Re: [time-nuts] World's most precise.... wall clock

[Tom Van Baak]

> In tboltmon, the signal "strength" indications are displayed in units
> called 'AMU' for which I've been unable to find a definition.

Amplitude Measurement Units? There was a discussion about this some 
years ago. The TBolt (and other Trimble receivers) give a user the 
choice of reported GPS signal level in either AMU or dBc units. Mark 
Sims (Heather author) collected data using both units to create a 
cross-reference. I've attached his data (file: 
2010-Sims-TBolt-AMU-dBc.zip).


His reply from 2010 is here:

> From: "Mark Sims" 
> To: 
> Sent: Saturday, February 13, 2010 8:48 AM
> Subject: [time-nuts] Thunderbolt AMU to dBc conversion
>
> The data was collected in 0.1 dB / AMU steps. There was a lot of noise
> in the raw data (maybe ± 1 dB or AMU), but the general trend of the
> curve was quite distinct. I smoothed it out by hand and filled in a few
> (maybe 15) of the missing steps that had no signal.
>
> The 0.1 resolution of the raw data causes the piecewise linear steps in
> the data. I was going to run a smoothing filter over it, but the curve
> is pretty good as-is (especially considering how it was generated).
>
> Heather now uses a table lookup from 0.0 to 25.5 AMU with a linear
> approximation over 25.5 AMU to convert AMU values to dBc values when
> drawing the signal level map if the receiver is in AMU mode. The plots
> collected in AMU mode and dBc mode are virtually indistinguishable
> (within the normal variation seen between two different runs in dBc 
mode).


The entire thread is worth reading from the archives. [1] [2]

See also table 7.3 on page 124 of:

ftp://geodesy.noaa.gov/pub/abilich/papers/ABilichThesis.pdf

/tvb

[1] https://www.febo.com/pipermail/time-nuts/2010-February/044968.html

[2] 
http://lists.febo.com/pipermail/time-nuts_lists.febo.com/2010-February/027397.html


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Re: [time-nuts] World's most precise.... wall clock

[Björn]

Sent from my iPhone

> On 10 Mar 2021, at 15:54, Dana 
> 
> I have convinced myself that the PPS output from my Tbolt is derived from
> the produced
> 10 MHz output, because if I trigger an o'scope from the PPS output, the 10
> MHz sinewave
> shows very little time jitter, perhaps 1 or 2 nsec.  So, I'm pretty happy
> with the T'bolt, with
> two (minor) exceptions:
> 
>> Its RF sensitivity seems rather poor compared to that of "modern"
> receivers (my unit
>was apparently made in the early 2000s).
> 
>> In tboltmon, the signal "strength" indications are displayed in units
> called 'AMU',
>for which I've been unable to find a definition.
> 
> Dana
>> 

Dana,

The Tbolt is different from most GPSDOs in that the 10MHz clocks the whole 
receiver. So there is no sawtooth error to correct for. Read the manual.

It is less sensitive, as was receivers from that manufacturer and age. Look in 
the manual what gain is expected at the antenna port.

AMU - “a mostly meaningless unit” is how I was described it from an industry 
insider. Note that you can change the unit to SNR if you want. Then SNR is also 
not always comparable  between manufacturers and models.

Kind regards,

  Björn 

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Re: [time-nuts] World's most precise.... wall clock

[Magnus Danielson]

Hi,

On 2021-03-11 00:38, Bob kb8tq wrote:
> Hi
>
>> On Mar 10, 2021, at 4:57 PM, Magnus Danielson  wrote:
>>
>> Hi,
>>
>> On 2021-03-10 17:04, Bob kb8tq wrote:
>>> Hi
>>>
 On Mar 10, 2021, at 9:39 AM, Charlie  wrote:

 Bob-

 As a rank amateur e astronomer, I am a  lurker. I am amazed at what I have
 learned here. I know that there are differences between the meaning of
 precision and accuracy, but please correct my understanding if I am
 imprecise.

