Quick question for u guys .. plz have a look

[Student Forever]

Hi guys.

tell me what u know about this question plz.



Explain how the AFC voltage is derived and used to control the Local oscillator.

 

[blueroomelectronics]

Have you tried Google?

 

[Student Forever]

yep.. but it confusing me

 

[Speakerguy]

D O Y O U R O W N H O M E W O R K

 

[Student Forever]

thanx for ur advise speakerguy79

 

[crutschow]

If you gave us some idea that you had actually thought about the answer to the question, perhaps we would be more likely to help.

 

[blueroomelectronics]

What part is confusing you?

 

[Student Forever]

I mean when i found an automatic frequency control threat , it doesn't talk about the oscillator or my subject.

 

[colin55]

What was the threat?

Do you realise WARS have been started over a simple spelling mistake.

 

[kchriste]

Think about this:
How does the discriminator in an FM demodulator work? What happens on the output of the discriminator when the received station is off ±frequency?

 

[audioguru]

The FM detector produces a DC voltage when the radio is tuned away from the center of the station. The DC voltage corrects the frequency of the voltage-controlled local oscillator.

It is that simple.
Cheap FM radios drift their tuning so they use AFC to correct it. Good FM radios do not drift and do not need AFC.

 

[Student Forever]

thanx alot audioguru

 

[q5101997]

What does AFC stand for?

 

[audioguru]

What does AFC stand for?

Automatic-Frequency-Control.
When you tune toward a station then the AFC circuit snaps the tuning toward the center of the station's frequency. When you tune away then it seems like the station's frequency is very wide then it snaps away.

Manufacturers of cheap radios use AFC because the frequency of the cheap radios drifts. They blame the drifting on the stations. But stations are crystal controlled and do not drift.

 

[q5101997]

Thanks Donald