FM circuit help

D

devil6600

New Member

• Dec 11, 2009

• #1

Hello

I have build the FM circuit posted at: FM Transmitter

Can some one tell me which part is oscillator and which part is frequency modulator? I am confused.
I would appreciate if some can tell me detailed working of the circuit.

Is it possible to make a high frequency (100 Mhz) oscillator using IC's?

Thanks

 

Dragon Tamer

Member

• Dec 11, 2009

• #2

the frequency modulator is C5 in the circuit. the oscillator is the tank circuit and the frequency output is determined by the equation: F= 1÷2 Pi √LC

I have heard of integrated circuits being used as the oscillators in trans miters, but I've never actual seen it being used. I suppose that if the IC can operate at high frequencies then it could be done. what kind of IC where you thinking about.

 

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B

BrownOut

Banned

• Dec 11, 2009

• #3

Q1 and it's assciated components form both the oscillator and modulator. It will oscillate at the fundamental frequency, but changes in the capacitance of Q1 due to the input from amplifier Q2 vary the osllation frequency for FM modulation. C5 is a fixed value capacitor, and does not change the frequency. Here is a pretty good article https://www.members.tripod.com/~transmitters/begin.htm

 

Last edited: Dec 11, 2009

D

devil6600

New Member

• Dec 12, 2009

• #4

thank you very much for the information, really appreciate that.

 

D

devil6600

New Member

• Dec 12, 2009

• #5

few days back i have opened my cell phone and I was surprised to see that there was no inductor there, so I think that means high frequency oscillators can be built using IC's

 

M

mneary

New Member

• Dec 12, 2009

• #6

The inductor is hiding in plain sight. Inductors at cell phone frequencies can be made 1mm long, sometimes even smaller.

 

mbarazeen

Member

• Dec 12, 2009

• #7

i know one IC used in small transmitters, BH1417F
see the data sheet.
BH1417F Datasheet pdf - Audio LSIs > High frequency signal processing > Wireless audio link IC - ROHM