super simple FM transmitter Analysis!!!

[undral]

I have built (attached) Super simple FM transmitter www.makezine.com/projects/super-simple-fm-transmitter/

I would really like to better understand how the one achieves FM, as the oscillator circuits are so similar. If anyone can shed some light on this, it would be appreciated.

Any additional info calculations involved would also be most welcome. There are so many novel designs posted, but the authors almost never provide a comprehensive explanation of how the component values are derived or their function in the circuit. The real question is how does this circut actually accomplish frequency modulation: Please use math on me!!!I have this information from another forum

( C2, c1, r1 form a band pass filter to cut out the low and high frequencies (above and below audio frequencies). The capacitors also mix the audio frequencies (audio in) with the rf frequencies of the oscillator.
Additionally, the two resistors (r1and r2) form a voltage divider to bias the transistor.

The middle (capacitor, inductor and resistor) form an LCR tank, the transistor maintains the tank. The tank allows an oscillation to develop and center on a frequency unique to the component values.

The capacitors on the right side are essentially a voltage divider and remove the DC component before sending the signal to the antenna. Also it is more like Colpitts common base oscillator.)
So I'm freshman in EE, i'm trying to understand these explained thing on internet but I cant really catch up. So please use Engineering terminology and Mathematical equations in your analysis

 

[JimB]

DO NOT create multiple threads on the same topic, it only spreads out the answers and creates confusion.
Looking "over the fence" I see that you were told about this on the AAC forum, don't do it there and don't do it here.

JimB

 

[MikeMl]

The audio signal voltage changes the base bias of the transistor, which effects its base-to-emitter and collector-to-emitter parasitic capacitance of those semiconductor junctions. The changing capacitance appears across the oscillating LC tank (the other function of the transistor) and slightly "pulls" its frequency of oscillation, generating a rudimentary low-power, very-unstable, toy, FM transmitter.

 

[JimB]

Variations of this BAD CIRCUIT have been discussed with varying conclusions all over the web.

As you have given up over at AAC, let me point you in the direction of a couple of threads here on ETO which discuss common base oscillators.
Look here:
https://www.electro-tech-online.com/threads/how-is-this-modulating.142203/
and here:
https://www.electro-tech-online.com/...plifiers-and-oscillators.127836/#post-1063103

JimB

 

[James Marsh]

Thnx JimB.........................

 

[Colin]

For a complete explanation of how each component works, see:

<Mod edit: you have been warned many times about blatantly advertising your site. If you have something to say, say it here.>

 

[Willen]

Yes he have a profit based site, but reading his many guides, pages, articles, a basic guy like 'undral' (OP) could learn manything from basic concept. Sorry, I am not supporting to anyone. I am just a hobbyist and learning basic still. Yes, anyone need to search basic and very common/frequently asked things over internet. Hundreds of posts are lying in the same topic in the ETO too. Once in the beginning days I asked almost 300+ question about such transmitter in a thread and the thread became so huge- https://www.electro-tech-online.com/threads/another-fm-transmitter-project.117981/

Undral (OP) could have some benefit from the thread too. Salute to Audioguru!