MH
Matt Huszagh
Tue, Feb 20, 2024 7:13 AM
To what extent is oscillator injection locking a risk when powering
multiple oscillators from the same power supply?
I measured a couple OCXOs to see how much of the output signal made its
way back into the power supply input. A Datum 1000B showed a 10 MHz
signal of -53 dBm for a +13 dBm output. A Wenzel 10 MHz ULN gave a
similar result. Curiously, the Wenzel showed much better isolation
(-74 dBm) with the output unterminated.
If we compare that to the reverse isolation of buffer/isolation
amplifiers, that seems to put the power supply isolation in the "ok"
territory, but possibly still a risk, depending on other characteristics
of the OCXO. Since the PSRR of many linear regulators is quite poor at
10 MHz (and even worse at higher typical OCXO frequencies), I would
expect using separate final regulators for each OCXO is probably only
slightly helpful. The same is probably true for the regulators internal
to the OCXOs themselves. There are exceptions to this, though. For
example, the LT3045 provides 50 dB PSRR at 10 MHz, assuming the layout
recommendations are followed.
I found Bruce's analysis page on injection locking
(http://www.ko4bb.com/~bruce/InjectionLocking.html) quite helpful in
this process. Unfortunately, I don't often know the Q factor of a given
OCXO or the amplitude of the tank circuit, so I just tried to guess.
Any thoughts on ways to minimize the risk of injection locking via power
supply connections? Am I right in thinking this is a genuine concern? I
was hoping to place a couple Datum 1000Bs in an enclosure and power them
all from the same AC/DC supply. Each would use separate LT3045 final
regulators. Given the good PSRR of that regulator, I should be ok, I
think. But I'm also curious about cases where the PSRR of the linear
regulator cannot be relied upon. I suppose ferrite beads in the form of
pi filters could be used, but ferrite beads generally aren't as
effective at 10 MHz as they are at 100 MHz. There are also DC power line
filters, sold by Schaffner and others. These can be quite effective at
10 MHz. I suppose these could be used if really needed.
Anyway, curious to hear thoughts and ideas. Thanks!
Matt
To what extent is oscillator injection locking a risk when powering
multiple oscillators from the same power supply?
I measured a couple OCXOs to see how much of the output signal made its
way back into the power supply input. A Datum 1000B showed a 10 MHz
signal of -53 dBm for a +13 dBm output. A Wenzel 10 MHz ULN gave a
similar result. Curiously, the Wenzel showed much better isolation
(-74 dBm) with the output unterminated.
If we compare that to the reverse isolation of buffer/isolation
amplifiers, that seems to put the power supply isolation in the "ok"
territory, but possibly still a risk, depending on other characteristics
of the OCXO. Since the PSRR of many linear regulators is quite poor at
10 MHz (and even worse at higher typical OCXO frequencies), I would
expect using separate final regulators for each OCXO is probably only
slightly helpful. The same is probably true for the regulators internal
to the OCXOs themselves. There are exceptions to this, though. For
example, the LT3045 provides 50 dB PSRR at 10 MHz, assuming the layout
recommendations are followed.
I found Bruce's analysis page on injection locking
(http://www.ko4bb.com/~bruce/InjectionLocking.html) quite helpful in
this process. Unfortunately, I don't often know the Q factor of a given
OCXO or the amplitude of the tank circuit, so I just tried to guess.
Any thoughts on ways to minimize the risk of injection locking via power
supply connections? Am I right in thinking this is a genuine concern? I
was hoping to place a couple Datum 1000Bs in an enclosure and power them
all from the same AC/DC supply. Each would use separate LT3045 final
regulators. Given the good PSRR of that regulator, I should be ok, I
think. But I'm also curious about cases where the PSRR of the linear
regulator cannot be relied upon. I suppose ferrite beads in the form of
pi filters could be used, but ferrite beads generally aren't as
effective at 10 MHz as they are at 100 MHz. There are also DC power line
filters, sold by Schaffner and others. These can be quite effective at
10 MHz. I suppose these could be used if really needed.
Anyway, curious to hear thoughts and ideas. Thanks!
Matt
PK
Poul-Henning Kamp
Tue, Feb 20, 2024 9:47 AM
Matt Huszagh via time-nuts writes:
Curiously, the Wenzel showed much better isolation
(-74 dBm) with the output unterminated.
That follows directly from the smaller power demand from the output amplifier.
Any thoughts on ways to minimize the risk of injection locking via power
supply connections?
As long as you have a constant load on the OCXO's output and moderately stable
temperature environment, their current-draw is going to be constant on timescales
of tens or hundreds of seconds.
That combined with the low power draw in steady state means that
you can put inductance measured in entire Henrys in series with the
OCXO's power-supply if you want, with suitable capacitors on both
sides, nothing we normally recognize as AC will get through.
--
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.
--------
Matt Huszagh via time-nuts writes:
> Curiously, the Wenzel showed much better isolation
> (-74 dBm) with the output unterminated.
That follows directly from the smaller power demand from the output amplifier.
> Any thoughts on ways to minimize the risk of injection locking via power
> supply connections?
As long as you have a constant load on the OCXO's output and moderately stable
temperature environment, their current-draw is going to be constant on timescales
of tens or hundreds of seconds.
