FSK modulation demodulation
1.1 ABSTRACT:
2 .1 BLOCK DIAGRAM:
Fig 2.1 Block diagram for FSK modulation and de-modulation
2.2.1 PIN DIAGRAM- IC 565 :
Fig 2.2 Pin diagram for IC 565
2.2.2 PIN DIAGRAM -IC 555:
Fig 2.3 Pin diagram for IC 555
3.1 DESIGN CALCULATION:3.1.1 FSK MODULATOR:ON time TH=0.693RBCOFF time TL=0.693(RA+RB)CTotal time T=TH+TL=0.693(RA+2RB)C
1f1= ————————– → (1)0.69(RA+2RB) C1
1f2= ———————————— →(2)0.69(RA+2RB) C 1C2———–C1+C2
Duty cycle D=ON time/Total time=(RB)/(RA+2RB)=0.3RB= 0.3RA+0.6RBRB=0.75RALet f1= 1050 Hz, f2= 1250 Hz, C1=0.
01μf
From (1)
11050 = ———————————0.69(RA+2*0.75RA) 0.01μf
1=———————————0.69*2.5RA*0.01μf
RA=55.2KΩRB=0.75RARB=41.4KΩ
From (2)
11250 = ————————————————0.69(55.2KΩ+2(41.4KΩ)) 0.01μf*C2—————-0.01μf+C2
0.01μf+C2 C2 = ———————————–0.69(138KΩ)1250*0.01μf
0.01μf+C2 C2 = —————1.19
1.19C2 – C2 = 0.01μf0.19C2 = 0.01μfC2 = 52.63 nf
3.1.2 FSK DEMODULATOR:
Upper cut off frequency of RC ladder circuit fH=1/(2πRC)Assume R2=R3=R4=RC2=C3=C4=CfH=(key in frequency+2 maximum frequency)/2
=(150+2(1250))/2=1325HzLet C=0.02μf then R=1/(2πCfH)=1/(2π*1325Hz*0.02μf )=7K Ω f0=0.3/(R1C1)f0=(f1+f2)/2=(1050+1250)/2=1150HzLet C1=0.01μfR1=0.3/(1150*0.01μf)=26K Ω
flock=8f0/10=(8*1150)/10=920Hz
fcapture should be less than flock.
Choose fcapture =400Hz
fcapture =(1/2π)(2π*flock)/(R0C0)R0=internal resistance=3.6K Ω
C0=(2πflock)/( R0)=920/(2π (400)2*3.6K Ω)=254nf
4.1 CIRCUIT DIAGRAM:4.1.1 MODULATOR:
Fig 4.1 Circuit diagram for FSK modulation
4.1.2 DE-MODULATOR:
Fig 4.2 Circuit diagram for FSK de-modulation
5.1 WORKING PRINCIPLE:
6.1 OUTPUT
Fig 6.1 Output for FSK modulation and de-modulation
6.2 OBSERVATION:INPUT:Amplitude = VON time TH = msOFF time TL= msFrequency f = Hz
FSK MODULATOR:For positive half cycleAmplitude = VON time TH = msOFF time TL= msFrequency f = Hz
For negative half cycleAmplitude = VON time TH = msOFF time TL= msFrequency f = Hz
FSK DEMODULATOR:Amplitude = VON time TH = msOFF time TL= msFrequency f = Hz
7.1 CONCLUSION:
7.2 APPLICATIONS:7.2.1 USED IN THE GSM MOBILE STANDARDMinimum frequency-shift keying or minimum-shift keying (MSK) is a particularly spectrally efficient form of coherent FSK. In MSK the difference between the higher and lower frequency is identical to half the bit rate. Consequently, the waveforms used to represent a 0 and a 1 bit differ by exactly half a carrier period. This is the smallest FSK modulation index that can be chosen such that the waveforms for 0 and 1 are orthogonal. A variant of MSK called GMSK is used in the GSM mobile phone standard. 7.2.2 USED IN CALLER ID
FSK is commonly used in Caller ID and remote metering applications. Audio frequency-shift keying (AFSK) is a modulation technique by which digital data is represented by changes in the frequency (pitch) of an audio tone, yielding an encoded signal suitable for transmission via radio or telephone. Normally, the transmitted audio alternates between two tones: one, the “mark”, represents a binary one; the other, the “space”, represents a binary zero. 7.2.3 USED TO MODULATE AN RF CARRIER FOR TRANSMISSION
AFSK differs from regular frequency-shift keying in performing the modulation at baseband frequencies. In radio applications, the AFSK-modulated signal normally is being used to modulate an RF carrier (using a conventional technique, such as AM or FM) for transmission.
7.3 ADVANTAGES:AFSK is not always used for high-speed data communications, since it is far less efficient in both power and bandwidth than most other modulation modes. In addition to its simplicity, however, AFSK has the advantage that encoded signals will pass through AC-coupled links, including most equipment originally designed to carry music or speech.
