a capacitor in FM modulator

Wendy

Joined Mar 24, 2008
23,415
This is a common base configuration on the transistor RF design. The capacitor grounds any RF signals, but is low enough in value it is fundamentally invisible at audio frequencies.
 

Thread Starter

baby_1

Joined Jun 3, 2011
39
hello and thanks for your response
could you tell me about how can we calculate this capacitor value according this circuit?
 

panic mode

Joined Oct 10, 2011
2,715
|Xc| = 1/(2*pi*f*C)

since frequencies of carrier and audio signal differ greatly, you can use any value in quite wide range, for example 100pF - 2.2nF will do.
 

BlackCow

Joined May 11, 2009
65
|Xc| = 1/(2*pi*f*C)

since frequencies of carrier and audio signal differ greatly, you can use any value in quite wide range, for example 100pF - 2.2nF will do.
Just in case the OP doesn't understand what this is this formula gives you the reactance of a capacitor at a given frequency in Ohms. Reactance is like resistance but only AC signals.
 

BlackCow

Joined May 11, 2009
65
|Xc| = 1/(2*pi*f*C)

since frequencies of carrier and audio signal differ greatly, you can use any value in quite wide range, for example 100pF - 2.2nF will do.
Perhaps the OP doesn't know what reactance is?

This is this formula gives you the reactance of a capacitor at a given frequency in Ohms.

Reactance is like resistance but only for AC signals.
 
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