I have built a simple FM transmitter with two transistors

[anwer_sbh]

I have built a simple FM transmitter with two transistors for lab purposes (to study and view the FM wave) , but the resulted wave (on the osciliscope) is not like the FM wave as in text book, what is the probelm?

 

[Audioguru]

You forgot to attach the schematic of your extremely simple FM transmitter (a child's toy?) and you forgot to attach the waveform shown on your 'scope.

You didn't even describe what you think is wrong with the waveform.

 

[anwer_sbh]

Re: I have built a simple FM transmitter with two transistor

this is the circuit. so i could not get the wave as in the text book to be displayed on the oscilliscop.

 

[bongkk]

Re: I have built a simple FM transmitter with two transistor

What scope are you using?Unless you have a very hi spec scope that can display up to 100MHz, you will only see a continuous band.

 

[Audioguru]

To see a 100MHz waveform the 'scope must have a response up to at least 1GHz so it shows any harmonics.

But the extremely simple transmitter has its antenna at its tuned circuit so the capacitance of the scope's probe will change the frequency.

You won't see the frequency changed by the modulation because loud modulation is only plus and minus 75kHz so the 100MHz changes only from 99.925mHz to 100.075MHz.

You might see a very small amount of AM modulation because the amplitude of the oscillator is changed while its frequency is changed by the modulation.