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