That combined with the low power draw in steady state means that
you can put inductance measured in entire Henrys in series with the
OCXO's power-supply if you want, with suitable capacitors on both
sides, nothing we normally recognize as AC will get through.
--
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.
JH
john.haine@haine-online.net
Tue, Feb 20, 2024 10:19 AM
How about putting a band-stop filter with a notch at the oscillator
frequency but passes DC in the supply to each oscillator, as close as
possible to the supply pin?
But I think you would need anyway to lay out the supply and ground
connections very carefully to make sure there isn't any signal bypassing the
filter.
John.
-----Original Message-----
From: Matt Huszagh via time-nuts time-nuts@lists.febo.com
Sent: Tuesday, February 20, 2024 7:13 AM
To: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com
Cc: Matt Huszagh huszaghmatt@gmail.com
Subject: [time-nuts] Injection locking via common power supply
To what extent is oscillator injection locking a risk when powering multiple
oscillators from the same power supply?
I measured a couple OCXOs to see how much of the output signal made its way
back into the power supply input. A Datum 1000B showed a 10 MHz signal of
-53 dBm for a +13 dBm output. A Wenzel 10 MHz ULN gave a similar result.
Curiously, the Wenzel showed much better isolation
(-74 dBm) with the output unterminated.
If we compare that to the reverse isolation of buffer/isolation amplifiers,
that seems to put the power supply isolation in the "ok"
territory, but possibly still a risk, depending on other characteristics of
the OCXO. Since the PSRR of many linear regulators is quite poor at
10 MHz (and even worse at higher typical OCXO frequencies), I would expect
using separate final regulators for each OCXO is probably only slightly
helpful. The same is probably true for the regulators internal to the OCXOs
themselves. There are exceptions to this, though. For example, the LT3045
provides 50 dB PSRR at 10 MHz, assuming the layout recommendations are
followed.
I found Bruce's analysis page on injection locking
(http://www.ko4bb.com/~bruce/InjectionLocking.html) quite helpful in this
process. Unfortunately, I don't often know the Q factor of a given OCXO or
the amplitude of the tank circuit, so I just tried to guess.
Any thoughts on ways to minimize the risk of injection locking via power
supply connections? Am I right in thinking this is a genuine concern? I was
hoping to place a couple Datum 1000Bs in an enclosure and power them all
from the same AC/DC supply. Each would use separate LT3045 final regulators.
Given the good PSRR of that regulator, I should be ok, I think. But I'm also
curious about cases where the PSRR of the linear regulator cannot be relied
upon. I suppose ferrite beads in the form of pi filters could be used, but
ferrite beads generally aren't as effective at 10 MHz as they are at 100
MHz. There are also DC power line filters, sold by Schaffner and others.
These can be quite effective at
10 MHz. I suppose these could be used if really needed.
Anyway, curious to hear thoughts and ideas. Thanks!
Matt
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an
email to time-nuts-leave@lists.febo.com
How about putting a band-stop filter with a notch at the oscillator
frequency but passes DC in the supply to each oscillator, as close as
possible to the supply pin?
But I think you would need anyway to lay out the supply and ground
connections very carefully to make sure there isn't any signal bypassing the
filter.
John.
-----Original Message-----
From: Matt Huszagh via time-nuts <time-nuts@lists.febo.com>
Sent: Tuesday, February 20, 2024 7:13 AM
To: Discussion of precise time and frequency measurement
<time-nuts@lists.febo.com>
Cc: Matt Huszagh <huszaghmatt@gmail.com>
Subject: [time-nuts] Injection locking via common power supply
To what extent is oscillator injection locking a risk when powering multiple
oscillators from the same power supply?
I measured a couple OCXOs to see how much of the output signal made its way
back into the power supply input. A Datum 1000B showed a 10 MHz signal of
-53 dBm for a +13 dBm output. A Wenzel 10 MHz ULN gave a similar result.
Curiously, the Wenzel showed much better isolation
(-74 dBm) with the output unterminated.
If we compare that to the reverse isolation of buffer/isolation amplifiers,
that seems to put the power supply isolation in the "ok"
territory, but possibly still a risk, depending on other characteristics of
the OCXO. Since the PSRR of many linear regulators is quite poor at
10 MHz (and even worse at higher typical OCXO frequencies), I would expect
using separate final regulators for each OCXO is probably only slightly
helpful. The same is probably true for the regulators internal to the OCXOs
themselves. There are exceptions to this, though. For example, the LT3045
provides 50 dB PSRR at 10 MHz, assuming the layout recommendations are
followed.
I found Bruce's analysis page on injection locking
(http://www.ko4bb.com/~bruce/InjectionLocking.html) quite helpful in this
process. Unfortunately, I don't often know the Q factor of a given OCXO or
the amplitude of the tank circuit, so I just tried to guess.
Any thoughts on ways to minimize the risk of injection locking via power
supply connections? Am I right in thinking this is a genuine concern? I was
hoping to place a couple Datum 1000Bs in an enclosure and power them all
from the same AC/DC supply. Each would use separate LT3045 final regulators.
Given the good PSRR of that regulator, I should be ok, I think. But I'm also
curious about cases where the PSRR of the linear regulator cannot be relied
upon. I suppose ferrite beads in the form of pi filters could be used, but
ferrite beads generally aren't as effective at 10 MHz as they are at 100
MHz. There are also DC power line filters, sold by Schaffner and others.
