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Help me in my VCO design please!


bere
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i want to design a vco to produce 60MHZ with frequency stability being provided by a crystal reference.i heard the best way to do it is through a phase locked loop.could you help me with possible circuits?can i show the output on an oscilloscope as i have a breadboard.how do i calculate the values of resistors and capacitors as well as inductance in a vco?are there any formulas?help me please.my e-mail is [email protected]

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You can use the following circuit with minor modifications (capacitors slightly larger and one or two more turns to the coil).
http://users.cableaz.com/~cappels/dproj/FMVFO/fmvfo.htm
In order to servo its frequency, you have to follow it with a frequency divider that brings the frequency to some convenient value: 100KHz fe.
You feed this frequency and your reference derived from a crystal into a phase comparator and you use the output to control the VCO.

Alternatively you could use a synthetised FM tuner: the local oscillator normally runs 10.7MHz above the received frequency which means that when the top frequency of 108MHz is displayed the oscillator runs at 119.5MHz. If you divide by two this frequency, you get pretty close to 60MHz. You can reach the exact frequency by replacing the crystal of the synthetiser IC with a slightly higher one. It needs not be exact because you can always correct the value by choosing another receiving frequency than 108MHz.
Alternatively you could run the local oscillator directly on 60MHz, but this implies some changes to the oscillator itself in addition to the synthetiser crystal.
Lou

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