Re: [time-nuts] Effect of EFC noise on phase noise
A good filter in the cable is highly recommended, 5 KOhm & 1000 uF cleans
many things
In a message dated 8/1/2016 11:12:51 A.M. Eastern Daylight Time,
kb8tq@n1k.org writes:
Hi
It’s just very standard FM modulation math. The only gotcha is the
(often unknown) bandwidth of the EFC port. Even on a precision
OCXO, it might be <10 Hz, it might be over a KHz …. The trap many
fall into is the “small angle” restriction. You can get into modulation
indexes that will get the second and third order terms contributing.
It’s more common to see on vibration, but it can happen on a noisy
EFC.
Bob
On Aug 1, 2016, at 9:46 AM, Attila Kinali attila@kinali.ch wrote:
Moin,
I need some formulas that relate EFC noise to the (added) phase noise of
an OCXO. It shouldn't be too difficult to come up with something. But
before I make some stupid mistakes, i wanted to ask whether someone
has already done this or has any references to papers? My google-foo
was not strong enough to find something.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
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Hi
….. until you discover that you picked the wrong capacitor manufacturer and you have
more noise from leakage in the cap than you did to start out with :) In general “big C and
small R” is the better solution than “big R and small C”.
The pesky part is that with electrolytic caps, the whole “noise current” thing changes as
the voltage moves around. You go to measure things and by the time the gear is set up,
the noise has dropped. Turn it all off, come back the next day and it’s noisy again.
An even more subtle issue can be capacitor temperature coefficient on really long Tau filters. If C
changes (due to temperature fluxuations) faster than the settling time of the filter, you get noise. Charge
is the same so delta C gives delta V.
I wish I could tell you that was all purely theoretical. Unfortunately it’s based on empirical data
collected in the “how could I be so stupid” fashion.
Bob
On Aug 1, 2016, at 11:21 AM, KA2WEU--- via time-nuts time-nuts@febo.com wrote:
A good filter in the cable is highly recommended, 5 KOhm & 1000 uF cleans
many things
In a message dated 8/1/2016 11:12:51 A.M. Eastern Daylight Time,
kb8tq@n1k.org writes:
Hi
It’s just very standard FM modulation math. The only gotcha is the
(often unknown) bandwidth of the EFC port. Even on a precision
OCXO, it might be <10 Hz, it might be over a KHz …. The trap many
fall into is the “small angle” restriction. You can get into modulation
indexes that will get the second and third order terms contributing.
It’s more common to see on vibration, but it can happen on a noisy
EFC.
Bob
On Aug 1, 2016, at 9:46 AM, Attila Kinali attila@kinali.ch wrote:
Moin,
I need some formulas that relate EFC noise to the (added) phase noise of
an OCXO. It shouldn't be too difficult to come up with something. But
before I make some stupid mistakes, i wanted to ask whether someone
has already done this or has any references to papers? My google-foo
was not strong enough to find something.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
and follow the instructions there.
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On Mon, 1 Aug 2016 11:21:10 -0400
KA2WEU--- via time-nuts time-nuts@febo.com wrote:
A good filter in the cable is highly recommended, 5 KOhm & 1000 uF cleans
many things
Uhmm.. with 1mF in capacitors... don't you run into into microphonics problems?
Or all these capacitors supposed to be tantalum/aluminium caps?
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
In message 20160801180601.3d27b82227616e847f34014c@kinali.ch, Attila Kinali w
rites:
On Mon, 1 Aug 2016 11:21:10 -0400
KA2WEU--- via time-nuts time-nuts@febo.com wrote:
A good filter in the cable is highly recommended, 5 KOhm & 1000 uF cleans
many things
Uhmm.. with 1mF in capacitors... don't you run into into microphonics problems?
Or all these capacitors supposed to be tantalum/aluminium caps?
You certainly run into a separate source of temperature dependence, but
of course only second order (change of temp).
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
This duplicates the problems encountered when trying to quantify low
frequency noise from a voltage reference; it is difficult to make an
low frequency high pass filter with lower noise than the lowest noise
references and the capacitor is the problem.
In Linear Technology Application Note 124, Jim Williams discusses the
problems with electrolytic capacitors for this type of application. I
have read that you can get away with aluminum electrolytics if you
grade them for low leakage and low noise. The dielectric absorption
is also a problem unless you can wait hours for best performance.