These can be quite effective at
10 MHz. I suppose these could be used if really needed.
Anyway, curious to hear thoughts and ideas. Thanks!
Matt
_______________________________________________
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an
email to time-nuts-leave@lists.febo.com
AT
Andy Talbot
Tue, Feb 20, 2024 10:32 AM
Or just plenty of L/C low pass filtering in the supply rails
Saves having to tune a notch
Andy
www.g4jnt.com
On Tue, 20 Feb 2024 at 10:25, john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
How about putting a band-stop filter with a notch at the oscillator
frequency but passes DC in the supply to each oscillator, as close as
possible to the supply pin?
But I think you would need anyway to lay out the supply and ground
connections very carefully to make sure there isn't any signal bypassing
the
filter.
John.
-----Original Message-----
From: Matt Huszagh via time-nuts time-nuts@lists.febo.com
Sent: Tuesday, February 20, 2024 7:13 AM
To: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com
Cc: Matt Huszagh huszaghmatt@gmail.com
Subject: [time-nuts] Injection locking via common power supply
To what extent is oscillator injection locking a risk when powering
multiple
oscillators from the same power supply?
I measured a couple OCXOs to see how much of the output signal made its way
back into the power supply input. A Datum 1000B showed a 10 MHz signal of
-53 dBm for a +13 dBm output. A Wenzel 10 MHz ULN gave a similar result.
Curiously, the Wenzel showed much better isolation
(-74 dBm) with the output unterminated.
If we compare that to the reverse isolation of buffer/isolation amplifiers,
that seems to put the power supply isolation in the "ok"
territory, but possibly still a risk, depending on other characteristics of
the OCXO. Since the PSRR of many linear regulators is quite poor at
10 MHz (and even worse at higher typical OCXO frequencies), I would expect
using separate final regulators for each OCXO is probably only slightly
helpful. The same is probably true for the regulators internal to the OCXOs
themselves. There are exceptions to this, though. For example, the LT3045
provides 50 dB PSRR at 10 MHz, assuming the layout recommendations are
followed.
I found Bruce's analysis page on injection locking
(http://www.ko4bb.com/~bruce/InjectionLocking.html) quite helpful in this
process. Unfortunately, I don't often know the Q factor of a given OCXO or
the amplitude of the tank circuit, so I just tried to guess.
Any thoughts on ways to minimize the risk of injection locking via power
supply connections? Am I right in thinking this is a genuine concern? I was
hoping to place a couple Datum 1000Bs in an enclosure and power them all
from the same AC/DC supply. Each would use separate LT3045 final
regulators.
Given the good PSRR of that regulator, I should be ok, I think. But I'm
also
curious about cases where the PSRR of the linear regulator cannot be relied
upon. I suppose ferrite beads in the form of pi filters could be used, but
ferrite beads generally aren't as effective at 10 MHz as they are at 100
MHz. There are also DC power line filters, sold by Schaffner and others.
These can be quite effective at
10 MHz. I suppose these could be used if really needed.
Anyway, curious to hear thoughts and ideas. Thanks!
Matt
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an
email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Or just plenty of L/C low pass filtering in the supply rails
Saves having to tune a notch
Andy
www.g4jnt.com
On Tue, 20 Feb 2024 at 10:25, john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
> How about putting a band-stop filter with a notch at the oscillator
> frequency but passes DC in the supply to each oscillator, as close as
> possible to the supply pin?
>
> But I think you would need anyway to lay out the supply and ground
> connections very carefully to make sure there isn't any signal bypassing
> the
> filter.
>
> John.
>
> -----Original Message-----
> From: Matt Huszagh via time-nuts <time-nuts@lists.febo.com>
> Sent: Tuesday, February 20, 2024 7:13 AM
> To: Discussion of precise time and frequency measurement
> <time-nuts@lists.febo.com>
> Cc: Matt Huszagh <huszaghmatt@gmail.com>
> Subject: [time-nuts] Injection locking via common power supply
>
> To what extent is oscillator injection locking a risk when powering
> multiple
> oscillators from the same power supply?
>
> I measured a couple OCXOs to see how much of the output signal made its way
> back into the power supply input. A Datum 1000B showed a 10 MHz signal of
> -53 dBm for a +13 dBm output. A Wenzel 10 MHz ULN gave a similar result.
> Curiously, the Wenzel showed much better isolation
> (-74 dBm) with the output unterminated.
>
> If we compare that to the reverse isolation of buffer/isolation amplifiers,
> that seems to put the power supply isolation in the "ok"
> territory, but possibly still a risk, depending on other characteristics of
> the OCXO. Since the PSRR of many linear regulators is quite poor at
> 10 MHz (and even worse at higher typical OCXO frequencies), I would expect
> using separate final regulators for each OCXO is probably only slightly
> helpful. The same is probably true for the regulators internal to the OCXOs
> themselves. There are exceptions to this, though. For example, the LT3045
> provides 50 dB PSRR at 10 MHz, assuming the layout recommendations are
> followed.
>
> I found Bruce's analysis page on injection locking
> (http://www.ko4bb.com/~bruce/InjectionLocking.html) quite helpful in this
> process. Unfortunately, I don't often know the Q factor of a given OCXO or
> the amplitude of the tank circuit, so I just tried to guess.
