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Jumpy Silver Mica Capacitors ?
A year or so ago I was working on a microwave local oscillator (at
about 2.5 GHz) multiplied up from a crystal oscillator near 40 MHz. The output was found to jump in frequency by tens or hundreds of Hz many times as the LO chain was warming up. I was able to reduce this jumping by replacing all the dipped silver mica capacitors in the crystal oscillator stage with NP0 ceramics. There is still a bit of jumping which may come from some silver micas which remain in the stage following the crystal oscillator. I have just been observing the same sort of frequent jumping behaviour (up to a kHz or so at a time) in another local oscillator (output at about 10.5 GHz, phase locked to a crystal oscillator around 100 MHz). I note that this one also has dipped silver mica caps in the crystal oscillator and I wonder if it too would be improved by replacing them with NP0 ceramics. The capacitors used in both cases are from unknown sources and were probably manufactured in the early 1980's. Has anyone else experienced this behaviour ? Steve (VE3SMA) |
Steve Kavanagh wrote: A year or so ago I was working on a microwave local oscillator (at about 2.5 GHz) multiplied up from a crystal oscillator near 40 MHz. The output was found to jump in frequency by tens or hundreds of Hz many times as the LO chain was warming up. I was able to reduce this Steve, I've had several silver micas go weird in 20 odd year old Racal radios that I've fixed, they're second only to Tantalum caps as a cause of faults in those. But at least they don't explode! Regards Dan AC6AO G3NCR |
Steve Kavanagh wrote: A year or so ago I was working on a microwave local oscillator (at about 2.5 GHz) multiplied up from a crystal oscillator near 40 MHz. The output was found to jump in frequency by tens or hundreds of Hz many times as the LO chain was warming up. I was able to reduce this Steve, I've had several silver micas go weird in 20 odd year old Racal radios that I've fixed, they're second only to Tantalum caps as a cause of faults in those. But at least they don't explode! Regards Dan AC6AO G3NCR |
In article ,
Steve Kavanagh wrote: A year or so ago I was working on a microwave local oscillator (at about 2.5 GHz) multiplied up from a crystal oscillator near 40 MHz. The output was found to jump in frequency by tens or hundreds of Hz many times as the LO chain was warming up. I was able to reduce this jumping by replacing all the dipped silver mica capacitors in the crystal oscillator stage with NP0 ceramics. #snip# Has anyone else experienced this behaviour ? Not personally, but I believe I've seen it mentioned in one of Doug DeMaw W1FB's books on QRP transceiver design. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
In article ,
Steve Kavanagh wrote: A year or so ago I was working on a microwave local oscillator (at about 2.5 GHz) multiplied up from a crystal oscillator near 40 MHz. The output was found to jump in frequency by tens or hundreds of Hz many times as the LO chain was warming up. I was able to reduce this jumping by replacing all the dipped silver mica capacitors in the crystal oscillator stage with NP0 ceramics. #snip# Has anyone else experienced this behaviour ? Not personally, but I believe I've seen it mentioned in one of Doug DeMaw W1FB's books on QRP transceiver design. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Yes, a long time ago I saw just the same sort of behavior in LC
oscillators using silvered mica caps. Ever since, I haven't trusted them, and use NPO/C0G instead for frequency control applications. Cheers, Tom (Steve Kavanagh) wrote in message . com... .... Has anyone else experienced this behaviour ? |
Yes, a long time ago I saw just the same sort of behavior in LC
oscillators using silvered mica caps. Ever since, I haven't trusted them, and use NPO/C0G instead for frequency control applications. Cheers, Tom (Steve Kavanagh) wrote in message . com... .... Has anyone else experienced this behaviour ? |
Hi,
Have a look at the 'Mica' section of this - http://my.execpc.com/~endlr/misc__dielectrics.html It won't answer your question but should give you an idea as to why that particular dielectric should be avoided in certain situations. Cheers - Joe |
Hi,
