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variable HF oscillator

Discussion in 'Electronic Basics' started by Nelly, Jun 1, 2007.

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  1. Nelly

    Nelly Guest

    I need to vary the frequency of operation of a transceiver IC from
    7MHz to 9MHz. The oscillator needs to feed into the crystal
    oscillator input and crystal oscillator output pins of the IC (the
    current design does not have a variable oscillator and is just using a
    crystal). Ideally I would like to control the frequency of the
    oscillator using the PWM of a micro controller (unfortunately the
    current micro does not have a DAC). Any ideas on the best way to do

  2. would be a better place to ask for this

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  3. Don Bowey

    Don Bowey Guest

    Many xtal oscillator circuits work well by just replacing the xtal with a
    series LC network.

  4. Jamie

    Jamie Guest

    You can emulate PWM output with the processor.
    all you need is to use a timer (IRQ) driven to
    generate the output pulse on the pin of your selection.

    Normally the IRQ rate is put at multiples of the shortest
    PWM pulse you may generate. With this, you simply use a
    scalar counter to adjust the output duty cycle.

    As far as the OSC goes, you can replace the Xstyle with an
    LC and Variac tuning diode assembly how ever, I don't know
    what you have planned to monitor the freq for stability?
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