>
> Any thoughts on ways to minimize the risk of injection locking via power
> supply connections? Am I right in thinking this is a genuine concern? I was
> hoping to place a couple Datum 1000Bs in an enclosure and power them all
> from the same AC/DC supply. Each would use separate LT3045 final
> regulators.
> Given the good PSRR of that regulator, I should be ok, I think. But I'm
> also
> curious about cases where the PSRR of the linear regulator cannot be relied
> upon. I suppose ferrite beads in the form of pi filters could be used, but
> ferrite beads generally aren't as effective at 10 MHz as they are at 100
> MHz. There are also DC power line filters, sold by Schaffner and others.
> These can be quite effective at
> 10 MHz. I suppose these could be used if really needed.
>
> Anyway, curious to hear thoughts and ideas. Thanks!
>
> Matt
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an
> email to time-nuts-leave@lists.febo.com
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe send an email to time-nuts-leave@lists.febo.com
>
BC
Bob Camp
Tue, Feb 20, 2024 1:25 PM
Hi
RF running back thru the supply lead is pretty unlikely. You have a lot of regulation and bypassing between the oscillator and other internals to that supply. If it worries you, put more bypass on the supply pins to the OCXO. You always should put some sort of simple bypass there when you wire things up.
RF looping through a common ground can always be a problem. That’s going to be a problem pretty much whatever you do. Handling that needs to be looked at as a separate issue.
Injection locking when running two OCXO’s into one device (like maybe a phase detector in a DMTD) is indeed quite possible. This is a signal coming right back through the RF output pin. The power supply really isn’t in the act. Isolation amplifiers are the answer here (and possibly other items like transformers and common mode chokes ….).
While we’re talking about wiring up OCXO’s and weird problems, here’s another one.It is a completely different issue that really isn’t injection locking at all (but is a form of locking ….):
OCXO heaters are a negative resistance. They pull more current as the voltage drops. This is the same thing as saying they are a constant power load. As we all know negative resistance is one of those things that you need to make an oscillator work …. hmmm …...
If you have a rack full of OCXO’s they pull more than a little bit of power, even after warmup.
Plug them all in through some (highly) questionable connectors and (badly frayed) wires. You get a bit of resistance between the supply and your rack of OCXO’s. Just how much resistance it’s going to take and how obvious those issues with the cables are ….. very much a “that depends” sort of thing
That combination can indeed get the whole rack full of OCXO’s swinging back and forth current wise. They will “oscillate” up and down at some sort of 10’s of seconds sort of period. The period is going to depend on the mass of the oven, some fiddly details about the thermal gain of the controller, and the amount of resistance involved.
If you have a current meter on your supply, it will be easy to spot. With just a voltage at the supply …. not so much. A good DVM on the rack of units will indeed spot what’s going on.
Simple answer is to attack the offending cables and connector with a hammer. (yes, remove them from the supply and rack first …). Then toss them in the trash. Once you put in proper cables …. problem solved.
If you don’t both destroy the cables and throw them away, they will somehow pop back up a few weeks later creating the same problem. I have data on this. Do they creep back and re-install themselves? Maybe they do …. :) :) :)
Is this a rare problem to run into? Sure it is. It’s not exactly easy to spot without that current meter ….
Fun !!!
Bob
On Feb 20, 2024, at 2:13 AM, Matt Huszagh via time-nuts time-nuts@lists.febo.com wrote:
To what extent is oscillator injection locking a risk when powering
multiple oscillators from the same power supply?
I measured a couple OCXOs to see how much of the output signal made its
way back into the power supply input. A Datum 1000B showed a 10 MHz
signal of -53 dBm for a +13 dBm output. A Wenzel 10 MHz ULN gave a
similar result. Curiously, the Wenzel showed much better isolation
(-74 dBm) with the output unterminated.
If we compare that to the reverse isolation of buffer/isolation
amplifiers, that seems to put the power supply isolation in the "ok"
territory, but possibly still a risk, depending on other characteristics
of the OCXO. Since the PSRR of many linear regulators is quite poor at
10 MHz (and even worse at higher typical OCXO frequencies), I would
expect using separate final regulators for each OCXO is probably only
slightly helpful. The same is probably true for the regulators internal
to the OCXOs themselves. There are exceptions to this, though. For
example, the LT3045 provides 50 dB PSRR at 10 MHz, assuming the layout
recommendations are followed.
I found Bruce's analysis page on injection locking
(http://www.ko4bb.com/~bruce/InjectionLocking.html) quite helpful in
this process. Unfortunately, I don't often know the Q factor of a given
OCXO or the amplitude of the tank circuit, so I just tried to guess.
Any thoughts on ways to minimize the risk of injection locking via power
supply connections? Am I right in thinking this is a genuine concern? I
was hoping to place a couple Datum 1000Bs in an enclosure and power them
all from the same AC/DC supply. Each would use separate LT3045 final
regulators. Given the good PSRR of that regulator, I should be ok, I
think. But I'm also curious about cases where the PSRR of the linear
regulator cannot be relied upon. I suppose ferrite beads in the form of
pi filters could be used, but ferrite beads generally aren't as
effective at 10 MHz as they are at 100 MHz. There are also DC power line
filters, sold by Schaffner and others. These can be quite effective at
10 MHz. I suppose these could be used if really needed.
Anyway, curious to hear thoughts and ideas. Thanks!
