Looking closer at the chart posted previously?from Diz's?diodes page



SMD/SMT Varactor 1SV322.?would be a good choice.??

The V/C curve is about the same as the thru-hole?MV-209 or?BB910.

Note that the curves for these two are plotted differently:? SMT part is linear/log and the Thru part is log/linear.? It gives the? plot a different look even though they are much the same.? Depends on what the marketing folks want to emphasize...8^)

Plot them linear/linear if you're curious?about?the "real" shape of the?V/C?curve.
--
Chuck, W5USJ (ex K2OFN)
Point, Rains Co, TX? EM22cv

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I think the curves on Diz's page are in the best format for varactor capacitance. We normally consider the voltage input linearly. If I'm graphing one, I automatically mark off the V (x) axis in evenly spaced volt increments. But I'm normally looking for something different on the output. Marking the C (y) axis linearly makes no sense. We are rarely looking at the linear response of a varactor because we aren't really concerned with capacitance. We're normally concerned with the resulting resonant frequency response in a tuned circuit. Log/linear can help us with that.

Most of the time, I want a frequency readout to be linear. A varactor capacitance with a non-linear response to voltage is going to give me that. On Diz's graphs, I see a linear voltage input. If I see a fairly straight curve for C, I'm probably going to get a fairly linear frequency response. So log/linear makes sense. If he used linear/linear, you would see a deceptively "hooked" curve that truly shows how C responds, but it wouldn't be as useful for predicting frequency response. Log/linear provides more insight that you can use.

Some of the newer hams may not have noticed the shape of the plates on larger "tuning" capacitors. They weren't symmetrical. They were very oddly shaped to make the dial calibration more linear.

There. Marketing guys owe me one.

BTW, I used to follow your website pretty closely in the Rock Mite days. Fun stuff.

Eric KE6US

Eric,

Good info, makes sense when you relate the shape to functional applications.? On the O/T about the capacitor plates.? In my Vast Experience (or maybe Half-) I knew that tapered plate style as logarithmic and for the reason you mentioned.? And also, I'm rebuilding a z-match using dual 360pF poly caps. The plates in these little gems are of the tapered type making adjustment? a little smoother, I think...8^)

Not much happening with RMs? and RM][s?these days.?Rigs like the QCX have captured the interest with all the great features and functions at a good price.

Still...Fun Stuff

--
Chuck, W5USJ (ex K2OFN)
Point, Rains Co, TX? EM22cv