Empathy List Archives

PM

Peter McCollum

Wed, Jan 15, 2025 2:52 AM

Just curious if this is normal behavior.
I use an X-Y display to show a Lissajous of my CW12-TIM module vs a fairly
stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz.
The CW12's output gives an (apparently) very solid output averaged over
many seconds or longer.
But in the short term, the Lissajous does a "breathing" behavior - every 3
or 4 seconds (it's variable), the pattern expands a few degrees in one
direction, then goes back in the other direction. It's NOT a sudden jump,
rather it is very much like watching someone's lungs taking a breath then
letting it out.

Is it normal, or does it imply that the "discipline" in the GPSDO is
repeatedly needing a correction?

Thanks for any comments!

Pete

Just curious if this is normal behavior. I use an X-Y display to show a Lissajous of my CW12-TIM module vs a fairly stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz. The CW12's output gives an (apparently) very solid output averaged over many seconds or longer. But in the short term, the Lissajous does a "breathing" behavior - every 3 or 4 seconds (it's variable), the pattern expands a few degrees in one direction, then goes back in the other direction. It's NOT a sudden jump, rather it is very much like watching someone's lungs taking a breath then letting it out. Is it normal, or does it imply that the "discipline" in the GPSDO is repeatedly needing a correction? Thanks for any comments! Pete

AB

Azelio Boriani

Wed, Jan 15, 2025 7:57 AM

The CW12-TIM is not a GPSDO, the frequency output is not disciplined, it
is, like the PPS, derived from the division of the free running internal
clock, driving the divisor (someway: added/skipped cycles) to align it with
the GPS. To mitigate the "breathing" there should be a sort of sawtooth
correction also for the frequency output (not possible for that speed).

On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts <
time-nuts@lists.febo.com> wrote:

Just curious if this is normal behavior.
I use an X-Y display to show a Lissajous of my CW12-TIM module vs a fairly
stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz.
The CW12's output gives an (apparently) very solid output averaged over
many seconds or longer.
But in the short term, the Lissajous does a "breathing" behavior - every 3
or 4 seconds (it's variable), the pattern expands a few degrees in one
direction, then goes back in the other direction. It's NOT a sudden jump,
rather it is very much like watching someone's lungs taking a breath then
letting it out.

Is it normal, or does it imply that the "discipline" in the GPSDO is
repeatedly needing a correction?

Thanks for any comments!

Pete

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

The CW12-TIM is not a GPSDO, the frequency output is not disciplined, it is, like the PPS, derived from the division of the free running internal clock, driving the divisor (someway: added/skipped cycles) to align it with the GPS. To mitigate the "breathing" there should be a sort of sawtooth correction also for the frequency output (not possible for that speed). On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts < time-nuts@lists.febo.com> wrote: > Just curious if this is normal behavior. > I use an X-Y display to show a Lissajous of my CW12-TIM module vs a fairly > stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz. > The CW12's output gives an (apparently) very solid output averaged over > many seconds or longer. > But in the short term, the Lissajous does a "breathing" behavior - every 3 > or 4 seconds (it's variable), the pattern expands a few degrees in one > direction, then goes back in the other direction. It's NOT a sudden jump, > rather it is very much like watching someone's lungs taking a breath then > letting it out. > > Is it normal, or does it imply that the "discipline" in the GPSDO is > repeatedly needing a correction? > > Thanks for any comments! > > Pete > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com >

PM

Peter McCollum

Wed, Jan 15, 2025 2:19 PM

Azelio wrote:

The CW12-TIM is not a GPSDO

From the CW12-TIM manual:
"The graph below demonstrates the ability of the CW12-TIM GPS to continue
to provide a GPS disciplined output
frequency with the GPS aerial located completely inside a building..."

Is it just a matter of semantics, or is there a firm definition of
"disciplined"?

Pete

On Wed, Jan 15, 2025 at 3:01 AM Azelio Boriani via time-nuts <
time-nuts@lists.febo.com> wrote:

The CW12-TIM is not a GPSDO, the frequency output is not disciplined, it
is, like the PPS, derived from the division of the free running internal
clock, driving the divisor (someway: added/skipped cycles) to align it with
the GPS. To mitigate the "breathing" there should be a sort of sawtooth
correction also for the frequency output (not possible for that speed).

On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts <
time-nuts@lists.febo.com> wrote:

Just curious if this is normal behavior.
I use an X-Y display to show a Lissajous of my CW12-TIM module vs a

fairly

stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz.
The CW12's output gives an (apparently) very solid output averaged over
many seconds or longer.
But in the short term, the Lissajous does a "breathing" behavior - every

3

or 4 seconds (it's variable), the pattern expands a few degrees in one
direction, then goes back in the other direction. It's NOT a sudden jump,
rather it is very much like watching someone's lungs taking a breath then
letting it out.

Is it normal, or does it imply that the "discipline" in the GPSDO is
repeatedly needing a correction?

Thanks for any comments!

Pete

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Azelio wrote: >The CW12-TIM is not a GPSDO From the CW12-TIM manual: "The graph below demonstrates the ability of the CW12-TIM GPS to continue to provide a GPS disciplined output frequency with the GPS aerial located completely inside a building..." Is it just a matter of semantics, or is there a firm definition of "disciplined"? Pete On Wed, Jan 15, 2025 at 3:01 AM Azelio Boriani via time-nuts < time-nuts@lists.febo.com> wrote: > The CW12-TIM is not a GPSDO, the frequency output is not disciplined, it > is, like the PPS, derived from the division of the free running internal > clock, driving the divisor (someway: added/skipped cycles) to align it with > the GPS. To mitigate the "breathing" there should be a sort of sawtooth > correction also for the frequency output (not possible for that speed). > > On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts < > time-nuts@lists.febo.com> wrote: > > > Just curious if this is normal behavior. > > I use an X-Y display to show a Lissajous of my CW12-TIM module vs a > fairly > > stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz. > > The CW12's output gives an (apparently) very solid output averaged over > > many seconds or longer. > > But in the short term, the Lissajous does a "breathing" behavior - every > 3 > > or 4 seconds (it's variable), the pattern expands a few degrees in one > > direction, then goes back in the other direction. It's NOT a sudden jump, > > rather it is very much like watching someone's lungs taking a breath then > > letting it out. > > > > Is it normal, or does it imply that the "discipline" in the GPSDO is > > repeatedly needing a correction? > > > > Thanks for any comments! > > > > Pete > > _______________________________________________ > > 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

R

rbenward@verizon.net

Wed, Jan 15, 2025 4:57 PM

Hi Pete,
Can you provide a picture of your Lissajous pattern? The Lissajous reflects
the phase of two signals. You use the term "breathing". As long as the
pattern does not collapse, you remain within 1Hz of the "reference" signal.
Once the signal collapses to a thin line, unless there is momentum in a
particular direction, you cannot tell if the drift has stopped and moved in
the other direction. If you never reach the collapse, you are within 1
cycle (not Hz!). If your pattern is going from a circle to an ellipse, and
back and forth it simply means your signal is drifting back and forth around
the reference.

If you are rolling over once a seconds, you are within 1Hz.
If you are rolling over once every ten seconds, you are within 1/10Hz.
100sec, 0.01Hz, etc...