Matt
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Hi
RF running back thru the supply lead is pretty unlikely. You have a lot of regulation and bypassing between the oscillator and other internals to that supply. If it worries you, put more bypass on the supply pins to the OCXO. You always should put some sort of simple bypass there when you wire things up.
RF looping through a common ground can always be a problem. That’s going to be a problem pretty much whatever you do. Handling that needs to be looked at as a separate issue.
Injection locking when running two OCXO’s into one device (like maybe a phase detector in a DMTD) is indeed quite possible. This is a signal coming right back through the RF output pin. The power supply really isn’t in the act. Isolation amplifiers are the answer here (and possibly other items like transformers and common mode chokes ….).
While we’re talking about wiring up OCXO’s and weird problems, here’s another one.It is a completely different issue that really isn’t injection locking at all (but is a form of locking ….):
OCXO heaters are a negative resistance. They pull more current as the voltage drops. This is the same thing as saying they are a constant power load. As we all know negative resistance is one of those things that you need to make an oscillator work …. hmmm …...
If you have a rack full of OCXO’s they pull more than a little bit of power, even after warmup.
Plug them all in through some (highly) questionable connectors and (badly frayed) wires. You get a bit of resistance between the supply and your rack of OCXO’s. Just how much resistance it’s going to take and how obvious those issues with the cables are ….. very much a “that depends” sort of thing
That combination can indeed get the whole rack full of OCXO’s swinging back and forth current wise. They will “oscillate” up and down at some sort of 10’s of seconds sort of period. The period is going to depend on the mass of the oven, some fiddly details about the thermal gain of the controller, and the amount of resistance involved.
If you have a current meter on your supply, it will be easy to spot. With just a voltage at the supply …. not so much. A good DVM on the rack of units will indeed spot what’s going on.
Simple answer is to attack the offending cables and connector with a hammer. (yes, remove them from the supply and rack first …). Then toss them in the trash. Once you put in proper cables …. problem solved.
If you don’t both destroy the cables *and* throw them away, they will somehow pop back up a few weeks later creating the same problem. I have data on this. Do they creep back and re-install themselves? Maybe they do …. :) :) :)
Is this a rare problem to run into? Sure it is. It’s not exactly easy to spot without that current meter ….
Fun !!!
Bob
> On Feb 20, 2024, at 2:13 AM, Matt Huszagh via time-nuts <time-nuts@lists.febo.com> wrote:
>
> To what extent is oscillator injection locking a risk when powering
> multiple oscillators from the same power supply?
>
> I measured a couple OCXOs to see how much of the output signal made its
> way back into the power supply input. A Datum 1000B showed a 10 MHz
> signal of -53 dBm for a +13 dBm output. A Wenzel 10 MHz ULN gave a
> similar result. Curiously, the Wenzel showed much better isolation
> (-74 dBm) with the output unterminated.
>
> If we compare that to the reverse isolation of buffer/isolation
> amplifiers, that seems to put the power supply isolation in the "ok"
> territory, but possibly still a risk, depending on other characteristics
> of the OCXO. Since the PSRR of many linear regulators is quite poor at
> 10 MHz (and even worse at higher typical OCXO frequencies), I would
> expect using separate final regulators for each OCXO is probably only
> slightly helpful. The same is probably true for the regulators internal
> to the OCXOs themselves. There are exceptions to this, though. For
> example, the LT3045 provides 50 dB PSRR at 10 MHz, assuming the layout
> recommendations are followed.
>
> I found Bruce's analysis page on injection locking
> (http://www.ko4bb.com/~bruce/InjectionLocking.html) quite helpful in
> this process. Unfortunately, I don't often know the Q factor of a given
> OCXO or the amplitude of the tank circuit, so I just tried to guess.
>
> Any thoughts on ways to minimize the risk of injection locking via power
> supply connections? Am I right in thinking this is a genuine concern? I
> was hoping to place a couple Datum 1000Bs in an enclosure and power them
> all from the same AC/DC supply. Each would use separate LT3045 final
> regulators. Given the good PSRR of that regulator, I should be ok, I
> think. But I'm also curious about cases where the PSRR of the linear
> regulator cannot be relied upon. I suppose ferrite beads in the form of
> pi filters could be used, but ferrite beads generally aren't as
> effective at 10 MHz as they are at 100 MHz. There are also DC power line
> filters, sold by Schaffner and others. These can be quite effective at
> 10 MHz. I suppose these could be used if really needed.
>
> Anyway, curious to hear thoughts and ideas. Thanks!
>
> Matt
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe send an email to time-nuts-leave@lists.febo.com
JH
john.haine@haine-online.net
Thu, Feb 22, 2024 1:54 PM
Indeed, but remember that what seems to be "plenty of low pass filtering"
may not turn out as you intended. A series L will be capacitive above its
self-resonant frequency and shunt Cs inductive above theirs. Careful choice
of components and good layout is needed. Since what you are aiming for is
to reject a single frequency it can be better to focus the filter's
attenuation around that frequency.
-----Original Message-----
From: Andy Talbot via time-nuts time-nuts@lists.febo.com
Sent: Tuesday, February 20, 2024 10:32 AM
To: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com
Cc: Matt Huszagh huszaghmatt@gmail.com; john.haine@haine-online.net; Andy
Talbot andy.g4jnt@gmail.com
Subject: [time-nuts] Re: Injection locking via common power supply
Or just plenty of L/C low pass filtering in the supply rails Saves having to
tune a notch
Andy
www.g4jnt.com
On Tue, 20 Feb 2024 at 10:25, john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
How about putting a band-stop filter with a notch at the oscillator
frequency but passes DC in the supply to each oscillator, as close as
possible to the supply pin?