 I have a need for precise time, as all sorts of calculations are dependent
 on precise geocentric position, and of course time to convert to other 
 times
 e.g. sidereal, utc, etc., as related to the motion control of a large
 telescope.

 I have an old hp z3805a; seems to be really precise, agreeing with my
 location (surveyed). Other gps's that I have seem to wander more.
>>> I suspect that is a function of how the 3805 presents the data. 
>>>
 My question is thus: It seems that procuring a more precise PPS/time output
 unit is quite a bit more costly than what I have; even more costly is a 
 unit
 that has both more precise PPS/time output, and a really stable 10 Mhz
 output ( I might add that I am a Ham, where 1 uhz  error is detrimental).
>>> Sub ns *jitter* is doing well at 1 second with GPS. Accuracy is different 
>>> than jitter. Since the GPS clock is not a direct expression of UTC from 
>>> BIH ( nothing is … sorry about that …) there is some back tracking to get
>>> *very* accurate time. 
>>>
 Assuming I can afford an upgrade, would  getting a more precise PPS/time
 unit then and feed that data into separate OCXO? Getting both seems out of
 my league.
>>> If you have the $300 to $2000 for a multi band GNSS timing receiver, it 
>>> will 
>>> indeed help a bit. How much will depend a lot on the state of the 
>>> ionosphere 
>>> and the correction process. Troposphere also gets into things. I don’t know 
>>> of
>>> any receiver that directly estimates Tropo delay. 
>> There is means to infer Tropo-delay with single receivers, but it is not
>> very accurate that I've seen. However, the usual way is to use nearby
>> receivers as reference. Eventually as the actual position is known,
>> tropo errors can be inferred more directly for a fixed receiver.
> If you have a “Tropo Observatory” that gives you anything close to 
> 24 / 7 / 365 data you are *very* lucky. Indeed there are people doing
> Tropo by looking at GPS and saying “what’s left is Tropo” ….. If
> that’s the approach your local observatory is using …. h …..

Well, there is a high correlation with near-by stations on the tropo.
Post-processing pushes the errors way down.

It used to be that you had local sensory package to provide input for
tropo estimation. That faded out because it was not providing much
improved result than nearby observations.

Also, tropo has a different function for how it adds up in the
pseudo-range measurements to that of other sources, such as ionsphere.
So, separation can be done once the ionsphere shift is gone, which
double-frequency allows. Higher-order parts of ionsphere can be observed
if you like, and that gives a finer detail about the wavefront angle
into the tropo, if you want to play that game. Yeah, the signal does not
go line-of-sight through any of those, that's an approximation in
itself. There are people scratching their heads and refining it over time.

Kind of pitty that tropo has the same sign on code and carrier and seems
relative insensitive to frequency. Ah well, at least we can cancel the
ionspheric shift.

Cheers,
Magnus


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Re: [time-nuts] World's most precise.... wall clock

[Bob kb8tq]

