Good RF caps

[Lee697]

This is probably a pretty basic question, but I've become a little bewildered on Mouser to say the least.....

I'm building a lightning detector circuit from techlib.com ('Sferics detector'). One of the caps the author has suggested 'use a good RF cap' - 2.2nF, part of an LC tank on the inputs of a TL592 amp chip. I'll probably need a 200pF one to match the inductor I have... but what one??

My research suggests maybe a ceramic in C0G? Kemet seem to have a bunch on Mouser, like this one 80-C322C222J5G ?
Is this what I should be getting a few of?
Thanks for any assistance!

[T3sl4co1l]

Is this, say, <30MHz?

Yes, C0G will do fine, as well as PP film if you need somewhat bigger values anywhere.  X7R, Y5P or even Z5U ceramics are fine for bypass or coupling capacitors, or electrolytics for much larger bypass.

SMT chips are desirable at higher frequencies, but if this thing isn't doing anything crazy or powerful, leaded should be fine.

Note that leaded MLCCs don't handle much voltage beyond their rating.  Duh, I guess, but ceramic disc types can often survive many times their rating, a handy tip in a pinch, or when transients are expected.   (Which, heh, not like picking up distant lightning, more like nearby ESD or lightning-induced surge.)

Tim

[A.Z.]

I'm building a lightning detector circuit from techlib.com ('Sferics detector'). One of the caps the author has suggested 'use a good RF cap' - 2.2nF, part of an LC tank on the inputs of a TL592 amp chip. I'll probably need a 200pF one to match the inductor I have... but what one??

My research suggests maybe a ceramic in C0G? Kemet seem to have a bunch on Mouser, like this one 80-C322C222J5G ?
Is this what I should be getting a few of?

Did you try contacting the man behind the Techlib website ? As far as I can tell, he replies to emails, so you may just ask him your question !

[radiolistener]

author has suggested 'use a good RF cap' - 2.2nF, part of an LC tank

you're needs low noise high Q capacitor for such purposes, such as ATC100B series.

[M0HZH]

Generally "RF" caps are meant for UHF and higher. Good general purpose MLCC C0G SMD will be fine up to a few hundred MHz, which is more than enough for your application.

High RF current applications might be different, you would need high-grade RF caps even at HF as thermal dissipation becomes an issue so you want the absolute minimal losses.

[A.Z.]

just in case, the circuit should be this one

http://techlib.com/electronics/spherics.htm

[jmw]

Silver mica is what comes to mind for RF + capacitor, and they're still reasonably priced at 200 pF. At 2.2 nF, they're starting to get a little chonky and expensive, but still usable.

[Lee697]

Did you try contacting the man behind the Techlib website ? As far as I can tell, he replies to emails, so you may just ask him your question !

Yes, and he is excellent at replying, very helpful, and actually generous too, at sending components (internationally, for free too).... but I've asked him so many questions lately, thought I'd spread the load a bit....

[Lee697]

Generally "RF" caps are meant for UHF and higher. Good general purpose MLCC C0G SMD will be fine up to a few hundred MHz, which is more than enough for your application.

High RF current applications might be different, you would need high-grade RF caps even at HF as thermal dissipation becomes an issue so you want the absolute minimal losses.

Cheers, this circuit only runs in the 300kHz range, I'll give the C0G's a try.

[cdev]

I am building a loop antenna that I hope to transmit into in the future, so I am wondering about good capacitors for RF at medium power. Beeft caps for power?

Preferably high Q. Mica? Vaccum? Ceramic? What are the best/cheapest caps for filters, loops and other high Q applications if you're on s budget?

[A.Z.]

I am building a loop antenna that I hope to transmit into in the future, so I am wondering about good capacitors for RF at medium power. Beeft caps for power?

Preferably high Q. Mica? Vaccum? Ceramic? What are the best/cheapest caps for filters, loops and other high Q applications if you're on s budget?

You're OT here, if you want, please open a new thread.

[cdev]

Yes, and that is, according to the experts, a huge problem with this kind of application. For example trimmer caps get hot or  melt. Even at low power levels, if they are not really high q.

Generally "RF" caps are meant for UHF and higher. Good general purpose MLCC C0G SMD will be fine up to a few hundred MHz, which is more than enough for your application.

High RF current applications might be different, you would need high-grade RF caps even at HF as thermal dissipation becomes an issue so you want the absolute minimal losses.