Chapter 2: Concepts and Equations

Question 1

Standard AM Range

Answer 1

535 -1605 Hz

Question 2

How does modulation affect antenna size

Answer 2

carrier’s frequency wavelength is shorter / so shorter antenna. longer wavelengths require larger antennas

Question 3

Process of impressing low-frequency information signals to higher frequency signal. changing one or more property of carrier signal to adjust for the information signal

Answer 3

Modulation

Question 4

The signal that is modulated and used to carry information

Answer 4

Carrier signal

Question 5

Also known as modulating signal, baseband signal or intelligence

Answer 5

Information

Question 6

constant: standard AM Intermediate frequency

Answer 6

455 KHZ

Question 7

known as coefficient of modulation or both of modulation or amount of amplitude change

Answer 7

AM Modulation index

Question 8

formulas:
Modulation index
AM Percent Modulation

concept:
What should the modulation in index’s value be?

Answer 8

m= Vm/Vc
m= Vmax-Vmin/Vmax+Vmin
%m=m x 100%

Typically less than 1, ideally should be 1 , If more than 1then that’s overshoot

Vm= modulating signal Peak voltage
Vc = carrier signal peak voltage
Vmax= AM signal max voltage
Vmin=AM signal min voltage

Question 9

Formula
AM current and voltage Relationship

Answer 9

IT = Ic sqrt ( 1 + (m^2/2 ) )
VT = vc sqrt( 1 +( m^2/2) ).

IT= Total or modulated current
VT = Total or modulated voltage
lc =carrier or unmodulated current
vc =carrier or unmodulated voltage
m= modulation index

Question 10

Formula
AM Power Relationships

Answer 10

PT= Pc + 2 PSB
PSB = Pc ( m^2 /4)
PSBT = Pc ( m^2)
PT = Pc ( 1 + (m^2 /2))

PC = carrier or unmodulated power
PSB=power in one sideband
PTSB=total power in two sideband
m=modulation index

Question 11

Bandwidth AM Requirements

Answer 11

B = 2 fmax
AM Bandwidth
fmax= max modulating frequency

Question 12

Formula
Modulation by several signals

Answer 12

VT = sqrt ( v1^2 + v2^2…)
IT = sqrt ( I1^2 + I2^2…).
PSBT= PSB 1 + PSB2 …
meff= sqrt ( m1^2 + m2^2…)

VT = Total modulated voltage
IT = Total modulated current
meff=effective total modulation index
PSBT = total power of side bands

Question 13

The useful power of an AM signal is? It is 1/3 of the total power or 33%

Answer 13

sideband power

Question 14

→class A RF amplifier that isolates crystal oscillator to improve stability . Has high input impedance and low output impedance
→ class c RF amplifier used to increase output of buffer to drive the modulating signal
→class B amplifier that varies the plate voltage

Answer 14

Buffer amplifier - Intermediate power amplifier - push pull modulator

Question 15

This means the extraction of information signal from the AM signal
→this is also known as the peak detector

Answer 15

Detection- Diode envelope detector

Question 16

It is one of the earliest types of AM receivers, and is probably the simplest designed radio receivers available today.
Its components includes: antenna, RF amplifier, detector, AF amplifier, and speaker.

Its bandwidth is inconsistent

What are the parts;

Answer 16

TRF (Tuned Radio Frequency) Receiver

RF Amplifier - Detector- AF Amplifier

Question 17

—- means to mix two frequencies together in a nonlinear device or to translate one frequency to another using nonlinear mixing

—–was invented by Edwin Armstrong, its gain, selectivity and sensitivity is far superior to the other receivers

Answer 17

Heterodyning
Super heterodyne reciever

Question 18

Parts of superHet

Answer 18

Local Oscillator -Mixer(converts RF to IF) - IF Section ( Amplification and selectivity ) - Second detector

Question 19

Formula :
Q Factor

The higher the Q factor the … the circuit

Answer 19

Q= XL/ R
fR = 1/ ( 2 pi sqrt ( LC) )
B=fR/Q

the Better

XL= inductive reactance ( ohms)
C=Farads
L=Henrys
B=Bandwidth

Question 20

Formula :Improvement
Bandwidth improvement
Noise Figure Improvement
High and Low Side Injection

Answer 20

BI= B RF / B IF
NFI = 10log (BI)
fHi = f RF + IF
fLo = f RF - IF

Question 21

Concept: Any frequency other than selected RF carrier will produce a cross product frequency

Formula : of answer above
Formula : IFRR ( The higher the better)
IFRR in dB

Answer 21

Image frequency ( High and Low injection ):
fimage = f RF + 2IF
fimage = f RF - 2IF

IFRR=sqrt(1+Q^2p^2)
IFRR dB=20 log(IFRR) [20 for both high and low]
p=(fimage/fRF)-(fRF/fimage)

Q=Q factor
fRF = incoming radio frequency

Question 22

Concept Notes: frequencies between RF and original frequencies

How can image frequency be prevented ? Increase ….. or use …… amplifier BEFORE the mixer