Have a look at the 'Mica' section of this - http://my.execpc.com/~endlr/misc__dielectrics.html It won't answer your question but should give you an idea as to why that particular dielectric should be avoided in certain situations. Cheers - Joe |
On a sunny day (Sun, 16 May 2004 21:16:23 +0100) it happened Joe McElvenney
wrote in : Hi, Have a look at the 'Mica' section of this - http://my.execpc.com/~endlr/misc__dielectrics.html It won't answer your question but should give you an idea as to why that particular dielectric should be avoided in certain situations. Cheers - Joe Nice page, I like these oldies, remind me of the past: http://www.orenelliottproducts.com/capacito.htm JP |
On a sunny day (Sun, 16 May 2004 21:16:23 +0100) it happened Joe McElvenney
wrote in : Hi, Have a look at the 'Mica' section of this - http://my.execpc.com/~endlr/misc__dielectrics.html It won't answer your question but should give you an idea as to why that particular dielectric should be avoided in certain situations. Cheers - Joe Nice page, I like these oldies, remind me of the past: http://www.orenelliottproducts.com/capacito.htm JP |
"Steve Kavanagh" wrote in message om... A year or so ago I was working on a microwave local oscillator (at about 2.5 GHz) multiplied up from a crystal oscillator near 40 MHz. The output was found to jump in frequency by tens or hundreds of Hz many times as the LO chain was warming up. I was able to reduce this jumping by replacing all the dipped silver mica capacitors [...snip] The capacitors used in both cases are from unknown sources and were probably manufactured in the early 1980's. Has anyone else experienced this behaviour ? Steve (VE3SMA) Steve, Although I didn't figure it out at the time, my Knight-Kit Space Spanner circa 1960 had terrible microphonics - very noisy. I cleaned the entire chassis & rewired it to no avail. Today I suspect a mica cap, the old square type, since I heard of same thing this some time ago. |
"Steve Kavanagh" wrote in message om... A year or so ago I was working on a microwave local oscillator (at about 2.5 GHz) multiplied up from a crystal oscillator near 40 MHz. The output was found to jump in frequency by tens or hundreds of Hz many times as the LO chain was warming up. I was able to reduce this jumping by replacing all the dipped silver mica capacitors [...snip] The capacitors used in both cases are from unknown sources and were probably manufactured in the early 1980's. Has anyone else experienced this behaviour ? Steve (VE3SMA) Steve, Although I didn't figure it out at the time, my Knight-Kit Space Spanner circa 1960 had terrible microphonics - very noisy. I cleaned the entire chassis & rewired it to no avail. Today I suspect a mica cap, the old square type, since I heard of same thing this some time ago. |
In article ,
Steve Kavanagh wrote: [...] I have just been observing the same sort of frequent jumping behaviour (up to a kHz or so at a time) in another local oscillator (output at about 10.5 GHz, phase locked to a crystal oscillator around 100 MHz). I note that this one also has dipped silver mica caps in the crystal oscillator and I wonder if it too would be improved by replacing them with NP0 ceramics. Do the silver mica caps say "made in china" on them? Are they a light tan color? If either of these are true chances are you will get a better cap made from ear wax and tin foil. Somewhere in China there was, and perhaps still is a factory, that made silver mica caps that change value if you squeeze them between your fingers and go open if you heat cycle them. I've never had much trouble with CDE caps. -- -- forging knowledge |
In article ,
Steve Kavanagh wrote: [...] I have just been observing the same sort of frequent jumping behaviour (up to a kHz or so at a time) in another local oscillator (output at about 10.5 GHz, phase locked to a crystal oscillator around 100 MHz). I note that this one also has dipped silver mica caps in the crystal oscillator and I wonder if it too would be improved by replacing them with NP0 ceramics. Do the silver mica caps say "made in china" on them? Are they a light tan color? If either of these are true chances are you will get a better cap made from ear wax and tin foil. Somewhere in China there was, and perhaps still is a factory, that made silver mica caps that change value if you squeeze them between your fingers and go open if you heat cycle them. I've never had much trouble with CDE caps. -- -- forging knowledge |
On 16 May 2004 07:06:24 -0700 (Steve