Bob

-----Original Message-----
From: Peter McCollum via time-nuts time-nuts@lists.febo.com
Sent: Tuesday, January 14, 2025 9:52 PM
To: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com
Cc: Peter McCollum saipan1959@gmail.com
Subject: [time-nuts] GPSDO "breathing" behavior
Importance: High

Just curious if this is normal behavior.
I use an X-Y display to show a Lissajous of my CW12-TIM module vs a fairly
stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz.
The CW12's output gives an (apparently) very solid output averaged over many
seconds or longer.
But in the short term, the Lissajous does a "breathing" behavior - every 3
or 4 seconds (it's variable), the pattern expands a few degrees in one
direction, then goes back in the other direction. It's NOT a sudden jump,
rather it is very much like watching someone's lungs taking a breath then
letting it out.

Is it normal, or does it imply that the "discipline" in the GPSDO is
repeatedly needing a correction?

Thanks for any comments!

Pete

time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an
email to time-nuts-leave@lists.febo.com

Hi Pete, Can you provide a picture of your Lissajous pattern? The Lissajous reflects the phase of two signals. You use the term "breathing". As long as the pattern does not collapse, you remain within 1Hz of the "reference" signal. Once the signal collapses to a thin line, unless there is momentum in a particular direction, you cannot tell if the drift has stopped and moved in the other direction. If you never reach the collapse, you are within 1 cycle (not Hz!). If your pattern is going from a circle to an ellipse, and back and forth it simply means your signal is drifting back and forth around the reference. If you are rolling over once a seconds, you are within 1Hz. If you are rolling over once every ten seconds, you are within 1/10Hz. 100sec, 0.01Hz, etc... Bob -----Original Message----- From: Peter McCollum via time-nuts <time-nuts@lists.febo.com> Sent: Tuesday, January 14, 2025 9:52 PM To: Discussion of precise time and frequency measurement <time-nuts@lists.febo.com> Cc: Peter McCollum <saipan1959@gmail.com> Subject: [time-nuts] GPSDO "breathing" behavior Importance: High Just curious if this is normal behavior. I use an X-Y display to show a Lissajous of my CW12-TIM module vs a fairly stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz. The CW12's output gives an (apparently) very solid output averaged over many seconds or longer. But in the short term, the Lissajous does a "breathing" behavior - every 3 or 4 seconds (it's variable), the pattern expands a few degrees in one direction, then goes back in the other direction. It's NOT a sudden jump, rather it is very much like watching someone's lungs taking a breath then letting it out. Is it normal, or does it imply that the "discipline" in the GPSDO is repeatedly needing a correction? Thanks for any comments! Pete _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com

AB

Azelio Boriani

Wed, Jan 15, 2025 5:34 PM

If it is the credit card sized board of the CW12, then it cannot be a
disciplined oscillator time-nuts vise.

Here what Ed Palmer wrote on Sat Jun 26 2010 on this list about the
frequency output of the CW12:

Another GPS board with a 10 MHz output is the Navsync CW-12 module
(price ~US$85-90). I measured the 1 PPS output and found a Standard
Deviation of < 5 ns with a range of < 30 ns. The 10 MHz output is kept
on frequency by occasionally adjusting the period of the 10 MHz output
by one cycle of the CPU clock (~8.3 ns = 120 MHz). How often this
happens depends on the exact clock frequency of the particular unit. On
mine it happens about 200 times per second.

On Wed, Jan 15, 2025 at 5:51 PM Peter McCollum via time-nuts <
time-nuts@lists.febo.com> wrote:

Azelio wrote:

The CW12-TIM is not a GPSDO

From the CW12-TIM manual:
"The graph below demonstrates the ability of the CW12-TIM GPS to continue
to provide a GPS disciplined output
frequency with the GPS aerial located completely inside a building..."

Is it just a matter of semantics, or is there a firm definition of
"disciplined"?

Pete

On Wed, Jan 15, 2025 at 3:01 AM Azelio Boriani via time-nuts <
time-nuts@lists.febo.com> wrote:

The CW12-TIM is not a GPSDO, the frequency output is not disciplined, it
is, like the PPS, derived from the division of the free running internal
clock, driving the divisor (someway: added/skipped cycles) to align it

with

the GPS. To mitigate the "breathing" there should be a sort of sawtooth
correction also for the frequency output (not possible for that speed).

On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts <
time-nuts@lists.febo.com> wrote:

Just curious if this is normal behavior.
I use an X-Y display to show a Lissajous of my CW12-TIM module vs a

fairly

stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz.
The CW12's output gives an (apparently) very solid output averaged over
many seconds or longer.
But in the short term, the Lissajous does a "breathing" behavior -

every

3

or 4 seconds (it's variable), the pattern expands a few degrees in one
direction, then goes back in the other direction. It's NOT a sudden

jump,

rather it is very much like watching someone's lungs taking a breath

then

letting it out.

Is it normal, or does it imply that the "discipline" in the GPSDO is
repeatedly needing a correction?

Thanks for any comments!

Pete

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

If it is the credit card sized board of the CW12, then it cannot be a disciplined oscillator time-nuts vise. Here what Ed Palmer wrote on Sat Jun 26 2010 on this list about the frequency output of the CW12: Another GPS board with a 10 MHz output is the Navsync CW-12 module (price ~US$85-90). I measured the 1 PPS output and found a Standard Deviation of < 5 ns with a range of < 30 ns. The 10 MHz output is kept on frequency by occasionally adjusting the period of the 10 MHz output by one cycle of the CPU clock (~8.3 ns = 120 MHz). How often this happens depends on the exact clock frequency of the particular unit. On mine it happens about 200 times per second. On Wed, Jan 15, 2025 at 5:51 PM Peter McCollum via time-nuts < time-nuts@lists.febo.com> wrote: > Azelio wrote: > >The CW12-TIM is not a GPSDO > > From the CW12-TIM manual: > "The graph below demonstrates the ability of the CW12-TIM GPS to continue > to provide a GPS disciplined output > frequency with the GPS aerial located completely inside a building..." > > Is it just a matter of semantics, or is there a firm definition of > "disciplined"? > > Pete > > > > On Wed, Jan 15, 2025 at 3:01 AM Azelio Boriani via time-nuts < > time-nuts@lists.febo.com> wrote: > > > The CW12-TIM is not a GPSDO, the frequency output is not disciplined, it > > is, like the PPS, derived from the division of the free running internal > > clock, driving the divisor (someway: added/skipped cycles) to align it > with > > the GPS. To mitigate the "breathing" there should be a sort of sawtooth > > correction also for the frequency output (not possible for that speed). > > > > On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts < > > time-nuts@lists.febo.com> wrote: > > > > > Just curious if this is normal behavior. > > > I use an X-Y display to show a Lissajous of my CW12-TIM module vs a > > fairly > > > stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz. > > > The CW12's output gives an (apparently) very solid output averaged over > > > many seconds or longer. > > > But in the short term, the Lissajous does a "breathing" behavior - > every > > 3 > > > or 4 seconds (it's variable), the pattern expands a few degrees in one > > > direction, then goes back in the other direction. It's NOT a sudden > jump, > > > rather it is very much like watching someone's lungs taking a breath > then > > > letting it out. > > > > > > Is it normal, or does it imply that the "discipline" in the GPSDO is > > > repeatedly needing a correction? > > > > > > Thanks for any comments! > > > > > > Pete > > > _______________________________________________ > > > 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

BC

Bob Camp

Wed, Jan 15, 2025 7:29 PM

Hi

GPSDO = GPS Disciplined Oscilator

They have:

A GPS module of some sort
A control loop that also acts as a noise filter
An independent oscillator that the control loop manages.