What about the alternative of buffering the signal with a low noise
low input bias current operational amplifier so that a large film
capacitor can be used instead? Is the low frequency noise of a good
operational amplifier still too much? What about a chopper stabilized
amplifier without suitable output filter?
On Mon, 1 Aug 2016 11:46:51 -0400, you wrote:
Hi
.. until you discover that you picked the wrong capacitor manufacturer and you have
more noise from leakage in the cap than you did to start out with :) In general big C and
small R is the better solution than big R and small C.
The pesky part is that with electrolytic caps, the whole noise current thing changes as
the voltage moves around. You go to measure things and by the time the gear is set up,
the noise has dropped. Turn it all off, come back the next day and its noisy again.
An even more subtle issue can be capacitor temperature coefficient on really long Tau filters. If C
changes (due to temperature fluxuations) faster than the settling time of the filter, you get noise. Charge
is the same so delta C gives delta V.
I wish I could tell you that was all purely theoretical. Unfortunately its based on empirical data
collected in the how could I be so stupid fashion.
Bob
On Aug 1, 2016, at 11:21 AM, KA2WEU--- via time-nuts time-nuts@febo.com wrote:
A good filter in the cable is highly recommended, 5 KOhm & 1000 uF cleans
many things
Hi
If you wire up all the possible circuits and check them all out … the
answer is that big C / small R wins. Big R gets you into resistor noise issues
and stray pickup.
Bob
On Aug 1, 2016, at 4:16 PM, David davidwhess@gmail.com wrote:
This duplicates the problems encountered when trying to quantify low
frequency noise from a voltage reference; it is difficult to make an
low frequency high pass filter with lower noise than the lowest noise
references and the capacitor is the problem.
In Linear Technology Application Note 124, Jim Williams discusses the
problems with electrolytic capacitors for this type of application. I
have read that you can get away with aluminum electrolytics if you
grade them for low leakage and low noise. The dielectric absorption
is also a problem unless you can wait hours for best performance.
What about the alternative of buffering the signal with a low noise
low input bias current operational amplifier so that a large film
capacitor can be used instead? Is the low frequency noise of a good
operational amplifier still too much? What about a chopper stabilized
amplifier without suitable output filter?
On Mon, 1 Aug 2016 11:46:51 -0400, you wrote:
Hi
.. until you discover that you picked the wrong capacitor manufacturer and you have
more noise from leakage in the cap than you did to start out with :) In general big C and
small R is the better solution than big R and small C.
The pesky part is that with electrolytic caps, the whole noise current thing changes as
the voltage moves around. You go to measure things and by the time the gear is set up,
the noise has dropped. Turn it all off, come back the next day and its noisy again.
An even more subtle issue can be capacitor temperature coefficient on really long Tau filters. If C
changes (due to temperature fluxuations) faster than the settling time of the filter, you get noise. Charge
is the same so delta C gives delta V.
I wish I could tell you that was all purely theoretical. Unfortunately its based on empirical data
collected in the how could I be so stupid fashion.
Bob
On Aug 1, 2016, at 11:21 AM, KA2WEU--- via time-nuts time-nuts@febo.com wrote:
A good filter in the cable is highly recommended, 5 KOhm & 1000 uF cleans
many things
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
The broadband thermal noise at a circuit point with a cap is always kT/c
On Monday, 1 August 2016, Bob Camp kb8tq@n1k.org wrote:
Hi
If you wire up all the possible circuits and check them all out … the
answer is that big C / small R wins. Big R gets you into resistor noise
issues
and stray pickup.
Bob
On Aug 1, 2016, at 4:16 PM, David <davidwhess@gmail.com javascript:;>
wrote:
This duplicates the problems encountered when trying to quantify low
frequency noise from a voltage reference; it is difficult to make an
low frequency high pass filter with lower noise than the lowest noise
references and the capacitor is the problem.
In Linear Technology Application Note 124, Jim Williams discusses the
problems with electrolytic capacitors for this type of application. I
have read that you can get away with aluminum electrolytics if you
grade them for low leakage and low noise. The dielectric absorption
is also a problem unless you can wait hours for best performance.
What about the alternative of buffering the signal with a low noise
low input bias current operational amplifier so that a large film
capacitor can be used instead? Is the low frequency noise of a good
operational amplifier still too much? What about a chopper stabilized
amplifier without suitable output filter?
