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Help with VCO design

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Sylvia

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Hi,

I have a project to design a VCO which i have difficulties with. Could
someone please help me out? I have the following specifications:
band: 1430 to 2230 MHz
comparison frequency: 7.8125 kHz
VCO output power: 10 mW

I don't know how to find the value of the needed varactors, the rest of the elements and the s-parameters.

A help or a direction would be much appreciated!

2l87kj.jpg
 
Looks like a home work question.

The Ctun(s) are in series. Ctun(totoal)=???Ctun1 ???Ctun2 (you find the formulas)
Cp and Ctun(total) are in parallel. C=Cp+Ctun(total)
You know or can find the resonance formula. F=???CL

Find what diodes are available. Look in a catalog or look on the internet.

At high frequency the frequency is mostly L and Cp because Ctun(s) is small.
At low frequency the frequency is more related to Ctun because Ctun in large.

I use a spread sheet and put the formulas in and play with values.

Your ratio of frequency is 1.55 F(Max/Min) So choose a diode that can do more than that.
Example BB814 has a cap value of 2.25 to 22.7pF. This will leave your Cp value very small. Should work.

Show your work and post back when you are done.
 

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