With just the module you are missing 2 and 3.

GPS modules have provided “chopped up” output signals for at least two decades and closer to three.
What they provide is not the same thing as what a GPSDO delivers.

Bob

On Jan 15, 2025, at 9:19 AM, Peter McCollum via time-nuts time-nuts@lists.febo.com wrote:

Azelio wrote:

The CW12-TIM is not a GPSDO

From the CW12-TIM manual:
"The graph below demonstrates the ability of the CW12-TIM GPS to continue
to provide a GPS disciplined output
frequency with the GPS aerial located completely inside a building..."

Is it just a matter of semantics, or is there a firm definition of
"disciplined"?

Pete

On Wed, Jan 15, 2025 at 3:01 AM Azelio Boriani via time-nuts <
time-nuts@lists.febo.com> wrote:

The CW12-TIM is not a GPSDO, the frequency output is not disciplined, it
is, like the PPS, derived from the division of the free running internal
clock, driving the divisor (someway: added/skipped cycles) to align it with
the GPS. To mitigate the "breathing" there should be a sort of sawtooth
correction also for the frequency output (not possible for that speed).

On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts <
time-nuts@lists.febo.com> wrote:

Just curious if this is normal behavior.
I use an X-Y display to show a Lissajous of my CW12-TIM module vs a

fairly

stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz.
The CW12's output gives an (apparently) very solid output averaged over
many seconds or longer.
But in the short term, the Lissajous does a "breathing" behavior - every

3

or 4 seconds (it's variable), the pattern expands a few degrees in one
direction, then goes back in the other direction. It's NOT a sudden jump,
rather it is very much like watching someone's lungs taking a breath then
letting it out.

Is it normal, or does it imply that the "discipline" in the GPSDO is
repeatedly needing a correction?

Thanks for any comments!

Pete

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Hi GPSDO = GPS Disciplined Oscilator They have: 1) A GPS module of some sort 2) A control loop that also acts as a noise filter 3) An independent oscillator that the control loop manages. With just the module you are missing 2 and 3. GPS modules have provided “chopped up” output signals for at least two decades and closer to three. What they provide is not the same thing as what a GPSDO delivers. Bob > On Jan 15, 2025, at 9:19 AM, Peter McCollum via time-nuts <time-nuts@lists.febo.com> wrote: > > Azelio wrote: >> The CW12-TIM is not a GPSDO > > From the CW12-TIM manual: > "The graph below demonstrates the ability of the CW12-TIM GPS to continue > to provide a GPS disciplined output > frequency with the GPS aerial located completely inside a building..." > > Is it just a matter of semantics, or is there a firm definition of > "disciplined"? > > Pete > > > > On Wed, Jan 15, 2025 at 3:01 AM Azelio Boriani via time-nuts < > time-nuts@lists.febo.com> wrote: > >> The CW12-TIM is not a GPSDO, the frequency output is not disciplined, it >> is, like the PPS, derived from the division of the free running internal >> clock, driving the divisor (someway: added/skipped cycles) to align it with >> the GPS. To mitigate the "breathing" there should be a sort of sawtooth >> correction also for the frequency output (not possible for that speed). >> >> On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts < >> time-nuts@lists.febo.com> wrote: >> >>> Just curious if this is normal behavior. >>> I use an X-Y display to show a Lissajous of my CW12-TIM module vs a >> fairly >>> stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz. >>> The CW12's output gives an (apparently) very solid output averaged over >>> many seconds or longer. >>> But in the short term, the Lissajous does a "breathing" behavior - every >> 3 >>> or 4 seconds (it's variable), the pattern expands a few degrees in one >>> direction, then goes back in the other direction. It's NOT a sudden jump, >>> rather it is very much like watching someone's lungs taking a breath then >>> letting it out. >>> >>> Is it normal, or does it imply that the "discipline" in the GPSDO is >>> repeatedly needing a correction? >>> >>> Thanks for any comments! >>> >>> Pete >>> _______________________________________________ >>> 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

PM

Peter McCollum

Wed, Jan 15, 2025 9:06 PM

Thanks for the comments so far folks! I am definitely NOT questioning
anyone's expertise, but I remain somewhat confused about the assertion that
the CW12-TIM is "not a GPSDO". If not, then what is it? It obviously
"disciplines an oscillator" in some way (see data below).

To clarify the "breathing" behavior:
Attached is a pic of the Lissajous, comparing the Sulzer vs the CW12-TIM
outputs, both at 1 Mhz. I have adjusted the fine-tuning on the Sulzer such
that the ellipse gradually changes shape over a period of many minutes.
BUT, over a period of perhaps 3 or 4 seconds, the ellipse goes back and
forth between the two versions shown in the picture. As I mentioned before,
it is NOT a sudden change, but rather looks like a lung expanding and
contracting somewhat.
I interpret that to mean that there is a temporary change in freq,
lasting less than 0.5 seconds or so, then the freq does the same thing in
the opposite direction, and the ellipse is back to it's original
shape/size. In the time frame of (say) a minute or two, there is NO overall
change to the ellipse.
This behavior is only seen with the CW12-TIM output - if I compare the
Sulzer against something else that is "pretty stable" (such as an HP
5345A), I don't see the "breathing".

Another data point:
If I power up the CW12-TIM with its antenna shielded to limit its access to
GPS signals, the Lissajous "rotates" at a rate of perhaps 1.5-2 Hz (out of
1 Mhz). Then, as soon as it starts to acquire sats, the Lissajous stops
moving... The datasheet says that the freq output is reliable when it has a
2-D solution.

Also attached is two pages from the CW12-TIM docs.
Is that NOT describing a "true GPSDO" ?
I see that the doc says "full PCR MTIE performance", although I certainly
don't understand the implications of that statement...

Pete

On Wed, Jan 15, 2025 at 1:06 PM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:

Hi

GPSDO = GPS Disciplined Oscilator

They have:

A GPS module of some sort
A control loop that also acts as a noise filter
An independent oscillator that the control loop manages.

With just the module you are missing 2 and 3.

GPS modules have provided “chopped up” output signals for at least two
decades and closer to three.
What they provide is not the same thing as what a GPSDO delivers.

Bob

On Jan 15, 2025, at 9:19 AM, Peter McCollum via time-nuts <

time-nuts@lists.febo.com> wrote:

Azelio wrote:

The CW12-TIM is not a GPSDO

From the CW12-TIM manual:
"The graph below demonstrates the ability of the CW12-TIM GPS to continue
to provide a GPS disciplined output
frequency with the GPS aerial located completely inside a building..."

Is it just a matter of semantics, or is there a firm definition of
"disciplined"?