On Mon, 1 Aug 2016 11:46:51 -0400, you wrote:
Hi
.. until you discover that you picked the wrong capacitor manufacturer
and you have
more noise from leakage in the cap than you did to start out with :)
In general “big C and
small R” is the better solution than “big R and small C”.
The pesky part is that with electrolytic caps, the whole “noise
current” thing changes as
the voltage moves around. You go to measure things and by the time the
gear is set up,
the noise has dropped. Turn it all off, come back the next day and it’s
noisy again.
An even more subtle issue can be capacitor temperature coefficient on
really long Tau filters. If C
changes (due to temperature fluxuations) faster than the settling time
of the filter, you get noise. Charge
is the same so delta C gives delta V.
I wish I could tell you that was all purely theoretical.
Unfortunately it’s based on empirical data
collected in the “how could I be so stupid” fashion.
Bob
On Aug 1, 2016, at 11:21 AM, KA2WEU--- via time-nuts <
time-nuts@febo.com javascript:;> wrote:
A good filter in the cable is highly recommended, 5 KOhm & 1000 uF
cleans
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com javascript:;
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
HI
Broadband is not where you run into the trouble on any of these circuits. It’s
always what happens within a decade or two past cutoff or inside the pass band.
Bob
On Aug 1, 2016, at 4:50 PM, Scott Stobbe scott.j.stobbe@gmail.com wrote:
The broadband thermal noise at a circuit point with a cap is always kT/c
On Monday, 1 August 2016, Bob Camp kb8tq@n1k.org wrote:
Hi
If you wire up all the possible circuits and check them all out … the
answer is that big C / small R wins. Big R gets you into resistor noise
issues
and stray pickup.
Bob
On Aug 1, 2016, at 4:16 PM, David <davidwhess@gmail.com javascript:;>
wrote:
This duplicates the problems encountered when trying to quantify low
frequency noise from a voltage reference; it is difficult to make an
low frequency high pass filter with lower noise than the lowest noise
references and the capacitor is the problem.
In Linear Technology Application Note 124, Jim Williams discusses the
problems with electrolytic capacitors for this type of application. I
have read that you can get away with aluminum electrolytics if you
grade them for low leakage and low noise. The dielectric absorption
is also a problem unless you can wait hours for best performance.
What about the alternative of buffering the signal with a low noise
low input bias current operational amplifier so that a large film
capacitor can be used instead? Is the low frequency noise of a good
operational amplifier still too much? What about a chopper stabilized
amplifier without suitable output filter?
On Mon, 1 Aug 2016 11:46:51 -0400, you wrote:
Hi
.. until you discover that you picked the wrong capacitor manufacturer
and you have
more noise from leakage in the cap than you did to start out with :)
In general “big C and
small R” is the better solution than “big R and small C”.
The pesky part is that with electrolytic caps, the whole “noise
current” thing changes as
the voltage moves around. You go to measure things and by the time the
gear is set up,
the noise has dropped. Turn it all off, come back the next day and it’s
noisy again.
An even more subtle issue can be capacitor temperature coefficient on
really long Tau filters. If C
changes (due to temperature fluxuations) faster than the settling time
of the filter, you get noise. Charge
is the same so delta C gives delta V.
I wish I could tell you that was all purely theoretical.
Unfortunately it’s based on empirical data
collected in the “how could I be so stupid” fashion.
Bob
On Aug 1, 2016, at 11:21 AM, KA2WEU--- via time-nuts <
time-nuts@febo.com javascript:;> wrote:
A good filter in the cable is highly recommended, 5 KOhm & 1000 uF
cleans
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com javascript:;
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
With my filter , I had good success and 5 K is not too high , Ulrich
Sent from my iPhone
On Aug 1, 2016, at 11:46 AM, Bob Camp kb8tq@n1k.org wrote:
Hi
….. until you discover that you picked the wrong capacitor manufacturer and you have
more noise from leakage in the cap than you did to start out with :) In general “big C and
small R” is the better solution than “big R and small C”.
The pesky part is that with electrolytic caps, the whole “noise current” thing changes as
the voltage moves around. You go to measure things and by the time the gear is set up,
the noise has dropped. Turn it all off, come back the next day and it’s noisy again.
