Posted on Friday, April 23, 2010 • Category: FM Transmitters
This PLL has been designed with an old Motorola circuit :the MC145151.
The VCO is based on a "Colpitz" oscillator equiped with a Fet Transistor.(J310)
Two varicap Diodes are used in order to reduce the global noise of the VCO.
In addition,these two diodes allow the PLL to keep the lock status through a large range of climatic conditions.
An another J310 is used in order to match the impedance between the oscillator and the fist amplifier stage.
A MSA1105 from Minicircuits increases the RF power level coming from the VCO to +14dBm.
A simple low pass filter rejects the second harmonic to -20 dB.(Worst case)
Finally, a 7 dB attenuator and a second amplifier stage (BFR96S) achieve this radio design.
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