Kavanagh) wrote: The capacitors used in both cases are from unknown sources and were probably manufactured in the early 1980's. That may be the secret here. In the past, I've used silver mica caps in a number of applications with positive results. The only problem I've ever seen with good quality ones was a single one in a 40 year old HP amplifier that had become leaky. - ----------------------------------------------- Jim Adney Madison, WI 53711 USA ----------------------------------------------- |
"Jim Adney" wrote in message
... On 16 May 2004 07:06:24 -0700 (Steve Kavanagh) wrote: The capacitors used in both cases are from unknown sources and were probably manufactured in the early 1980's. That may be the secret here. In the past, I've used silver mica caps in a number of applications with positive results. The only problem I've ever seen with good quality ones was a single one in a 40 year old HP amplifier that had become leaky. If silvered mica caps are so crappy, why did they ever use them in the first place? Thanks, Rich |
"Jim Adney" wrote in message
... On 16 May 2004 07:06:24 -0700 (Steve Kavanagh) wrote: The capacitors used in both cases are from unknown sources and were probably manufactured in the early 1980's. That may be the secret here. In the past, I've used silver mica caps in a number of applications with positive results. The only problem I've ever seen with good quality ones was a single one in a 40 year old HP amplifier that had become leaky. If silvered mica caps are so crappy, why did they ever use them in the first place? Thanks, Rich |
Space Spanner.. O'Man, I could only afford the Ocean Hopper.. Man, them
were the days! Joel AG4QC "Steve Nosko" wrote in message ... Steve, Although I didn't figure it out at the time, my Knight-Kit Space Spanner circa 1960 had terrible microphonics - very noisy. I cleaned the entire chassis & rewired it to no avail. Today I suspect a mica cap, the old square type, since I heard of same thing this some time ago. |
Space Spanner.. O'Man, I could only afford the Ocean Hopper.. Man, them
were the days! Joel AG4QC "Steve Nosko" wrote in message ... Steve, Although I didn't figure it out at the time, my Knight-Kit Space Spanner circa 1960 had terrible microphonics - very noisy. I cleaned the entire chassis & rewired it to no avail. Today I suspect a mica cap, the old square type, since I heard of same thing this some time ago. |
"Rich Grise" wrote in message ... "Jim Adney" wrote in message ... On 16 May 2004 07:06:24 -0700 (Steve Kavanagh) wrote: [snip] If silvered mica caps are so crappy, why did they ever use them in the first place? Thanks, Rich Well made, they are very stable & handle considerable current. These were top of the line. If they make junk now, so be it. -- Steve N, K,9;d, c. i My email has no u's. |
"Rich Grise" wrote in message ... "Jim Adney" wrote in message ... On 16 May 2004 07:06:24 -0700 (Steve Kavanagh) wrote: [snip] If silvered mica caps are so crappy, why did they ever use them in the first place? Thanks, Rich Well made, they are very stable & handle considerable current. These were top of the line. If they make junk now, so be it. -- Steve N, K,9;d, c. i My email has no u's. |
"Joel" wrote in message ... That "Steve Nosko" wrote in message ... Steve, Although I didn't figure it out at the time, my Knight-Kit Space Spanner circa 1960 had terrible microphonics - very noisy. I cleaned the entire chassis & rewired it to no avail. Today I suspect a mica cap, the old square type, since I heard of same thing this some time ago. Space Spanner.. O'Man, I could only afford the Ocean Hopper.. Man, them were the days! Joel AG4QC Yea! AND, get this, I think I took plates off, or bent some, of the bandspread cap to reduce its range and calibrated it for 40 M. Every Saturday morning I'd listen to the same group on SSB talking about their Collins rigs and inverted Vees. Wish I still had it and the Knight-Kit crystal set. Had it hooked up to a loud speaker in my room (course I was in Wood Dale, IL., not too far from the WBBM and WGN AM transmitters...) 73 -- Steve N, K,9;d, c. i My email has no u's. |
