Errand Posted September 3, 2006 Report Share Posted September 3, 2006 Hi all!I'm starting with RF design (I'm experienced in digital and analogue electronics)...I found this design on the web.Could you help me to understand the simple design? ???I've already saw oscillating circuits, but this one is different from all the circuit teached at school...Thanks! Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 4, 2006 Report Share Posted September 4, 2006 Look up Colpitts Oscillator in Google. Quote Link to comment Share on other sites More sharing options...
Errand Posted September 4, 2006 Author Report Share Posted September 4, 2006 Thanks audioguru!I'm jet a bit confused...Take a look at "standard" Colpitts Oscillator (attached in the post).There are some substantial differences: 1. there isn't the emitter resistance 2. there isn't the second resistance needed to polarize the transistor (from base to Val) 3. C2 is connected to Val, instead it should be connected to ground (provided the presence of Re!)Could I ignore "Re" and "Rbias"?Could I connect C2 to Val instead of ground? (obviously in signal analysis it doesn't matter: in small signal analysis power source are replaced with "short circuits") Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 4, 2006 Report Share Posted September 4, 2006 Your "standard" Colpitts oscillator feeds positive feedback from the collector to the emitter, in phase.The telephone bug Collipitts oscillator feeds the inverted signal of the collector. C1 and C2 have their junction grounded, but since they are in series across the coil, their ends are with the opposite phase. Then C2 feeds its signal to the base of the transistor that inverts it so that it is positive feedback.There are two resistors and a single resistor ways to bias a transistor.I re-drew the Telephone Bug circuit so that it is easier to see. Quote Link to comment Share on other sites More sharing options...
Errand Posted September 4, 2006 Author Report Share Posted September 4, 2006 Great, audioguru!!!!! ;)You are a very good teacher!Thank you a lot!PS: what's your job?!See you!Errand Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 5, 2006 Report Share Posted September 5, 2006 PS: what's your job?I am a retired old geezer. ;DI just relax all day, every day and bum around the internet and my town. Quote Link to comment Share on other sites More sharing options...
mik3ca Posted September 6, 2006 Report Share Posted September 6, 2006 I also like Audioguru's version better than the original version, because a +ve and -ve pole is much better defined.If one pole is missing, no circuit will function. Its just the same as connecting the -ve end of the battery to the circuit and leaving the +ve end in mid-air. Quote Link to comment Share on other sites More sharing options...
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