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Voltage Controlled Oscillator

Voltage Controlled Oscillator

The VCO is based on a Hartley oscillator. The frequency is determined by L1 and capacitor C1. The Vtuning voltage will change the capacitance in the varactor BB132 wich will change the oscillation-frequency.The VCO can be adjusted from 70-210 MHz.
The value of capacitor C2 will determine how much the frequency can be changed by the tuning voltage. The larger value the more the frequency will change. This VCO is based on two dual-gate FET. First FET is a Hartley oscillator where the frequency is determined by the value of L1, C1, C2 and the varicap diod. C2 set the span of the VCO. The second FET is just an amplifier. The gain is less than 1, but the current will be higher and the oscillator will not be loaded.
The output amplitud changes depending on the frequency and how many turns there is on L1.
By changing the voltage on g2 at FET1 you can set the amplitud. By adding a resistor to ground you will lower the amplitud.
In this schematic I have conected g2 to Vcc (through R1) wich will give the highest gain.

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