[SOLVED] I need an urgent help (FM MODULATOR)

I am working on a project right now that require for me to use a frequency synthesizer as a carrier frequency generator see the picture below plz



my problem is i cant find a circuit that can take two input which are the carrier frequency generated by the synthesizer and the message signal and do the fm modulation

most of the circuits that i have found only take the message signal and do frequency modulation based on the internal component of its construction


could u plz help me i need to figure out this by today

Hey Buddy!
Hi
How much power do you need in your out put? if your power is low , why you don't use from a simple RE generative FM modulator? it is easy to design , really .
Best Wishes
Goldsmith

yes my power is low , could u please give me the schematic to the circuit that you have mentioned in your post and how am gonna to use it with frequency synthesizer

Hey Buddy!
Hi
of course!
See this simple circuit:

This is a Simple HF oscillator , with giving an AF signal to the input , according to the miller effect , the value of internal capacitor of the transistor , will change , then the frequency of oscillator will change as well as .
Best Regards
Goldsmith

You have not specified any parameters of the frequency-modulated signal, nor of the modulating signal.
If you already have a frequency synthesizer, you could modulate its frequency by applying the modulating signal to the control bits of the synthesizer. If you want to keep the synthesized carrier and apply a frequency modulation to it, then you can use a phase modulator.

Using a phase modulator will give you a narrow-band FM. If you need a wideband FM upon a fixed frequency, you will have to use a frequency translator method: you should build a lower-frequency frequency-modulated oscillator, then apply its output and synthesizer output to a mixer. The mixer output will contain combination bands, then using a band-pass filter you can select one band which you want.

---------- Post added at 17:53 ---------- Previous post was at 17:51 ----------

You can also add the modulating signal to Vo(t) in your schematic; this will achieve the frequency modulation, but you must test the system response with a real modulation voltage applied to VCO, so the feedback loop response is stable. I guess you can only achieve a narrow-band FM this way.

thanks alot guys you helped me alot