Simple FM Radio Transmitter Operation and Theory

This video will describe the theory and operation of simple FM radio transmitters. Inline FM telephone transmitters that are powered by the phone line will be covered.

[@UpcycleElectronics]

Nice explanation... If I still had a land line I'd build and try this one. Thanks for sharing.

[@micarifamily1]

Another great video thank you for the link to this one!

[@omarosama854]

Very great video, thanks a lot !!

[@0033mer]

You are welcome!

[@lasersbee]

Love the circuit explanation. Would have been helpful with values and specs for the other parts of the circuit.

[@juliomotorsikloatibapa5412]

good presentation

[@ShopperPlug]

can you use this circuit to make a wire cable tracer like fox and hound?

[@Wtfinc]

They are so cute and refreshing after watching an idian guy solder a 9v battery, a resistor, a coiled antenna and a surface mount crystal and called it an FM transmitter and not one person called cap except me. Oh it had a mic too.

[@kenyisamuel6190]

hi... . I would like really understand the use of each component in the circuit please

[@ammarsyaf3035]

Now i can tap my friend's phone ;).

[@shahzebnoor1683]

here the capactiors act as a parallel? because Vcc acts as a short for AC signals

[@0033mer]

Yes... the RF signal sees the power supply as an AC short so the base to collector capacitance is actually across the tank circuit.

[@shahzebnoor1683]

yes and also the feedback capacitor is in parallel with tank circuit. when we want find the resonant frequency capacitor should be added because they are now in parallel

[@ferminenriquezamorapineda2832]

What is the advantage of feedback to the emitter instead to the base of the transistor?

[@0033mer]

The capacitor from the base lead to ground is an AC short so the circuit is a common base amplifier where the input is the emitter. The tapped coil on the Hartley oscillator is fed back to the emitter (positive feedback) which causes the circuit to oscillate.

[@sbybill3271]

What is the function of 220 ohm resistor across bridge rectifier?

[@0033mer]

When the phone goes off hook, loop current flows through the 220 ohm resistor creating a voltage drop which powers the transmitter and enables the phone set to work properly. Explanation starts at 3:00.

[@Algator314]

Have plans or schematic?

[@SpeccyMan]

Your circuit shows a Hartley oscillator (tapped inductance) and not a Colpitts oscillator (tapped capacitance.)

[@0033mer]

Yes .. your are correct, the circuit diagram shows a Hartley oscillator. The other transmitter with the insulated wire coil is a Colpitts oscillator which I original used in my diagram but changed when I made the video.

[@rafaelfrequiao]

2N2222 FTW!!! Is there any schematics in PDF or Eagle ? I saw it on the video.

[@rafaelfrequiao]

Aluminium Soup "for the win". Because the 2N2222 transistor is my best and stable choice to do this job.

[@igrewold]

duckduckgo.com/?q=Inline+FM+telephone+transmitter+circuit&iar=images&iax=images&ia=images

[@waelsadek81]

Where's the positive feedback, shouldn't it be connected to the base ?

[@0033mer]

The capacitor from the base lead to ground is an AC short so the circuit is a common base amplifier where the input is the emitter. The tapped coil on the Hartley oscillator is fed back to the emitter (positive feedback) which causes the circuit to oscillate.