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Roy,
We were talking about bypass type ceramics. See the 3/20 10:13AM posting. BTW, I think with SM you are pretty much forced into using ceramics. Tam/WB2TT |
Tam/WB2TT wrote:
Roy, We were talking about bypass type ceramics. See the 3/20 10:13AM posting. BTW, I think with SM you are pretty much forced into using ceramics. Tam/WB2TT Perhaps you were talking about bypass type ceramics, but the posting I responded to: Yes, ceramics are *hopeless* for tuned circuits; I wouldn't trust the black tipped ones, either. You can't beat silver mica but they're a bit hard to find and expensive. made no such qualification, and even specifically mentioned "black tipped" (usually NPO) capacitors. As far as I know, silver micas are getting pretty rare, except maybe for very high power, high current RF applications, if they're being used for even that any more. I doubt if they exist as surface mount parts. The reason silver micas are hard to find and expensive is that they've been made obsolete for nearly all applications by generally superior ceramic types. Roy Lewallen, W7EL |
Tam/WB2TT wrote:
Roy, We were talking about bypass type ceramics. See the 3/20 10:13AM posting. BTW, I think with SM you are pretty much forced into using ceramics. Tam/WB2TT Perhaps you were talking about bypass type ceramics, but the posting I responded to: Yes, ceramics are *hopeless* for tuned circuits; I wouldn't trust the black tipped ones, either. You can't beat silver mica but they're a bit hard to find and expensive. made no such qualification, and even specifically mentioned "black tipped" (usually NPO) capacitors. As far as I know, silver micas are getting pretty rare, except maybe for very high power, high current RF applications, if they're being used for even that any more. I doubt if they exist as surface mount parts. The reason silver micas are hard to find and expensive is that they've been made obsolete for nearly all applications by generally superior ceramic types. Roy Lewallen, W7EL |
In article ,
Tam/WB2TT wrote: Roy, We were talking about bypass type ceramics. See the 3/20 10:13AM posting. BTW, I think with SM you are pretty much forced into using ceramics. Cornell Dubilier / Waldom makes surace mount siler mico caps. You can get them from Digikey for under $10 US. You can get standard PPS film capacitors from several makers. If you don't mind the fact that they are very touchy and have a higher failure rate they may be an option. If you want a little better, you can buy the more costly coated ones. I wouldn't say that you are forced into using ceramic. It is an option you may perfer. -- -- forging knowledge |
In article ,
Tam/WB2TT wrote: Roy, We were talking about bypass type ceramics. See the 3/20 10:13AM posting. BTW, I think with SM you are pretty much forced into using ceramics. Cornell Dubilier / Waldom makes surace mount siler mico caps. You can get them from Digikey for under $10 US. You can get standard PPS film capacitors from several makers. If you don't mind the fact that they are very touchy and have a higher failure rate they may be an option. If you want a little better, you can buy the more costly coated ones. I wouldn't say that you are forced into using ceramic. It is an option you may perfer. -- -- forging knowledge |
On Tue, 23 Mar 2004 14:44:30 +0000 (UTC),
(Ken Smith) wrote: In article , Tam/WB2TT wrote: Roy, We were talking about bypass type ceramics. See the 3/20 10:13AM posting. BTW, I think with SM you are pretty much forced into using ceramics. Cornell Dubilier / Waldom makes surace mount siler mico caps. You can get them from Digikey for under $10 US. The CDE "MC" series of cazapitors are "mica", not "silver mica". The difference is that silver mica caps have to be sealed (dipped) or the silver plating reacts with everything. I'm not sure what plating is used for the "MC" series of surface mount mica. My guess(tm) is aluminum. http://www.cornell-dubilier.com/mica/mica.htm http://www.cornell-dubilier.com/film/hmc.htm http://www.cornell-dubilier.com/catalogs/MC.pdf The big advantages of silver mica is stability, wide temp range, very low dissipation, and tolerance to over voltage spikes. Many years ago, I wasted a month working over an HF xmitter, trying to design out the expensive silver mica and porcelain cazapitors and replace them with cheaper ceramics. It was possible for the low power drivers but a waste of time in areas that had high RF currents or required good stability. A similar cost reduction exercise was also being done on the automagic antenna tuner (by someone else) with similar results. The project ended when someone suggested using high temp silver solder to prevent the ceramic caps from reflowing their solder connections and falling off the board. I guess(tm) the reason that silver mica caps are difficult to find is that there are few companies producing high power RF products as compared to the huge number of low power RF products. It's not a big market that probably can only support a few specialty component vendors. -- Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 (831)421-6491 pgr (831)336-2558 home http://www.LearnByDestroying.com AE6KS |
