NTC capacitors

It would be grotty, but... could you fabricate one yourself? Use a couple of tabs of stiff conductive material - maybe brass sheet - spaced apart by a small glued-on peg or two of a material with a positive coefficient-of-length-by-temperature. When the temperature rises, the two plates would be moved apart slightly and capacitance would drop. Since most of the dielectric would be air, changes in the spacer material's dielectric constant with temperature wouldn't matter much.

I've seen amateur radio receiver designs that use temperature-compensated varicaps, running open-loop, for the main tuning.

Frequency variation with temperature was claimed to be minimal.

You could do something like that with your bigger varactor, using most of the voltage range to adjust the varactor for temperature variations, and then a little bit to actually tune.

Of course, when an amateur designer says "this really works great!" it doesn't necessarily map back to anyone else's "great!".

How big a batch?

Do the initial brewing in pans, like steam beer.

Maybe -- maybe equilibrium happens when the yeast kills itself.

Hey, did the Capax people get back to you? Those looked like what the doctor ordered... If they came in the right values/ TC's.

George H.

Not so far.

I know you could order calibrated caps, about 12 years ago. Most two way r adio systems were just getting done using Frequency Determining Elements or "Channel Elements" back then, an FDE/CE was a quartz crystal in a module with temperature compensating elements. FDE's avoided the use of ovens, an d were thus "instant on". Of course with PLLs ruling the world, all you n eed now is a TCXO.

I lost a consulting contract to monitor and supervise the rebuilding o f data radios because the technicians disregarded my instructions to order the compensating caps. The caps were chosen against the manufacturer's meas ured tempco data on the quartz crystal. The techs were paid per radio ship ped plus their base salary.

After 20 radios submitted for frequency changes came back from customers, it became obvious what happened. The techs ordered a pile of 20 pf caps fro m Digikey and shipped handheld radios which did not work well in frozen war ehouses. This was FM, and the modulation scheme employed needed to be cente red in the IF bandwidth and stay there.

Try Presidio:

If you just want a handful for verification:

The old days..

Steve

They stored the vats in caverns. They didn't have the problem that the Federales (BLM, EPA and whatnot) came waltzing in the minute you dug a hole. Other than that beer making in the not always so good old days was hit and miss. They didn't have yeast or hops. Often whole batches would be undrinkable. Or only the funky-looking stirring stick of Haakon's grandpa would work and not any of the others.

It's not going to go nuclear but when yeast goes crazy active there will be fusel oils in the beer. Aside from not being good for your health those can cause a bad case of hangover.

Or Donald vs. Hillary :-)

Five gallons each. I started this summer and now batch #4 and #5 are in the fermenters, a Koelsch Style and a Cream Ale. I bought a 2nd fermenter so I can brew more of a variety and two batches in staggered fashion. That allows me to do 2nd fermentation where a beer absolutely needs it.

The taste is so much fresher that now even many of the more expensive store-bought beers taste sort of bland to me. Homebrew compares well to a fresh growler from the brewpub. Until a batch goes south on me which is bound to happen some day.

Too often it is a simple misspelling of of "grate".

Numbers are all over the place, but that's about the highest I've seen. What physical arrangement of electrodes are we talking?

I get around -43ppm from the physical effect, if dielectric constant was really constant. But that's disregarding edge effects. Maybe they matter.

--sp

Make America Grate Again?

Grate Britain :(

It's funny that I was just trying to read up on FR4 dielectric capacitors and found an article on why the glass temperature matters. Seems that while the FR4 wants to expand in all three directions, the copper and glass prevent it from expanding much in the X,Y plane so it expands greatly in the Z direction. The concern is that it pops vias.

So if the FR4 doesn't expand in the X,Y direction, how can it have such a high positive tempco? Is the dielectric constant changing so much?

I finally found a document that shows this. The TcDK for FR-4 seems to be extremely high. See Figure 2. This graph seems to show around 3000 PPM/K.

Am 05.10.2016 um 01:21 schrieb rickman:

- FR4 also pops vias when it is exposed to hydrocarbons. It soaks them up like a sponge. We used to make the boards for our pipeline pigs from Kevlar for that reason. Kevlar prepregs have a very short shelf life. Your board manufacturer might be tempted to use what he still has. That may lead to delamination etc.

- There are now FR4 mutations with elevated glass temperature.

- Johanson had LARGE NP0 capacitors upto > 10 uF IIRC, including stacked chips & such. I could not find them recently on their web site.

regards, Gerhard

I measured the capacitance of a square foot slab of copperclad. But various references do present wildly varying numbers for the tempco of FR4.

I just tried another random slab of copperclad FR4, 0.032" thick including the copper, 96 square inches

C = 3350 pF == 35 pF/sq inch

Tempco = +837 PPM/K

...he uses slide panels.

What about a gimmick?

Tim