Chap 8 - Fm Reception

7/24/2019 Chap 8 - Fm Reception

1/27


2/27


3/27

uned-Circuit Frequency Discriminators. convert FM to AM and then demodulate AM envelope %ith conventional pea2 detectors. reuires '3(( phase inverter4 adder circuit and freuency.dependent circuits

- 5onverts FM to AM- !ess linear output

- t%o.single.ended slope detector connected in parallel and fed

'3(( out of phase. !a4 5a4!b4 5b4. perform FM to

AM conversion- D'4 5'4R'4 D64564R6 . remove inf

from AM envelope-

more linear output- !ac2s limiting circuit

a. Slope Detector

b. Balanced Slope Detector


4/27

Foster-Seeley Discriminator

. Similar to balanced slope detector


5/27

d. Ratio Detector

- #mmune to amplitude variations


6/27

B. Phase Locked-Loop Demodulators. reuires no tuned circuits. automatically compensates for changes in the carrier freuency

due to

instability in the transmit oscillator


7/27

C. Quadrature FM Demodulator. sometimes called a coincidence detector. e$tracts the original information signal from the composite #F

%aveform by

multiplying t%o uadrature -7((

out of phase/ signals


8/27

8oise Suppression. suppresses noise in the form of amplitude variations. uses limiter circuit

mplitude Limiters ! FM Thresholdin"


9/27

reshold4 uieting or capture level prescribed minimum input level

. 8oise limiters can improve S:8 by 6(d;

M thresholding also 2no%n as FM uieting or FM capture e? '( d; or greater)) #F signal must be su@ciently ampli"ed to overdrive the limiter)) Signal must have a modulation inde$ >? ')


10/27

6) !imiter 5ircuits


11/27

FM 5apture


12/27

blem For an FM receiver %ith a band%idth ; ?6(( 2+,4 a po%er noise "gure 8and an input noise temperature 9 ? '(( B4 determine the minimum receivecarrier po%er necessary to achieve a postdetection S:8 of =* d;) Cse thereceiver bloc2 diagram belo% as the receiver model and the FM thresholding csho%n for m?')


13/27


14/27

requency #s Phase Modulation

PM FM

Advantages

;etter S:8 5an be demodulated usingnoncoherent demod %hichare less e$pensive

Does not reuire preemphasiscircuit

5Es can produce high.freuency deviation andhigh m

5an use crystal oscillatorbecause modulation isperformed in a separate circuitfrom carrier osc)

Disadvantages

Reuires coherentdemodulation

!o%er S:8 than PM

5annot use crystal oscillator


15/27

FM $T%&%' B&'ADCA$T()*

Monophonic single 1(.+, to '1 2+, audio channel made up the entire voicand music information freuency spectrum. can separate the high freuency signal -t%eeters/ and lo% freuencysignal -%oofers/ but impossible to separate sound spatially -no

directivity to the sound/. before '71' FM transmission

Stereophonic information signal is spatially divided into t%o 1(.+, to '1 2+audio channels -left & right channels/. separate music or sound by tonal uality such as percussion4 strings4 horns and so on

8otes-

Stereophonic receivers can receive monophonic signals- Monophonic receivers can also receive stereophonic signals- 0(d; separation bet%een the t%o channels


16/27

S5A Subsidiary 5ommunications

Authori,ations . subcarrier transmission during

'711 . used to broadcast uninterrupt music to private subscribers such as dept stores4 restaurant etc)) uipped %ith special S5 receivers . subcarrier ranged from 61 2+ *1 2+, and later standardi,ed

* 2+,


17/27

Ma$imum freuency deviation for stereo FM ? *1 2+, S5A ? '(G of *1 2+, ? *)1 2+, '7.2+, stereo pilot ? '(G of *1 2+, ? *)1 2+, !HR transmission ? ( 2+,

FM Transmission


18/27

and L-& channel interlea,in"


19/27


20/27

m $tereo &eception


21/27

rge.Scale #ntegration Stereo Demodulator


22/27

'-A M'B(L% C'MM/)(CAT(')$ $%(C%$

9ypes of 6.%ay radio communication systems') 9%o.%ay mobile radio

+alf.duple$4 one to many radio comm %ith no dial tonea) 5lass D citi,ens band -5;/ radio 6)7 to 6*)0' M+,b) Amateur -ham/ radio ? ')3 M+, to =(( M+,c) Aeronautical ;roadcasting Service -A;S/ 6)3M+, to 01* M+,d) Private land mobile radio services

Public safety radio Special emergency radio #ndustrial radio

6) Mobile.telephone services Analog cellular radio Digital cellular radio

Personal communications satellite service -P5SS/


23/27

T'-A FM &AD(' C'MM/)(CAT(')$

- Cses the follo%ing bands

'=6 M+, to '*0 M+, 01( M+, to 0*( M+, 3( M+, to 70* M+,

- +as freuency deviation ? 1 2+, and fm?= 2+,- Deviation ratio ? ')*

- Ma$imum ;essel band%idth ? 60 2+,- +alf.duple$


24/27

o-0ay FM &adio Transmitter


25/27


26/27

o-ay FM &adio &ecei,er


27/27

Squelch Circuit

Chap 8 - Fm Reception

Documents

Transcript of Chap 8 - Fm Reception