But I think you would need anyway to lay out the supply and ground
connections very carefully to make sure there isn't any signal
bypassing the filter.
John.
-----Original Message-----
From: Matt Huszagh via time-nuts time-nuts@lists.febo.com
Sent: Tuesday, February 20, 2024 7:13 AM
To: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com
Cc: Matt Huszagh huszaghmatt@gmail.com
Subject: [time-nuts] Injection locking via common power supply
To what extent is oscillator injection locking a risk when powering
multiple oscillators from the same power supply?
I measured a couple OCXOs to see how much of the output signal made
its way back into the power supply input. A Datum 1000B showed a 10
MHz signal of
-53 dBm for a +13 dBm output. A Wenzel 10 MHz ULN gave a similar result.
Curiously, the Wenzel showed much better isolation
(-74 dBm) with the output unterminated.
If we compare that to the reverse isolation of buffer/isolation
amplifiers, that seems to put the power supply isolation in the "ok"
territory, but possibly still a risk, depending on other
characteristics of the OCXO. Since the PSRR of many linear regulators
is quite poor at
10 MHz (and even worse at higher typical OCXO frequencies), I would
expect using separate final regulators for each OCXO is probably only
slightly helpful. The same is probably true for the regulators
internal to the OCXOs themselves. There are exceptions to this,
though. For example, the LT3045 provides 50 dB PSRR at 10 MHz,
assuming the layout recommendations are followed.
I found Bruce's analysis page on injection locking
(http://www.ko4bb.com/~bruce/InjectionLocking.html) quite helpful in
this process. Unfortunately, I don't often know the Q factor of a
given OCXO or the amplitude of the tank circuit, so I just tried to guess.
Any thoughts on ways to minimize the risk of injection locking via
power supply connections? Am I right in thinking this is a genuine
concern? I was hoping to place a couple Datum 1000Bs in an enclosure
and power them all from the same AC/DC supply. Each would use separate
LT3045 final regulators.
Given the good PSRR of that regulator, I should be ok, I think. But
I'm also curious about cases where the PSRR of the linear regulator
cannot be relied upon. I suppose ferrite beads in the form of pi
filters could be used, but ferrite beads generally aren't as effective
at 10 MHz as they are at 100 MHz. There are also DC power line
filters, sold by Schaffner and others.
These can be quite effective at
10 MHz. I suppose these could be used if really needed.
Anyway, curious to hear thoughts and ideas. Thanks!
Matt
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Indeed, but remember that what seems to be "plenty of low pass filtering"
may not turn out as you intended. A series L will be capacitive above its
self-resonant frequency and shunt Cs inductive above theirs. Careful choice
of components and good layout is needed. Since what you are aiming for is
to reject a single frequency it can be better to focus the filter's
attenuation around that frequency.
-----Original Message-----
From: Andy Talbot via time-nuts <time-nuts@lists.febo.com>
Sent: Tuesday, February 20, 2024 10:32 AM
To: Discussion of precise time and frequency measurement
<time-nuts@lists.febo.com>
Cc: Matt Huszagh <huszaghmatt@gmail.com>; john.haine@haine-online.net; Andy
Talbot <andy.g4jnt@gmail.com>
Subject: [time-nuts] Re: Injection locking via common power supply
Or just plenty of L/C low pass filtering in the supply rails Saves having to
tune a notch
Andy
www.g4jnt.com
On Tue, 20 Feb 2024 at 10:25, john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
> How about putting a band-stop filter with a notch at the oscillator
> frequency but passes DC in the supply to each oscillator, as close as
> possible to the supply pin?
>
> But I think you would need anyway to lay out the supply and ground
> connections very carefully to make sure there isn't any signal
> bypassing the filter.
>
> John.
>
> -----Original Message-----
> From: Matt Huszagh via time-nuts <time-nuts@lists.febo.com>
> Sent: Tuesday, February 20, 2024 7:13 AM
> To: Discussion of precise time and frequency measurement
> <time-nuts@lists.febo.com>
> Cc: Matt Huszagh <huszaghmatt@gmail.com>
> Subject: [time-nuts] Injection locking via common power supply
>
> To what extent is oscillator injection locking a risk when powering
> multiple oscillators from the same power supply?
>
> I measured a couple OCXOs to see how much of the output signal made
> its way back into the power supply input. A Datum 1000B showed a 10
> MHz signal of
> -53 dBm for a +13 dBm output. A Wenzel 10 MHz ULN gave a similar result.
> Curiously, the Wenzel showed much better isolation
> (-74 dBm) with the output unterminated.
>
> If we compare that to the reverse isolation of buffer/isolation
> amplifiers, that seems to put the power supply isolation in the "ok"
> territory, but possibly still a risk, depending on other
> characteristics of the OCXO. Since the PSRR of many linear regulators
> is quite poor at
> 10 MHz (and even worse at higher typical OCXO frequencies), I would
> expect using separate final regulators for each OCXO is probably only
> slightly helpful. The same is probably true for the regulators
> internal to the OCXOs themselves. There are exceptions to this,
> though. For example, the LT3045 provides 50 dB PSRR at 10 MHz,
> assuming the layout recommendations are followed.
