In article , Henry
Kolesnik writes
Mark
Any more info on the jumpy HPs appreciated.
--
73
This thread seems to be cloned from last week ; anyway as I said then
silver mica are known to be subject to scintillation which may be due to
de-lamination , later mica used powdered mica which may or maynot be
better. Encapsulated low value caps are often degraded by the
encapsulation material so sm would be better use NPO ceramic, microwave
types should be lower loss.
Crystals jump in a changing temperature due to unwanted modes passing
through the main mode as they have different temperature coeggicient.
These are fairly gross effects of .01 to 10ppm jumps.

--
ddwyer

In article , Henry
Kolesnik writes
Mark
Any more info on the jumpy HPs appreciated.
--
73
This thread seems to be cloned from last week ; anyway as I said then
silver mica are known to be subject to scintillation which may be due to
de-lamination , later mica used powdered mica which may or maynot be
better. Encapsulated low value caps are often degraded by the
encapsulation material so sm would be better use NPO ceramic, microwave
types should be lower loss.
Crystals jump in a changing temperature due to unwanted modes passing
through the main mode as they have different temperature coeggicient.
These are fairly gross effects of .01 to 10ppm jumps.

--
ddwyer

Mark
Any more info on the jumpy HPs appreciated.
--
73
Hank WD5JFR
"qrk" wrote in message
...
On 19 May 2004 06:08:37 -0700, (Steve
Kavanagh) wrote:

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

Crystals can also jump. Just look at HP oven oscillators used in the
GPS time/frequency references. Very jumpy. A collegue tried 5
oscillators in the GPS time/freq reference and all were jumpy to
various degrees. He was noting sub-ppb jumps.

Mark

In article ,
(Steve Kavanagh) writes:

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.

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.

If you are locking the X-band source to a crystal reference, then
there is a great deal of this frequency-control subsystem which can
be a cause for the "jumps." That can be the sampler or prescaler,
the phase detector (assuming it is a form of PLL), the loop filter, and
even the power supply rail voltage (affecting the voltage control of the
presumed voltage-controlled frequency adjuster circuit). ANY of
those can be the culprit in small frequency "jumps." That would
include whatever it is you are using to heterodyne with the X-band
source to enable frequency measurement.

I'm going to question all those others' claims about "jumpy silver
mica capacitors" after about 54 years of having hands-on
experience in RF and pulse circuitry. I'm talking primarily the
"dipped" coating DMs with some excursions into the molded
plastic case axial lead models. I've never had one either open or
shorted and never "jumpy" in value and that includes the full-on
military environment testing of temperature, altitude, shock,
vibration, etc. A very few were found not quite within the capacity
value tolerance and not a single one experienced any "jumping"
of value. I've not heard of any such stories from contemporaries
in the industry...and I HAVE heard lots of urban-myth stories on
other things within all of electronics.

Len Anderson
retired (from regular hours) electronic engineer person

On 19 May 2004 06:08:37 -0700, (Steve
Kavanagh) wrote:

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

Crystals can also jump. Just look at HP oven oscillators used in the
GPS time/frequency references. Very jumpy. A collegue tried 5
oscillators in the GPS time/freq reference and all were jumpy to
various degrees. He was noting sub-ppb jumps.

Mark

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
-----------------------------------------------

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)

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

In article , Steve
Kavanagh writes
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)
in the crystal oscillator business silver mica capacitors were known for
scintillation . The potting compound of sm capacitors was ofteen the
cause of temperature coefficient drift. Scintilation was probably due to
delamination of the mica.
Modern NPO ceramic are probably better particularly unencapsulated
surface mount.


--
ddwyer