is applied to the primary
winding and extracted from the secondary
winding.
• Voltage transformation depends on the
number of windings of the primary and
secondary.
ES N S

EP N P
NS
ES  E P 
NP
• Example
– Calculate the secondary voltage if the applied
voltage is 120 V ac, the primary has 500
turns, and the secondary has 2000 turns.
– What turns ratio would be required to
transform 120 V ac to 1000 V ac?
Reactance and Impedance
• Resistors resist the flow of AC current the
same for all frequencies.
• Inductors and capacitors resist the flow of
AC current in a frequency dependent way.
• Reactance is the measure of the
resistance to AC by inductors and
capacitors. Reactance is measured in
ohms and uses the symbol X. Reactance
is caused by the property of inductors and
capacitors to store energy.
• Capacitive Reactance, XC, decreases with
frequency.
1
XC 
2 fC
• Inductive reactance, XL, increases with
frequency.
X L  2 fL
• Examples
– Calculate the capacitive reactance of a 2nF
capacitor at 3 MHz.
– Calculate the inductive reactance of a 10 mH
inductor at 1 MHz.
• Impedance, Z, is the combined effect of
resistance and reactances in a circuit.
Impedance is also measured in ohms.
• Resonance occurs when a circuit (or
antenna) is purely resistive with no
reactance. This occurs when capacitive
reactance equals inductive reactance.
• The figure below shows a series resonant
circuit.
• Maximum power transfer occurs when the
impedance of the source equals the
impedance of the load. An impedance
matching LC circuit can be used between
a transmitter and an antenna to improve
the power transfer.
• Impedances can be matched using a
transformer.
2
 NP 
ZP  ZS 

 NS 
ZP NP

ZS NS
• Example
– What turns ratio is required to transform a 200 Ω
impedance to a 40 Ω impedance?
• Impedances can be matched using special
lengths of transmission lines.
Semiconductor Components
• Semiconductors are made from Silicon
(Si) or Germanium (Ge) with added
elements, such as Indium (In) or
Phosphorus (P), called dopants. These
dopants create either an N-type
semiconductor, or P-type semiconductor.
– N-type semiconductors conduct electricity
with electrons
– P-type semiconductors conduct electricity with
“holes”, which are positive charges caused by
a missing electron bond.
Diodes
• A diode is the simplest semiconductor device
and is formed from a PN junction.
• The junction threshold voltage, VF, is typically
0.3 V for germanium and 0.7 V for silicon.
• Forward bias is when the positive voltage
is applied to the P-type material (anode)
and the negative voltage is applied to the
N-type material (cathode). A large current
can flow in forward bias.
• Reverse bias is the opposite polarity from
forward bias and no current flows.
• The ratings for a semiconductor diode are;
– Peak Inverse Voltage (PIV) is the largest
reverse voltage a diode can withstand before
reverse breakdown occurs.
• Average Forward Current is the limiting current
before a diode will overheat. The dissipated
power is IF × VF.
• The junction of a diode also has some
capacitance. A varactor diode is a special diode
designed to act a voltage variable capacitor.
• Schottky diodes use a metal for the N-material
and are useful at very high frequencies (1012
Hz).
• Zener diodes are used as voltage regulators due
to their precise reverse breakdown voltage.
• PIN diodes have a VF and are used for
switching.
Bipolar and Field Effect Transistors
• Bipolar Junction Transistors (BJT) are
formed with three layers, PNP or NPN.
• The three electrodes of a BJT transistor
are the collector (C), base (B), and emitter
(E).
• The base current controls the collectoremitter current flow.
• Field Effect Transistors (FET) also have
three terminals, drain (D), source (S), and
gate (G). The gate voltage controls the
drain-source current.
• A junction FET (JFET) has the junction in
contact with the channel.
• Metal-Oxide-Semiconductor FET
(MOSFET) and Insulated-Gate FET
(IGFET) have an insulating layer between
the gate and channel.
• The high gain of transistors (FET’s and
BJT’s) make them excellent as switches in
digital circuits.
• High power transistors have metal cases
to improve heat dissipation. Be careful
when installing such transistors to avoid
short circuits.
