From: firstname.lastname@example.org (carltons)
Subject: Re: hi-capacity voltage controlled capacitor?
References: <email@example.com> <firstname.lastname@example.org> <email@example.com>
User-Agent: NewsWatcher-X 2.2.3b2
NNTP-Posting-Date: Sun, 13 Oct 2002 22:32:11 GMT
Date: Sun, 13 Oct 2002 22:32:11 GMT
In article <firstname.lastname@example.org>,
email@example.com (Andre) wrote:
> firstname.lastname@example.org (N. Thornton) wrote in message
> > email@example.com (transformer) wrote in message
> > > The truth is that I have built such a device but do not know if it is
> > > a useful invention.I see that there are no such devices present. Could
> > > anybody comment on its usage. The invented device varies between 2uF -
> > > 100nF and has bad linearity.
> > > Thanks
> > I don't think you're the first, as is usually the case. Most ideas
> > fall at some hurdle.
> > One can take a 1930s style paper capacitor, wind it loosely instead of
> > tight, and just vary the pressure on the resulting paper stack. Voila,
> > one variable cap.
> > Or make a wet electrolytic and vary the liquid level.
> How about paralleling standard varicaps ? They go to 10pF IIRC, so
> 1000 in parallel = 10 nF .
> Just a (fairly pointless) idea . Imagine troubleshooting something
> like that ! :)
> Alternative idea . How about using a standard device but reverse
> biased ? Something like a large area transistor.
> How about a MOSFET ? Those have a pretty large gate capacitance,
> especially the old style devices . For example, the 2SK2038 has a gate
> capacitance of 4 nF according to my RS meter , with drain and source
> shorted .
> One way it measures 1 Mohm , the other it measures open .
> > I don't know of any example of such a thing being used.
> > Whatever haps with your idea, if you can have one you can have
> > another, and another... and at some time you'll get a goodie
> > hopefully. Thats how it worked for me.
> > Regards, NT
> > > > > Dear All,
> > > > > 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?
Bottom line: you ARE dreaming. You could try a Miller Integrator to
simulate a big cap maybe, but linearity would be poor I would be willing
to bet. You might consider varying the inductance of a coil via core
saturation curves. See a description of magnetic amplifiers. I hope that
you don't expect freq response to be from DC to Blue light. Another
question: Why do people get interested in electronics anyway? It seems
silly to me. Look at me. I'm glued to my keyboard and am answering
questions as I can, but I feel like I'm talking to the sky. Maybe I am.
Isn't the sky at 377 ohms and has a lot of blue light behind it? Right
? CQ, CQ, CQ......Pluto do you hear me?......Venus, come in
please.....how about you guys on Ceres?......
I'll just QRT and everything in the morning will look better. :-)
Flakey Steve WB4CZR