Hi everyone, this is my first post in this forum. I've bought one fm transmitter hobby project kit. The circuit diagram is shown below.
I did some calculations of voltage (shown in second image). However I'm not certain about some calculation cos when I bring the oscillosope probe near the transistor c1959 there's lot of noise.
So here are my questions
- why they put a voltage divider (which is connected to ground), which comprise of 150k and 4k7 (x2) resistors at the base of 1st transistor c945
- I think the first transistor c945 amplifies the voltage and current and inverts it. Is this correct? This voltage was 1.9v (with osc.) and it was a dc with small signal coming from the mic
- the second transistor of c945 again amplifies this signal and inverts again. which is in phase with the modulating signal. Is this correct?
- The output of the circuit, from the second c945 transistor is the modulating signal right?
- I don't understand how does the oscillator circuit, consisting of 2 C1959 transistors, produces oscillations (the carrier). Can any body tell me how this oscillation is produced?
- The pcb coils values were not given in the schematic, cos it was in the pcb and there was no inductance. Can i calculate the inductance in any way?
- the output frequency was 92.4 Mhz. So i used the resonant freqeuency formula, excluding the inductive resistance and capacitive resistance, the ideal formula (fr = 1/2pi root LC) to roughly calculate the inductance. Which was roughly 9nH. Any suggestions?
- I calculated the voltage difference in c1959. I don't know how that works. Can anyone plz tell me how this transistor operates and produce oscillations in this circuit?
- The Antenna has + and - connections. Is this a Dipole Antenna?
If anyone needs any requirements to answer these questions, plz let me know.