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Calculate a Mixer frequency Response

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baby_1

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hello
for example you assume that we have this circuit

now how can we defined the bandwidth of transmitter before inject the audio signal and after that?
could you tell me theory of this calculation?
 

Estimating the FM sensitivity is not an easy thing to do unless you have the large signal model of the device.
I don't know for sure but it appears the above design of a Colpitts Osc will change freq with the device Miller capacitance on the collector. modulating the current in Q1 affects the gain bandwidth product (GBW) and presumably the collector capacitance.

This non-linear characteristic is like a tuning diode that is DC voltage controlled except not well defined and overall very sensitive to the location of the antenna near L1 and the layout of the board. I'm not sure how from looking at the specs.

http://www.datasheetcatalog.org/datasheet/MicroElectronics/mXqwswz.pdf
http://www.datasheetcatalog.org/datasheet/philips/BF494B.pdf

I would choose another design more stable with more linear design characteristics such as a varicap tuned VCXO or VCO
 
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