Vacuum Tubes
• Vacuum tubes were used before
transistors were available.
• The filament or heater heats the cathode so that
it emits electrons.
• The cathode emits electrons.
• The control grid controls the flow of electrons
from the cathode to the plate.
• The screen grid reduces the grid-plate
capacitance which diminishes high frequency
performance.
• The suppressor grid prevents electrons from
traveling from the plate to the other grids.
• The plate collects the electrons from the
cathode. This is called the plate current.
• FET’s are analogous in operation to a vacuum
tube.
Analog and Digital Integrated Circuits
• An integrated circuit (IC) or “chip” is a
collection of transistors, diodes, resistors,
capacitors, and inductors on a single wafer
of silicon.
• Analog IC’s operate over a continuous
range of voltages or currents.
– Operational Amplifiers (Op Amps) are
inexpensive amplifiers for DC and audio
circuits.
– Linear Voltage Regulators are used in power
supplies to provide a regulated voltage.
• Digital IC’s operate at two discrete values
of voltage representing on or off (the
binary values of 1 or 0).
• Logic families
– Resistor Transistor Logic (RTL) is no longer
used.
– Transistor Transistor Logic (TTL) is still in use
but not for low power circuits.
– Complementary Metal Oxide Semiconductor
(CMOS) Logic is very high speed with low
power consumption.
• Digital circuits are combinations of gates.
• Flip-flops can be connected together to
create shift registers and counters.
– A shift register can store binary data.
– A counter can count up to 2N where N is the
number of shift registers. A 4 bit (N = 4)
counter can count to 24 = 2 × 2 × 2 × 2 = 16.
• Microprocessors contain thousands of
gates on a single chip.
– Microcontrollers have interfaces for external
signal and control circuits.
• Digital Interfaces
– Serial interfaces process data one bit (1 or 0)
at a time.
• RS232 (COM port)
• USB (Universal Serial Bus) has replaced the
RS232 port
• Network (WiFi, Ethernet, Bluetooth)
– Parallel Interfaces process several bits at a
time.
• Parallel port (LPT or line printer port).
• Visual Interfaces
– Cathode Ray Tube (CRT)
– Liquid Crystal Display (LCD) are very low
power but have no light. LCD displays require
an external light source.
– Light Emitting Diode (LED) is a PN junction
diode which emits light when forward biased.
• RF Integrated Circuits
– Monolithic Microwave Integrated Circuit
(MMIC) are used in cell phones and GPS
receivers.
Rectifiers and Power Supplies
• A linear power supply has three basic parts; an
input transformer, a rectifier, and a filter and
regulating circuit.
• A diode is used as a rectifier because it can
block the current flow in one direction and pass it
in the other direction.
• A half wave rectifier permits current flow for only
half of an AC signal’s cycle.
• A full wave rectifier permits current flow over the
whole AC signal’s cycle. The output is twice the
frequency of the input.
– Full wave rectification can be achieved with two
diodes and a center tapped transformer or with a
bridge rectifier without a center tapped transformer.
• In a half wave rectifier circuit;
– The diode must be able to withstand twice
the supply’s peak output voltage.
– The diode carries the entire current load of
the power supply.
• In a full wave bridge rectifier;
– The diodes must be able to withstand only
the supply’s peak output voltage.
– Each diode carries only half the current load
of the power supply.
• Diodes can be put in parallel to increase
the current carrying capacity, or in series
to increase the voltage rating.
– A small resistor (~0.1 Ω) is used to help
balance the current and voltage in the diodes.
• Filter Circuits
– A filter circuit usually consists of a large filter
capacitor. Inductors can also be used.
– Electrolytic capacitors provide the high
capacitance required.
• Capacitors have losses due to current flow
through the electrolytic paste and
resistance in the conducting surfaces of
the plates. Equivalent series resistance
(ESR) is the term for this parasitic
resistance.
• Bleeder resistors are used to discharge
stored energy in the filter capacitors when
the power supply is turned off. You should
wait long enough for the bleeder resistors
to discharge the capacitors before working
on a power supply.
• Switch-mode or switching supply are
another type of power supply.