Pete

On Wed, Jan 15, 2025 at 3:01 AM Azelio Boriani via time-nuts <
time-nuts@lists.febo.com> wrote:

The CW12-TIM is not a GPSDO, the frequency output is not disciplined, it
is, like the PPS, derived from the division of the free running internal
clock, driving the divisor (someway: added/skipped cycles) to align it

with

the GPS. To mitigate the "breathing" there should be a sort of sawtooth
correction also for the frequency output (not possible for that speed).

On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts <
time-nuts@lists.febo.com> wrote:

Just curious if this is normal behavior.
I use an X-Y display to show a Lissajous of my CW12-TIM module vs a

fairly

stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz.
The CW12's output gives an (apparently) very solid output averaged over
many seconds or longer.
But in the short term, the Lissajous does a "breathing" behavior -

every

3

or 4 seconds (it's variable), the pattern expands a few degrees in one
direction, then goes back in the other direction. It's NOT a sudden

jump,

rather it is very much like watching someone's lungs taking a breath

then

letting it out.

Is it normal, or does it imply that the "discipline" in the GPSDO is
repeatedly needing a correction?

Thanks for any comments!

Pete

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Thanks for the comments so far folks! I am definitely NOT questioning anyone's expertise, but I remain somewhat confused about the assertion that the CW12-TIM is "not a GPSDO". If not, then what is it? It obviously "disciplines an oscillator" in some way (see data below). To clarify the "breathing" behavior: Attached is a pic of the Lissajous, comparing the Sulzer vs the CW12-TIM outputs, both at 1 Mhz. I have adjusted the fine-tuning on the Sulzer such that the ellipse gradually changes shape over a period of many minutes. BUT, over a period of perhaps 3 or 4 seconds, the ellipse goes back and forth between the two versions shown in the picture. As I mentioned before, it is NOT a sudden change, but rather looks like a lung expanding and contracting somewhat. I interpret that to mean that there is a *temporary* change in freq, lasting less than 0.5 seconds or so, then the freq does the same thing in the opposite direction, and the ellipse is back to it's original shape/size. In the time frame of (say) a minute or two, there is NO overall change to the ellipse. This behavior is only seen with the CW12-TIM output - if I compare the Sulzer against something else that is "pretty stable" (such as an HP 5345A), I don't see the "breathing". Another data point: If I power up the CW12-TIM with its antenna shielded to limit its access to GPS signals, the Lissajous "rotates" at a rate of perhaps 1.5-2 Hz (out of 1 Mhz). Then, as soon as it starts to acquire sats, the Lissajous stops moving... The datasheet says that the freq output is reliable when it has a 2-D solution. Also attached is two pages from the CW12-TIM docs. Is that NOT describing a "true GPSDO" ? I see that the doc says "full PCR MTIE performance", although I certainly don't understand the implications of that statement... Pete On Wed, Jan 15, 2025 at 1:06 PM Bob Camp via time-nuts < time-nuts@lists.febo.com> wrote: > Hi > > GPSDO = GPS Disciplined Oscilator > > They have: > > 1) A GPS module of some sort > > 2) A control loop that also acts as a noise filter > > 3) An independent oscillator that the control loop manages. > > With just the module you are missing 2 and 3. > > GPS modules have provided “chopped up” output signals for at least two > decades and closer to three. > What they provide is not the same thing as what a GPSDO delivers. > > Bob > > > On Jan 15, 2025, at 9:19 AM, Peter McCollum via time-nuts < > time-nuts@lists.febo.com> wrote: > > > > Azelio wrote: > >> The CW12-TIM is not a GPSDO > > > > From the CW12-TIM manual: > > "The graph below demonstrates the ability of the CW12-TIM GPS to continue > > to provide a GPS disciplined output > > frequency with the GPS aerial located completely inside a building..." > > > > Is it just a matter of semantics, or is there a firm definition of > > "disciplined"? > > > > Pete > > > > > > > > On Wed, Jan 15, 2025 at 3:01 AM Azelio Boriani via time-nuts < > > time-nuts@lists.febo.com> wrote: > > > >> The CW12-TIM is not a GPSDO, the frequency output is not disciplined, it > >> is, like the PPS, derived from the division of the free running internal > >> clock, driving the divisor (someway: added/skipped cycles) to align it > with > >> the GPS. To mitigate the "breathing" there should be a sort of sawtooth > >> correction also for the frequency output (not possible for that speed). > >> > >> On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts < > >> time-nuts@lists.febo.com> wrote: > >> > >>> Just curious if this is normal behavior. > >>> I use an X-Y display to show a Lissajous of my CW12-TIM module vs a > >> fairly > >>> stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz. > >>> The CW12's output gives an (apparently) very solid output averaged over > >>> many seconds or longer. > >>> But in the short term, the Lissajous does a "breathing" behavior - > every > >> 3 > >>> or 4 seconds (it's variable), the pattern expands a few degrees in one > >>> direction, then goes back in the other direction. It's NOT a sudden > jump, > >>> rather it is very much like watching someone's lungs taking a breath > then > >>> letting it out. > >>> > >>> Is it normal, or does it imply that the "discipline" in the GPSDO is > >>> repeatedly needing a correction? > >>> > >>> Thanks for any comments! > >>> > >>> Pete > >>> _______________________________________________ > >>> 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

BC

Bob Camp

Wed, Jan 15, 2025 10:41 PM

Hi

What the modules do both on the PPS and on their other signals is to “dither” an internal oscillator.
The oscillator is not tuned to frequency. It free runs at some independent frequency (and phase).
The edges of the output are shifted from time to time to drop or add one period of the internal
oscillator.

This is not the same thing as tuning the oscillator on frequency. That’s why the “disciplining” term
is important in “GPSDO”.

Bob

On Jan 15, 2025, at 4:06 PM, Peter McCollum via time-nuts time-nuts@lists.febo.com wrote:

Thanks for the comments so far folks! I am definitely NOT questioning
anyone's expertise, but I remain somewhat confused about the assertion that
the CW12-TIM is "not a GPSDO". If not, then what is it? It obviously
"disciplines an oscillator" in some way (see data below).

To clarify the "breathing" behavior:
Attached is a pic of the Lissajous, comparing the Sulzer vs the CW12-TIM
outputs, both at 1 Mhz. I have adjusted the fine-tuning on the Sulzer such
that the ellipse gradually changes shape over a period of many minutes.
BUT, over a period of perhaps 3 or 4 seconds, the ellipse goes back and
forth between the two versions shown in the picture. As I mentioned before,
it is NOT a sudden change, but rather looks like a lung expanding and
contracting somewhat.
I interpret that to mean that there is a temporary change in freq,
lasting less than 0.5 seconds or so, then the freq does the same thing in
the opposite direction, and the ellipse is back to it's original
shape/size. In the time frame of (say) a minute or two, there is NO overall
change to the ellipse.
This behavior is only seen with the CW12-TIM output - if I compare the
Sulzer against something else that is "pretty stable" (such as an HP
5345A), I don't see the "breathing".

Another data point:
If I power up the CW12-TIM with its antenna shielded to limit its access to
GPS signals, the Lissajous "rotates" at a rate of perhaps 1.5-2 Hz (out of
1 Mhz). Then, as soon as it starts to acquire sats, the Lissajous stops
moving... The datasheet says that the freq output is reliable when it has a
2-D solution.

