RF Frequency modulator recommendation

[I14R10]

The story goes like this. I want to build FM transmitter for 145MHz. At that high frequency oscillator like this one



will never be stable enough. So I will use either overtone crystal oscillator or oscillator like that one in the picture, but with PLL. But I will ask about that later, this is what I want to ask.

I have a signal from microphone and I have RF signal from oscillator, 145MHz frequency. I want to modulate that RF signal with signal from microphone. How do I do that? All that I can find is this



But this is not what I want, I want FM modulator that takes RF and AF in and outputs FM signal. Is it even possible? How does professional radios do FM modulation?

 

[BradtheRad]

Your second schematic looks like a simple FM broadcasting circuit. Not too different from a kit I purchased once. I spoke into the mic, and heard my voice through a radio nearby. I had to tune both of them to a vacant spot on the commercial fm band.

It's a good idea to compare it with others on the internet. Try a simulation too. Expect to make a lot of adjustments, until it works.

 

[FvM]

In principle, indirect FM modulation of a generator signal can be achieved via phase modulation. But because the message signal has to be integrated before being passed to the phase modulator, the required phase shift for low frequency message components would be unfeasibly high.

With modern signal generation techniques, a straightforward way is to inject the message signal into the loop of a PLL synthesizer. It's also possible to generate the FM modulated carrier by digital signal processing (SDR = software defined radio).

 

[I14R10]

I would avoid digital signal processing.

If I would use PLL, would the VCO from PLL need to work on 145MHz, or could I use lower frequency VCO and use frequency multiplier to achieve 145MHz frequency?