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variable HF oscillator

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 this?
Reply to
Nelly
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rec.radio.amateur.homebrew would be a better place to ask for this help.

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Michael A. Terrell
Central Florida
Reply to
Michael A. Terrell

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

Don

Reply to
Don Bowey

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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Reply to
Jamie

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