Also attached is two pages from the CW12-TIM docs.
Is that NOT describing a "true GPSDO" ?
I see that the doc says "full PCR MTIE performance", although I certainly
don't understand the implications of that statement...

Pete

On Wed, Jan 15, 2025 at 1:06 PM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:

Hi

GPSDO = GPS Disciplined Oscilator

They have:

A GPS module of some sort
A control loop that also acts as a noise filter
An independent oscillator that the control loop manages.

With just the module you are missing 2 and 3.

GPS modules have provided “chopped up” output signals for at least two
decades and closer to three.
What they provide is not the same thing as what a GPSDO delivers.

Bob

On Jan 15, 2025, at 9:19 AM, Peter McCollum via time-nuts <

time-nuts@lists.febo.com> wrote:

Azelio wrote:

The CW12-TIM is not a GPSDO

From the CW12-TIM manual:
"The graph below demonstrates the ability of the CW12-TIM GPS to continue
to provide a GPS disciplined output
frequency with the GPS aerial located completely inside a building..."

Is it just a matter of semantics, or is there a firm definition of
"disciplined"?

Pete

On Wed, Jan 15, 2025 at 3:01 AM Azelio Boriani via time-nuts <
time-nuts@lists.febo.com> wrote:

The CW12-TIM is not a GPSDO, the frequency output is not disciplined, it
is, like the PPS, derived from the division of the free running internal
clock, driving the divisor (someway: added/skipped cycles) to align it

with

the GPS. To mitigate the "breathing" there should be a sort of sawtooth
correction also for the frequency output (not possible for that speed).

On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts <
time-nuts@lists.febo.com> wrote:

Just curious if this is normal behavior.
I use an X-Y display to show a Lissajous of my CW12-TIM module vs a

fairly

stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz.
The CW12's output gives an (apparently) very solid output averaged over
many seconds or longer.
But in the short term, the Lissajous does a "breathing" behavior -

every

3

or 4 seconds (it's variable), the pattern expands a few degrees in one
direction, then goes back in the other direction. It's NOT a sudden

jump,

rather it is very much like watching someone's lungs taking a breath

then

letting it out.

Is it normal, or does it imply that the "discipline" in the GPSDO is
repeatedly needing a correction?

Thanks for any comments!

Pete

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

<Lissajous.JPG><p2.jpg><p1.jpg>_______________________________________________
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Hi What the modules do both on the PPS and on their other signals is to “dither” an internal oscillator. The oscillator is *not* tuned to frequency. It free runs at some independent frequency (and phase). The edges of the output are shifted from time to time to drop or add one period of the internal oscillator. This is not the same thing as tuning the oscillator on frequency. That’s why the “disciplining” term is important in “GPSDO”. Bob > On Jan 15, 2025, at 4:06 PM, Peter McCollum via time-nuts <time-nuts@lists.febo.com> wrote: > > Thanks for the comments so far folks! I am definitely NOT questioning > anyone's expertise, but I remain somewhat confused about the assertion that > the CW12-TIM is "not a GPSDO". If not, then what is it? It obviously > "disciplines an oscillator" in some way (see data below). > > To clarify the "breathing" behavior: > Attached is a pic of the Lissajous, comparing the Sulzer vs the CW12-TIM > outputs, both at 1 Mhz. I have adjusted the fine-tuning on the Sulzer such > that the ellipse gradually changes shape over a period of many minutes. > BUT, over a period of perhaps 3 or 4 seconds, the ellipse goes back and > forth between the two versions shown in the picture. As I mentioned before, > it is NOT a sudden change, but rather looks like a lung expanding and > contracting somewhat. > I interpret that to mean that there is a *temporary* change in freq, > lasting less than 0.5 seconds or so, then the freq does the same thing in > the opposite direction, and the ellipse is back to it's original > shape/size. In the time frame of (say) a minute or two, there is NO overall > change to the ellipse. > This behavior is only seen with the CW12-TIM output - if I compare the > Sulzer against something else that is "pretty stable" (such as an HP > 5345A), I don't see the "breathing". > > Another data point: > If I power up the CW12-TIM with its antenna shielded to limit its access to > GPS signals, the Lissajous "rotates" at a rate of perhaps 1.5-2 Hz (out of > 1 Mhz). Then, as soon as it starts to acquire sats, the Lissajous stops > moving... The datasheet says that the freq output is reliable when it has a > 2-D solution. > > Also attached is two pages from the CW12-TIM docs. > Is that NOT describing a "true GPSDO" ? > I see that the doc says "full PCR MTIE performance", although I certainly > don't understand the implications of that statement... > > Pete > > > > On Wed, Jan 15, 2025 at 1:06 PM Bob Camp via time-nuts < > time-nuts@lists.febo.com> wrote: > >> Hi >> >> GPSDO = GPS Disciplined Oscilator >> >> They have: >> >> 1) A GPS module of some sort >> >> 2) A control loop that also acts as a noise filter >> >> 3) An independent oscillator that the control loop manages. >> >> With just the module you are missing 2 and 3. >> >> GPS modules have provided “chopped up” output signals for at least two >> decades and closer to three. >> What they provide is not the same thing as what a GPSDO delivers. >> >> Bob >> >>> On Jan 15, 2025, at 9:19 AM, Peter McCollum via time-nuts < >> time-nuts@lists.febo.com> wrote: >>> >>> Azelio wrote: >>>> The CW12-TIM is not a GPSDO >>> >>> From the CW12-TIM manual: >>> "The graph below demonstrates the ability of the CW12-TIM GPS to continue >>> to provide a GPS disciplined output >>> frequency with the GPS aerial located completely inside a building..." >>> >>> Is it just a matter of semantics, or is there a firm definition of >>> "disciplined"? >>> >>> Pete >>> >>> >>> >>> On Wed, Jan 15, 2025 at 3:01 AM Azelio Boriani via time-nuts < >>> time-nuts@lists.febo.com> wrote: >>> >>>> The CW12-TIM is not a GPSDO, the frequency output is not disciplined, it >>>> is, like the PPS, derived from the division of the free running internal >>>> clock, driving the divisor (someway: added/skipped cycles) to align it >> with >>>> the GPS. To mitigate the "breathing" there should be a sort of sawtooth >>>> correction also for the frequency output (not possible for that speed). >>>> >>>> On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts < >>>> time-nuts@lists.febo.com> wrote: >>>> >>>>> Just curious if this is normal behavior. >>>>> I use an X-Y display to show a Lissajous of my CW12-TIM module vs a >>>> fairly >>>>> stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz. >>>>> The CW12's output gives an (apparently) very solid output averaged over >>>>> many seconds or longer. >>>>> But in the short term, the Lissajous does a "breathing" behavior - >> every >>>> 3 >>>>> or 4 seconds (it's variable), the pattern expands a few degrees in one >>>>> direction, then goes back in the other direction. It's NOT a sudden >> jump, >>>>> rather it is very much like watching someone's lungs taking a breath >> then >>>>> letting it out. >>>>> >>>>> Is it normal, or does it imply that the "discipline" in the GPSDO is >>>>> repeatedly needing a correction? >>>>> >>>>> Thanks for any comments! >>>>> >>>>> Pete >>>>> _______________________________________________ >>>>> 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 > <Lissajous.JPG><p2.jpg><p1.jpg>_______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

TV

Thomas Valerio

Thu, Jan 16, 2025 3:38 AM

I am probably one of the least qualified members on this list to comment.
HOWEVER, I think that the the fact that the CW12-TIM is meant to be a
((an) almost, maybe exact or better) drop in replacement for a Motorola
M12+, which by design has NEVER been or ASSERTED to be ANYTHING other than
only the GPS module for a GPSDO or frequency standard should be a MAJOR
clue. Just my $.02

Thomas Valerio

Thanks for the comments so far folks! I am definitely NOT questioning
anyone's expertise, but I remain somewhat confused about the assertion
that
the CW12-TIM is "not a GPSDO". If not, then what is it? It obviously
"disciplines an oscillator" in some way (see data below).

