Chapter 2: Concepts and Equations Flashcards
Standard AM Range
535 -1605 Hz
How does modulation affect antenna size
carrier’s frequency wavelength is shorter / so shorter antenna. longer wavelengths require larger antennas
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
Modulation
The signal that is modulated and used to carry information
Carrier signal
Also known as modulating signal, baseband signal or intelligence
Information
constant: standard AM Intermediate frequency
455 KHZ
known as coefficient of modulation or both of modulation or amount of amplitude change
AM Modulation index
formulas:
Modulation index
AM Percent Modulation
concept:
What should the modulation in index’s value be?
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
Formula
AM current and voltage Relationship
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
Formula
AM Power Relationships
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
Bandwidth AM Requirements
B = 2 fmax
AM Bandwidth
fmax= max modulating frequency
Formula
Modulation by several signals
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
The useful power of an AM signal is? It is 1/3 of the total power or 33%
sideband power
→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
Buffer amplifier - Intermediate power amplifier - push pull modulator
This means the extraction of information signal from the AM signal
→this is also known as the peak detector
Detection- Diode envelope detector
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;
TRF (Tuned Radio Frequency) Receiver
RF Amplifier - Detector- AF Amplifier
—- 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
Heterodyning
Super heterodyne reciever
Parts of superHet
Local Oscillator -Mixer(converts RF to IF) - IF Section ( Amplification and selectivity ) - Second detector
Formula :
Q Factor
The higher the Q factor the … the circuit
Q= XL/ R
fR = 1/ ( 2 pi sqrt ( LC) )
B=fR/Q
the Better
XL= inductive reactance ( ohms)
C=Farads
L=Henrys
B=Bandwidth
Formula :Improvement
Bandwidth improvement
Noise Figure Improvement
High and Low Side Injection
BI= B RF / B IF
NFI = 10log (BI)
fHi = f RF + IF
fLo = f RF - IF
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
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
Concept Notes: frequencies between RF and original frequencies
How can image frequency be prevented ? Increase ….. or use …… amplifier BEFORE the mixer
Intermediate frequencies (that’s why INTER mediate)
IFs or narrowband (narrow to not allow)
Concept : Form of amplitude modulation in which carrier is totally supressed
Formula:
●Its current and voltage relationship
●Its power relationship
●Power Saving
●Bandwidth Requirements
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
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
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)
