From: Lizard Blizzard
Subject: Re: hi-capacity voltage controlled capacitor?
Date: Tue, 08 Oct 2002 17:02:09 -0700
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Winfield Hill wrote:
> root wrote...
>>>I need a voltage controlled capacitor for the nF-uF range. I know the
>>>varactor diodes but they are in the pF range. Is there such a device
>>>present or am I dreaming?
>>The only real way to do this is electronically simulating a capacitor.
> I agree, e.g., a capacitance-multiplier circuit containing a multiplier,
> unless 5000pF is enough and you make a servo-controlled vaccuum-variable.
I know that the varicaps for AM are in the 300 ro 500 pF range, sdo ten
of those wouldn't be cheap, but feasible for 5 nF. I'm not sure what
advantage a vacuum would have, he could just use a bunch of regular All
American 5 AM radio tuning capacitors AKA 'condensers' to the old
timers. Put 'em all on the same shaft or dial cord, and each pair of
caps in parallel could give 600 or so pF. Obviously for RF, the size of
such an array could be a problem. I remember the old HP 200CD audio
oscillator had a big old variable capacitor behind that nice chrome
knob. Worked real well, too. The stuff HP is making today isn't as
good as it used to be...
I was over at Fry's the other day and stopped by the test equipment
aisle. I looked at some bench power supplies, and I was dissapointed
when I looked at the Agilent, now apparently back using the name HP,
power supply. The V adj pot is a single turn, and it's difficult to
adjust accurately. Years ago we could have bought a ten turn pot, or at
minimum, a range switch to make the pot less critical to adjust. Even
the cheap Elencos were easier to adjust than the HP.
> But there are many solutions to a problem, tell us the problem.
> - Win
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