To clarify the "breathing" behavior:
Attached is a pic of the Lissajous, comparing the Sulzer vs the CW12-TIM
outputs, both at 1 Mhz. I have adjusted the fine-tuning on the Sulzer such
that the ellipse gradually changes shape over a period of many minutes.
BUT, over a period of perhaps 3 or 4 seconds, the ellipse goes back and
forth between the two versions shown in the picture. As I mentioned
before,
it is NOT a sudden change, but rather looks like a lung expanding and
contracting somewhat.
I interpret that to mean that there is a temporary change in freq,
lasting less than 0.5 seconds or so, then the freq does the same thing in
the opposite direction, and the ellipse is back to it's original
shape/size. In the time frame of (say) a minute or two, there is NO
overall
change to the ellipse.
This behavior is only seen with the CW12-TIM output - if I compare the
Sulzer against something else that is "pretty stable" (such as an HP
5345A), I don't see the "breathing".

Another data point:
If I power up the CW12-TIM with its antenna shielded to limit its access
to
GPS signals, the Lissajous "rotates" at a rate of perhaps 1.5-2 Hz (out of
1 Mhz). Then, as soon as it starts to acquire sats, the Lissajous stops
moving... The datasheet says that the freq output is reliable when it has
a
2-D solution.

Also attached is two pages from the CW12-TIM docs.
Is that NOT describing a "true GPSDO" ?
I see that the doc says "full PCR MTIE performance", although I certainly
don't understand the implications of that statement...

Pete

On Wed, Jan 15, 2025 at 1:06â¯PM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:

Hi

GPSDO = GPS Disciplined Oscilator

They have:

A GPS module of some sort
A control loop that also acts as a noise filter
An independent oscillator that the control loop manages.

With just the module you are missing 2 and 3.

GPS modules have provided âchopped upâ output signals for at least
two
decades and closer to three.
What they provide is not the same thing as what a GPSDO delivers.

Bob

On Jan 15, 2025, at 9:19â¯AM, Peter McCollum via time-nuts <

time-nuts@lists.febo.com> wrote:

Azelio wrote:

The CW12-TIM is not a GPSDO

From the CW12-TIM manual:
"The graph below demonstrates the ability of the CW12-TIM GPS to

continue

to provide a GPS disciplined output
frequency with the GPS aerial located completely inside a building..."

Is it just a matter of semantics, or is there a firm definition of
"disciplined"?

Pete

On Wed, Jan 15, 2025 at 3:01â¯AM Azelio Boriani via time-nuts <
time-nuts@lists.febo.com> wrote:

The CW12-TIM is not a GPSDO, the frequency output is not disciplined,

it

is, like the PPS, derived from the division of the free running

internal

clock, driving the divisor (someway: added/skipped cycles) to align

it
with

the GPS. To mitigate the "breathing" there should be a sort of

sawtooth

correction also for the frequency output (not possible for that

speed).

On Wed, Jan 15, 2025 at 8:32â¯AM Peter McCollum via time-nuts <
time-nuts@lists.febo.com> wrote:

Just curious if this is normal behavior.
I use an X-Y display to show a Lissajous of my CW12-TIM module vs a

fairly

stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz.
The CW12's output gives an (apparently) very solid output averaged

over

many seconds or longer.
But in the short term, the Lissajous does a "breathing" behavior -

every

3

or 4 seconds (it's variable), the pattern expands a few degrees in

one

direction, then goes back in the other direction. It's NOT a sudden

jump,

rather it is very much like watching someone's lungs taking a breath

then

letting it out.

Is it normal, or does it imply that the "discipline" in the GPSDO is
repeatedly needing a correction?

Thanks for any comments!

Pete

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

I am probably one of the least qualified members on this list to comment. HOWEVER, I think that the the fact that the CW12-TIM is meant to be a ((an) almost, maybe exact or better) drop in replacement for a Motorola M12+, which by design has NEVER been or ASSERTED to be ANYTHING other than only the GPS module for a GPSDO or frequency standard should be a MAJOR clue. Just my $.02 Thomas Valerio > Thanks for the comments so far folks! I am definitely NOT questioning > anyone's expertise, but I remain somewhat confused about the assertion > that > the CW12-TIM is "not a GPSDO". If not, then what is it? It obviously > "disciplines an oscillator" in some way (see data below). > > To clarify the "breathing" behavior: > Attached is a pic of the Lissajous, comparing the Sulzer vs the CW12-TIM > outputs, both at 1 Mhz. I have adjusted the fine-tuning on the Sulzer such > that the ellipse gradually changes shape over a period of many minutes. > BUT, over a period of perhaps 3 or 4 seconds, the ellipse goes back and > forth between the two versions shown in the picture. As I mentioned > before, > it is NOT a sudden change, but rather looks like a lung expanding and > contracting somewhat. > I interpret that to mean that there is a *temporary* change in freq, > lasting less than 0.5 seconds or so, then the freq does the same thing in > the opposite direction, and the ellipse is back to it's original > shape/size. In the time frame of (say) a minute or two, there is NO > overall > change to the ellipse. > This behavior is only seen with the CW12-TIM output - if I compare the > Sulzer against something else that is "pretty stable" (such as an HP > 5345A), I don't see the "breathing". > > Another data point: > If I power up the CW12-TIM with its antenna shielded to limit its access > to > GPS signals, the Lissajous "rotates" at a rate of perhaps 1.5-2 Hz (out of > 1 Mhz). Then, as soon as it starts to acquire sats, the Lissajous stops > moving... The datasheet says that the freq output is reliable when it has > a > 2-D solution. > > Also attached is two pages from the CW12-TIM docs. > Is that NOT describing a "true GPSDO" ? > I see that the doc says "full PCR MTIE performance", although I certainly > don't understand the implications of that statement... > > Pete > > > > On Wed, Jan 15, 2025 at 1:06â¯PM Bob Camp via time-nuts < > time-nuts@lists.febo.com> wrote: > >> Hi >> >> GPSDO = GPS Disciplined Oscilator >> >> They have: >> >> 1) A GPS module of some sort >> >> 2) A control loop that also acts as a noise filter >> >> 3) An independent oscillator that the control loop manages. >> >> With just the module you are missing 2 and 3. >> >> GPS modules have provided âchopped upâ output signals for at least >> two >> decades and closer to three. >> What they provide is not the same thing as what a GPSDO delivers. >> >> Bob >> >> > On Jan 15, 2025, at 9:19â¯AM, Peter McCollum via time-nuts < >> time-nuts@lists.febo.com> wrote: >> > >> > Azelio wrote: >> >> The CW12-TIM is not a GPSDO >> > >> > From the CW12-TIM manual: >> > "The graph below demonstrates the ability of the CW12-TIM GPS to >> continue >> > to provide a GPS disciplined output >> > frequency with the GPS aerial located completely inside a building..." >> > >> > Is it just a matter of semantics, or is there a firm definition of >> > "disciplined"? >> > >> > Pete >> > >> > >> > >> > On Wed, Jan 15, 2025 at 3:01â¯AM Azelio Boriani via time-nuts < >> > time-nuts@lists.febo.com> wrote: >> > >> >> The CW12-TIM is not a GPSDO, the frequency output is not disciplined, >> it >> >> is, like the PPS, derived from the division of the free running >> internal >> >> clock, driving the divisor (someway: added/skipped cycles) to align >> it >> with >> >> the GPS. To mitigate the "breathing" there should be a sort of >> sawtooth >> >> correction also for the frequency output (not possible for that >> speed). >> >> >> >> On Wed, Jan 15, 2025 at 8:32â¯AM Peter McCollum via time-nuts < >> >> time-nuts@lists.febo.com> wrote: >> >> >> >>> Just curious if this is normal behavior. >> >>> I use an X-Y display to show a Lissajous of my CW12-TIM module vs a >> >> fairly >> >>> stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz. >> >>> The CW12's output gives an (apparently) very solid output averaged >> over >> >>> many seconds or longer. >> >>> But in the short term, the Lissajous does a "breathing" behavior - >> every >> >> 3 >> >>> or 4 seconds (it's variable), the pattern expands a few degrees in >> one >> >>> direction, then goes back in the other direction. It's NOT a sudden >> jump, >> >>> rather it is very much like watching someone's lungs taking a breath >> then >> >>> letting it out. >> >>> >> >>> Is it normal, or does it imply that the "discipline" in the GPSDO is >> >>> repeatedly needing a correction? >> >>> >> >>> Thanks for any comments! >> >>> >> >>> Pete >> >>> _______________________________________________ >> >>> 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 > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