>
> I found Bruce's analysis page on injection locking
> (http://www.ko4bb.com/~bruce/InjectionLocking.html) quite helpful in
> this process. Unfortunately, I don't often know the Q factor of a
> given OCXO or the amplitude of the tank circuit, so I just tried to guess.
>
> Any thoughts on ways to minimize the risk of injection locking via
> power supply connections? Am I right in thinking this is a genuine
> concern? I was hoping to place a couple Datum 1000Bs in an enclosure
> and power them all from the same AC/DC supply. Each would use separate
> LT3045 final regulators.
> Given the good PSRR of that regulator, I should be ok, I think. But
> I'm also curious about cases where the PSRR of the linear regulator
> cannot be relied upon. I suppose ferrite beads in the form of pi
> filters could be used, but ferrite beads generally aren't as effective
> at 10 MHz as they are at 100 MHz. There are also DC power line
> filters, sold by Schaffner and others.
> These can be quite effective at
> 10 MHz. I suppose these could be used if really needed.
>
> Anyway, curious to hear thoughts and ideas. Thanks!
>
> Matt
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send
> an email to time-nuts-leave@lists.febo.com
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send
> an email to time-nuts-leave@lists.febo.com
>
_______________________________________________
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email to time-nuts-leave@lists.febo.com
BC
Bob Camp
Thu, Feb 22, 2024 3:43 PM
Hi
A very normal way to do this is with decent ferrite beads / cores. Yes, they will be a bit bulky if you don’t want them to saturate. You also need to get the right material for your target frequency range. Since they are going to be resistive over the “target frequency range” there is very little concern about resonance.
If your capacitor is down in the < 10 mili ohm range, a bead that provides “only” 10 ohms would give you > 60 db of attenuation.
Since you also want a low source resistance for your supply, the “zero impact” of an add on bead / core has other advantages as well.
Bob
On Feb 22, 2024, at 8:54 AM, john.haine--- via time-nuts time-nuts@lists.febo.com wrote:
Indeed, but remember that what seems to be "plenty of low pass filtering"
may not turn out as you intended. A series L will be capacitive above its
self-resonant frequency and shunt Cs inductive above theirs. Careful choice
of components and good layout is needed. Since what you are aiming for is
to reject a single frequency it can be better to focus the filter's
attenuation around that frequency.
-----Original Message-----
From: Andy Talbot via time-nuts time-nuts@lists.febo.com
Sent: Tuesday, February 20, 2024 10:32 AM
To: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com
Cc: Matt Huszagh huszaghmatt@gmail.com; john.haine@haine-online.net; Andy
Talbot andy.g4jnt@gmail.com
Subject: [time-nuts] Re: Injection locking via common power supply
Or just plenty of L/C low pass filtering in the supply rails Saves having to
tune a notch
Andy
www.g4jnt.com
On Tue, 20 Feb 2024 at 10:25, john.haine--- via time-nuts <
time-nuts@lists.febo.com> wrote:
How about putting a band-stop filter with a notch at the oscillator
frequency but passes DC in the supply to each oscillator, as close as
possible to the supply pin?
But I think you would need anyway to lay out the supply and ground
connections very carefully to make sure there isn't any signal
bypassing the filter.
John.
-----Original Message-----
From: Matt Huszagh via time-nuts time-nuts@lists.febo.com
Sent: Tuesday, February 20, 2024 7:13 AM
To: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com
Cc: Matt Huszagh huszaghmatt@gmail.com
Subject: [time-nuts] Injection locking via common power supply
To what extent is oscillator injection locking a risk when powering
multiple oscillators from the same power supply?
I measured a couple OCXOs to see how much of the output signal made
its way back into the power supply input. A Datum 1000B showed a 10
MHz signal of
-53 dBm for a +13 dBm output. A Wenzel 10 MHz ULN gave a similar result.
Curiously, the Wenzel showed much better isolation
(-74 dBm) with the output unterminated.
If we compare that to the reverse isolation of buffer/isolation
amplifiers, that seems to put the power supply isolation in the "ok"
territory, but possibly still a risk, depending on other
characteristics of the OCXO. Since the PSRR of many linear regulators
is quite poor at
10 MHz (and even worse at higher typical OCXO frequencies), I would
expect using separate final regulators for each OCXO is probably only
slightly helpful. The same is probably true for the regulators
internal to the OCXOs themselves. There are exceptions to this,
though. For example, the LT3045 provides 50 dB PSRR at 10 MHz,
assuming the layout recommendations are followed.
I found Bruce's analysis page on injection locking
(http://www.ko4bb.com/~bruce/InjectionLocking.html) quite helpful in
this process. Unfortunately, I don't often know the Q factor of a
given OCXO or the amplitude of the tank circuit, so I just tried to guess.
Any thoughts on ways to minimize the risk of injection locking via
power supply connections? Am I right in thinking this is a genuine
concern? I was hoping to place a couple Datum 1000Bs in an enclosure
and power them all from the same AC/DC supply. Each would use separate
LT3045 final regulators.
Given the good PSRR of that regulator, I should be ok, I think. But
I'm also curious about cases where the PSRR of the linear regulator
cannot be relied upon. I suppose ferrite beads in the form of pi
filters could be used, but ferrite beads generally aren't as effective
at 10 MHz as they are at 100 MHz. There are also DC power line
filters, sold by Schaffner and others.