Answer 22

Intermediate frequencies (that’s why INTER mediate)
IFs or narrowband (narrow to not allow)

Question 23

Concept : Form of amplitude modulation in which carrier is totally supressed

Formula:
●Its current and voltage relationship
●Its power relationship
●Power Saving
●Bandwidth Requirements

Answer 23

Double sideband suppressed carrier
IT = Ic (m/sqrt( 2) )
VT = vc (m/sqrt( 2) )

IT= Total or modulated current
VT = Total or modulated voltage
lc =carrier or unmodulated current
VT = Total or modulated voltage voltage
m= modulation index

PT= 2 PSB
PT = Pc ( m ^ 2 / 2 )

PT = Total or modulated power
Pc = carrier or unmodulated power
PSB=power in one sideband

% PS=[(P AM-P DSBSC)/PAM) x 100%
P AM=AM signal total power
P DSBSC=DSBSC signal total power

B DSBSC=2fmax

Question 24

concept : form of AM modulation which carrier is totally suppressed and one of sidebands removed

Formulas :
●current and Voltage Relationship
●Power relationship
●power saving
●Peak envelope power
● Bandwidth requirement

Answer 24

SSBSC

IT = Ic (m/ 2)
VT = vc (m/2)

IT= Total or modulated current
VT = Total or modulated voltage
lc =carrier or unmodulated current
VT = Total or modulated voltage voltage
m= modulation index

PT= P SB
PT = Pc ( m^2 / 4 )
PSB = power in one sideband
PT=Total or modulated power
Pc =carrier or unmodulated power

% PS=[(P AM-P SSBSC)/PAM) x 100%
P AM=AMsignal total power

PEP = v RMS^2/RL
P AVE= PEP / 3
Pave = PEP / 4

VRMS=voltage source or root mean square
RL= Load Resistance (Ohms)

B(SSBBSC) = f(max)

Question 25

●Known as single sideband reinserted carrier. Carrier voltage is reduced to 10%
●single carrier frequency is independently modulated
●Only part of the second sideband is transmitted, but the carrier and one sideband are fully transmitted. This is used by picture portion of commercial television broadcasting

Answer 25

Single sideband reduced carrier, independent sideband, vestigial sideband

Question 26

Type of Analog modulation in which angle sinusoidal reference function is varied in accordance with modulation signal.

Its two types:

Answer 26

Angle modulation, frequency, and phase modulation

Question 27

Concept:
●Frequency of carrier is varied proportional to the information signal
●Standard Range?
●Standard Intermediate Frequency

Answer 27

Frequency modulation - 88-108 MHZ - 10.7 MHz

Question 28

Concept;
●Relative displacement of the carrier frequency - amount of change in carrier frequency
●Ratio of Deviation and modulating signal frequency. Determines significant pairs of sideband
●Worst case modulation index
●Ratio actual frequency deviation produced to max frequency dev allowed
●Peak to peak frequency deviation

Formula;
Formula(s) of each answer to concept above

Answer 28

Concept : Frequency Deviation
Formula: small delta=kf*Vm
kf~frequency deviation constant
Vm~modulating signal peak voltage

Concept : FM Modulation Index
Formula: m=small delta/fm
fm~modulating signal frequency

Concept : Deviation Ratio
Formula: m=small delta (max)/fm(max)

Concept : FM Percent Modulation
Formula: %m=(small delta/small delta (max)) x 100%

Concept : Carrier swing
Formula: CS=2*small delta

Question 29

Formulas: FM Bandwidth Requirements
Carson Rule
Narrowband FM
Wideband FM

Answer 29

B carson = 2 ( small delta + fm)
B NBFM = 2* fm
B WBFM = 2*small delta

Question 30

Concept note: AM has only two side bands but FM has?

Answer 30

Infinite number of sidebands

Question 31

concepts:
●Inherent ability of and FM reciever to diminish effect of interfering
● Noise reduction Effect that occurs for strong FM signals
●known as Clipper - used to remove sporadic high-amplitude noise transients of short duration - special circuit that removes unwanted amplitude variations

Answer 31

Capture Effect /threshold Effect/ Limiter

Question 32

Concept : Modulation Technique where info signal is analog and the phase of the carrieris varied proportional to info signal

concept Note: similar to FM with a phase shift of 90 degrees

Formula :
●Its Deviation
● Its Modulation Index

Answer 32

Answer to both: Phase Modulation

Phase Deviation Formula
kp*Vm

Modulation Index formula
m=Phase Deviation

Question 33

Advantages of Angle Modulation :
●From the use of limiters
●Due to thresholding
●In FM and PMthe total power remains the same regardless if modulation is present

Answer 33

Noise immunity / Improved signal to Noise ratio / Power efficiency

Question 34

concept notes: Why can the carrier and a sideband be omitted from transmission ?

Answer 34

The carrier does not contain any information, and two sidebands contain the same info. The other sideband is used for redundancy only