R

rbenward@verizon.net

Thu, Jan 16, 2025 4:56 PM

Hi Bob,
I agree with you, you don't "tune" the oscillator. To expand, the NCO has two parts, the oscillator, and the numerical control. The NCO is a very long digital divider, with single or multiple loops. The oscillator can be at any high frequency, and the NCO "tuning" is what gives you the span of 10Hz to 10MHz.

The oscillator will drift, but the processor will adjust the output by "tuning" the NCO. The tuning is simply writing new digital values to the NCO. I assume, whether the oscillator is built in to the NCO or separate, it's a tiny little oscillator, probably not even a TCXO. So, it drifts, again, I assume for the most part, in one direction. The processor will then periodically (1PPS) adjust the NCO before the phase rolls over. The oscillator, NCO, and the processor form what looks very much like a frequency synthesizer.

You mentioned "disciplining". Isn't that more of a processor disciplining? The processor learns the drift, and when in hold over, continues to adjust the EFC to zero the anticipated drift? Is the prediction function active when the 1PPS is available, or only when in holdover? Maybe it's all semantics!

Bob B

-----Original Message-----
From: Bob Camp via time-nuts time-nuts@lists.febo.com
Sent: Wednesday, January 15, 2025 5:41 PM
To: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Cc: Bob Camp kb8tq@n1k.org
Subject: [time-nuts] Re: GPSDO "breathing" behavior
Importance: High

Hi

What the modules do both on the PPS and on their other signals is to “dither” an internal oscillator.
The oscillator is not tuned to frequency. It free runs at some independent frequency (and phase).
The edges of the output are shifted from time to time to drop or add one period of the internal oscillator.

This is not the same thing as tuning the oscillator on frequency. That’s why the “disciplining” term is important in “GPSDO”.

Bob

On Jan 15, 2025, at 4:06 PM, Peter McCollum via time-nuts time-nuts@lists.febo.com wrote:

Thanks for the comments so far folks! I am definitely NOT questioning
anyone's expertise, but I remain somewhat confused about the assertion
that the CW12-TIM is "not a GPSDO". If not, then what is it? It
obviously "disciplines an oscillator" in some way (see data below).

To clarify the "breathing" behavior:
Attached is a pic of the Lissajous, comparing the Sulzer vs the
CW12-TIM outputs, both at 1 Mhz. I have adjusted the fine-tuning on
the Sulzer such that the ellipse gradually changes shape over a period of many minutes.
BUT, over a period of perhaps 3 or 4 seconds, the ellipse goes back
and forth between the two versions shown in the picture. As I
mentioned before, it is NOT a sudden change, but rather looks like a
lung expanding and contracting somewhat.
I interpret that to mean that there is a temporary change in freq,
lasting less than 0.5 seconds or so, then the freq does the same thing
in the opposite direction, and the ellipse is back to it's original
shape/size. In the time frame of (say) a minute or two, there is NO
overall change to the ellipse.
This behavior is only seen with the CW12-TIM output - if I compare the
Sulzer against something else that is "pretty stable" (such as an HP
5345A), I don't see the "breathing".

Another data point:
If I power up the CW12-TIM with its antenna shielded to limit its
access to GPS signals, the Lissajous "rotates" at a rate of perhaps
1.5-2 Hz (out of
1 Mhz). Then, as soon as it starts to acquire sats, the Lissajous
stops moving... The datasheet says that the freq output is reliable
when it has a 2-D solution.

Also attached is two pages from the CW12-TIM docs.
Is that NOT describing a "true GPSDO" ?
I see that the doc says "full PCR MTIE performance", although I
certainly don't understand the implications of that statement...

Pete

On Wed, Jan 15, 2025 at 1:06 PM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:

Hi

GPSDO = GPS Disciplined Oscilator

They have:

A GPS module of some sort
A control loop that also acts as a noise filter
An independent oscillator that the control loop manages.

With just the module you are missing 2 and 3.

GPS modules have provided “chopped up” output signals for at least
two decades and closer to three.
What they provide is not the same thing as what a GPSDO delivers.

Bob

On Jan 15, 2025, at 9:19 AM, Peter McCollum via time-nuts <

time-nuts@lists.febo.com> wrote:

Azelio wrote:

The CW12-TIM is not a GPSDO

From the CW12-TIM manual:
"The graph below demonstrates the ability of the CW12-TIM GPS to
continue to provide a GPS disciplined output frequency with the GPS
aerial located completely inside a building..."

Is it just a matter of semantics, or is there a firm definition of
"disciplined"?

Pete

On Wed, Jan 15, 2025 at 3:01 AM Azelio Boriani via time-nuts <
time-nuts@lists.febo.com> wrote:

The CW12-TIM is not a GPSDO, the frequency output is not
disciplined, it is, like the PPS, derived from the division of the
free running internal clock, driving the divisor (someway:
added/skipped cycles) to align it

with

the GPS. To mitigate the "breathing" there should be a sort of
sawtooth correction also for the frequency output (not possible for that speed).

