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You could do a lot of things but remember: To increase the tuning range, we want to increase the difference in capacitance across the range of voltage adjustment (~8V at one end, to negligible voltage at the other). When you place the two varactors in parallel, you are doubling the capacitance across the entire range. This would be fine if the varactors would go all the way to 0 capacitance. They don't. They have a lower range value. So by doubling, in effect, you are pushing the entire range of adjustment lower. This may be fine, as long as you don't mind "tuning down" from channels to get to desired frequencies. But, it's possible to move the whole range so far "south" that you can't even get to the base channel frequency. Increasing the supply voltage to the potentiometer end of the circuit does push things back "north" but not nearly enough and you can't go too high on the voltage without causing other problems within the circuit.

<blockquote data-quote="metalguy66" data-source="post: 796865" data-attributes="member: 63644">You could do a lot of things but remember: To increase the tuning range, we want to increase the difference in capacitance across the range of voltage adjustment (~8V at one end, to negligible voltage at the other). When you place the two varactors in parallel, you are doubling the capacitance across the entire range. This would be fine if the varactors would go all the way to 0 capacitance. They don&#039;t. They have a lower range value. So by doubling, in effect, you are pushing the entire range of adjustment lower. This may be fine, as long as you don&#039;t mind &quot;tuning down&quot; from channels to get to desired frequencies. But, it&#039;s possible to move the whole range so far &quot;south&quot; that you can&#039;t even get to the base channel frequency. Increasing the supply voltage to the potentiometer end of the circuit does push things back &quot;north&quot; but not nearly enough and you can&#039;t go too high on the voltage without causing other problems within the circuit.</blockquote>

[QUOTE="metalguy66, post: 796865, member: 63644"] You [I]could[/I] do a lot of things but remember: To increase the tuning range, we want to increase the difference in capacitance across the range of voltage adjustment (~8V at one end, to negligible voltage at the other). When you place the two varactors in parallel, you are doubling the capacitance across the entire range. This would be fine if the varactors would go all the way to 0 capacitance. They don't. They have a lower range value. So by doubling, in effect, you are pushing the entire range of adjustment lower. This may be fine, as long as you don't mind "tuning down" from channels to get to desired frequencies. But, it's possible to move the whole range so far "south" that you can't even get to the base channel frequency. Increasing the supply voltage to the potentiometer end of the circuit does push things back "north" but not nearly enough and you can't go too high on the voltage without causing other problems within the circuit. [/QUOTE]

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