– Switching supplies operate at very high
frequencies (20 kHz) compared to linear
supplies (60 Hz).
– Smaller components (transformers, inductors,
and capacitors) can be used.
Batteries and Chargers
• There are two basic types of batteries; primary
(or non-rechargeable) and secondary (or
rechargeable).
• Battery packs contain more than one cell in
series.
• Rechargeable batteries should not be
discharged past their minimum voltage. Doing
so can reverse charge a weak cell in the pack
and damage the life of the whole battery pack.
• Batteries with a low internal resistance (like
Nicads) can deliver high discharge currents.
• Never attempt to recharge a primary battery.
• Different rechargeable batteries require different
charging methods.
• Lead-acid batteries that aren’t sealed (like in
most cars) can give off explosive hydrogen gas
when charging.
• Batteries are the usual way to store energy from
alternative power sources like wind or solar.
– Solar cells are PN junction diodes. They develop a
0.5 volt open-circuit voltage in the sun.
– A series diode should be placed in a charging circuit
so that the storage batteries do not drain current back
through the wind generator or solar panel.
Connectors
• Plugs are connectors installed on the end
of a cable. Jacks are installed on
equipment.
• Adapters make connections between
different types of connectors.
• Power Connectors
– Keyed connectors, such as PowerPole
connectors, ensures the polarity is correct.
• Audio Connectors
– Some common types are phono (or RCA)
plugs, mini-DIN, 1/4” and 1/8” phone plugs.
• RF Connectors
– UHF connectors can be used up to 150 MHz
and at full legal power.
• SO-239 is the jack on the back of a radio
• PL-259 is the plug on the coaxial cable
– Type N connectors can be used up to 10 GHz
and at full legal power.
• Better moisture protection than UHF connector
– BNC connector
• Quick connect, but low power’
• Often used on handheld radios
– SMA connector is usable to 18 GHz.
• Sometimes used on handheld radios due to small
size.
• Data Connectors
– Parallel ports use DB-25 on the computer and
Centronics connector on the printer.
– Serial ports use a DB-25 or DB-9.
– Ethernet (network) uses RJ-45 connector.
– Data connectors on radios are usually are
mini-DIN or RJ-45.
Analog and Digital Meters
• A multimeter or VOM (volt-ohm-meter) will read
voltage, current, and resistance.
• Digital meters have a display showing the value
with digits.
– Digital multimeters (DMM) are better at making
precise measurements.
• Analog meters have a moving needle with a
calibrated scale.
– Analog meters are useful when tweaking a circuit
because it easier to see a needle reach a minimum or
maximum.
• A good voltmeter will have a high input
impedance so that it places a minimal load on
the circuit.
• Oscilloscopes are used to measure fast
changing digital, audio, and RF signals.
– The horizontal axis (or channel) is usually
time and the vertical axis (or channel) is
amplitude (voltage, power, or current).
• An analog oscilloscope uses a CRT. An
electron beam scans across the screen at
a fixed rate. The beam is deflected up or
down in step with the signal. The track of
the beam across the screen is called a
trace.
• An oscilloscope can monitor the RF output
of a transmitter, by connecting the
attenuated RF output to the vertical
channel of the oscilloscope.
– You can observe key clicks or audio distortion
• Digital oscilloscopes use LCD displays or
even connect to a computer via the USB
port to use the computer’s display.
Signal Generators
• Audio generators can be used to test
transmitters.
• RF generators can be used to test
receivers.
Impedance Measurements
• Antenna analyzers can be used to check
the impedance and SWR of antennas
without transmitting a high power signal.
• Antenna analyzers can also measure feed
line velocity factor, electrical length, and
loss.
• Antenna analyzers use very low power
test signals. Nearby strong signals can
cause inaccurate readings.
Field Strength and RF Power Meters
• A field strength meter can measure the
transmitted signal level.
– Compare relative RF levels during antenna
and transmitter adjustments.
– Measure the radiation pattern of an antenna.
• Directional wattmeters can transmitter
power in a feedline. It measures the
forward power (PF) and the reflected
power (PR).
– Standing Wave Ratio (SWR)
SWR 
1  PR / PF
1  PR / PF