On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts <
time-nuts@lists.febo.com> wrote:

Just curious if this is normal behavior.
I use an X-Y display to show a Lissajous of my CW12-TIM module vs
a

fairly

stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz.
The CW12's output gives an (apparently) very solid output averaged
over many seconds or longer.
But in the short term, the Lissajous does a "breathing" behavior -

every

3

or 4 seconds (it's variable), the pattern expands a few degrees in
one direction, then goes back in the other direction. It's NOT a
sudden

jump,

rather it is very much like watching someone's lungs taking a
breath

then

letting it out.

Is it normal, or does it imply that the "discipline" in the GPSDO
is repeatedly needing a correction?

Thanks for any comments!

Pete

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Hi Bob, I agree with you, you don't "tune" the oscillator. To expand, the NCO has two parts, the oscillator, and the numerical control. The NCO is a very long digital divider, with single or multiple loops. The oscillator can be at any high frequency, and the NCO "tuning" is what gives you the span of 10Hz to 10MHz. The oscillator will drift, but the processor will adjust the output by "tuning" the NCO. The tuning is simply writing new digital values to the NCO. I assume, whether the oscillator is built in to the NCO or separate, it's a tiny little oscillator, probably not even a TCXO. So, it drifts, again, I assume for the most part, in one direction. The processor will then periodically (1PPS) adjust the NCO before the phase rolls over. The oscillator, NCO, and the processor form what looks very much like a frequency synthesizer. You mentioned "disciplining". Isn't that more of a processor disciplining? The processor learns the drift, and when in hold over, continues to adjust the EFC to zero the anticipated drift? Is the prediction function active when the 1PPS is available, or only when in holdover? Maybe it's all semantics! Bob B -----Original Message----- From: Bob Camp via time-nuts <time-nuts@lists.febo.com> Sent: Wednesday, January 15, 2025 5:41 PM To: Discussion of precise time and frequency measurement <time-nuts@lists.febo.com> Cc: Bob Camp <kb8tq@n1k.org> Subject: [time-nuts] Re: GPSDO "breathing" behavior Importance: High Hi What the modules do both on the PPS and on their other signals is to “dither” an internal oscillator. The oscillator is *not* tuned to frequency. It free runs at some independent frequency (and phase). The edges of the output are shifted from time to time to drop or add one period of the internal oscillator. This is not the same thing as tuning the oscillator on frequency. That’s why the “disciplining” term is important in “GPSDO”. Bob > On Jan 15, 2025, at 4:06 PM, Peter McCollum via time-nuts <time-nuts@lists.febo.com> wrote: > > Thanks for the comments so far folks! I am definitely NOT questioning > anyone's expertise, but I remain somewhat confused about the assertion > that the CW12-TIM is "not a GPSDO". If not, then what is it? It > obviously "disciplines an oscillator" in some way (see data below). > > To clarify the "breathing" behavior: > Attached is a pic of the Lissajous, comparing the Sulzer vs the > CW12-TIM outputs, both at 1 Mhz. I have adjusted the fine-tuning on > the Sulzer such that the ellipse gradually changes shape over a period of many minutes. > BUT, over a period of perhaps 3 or 4 seconds, the ellipse goes back > and forth between the two versions shown in the picture. As I > mentioned before, it is NOT a sudden change, but rather looks like a > lung expanding and contracting somewhat. > I interpret that to mean that there is a *temporary* change in freq, > lasting less than 0.5 seconds or so, then the freq does the same thing > in the opposite direction, and the ellipse is back to it's original > shape/size. In the time frame of (say) a minute or two, there is NO > overall change to the ellipse. > This behavior is only seen with the CW12-TIM output - if I compare the > Sulzer against something else that is "pretty stable" (such as an HP > 5345A), I don't see the "breathing". > > Another data point: > If I power up the CW12-TIM with its antenna shielded to limit its > access to GPS signals, the Lissajous "rotates" at a rate of perhaps > 1.5-2 Hz (out of > 1 Mhz). Then, as soon as it starts to acquire sats, the Lissajous > stops moving... The datasheet says that the freq output is reliable > when it has a 2-D solution. > > Also attached is two pages from the CW12-TIM docs. > Is that NOT describing a "true GPSDO" ? > I see that the doc says "full PCR MTIE performance", although I > certainly don't understand the implications of that statement... > > Pete > > > > On Wed, Jan 15, 2025 at 1:06 PM Bob Camp via time-nuts < > time-nuts@lists.febo.com> wrote: > >> Hi >> >> GPSDO = GPS Disciplined Oscilator >> >> They have: >> >> 1) A GPS module of some sort >> >> 2) A control loop that also acts as a noise filter >> >> 3) An independent oscillator that the control loop manages. >> >> With just the module you are missing 2 and 3. >> >> GPS modules have provided “chopped up” output signals for at least >> two decades and closer to three. >> What they provide is not the same thing as what a GPSDO delivers. >> >> Bob >> >>> On Jan 15, 2025, at 9:19 AM, Peter McCollum via time-nuts < >> time-nuts@lists.febo.com> wrote: >>> >>> Azelio wrote: >>>> The CW12-TIM is not a GPSDO >>> >>> From the CW12-TIM manual: >>> "The graph below demonstrates the ability of the CW12-TIM GPS to >>> continue to provide a GPS disciplined output frequency with the GPS >>> aerial located completely inside a building..." >>> >>> Is it just a matter of semantics, or is there a firm definition of >>> "disciplined"? >>> >>> Pete >>> >>> >>> >>> On Wed, Jan 15, 2025 at 3:01 AM Azelio Boriani via time-nuts < >>> time-nuts@lists.febo.com> wrote: >>> >>>> The CW12-TIM is not a GPSDO, the frequency output is not >>>> disciplined, it is, like the PPS, derived from the division of the >>>> free running internal clock, driving the divisor (someway: >>>> added/skipped cycles) to align it >> with >>>> the GPS. To mitigate the "breathing" there should be a sort of >>>> sawtooth correction also for the frequency output (not possible for that speed). >>>> >>>> On Wed, Jan 15, 2025 at 8:32 AM Peter McCollum via time-nuts < >>>> time-nuts@lists.febo.com> wrote: >>>> >>>>> Just curious if this is normal behavior. >>>>> I use an X-Y display to show a Lissajous of my CW12-TIM module vs >>>>> a >>>> fairly >>>>> stable oscillator (Sulzer 5A, or Spectracom 8161), all at 1 MHz. >>>>> The CW12's output gives an (apparently) very solid output averaged >>>>> over many seconds or longer. >>>>> But in the short term, the Lissajous does a "breathing" behavior - >> every >>>> 3 >>>>> or 4 seconds (it's variable), the pattern expands a few degrees in >>>>> one direction, then goes back in the other direction. It's NOT a >>>>> sudden >> jump, >>>>> rather it is very much like watching someone's lungs taking a >>>>> breath >> then >>>>> letting it out. >>>>> >>>>> Is it normal, or does it imply that the "discipline" in the GPSDO >>>>> is repeatedly needing a correction? >>>>> >>>>> Thanks for any comments! >>>>> >>>>> Pete >>>>> _______________________________________________ >>>>> 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 > <Lissajous.JPG><p2.jpg><p1.jpg>_______________________________________ > ________ 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