|
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. |
| All times are GMT +1. The time now is 03:34 PM. |
Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
RadioBanter.com