An even more subtle issue can be capacitor temperature coefficient on really long Tau filters. If C
changes (due to temperature fluxuations) faster than the settling time of the filter, you get noise. Charge
is the same so delta C gives delta V.
I wish I could tell you that was all purely theoretical. Unfortunately it’s based on empirical data
collected in the “how could I be so stupid” fashion.
Bob
On Aug 1, 2016, at 11:21 AM, KA2WEU--- via time-nuts time-nuts@febo.com wrote:
A good filter in the cable is highly recommended, 5 KOhm & 1000 uF cleans
many things
In a message dated 8/1/2016 11:12:51 A.M. Eastern Daylight Time,
kb8tq@n1k.org writes:
Hi
It’s just very standard FM modulation math. The only gotcha is the
(often unknown) bandwidth of the EFC port. Even on a precision
OCXO, it might be <10 Hz, it might be over a KHz …. The trap many
fall into is the “small angle” restriction. You can get into modulation
indexes that will get the second and third order terms contributing.
It’s more common to see on vibration, but it can happen on a noisy
EFC.
Bob
On Aug 1, 2016, at 9:46 AM, Attila Kinali attila@kinali.ch wrote:
Moin,
I need some formulas that relate EFC noise to the (added) phase noise of
an OCXO. It shouldn't be too difficult to come up with something. But
before I make some stupid mistakes, i wanted to ask whether someone
has already done this or has any references to papers? My google-foo
was not strong enough to find something.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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and follow the instructions there.
Am 01.08.2016 um 22:16 schrieb David:
This duplicates the problems encountered when trying to quantify low
frequency noise from a voltage reference; it is difficult to make an
low frequency high pass filter with lower noise than the lowest noise
references and the capacitor is the problem.
I beg to differ. Voltage references are not that wonderful. Bandgaps
live from amplifying
small voltage differences and stable Zener references at 6 to 7 Volts
are plagued by
avalanche noise. And that includes the LT6655 band gap.
WRT short term stability all of these are eclipsed by 2.7 / 3.3 volt
zeners and by LEDs.
Even the LT6655 gains a lot of noise performance from an active filter
with AD797 /
ADA4898 op amps and even resistors and 6V/1000uF Nipon Chemi SMD
electrolytics.
I have made some absolute noise voltage measurements:
< https://www.flickr.com/photos/137684711@N07/albums/72157662535945536 >
LEDs and Zeners are measured with bias from a 1 or 2k wire resistor and a
14V NiMH battery. I find the HLMP6000 LED really impressive and the
LT3042 regulator.
The preamp is 20 ADA4898 op amps in parallel ( i.e. 220pV/sqrtHz), the 0
dB line is 1 nV/sqrt Hz.
Everything was fed from batteries in a box in box in a box and then
after +80 dB passed to
an 89441A vector signal analyzer.
The input capacitor of the preamp is 20 times 10uF WIMA foil, that is
not enough for the
low frequency corner as we do not see the real 1/f noise below 20 Hz.
What we see looks more like GR noise, spectrum-wise, and it is really
the insufficient shorting
of the 10K bias resistor through the input source and coupling cap.
I have bought some wet slug tantals as proposed by Jim Williams (see
below), 10000 uF bring
the right 1/f behaviour but at very substantial cost :-( At least for
small input voltages alu
electrolytics do not seem to make a difference. I did not test large
voltages.
I'm working on a new amplifier based on IF3602 or BF862 FETs that can
use 10u foil only.
When it's done I'll repeat these measurements.
In Linear Technology Application Note 124, Jim Williams discusses the
problems with electrolytic capacitors for this type of application. I
have read that you can get away with aluminum electrolytics if you
grade them for low leakage and low noise. The dielectric absorption
is also a problem unless you can wait hours for best performance.
JW has the added handicap that he wants to keep the the long term and
absolute stability
of his reference and so cannot afford any voltage drop on a series R. We
do not share that
problem on an EFC line because the C stands for control and if the
voltage there does
never change for some other reason we have probably made a bad decision
with regard
to loop gain.
And large resistors may feature more noise voltage, but that increases
only with the
root of the resistance. The filter corner drops in a linear way, so a
large resistor may
really help. The tiny noise voltage of a reasonable resistor must be
seen anyway in
the context of say, a 10811A that tunes +- 1 Hz for 10 Volts on the EFC.
regards, Gerhard