"Joel" wrote in message ... That "Steve Nosko" wrote in message ... Steve, Although I didn't figure it out at the time, my Knight-Kit Space Spanner circa 1960 had terrible microphonics - very noisy. I cleaned the entire chassis & rewired it to no avail. Today I suspect a mica cap, the old square type, since I heard of same thing this some time ago. Space Spanner.. O'Man, I could only afford the Ocean Hopper.. Man, them were the days! Joel AG4QC Yea! AND, get this, I think I took plates off, or bent some, of the bandspread cap to reduce its range and calibrated it for 40 M. Every Saturday morning I'd listen to the same group on SSB talking about their Collins rigs and inverted Vees. Wish I still had it and the Knight-Kit crystal set. Had it hooked up to a loud speaker in my room (course I was in Wood Dale, IL., not too far from the WBBM and WGN AM transmitters...) 73 -- Steve N, K,9;d, c. i My email has no u's. |
Real mica has to be real old and it sn't aging much in a capacitor because
it has been aging for eons and for all pracitcal purposes inert. If mica capacitors are jumpy it must be due to the plating or encapsulation! If there's no clue to the mfg it could be that these jumpy were not manufacutured for your application. JMHO 73 Hank WD5JFR "Steve Kavanagh" wrote in message om... A year or so ago I was working on a microwave local oscillator (at about 2.5 GHz) multiplied up from a crystal oscillator near 40 MHz. The output was found to jump in frequency by tens or hundreds of Hz many times as the LO chain was warming up. I was able to reduce this jumping by replacing all the dipped silver mica capacitors in the crystal oscillator stage with NP0 ceramics. There is still a bit of jumping which may come from some silver micas which remain in the stage following the crystal oscillator. I have just been observing the same sort of frequent jumping behaviour (up to a kHz or so at a time) in another local oscillator (output at about 10.5 GHz, phase locked to a crystal oscillator around 100 MHz). I note that this one also has dipped silver mica caps in the crystal oscillator and I wonder if it too would be improved by replacing them with NP0 ceramics. The capacitors used in both cases are from unknown sources and were probably manufactured in the early 1980's. Has anyone else experienced this behaviour ? Steve (VE3SMA) |
Real mica has to be real old and it sn't aging much in a capacitor because
it has been aging for eons and for all pracitcal purposes inert. If mica capacitors are jumpy it must be due to the plating or encapsulation! If there's no clue to the mfg it could be that these jumpy were not manufacutured for your application. JMHO 73 Hank WD5JFR "Steve Kavanagh" wrote in message om... A year or so ago I was working on a microwave local oscillator (at about 2.5 GHz) multiplied up from a crystal oscillator near 40 MHz. The output was found to jump in frequency by tens or hundreds of Hz many times as the LO chain was warming up. I was able to reduce this jumping by replacing all the dipped silver mica capacitors in the crystal oscillator stage with NP0 ceramics. There is still a bit of jumping which may come from some silver micas which remain in the stage following the crystal oscillator. I have just been observing the same sort of frequent jumping behaviour (up to a kHz or so at a time) in another local oscillator (output at about 10.5 GHz, phase locked to a crystal oscillator around 100 MHz). I note that this one also has dipped silver mica caps in the crystal oscillator and I wonder if it too would be improved by replacing them with NP0 ceramics. The capacitors used in both cases are from unknown sources and were probably manufactured in the early 1980's. Has anyone else experienced this behaviour ? Steve (VE3SMA) |
On Tue, 18 May 2004 02:31:08 GMT "Rich Grise"
wrote: "Jim Adney" wrote in message .. . On 16 May 2004 07:06:24 -0700 (Steve Kavanagh) wrote: The capacitors used in both cases are from unknown sources and were probably manufactured in the early 1980's. That may be the secret here. In the past, I've used silver mica caps in a number of applications with positive results. The only problem I've ever seen with good quality ones was a single one in a 40 year old HP amplifier that had become leaky. If silvered mica caps are so crappy, why did they ever use them in the first place? I was not suggesting that they were crappy. I was suggesting that of all the high quality ones I have worked with over many years, I've only seen 1 failure. His experience may well be due to the fact that his were of unknown origin and unknown quality. - ----------------------------------------------- Jim Adney Madison, WI 53711 USA ----------------------------------------------- |
