1.5 Volt Tracking Transmitter

[andrebc]

smart idea using the IC, but why did not you use a coupling capacitor before Q2?

 

[Nigel Goodwin]

smart idea using the IC, but why did not you use a coupling capacitor before Q2?

He does, what do you think C3 is?.

 

[Roff]

He does, what do you think C3 is?.

After reading Andrebc's posts, one wonders if he is looking at the same schematic we are.

 

[andrebc]

After reading Andrebc's posts, one wonders if he is looking at the same schematic we are.

Chill out Mr smart! dont get bothered by other members questions, just ignore them if you cant respond.

 

[andrebc]

C2 is only 100pF. It is a capacitor so it does not short the base to the emitter at DC, it stops the preamp transistor from amplifying the RF from the output of the transmitter. 100pF has a reactance of 80k ohms at 20kHz so it has no effect on the signal from the microphone. At 100MHz its reactance is only 16 ohms.

I believe C12 is a coupling capacitor, how come it's not the same value as C1 and C2. Is that because the audio frequency will be different after it passes the the first RC circuit?

 

[Nigel Goodwin]

I believe C12 is a coupling capacitor, how come it's not the same value as C1 and C2. Is that because the audio frequency will be different after it passes the the first RC circuit?

C12 is an RF coupling capacitor, and NOT an audio one.

 

[audioguru]

I believe C12 is a coupling capacitor, how come it's not the same value as C1 and C2.

C1 and C3 are 330nF (330,000pF) and pass audio frequencies from 30Hz to 15kHz.
C12 is 30pF and passes radio frequencies from 88MHz to 108MHz. The reactance of C12 at 100MHz is only 53 ohms so it passes the radio frequency very well.

Q2 is the radio frequency oscillator and its output to C12 is near 100MHz.

 

[Sceadwian]

Spam alert

 

[Roff]

Chill out Mr smart! dont get bothered by other members questions, just ignore them if you cant respond.

I have been duly chastised.