These can be quite effective at
10 MHz. I suppose these could be used if really needed.
Anyway, curious to hear thoughts and ideas. Thanks!
Matt
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send
an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send
an email to time-nuts-leave@lists.febo.com
Hi
A very normal way to do this is with decent ferrite beads / cores. Yes, they will be a bit bulky if you don’t want them to saturate. You also need to get the right material for your target frequency range. Since they are going to be resistive over the “target frequency range” there is very little concern about resonance.
If your capacitor is down in the < 10 mili ohm range, a bead that provides “only” 10 ohms would give you > 60 db of attenuation.
Since you also want a low source resistance for your supply, the “zero impact” of an add on bead / core has other advantages as well.
Bob
> On Feb 22, 2024, at 8:54 AM, john.haine--- via time-nuts <time-nuts@lists.febo.com> wrote:
>
> Indeed, but remember that what seems to be "plenty of low pass filtering"
> may not turn out as you intended. A series L will be capacitive above its
> self-resonant frequency and shunt Cs inductive above theirs. Careful choice
> of components and good layout is needed. Since what you are aiming for is
> to reject a single frequency it can be better to focus the filter's
> attenuation around that frequency.
>
> -----Original Message-----
> From: Andy Talbot via time-nuts <time-nuts@lists.febo.com>
> Sent: Tuesday, February 20, 2024 10:32 AM
> To: Discussion of precise time and frequency measurement
> <time-nuts@lists.febo.com>
> Cc: Matt Huszagh <huszaghmatt@gmail.com>; john.haine@haine-online.net; Andy
> Talbot <andy.g4jnt@gmail.com>
> Subject: [time-nuts] Re: Injection locking via common power supply
>
> Or just plenty of L/C low pass filtering in the supply rails Saves having to
> tune a notch
>
> Andy
> www.g4jnt.com
>
>
>
> On Tue, 20 Feb 2024 at 10:25, john.haine--- via time-nuts <
> time-nuts@lists.febo.com> wrote:
>
>> How about putting a band-stop filter with a notch at the oscillator
>> frequency but passes DC in the supply to each oscillator, as close as
>> possible to the supply pin?
>>
>> But I think you would need anyway to lay out the supply and ground
>> connections very carefully to make sure there isn't any signal
>> bypassing the filter.
>>
>> John.
>>
>> -----Original Message-----
>> From: Matt Huszagh via time-nuts <time-nuts@lists.febo.com>
>> Sent: Tuesday, February 20, 2024 7:13 AM
>> To: Discussion of precise time and frequency measurement
>> <time-nuts@lists.febo.com>
>> Cc: Matt Huszagh <huszaghmatt@gmail.com>
>> Subject: [time-nuts] Injection locking via common power supply
>>
>> To what extent is oscillator injection locking a risk when powering
>> multiple oscillators from the same power supply?
>>
>> I measured a couple OCXOs to see how much of the output signal made
>> its way back into the power supply input. A Datum 1000B showed a 10
>> MHz signal of
>> -53 dBm for a +13 dBm output. A Wenzel 10 MHz ULN gave a similar result.
>> Curiously, the Wenzel showed much better isolation
>> (-74 dBm) with the output unterminated.
>>
>> If we compare that to the reverse isolation of buffer/isolation
>> amplifiers, that seems to put the power supply isolation in the "ok"
>> territory, but possibly still a risk, depending on other
>> characteristics of the OCXO. Since the PSRR of many linear regulators
>> is quite poor at
>> 10 MHz (and even worse at higher typical OCXO frequencies), I would
>> expect using separate final regulators for each OCXO is probably only
>> slightly helpful. The same is probably true for the regulators
>> internal to the OCXOs themselves. There are exceptions to this,
>> though. For example, the LT3045 provides 50 dB PSRR at 10 MHz,
>> assuming the layout recommendations are followed.
>>
>> I found Bruce's analysis page on injection locking
>> (http://www.ko4bb.com/~bruce/InjectionLocking.html) quite helpful in
>> this process. Unfortunately, I don't often know the Q factor of a
>> given OCXO or the amplitude of the tank circuit, so I just tried to guess.
>>
>> Any thoughts on ways to minimize the risk of injection locking via
>> power supply connections? Am I right in thinking this is a genuine
>> concern? I was hoping to place a couple Datum 1000Bs in an enclosure
>> and power them all from the same AC/DC supply. Each would use separate
>> LT3045 final regulators.
>> Given the good PSRR of that regulator, I should be ok, I think. But
>> I'm also curious about cases where the PSRR of the linear regulator
>> cannot be relied upon. I suppose ferrite beads in the form of pi
>> filters could be used, but ferrite beads generally aren't as effective
>> at 10 MHz as they are at 100 MHz. There are also DC power line
>> filters, sold by Schaffner and others.
>> These can be quite effective at
>> 10 MHz. I suppose these could be used if really needed.
>>
>> Anyway, curious to hear thoughts and ideas. Thanks!
>>
>> Matt
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send
>> an email to time-nuts-leave@lists.febo.com
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send
>> an email to time-nuts-leave@lists.febo.com
>>
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an
> email to time-nuts-leave@lists.febo.com
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe send an email to time-nuts-leave@lists.febo.com
