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Old 1st Mar 2009, 4:07 pm   #5
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 4,423
Default Re: IF wobbulator design

Thanks Jim, I am still playing but having some success. The design above could do with a buffer.

What is actually happening is quite complex. It uses the AC signal to rectify a DC offset for the varicap diodes across C3. The time constant C3/R2 must also be long enough to keep the sawtooth straight.

My experience was this approach led to the amplitude dropping off at the low frequenciy end of the sweep presumably due to the high capacitance during part of the AC cycle when there is little/no reverse voltage across the varicap . I have been using a resistor to provide a DC offset.
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