On Tue, 18 May 2004 02:31:08 GMT "Rich Grise"
wrote: "Jim Adney" wrote in message .. . On 16 May 2004 07:06:24 -0700 (Steve Kavanagh) wrote: The capacitors used in both cases are from unknown sources and were probably manufactured in the early 1980's. That may be the secret here. In the past, I've used silver mica caps in a number of applications with positive results. The only problem I've ever seen with good quality ones was a single one in a 40 year old HP amplifier that had become leaky. If silvered mica caps are so crappy, why did they ever use them in the first place? I was not suggesting that they were crappy. I was suggesting that of all the high quality ones I have worked with over many years, I've only seen 1 failure. His experience may well be due to the fact that his were of unknown origin and unknown quality. - ----------------------------------------------- Jim Adney Madison, WI 53711 USA ----------------------------------------------- |
Thanks for all your comments. Since speculation has started here is
what I know about the capacitors. Those used in the 2.5 GHz source are surplus from a company that makes high quality stuff. They were probably procured to a military or space specification but I am not sure. The 10.5 GHz source was manufactured by MA/COM about 20 years ago. All of them are the usual deep maroon (is that the right word ?) to brown colour. Keep in mind I am being pretty picky. I consider short term frequency jumps of much over 100 Hz to be unsatisfactory - that is 10-40 parts per billion depending on which source is considered. The largest observed jumps are about ten times this. Of course, since these are crystal oscillators, the corresponding capacitance jumps must be much larger, since the crystal should dominate the oscillator stability. I would not consider them "crappy", just not as good as one might be led to expect. I have used capacitors from the same provenance as those in the 2.5 GHz source in LC oscillators at a few MHz with no observed problems. The smooth portion of the warm-up drift is reasonably normal in both cases...only the jumpiness is unusual. Steve |
Thanks for all your comments. Since speculation has started here is
what I know about the capacitors. Those used in the 2.5 GHz source are surplus from a company that makes high quality stuff. They were probably procured to a military or space specification but I am not sure. The 10.5 GHz source was manufactured by MA/COM about 20 years ago. All of them are the usual deep maroon (is that the right word ?) to brown colour. Keep in mind I am being pretty picky. I consider short term frequency jumps of much over 100 Hz to be unsatisfactory - that is 10-40 parts per billion depending on which source is considered. The largest observed jumps are about ten times this. Of course, since these are crystal oscillators, the corresponding capacitance jumps must be much larger, since the crystal should dominate the oscillator stability. I would not consider them "crappy", just not as good as one might be led to expect. I have used capacitors from the same provenance as those in the 2.5 GHz source in LC oscillators at a few MHz with no observed problems. The smooth portion of the warm-up drift is reasonably normal in both cases...only the jumpiness is unusual. Steve |
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In article ,
says... Coming in at the end of this discussion, I'll have to question the observation of the so-called "frequency jump." At 100 PPB we are talking quite serious test equipment hook-ups and a number of different techniques very much uncommon in home workshop practice. Not really. If he's working with a 1296 MHz SSB rig, for instance, then he's not going to be happy with 100 Hz jumps. -- jm ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ |
In article ,
says... Coming in at the end of this discussion, I'll have to question the observation of the so-called "frequency jump." At 100 PPB we are talking quite serious test equipment hook-ups and a number of different techniques very much uncommon in home workshop practice. Not really. If he's working with a 1296 MHz SSB rig, for instance, then he's not going to be happy with 100 Hz jumps. -- jm ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ |
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