On Tue, 23 Mar 2004 14:44:30 +0000 (UTC),
(Ken Smith) wrote: In article , Tam/WB2TT wrote: Roy, We were talking about bypass type ceramics. See the 3/20 10:13AM posting. BTW, I think with SM you are pretty much forced into using ceramics. Cornell Dubilier / Waldom makes surace mount siler mico caps. You can get them from Digikey for under $10 US. The CDE "MC" series of cazapitors are "mica", not "silver mica". The difference is that silver mica caps have to be sealed (dipped) or the silver plating reacts with everything. I'm not sure what plating is used for the "MC" series of surface mount mica. My guess(tm) is aluminum. http://www.cornell-dubilier.com/mica/mica.htm http://www.cornell-dubilier.com/film/hmc.htm http://www.cornell-dubilier.com/catalogs/MC.pdf The big advantages of silver mica is stability, wide temp range, very low dissipation, and tolerance to over voltage spikes. Many years ago, I wasted a month working over an HF xmitter, trying to design out the expensive silver mica and porcelain cazapitors and replace them with cheaper ceramics. It was possible for the low power drivers but a waste of time in areas that had high RF currents or required good stability. A similar cost reduction exercise was also being done on the automagic antenna tuner (by someone else) with similar results. The project ended when someone suggested using high temp silver solder to prevent the ceramic caps from reflowing their solder connections and falling off the board. I guess(tm) the reason that silver mica caps are difficult to find is that there are few companies producing high power RF products as compared to the huge number of low power RF products. It's not a big market that probably can only support a few specialty component vendors. -- Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 (831)421-6491 pgr (831)336-2558 home http://www.LearnByDestroying.com AE6KS |
Roy Lewallen wrote in message ...
Paul Burridge wrote: Yes, ceramics are *hopeless* for tuned circuits; I wouldn't trust the black tipped ones, either. You can't beat silver mica but they're a bit hard to find and expensive. I strongly disagree with this. I've successfully used ceramic capacitors many times for both high and low Q tuned circuits from HF to UHF. Years ago, I found that NPO ceramics were decidedly superior to silver micas for temperature stability, so I use them exclusively for VFO tank circuits. .... In agreement and support of what Roy wrote, I'd toss out some additional notes: o I've seen (been the vicitm of?) silvered micas that exhibit random tiny jumps in capacitance, which is a really bad thing in oscillators. o You can get X7R dielectric SMT caps in SMT up to at least 0.1uF in 0603 size, for low voltage ratings. See manufacturers' data sheets for the largest currently available values. I suspect reliability suffers if you try to use ones with too high a C*V/unit volume, though. o As someone recently pointed out to me (Sphero, I think it was), you can get C0G up to 0.1uF in SMT--I think he said in 1206 size. o It's possible to get 1% C0G caps. o A C0G is probably about the cheapest electronic component you'll find with a maximum 30ppm/C temperature coefficient (though beware, some C0Gs I've seen are rated up to 60ppm/C). o There are special high-Q ceramics that are better than standard C0Gs for use at microwave frequencies...generally above 1GHz. Cheers, Tom |
Roy Lewallen wrote in message ...
Paul Burridge wrote: Yes, ceramics are *hopeless* for tuned circuits; I wouldn't trust the black tipped ones, either. You can't beat silver mica but they're a bit hard to find and expensive. I strongly disagree with this. I've successfully used ceramic capacitors many times for both high and low Q tuned circuits from HF to UHF. Years ago, I found that NPO ceramics were decidedly superior to silver micas for temperature stability, so I use them exclusively for VFO tank circuits. .... In agreement and support of what Roy wrote, I'd toss out some additional notes: o I've seen (been the vicitm of?) silvered micas that exhibit random tiny jumps in capacitance, which is a really bad thing in oscillators. o You can get X7R dielectric SMT caps in SMT up to at least 0.1uF in 0603 size, for low voltage ratings. See manufacturers' data sheets for the largest currently available values. I suspect reliability suffers if you try to use ones with too high a C*V/unit volume, though. o As someone recently pointed out to me (Sphero, I think it was), you can get C0G up to 0.1uF in SMT--I think he said in 1206 size. o It's possible to get 1% C0G caps. o A C0G is probably about the cheapest electronic component you'll find with a maximum 30ppm/C temperature coefficient (though beware, some C0Gs I've seen are rated up to 60ppm/C). o There are special high-Q ceramics that are better than standard C0Gs for use at microwave frequencies...generally above 1GHz. Cheers, Tom |
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