Hi

> On Mar 10, 2021, at 4:57 PM, Magnus Danielson  wrote:
> 
> Hi,
> 
> On 2021-03-10 17:04, Bob kb8tq wrote:
>> Hi
>> 
>>> On Mar 10, 2021, at 9:39 AM, Charlie  wrote:
>>> 
>>> Bob-
>>> 
>>> As a rank amateur e astronomer, I am a  lurker. I am amazed at what I have
>>> learned here. I know that there are differences between the meaning of
>>> precision and accuracy, but please correct my understanding if I am
>>> imprecise.
>>> 
>>> I have a need for precise time, as all sorts of calculations are dependent
>>> on precise geocentric position, and of course time to convert to other times
>>> e.g. sidereal, utc, etc., as related to the motion control of a large
>>> telescope.
>>> 
>>> I have an old hp z3805a; seems to be really precise, agreeing with my
>>> location (surveyed). Other gps's that I have seem to wander more.
>> I suspect that is a function of how the 3805 presents the data. 
>> 
>>> My question is thus: It seems that procuring a more precise PPS/time output
>>> unit is quite a bit more costly than what I have; even more costly is a unit
>>> that has both more precise PPS/time output, and a really stable 10 Mhz
>>> output ( I might add that I am a Ham, where 1 uhz  error is detrimental).
>> Sub ns *jitter* is doing well at 1 second with GPS. Accuracy is different 
>> than jitter. Since the GPS clock is not a direct expression of UTC from 
>> BIH ( nothing is … sorry about that …) there is some back tracking to get
>> *very* accurate time. 
>> 
>>> Assuming I can afford an upgrade, would  getting a more precise PPS/time
>>> unit then and feed that data into separate OCXO? Getting both seems out of
>>> my league.
>> If you have the $300 to $2000 for a multi band GNSS timing receiver, it will 
>> indeed help a bit. How much will depend a lot on the state of the ionosphere 
>> and the correction process. Troposphere also gets into things. I don’t know 
>> of
>> any receiver that directly estimates Tropo delay. 
> 
> There is means to infer Tropo-delay with single receivers, but it is not
> very accurate that I've seen. However, the usual way is to use nearby
> receivers as reference. Eventually as the actual position is known,
> tropo errors can be inferred more directly for a fixed receiver.

If you have a “Tropo Observatory” that gives you anything close to 
24 / 7 / 365 data you are *very* lucky. Indeed there are people doing
Tropo by looking at GPS and saying “what’s left is Tropo” ….. If
that’s the approach your local observatory is using …. h …..

Bob

> 
> It is worth noting that you do not only want a good multi band GNSS
> timing receiver, you also want a good phase-stable and multi-path
> rejecting antenna to go with it, such as choke-ring or pin-wheel. Much
> of carrier-phase properties is lost in a bad antenna.
> 
> Another aspect is that if you care about very accurate time, you need
> the antenna, cable and receiver calibrated, as the delay through these
> is not fully cancelled in the reception processing. In precise
> positioning processing, the antenna should be of known type and properly
> orienter such that the phase center calibration is compensated actively.
> 
> If you do not need a paper to show how good you are, you can do pretty
> good guestimates to roughly your delays and compensate those. At some
> point you end up wanting to do a real calibration anyway, if you try to
> push the limit downwards.
> 
>> 
>>> Seems that  could the best of both worlds.
>> Best would team the fancy receiver with a fancy standard. An OCXO is better
>> than a TCXO. Most Rb's beats the OCXO long term. A Cs will beat them both
>> if you run out long enough. You then get into things like GNSS disciplined 
>> Passive Hydrogen Masers. Properly done they should perform quite well. A
>> disciplined Active Maser would / could beat a Passive Maser …..
>> 
>> The better the “flywheel” the better the result, at least for frequency / 
>> stability. 
>> It will count off seconds quite nicely. Just how far off from “right” those 
>> seconds
>> are is a bit unclear. ( = you still are not accurate)
>> 
>> For accuracy you need a path back to BIH and the “official” definition of 
>> UTC.
>> That’s true even with the brand new fresh from the factory disciplined Active
>> Maser that you sold the house to buy ….. There are lots of nasty little 
>> delays
>> that creep into the mix …. All of them need to be taken care of to below your
>> target error level. If you are after < 10 ns accuracy, this could get pretty 
>> exciting. 
> 
> BIPM these days, not BIH. There is plenty of things and thorns. I've
> touched on some.
> 
> I've seen some crazy stuff. Temperature stabilized concrete pillars,
> temperature stabilized coax. All depends on how deep your pockets goes
> and crazyness.
> 
> I have yet to go that crazy, but at times I wonder.
> 
> Cheers,
> Magnus
> 
> 
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> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe, go to 
> 

Re: [time-nuts] World's most precise.... wall clock

[Magnus Danielson]

Hi,

On 2021-03-10 17:04, Bob kb8tq wrote:
> Hi
>
>> On Mar 10, 2021, at 9:39 AM, Charlie  wrote:
>>
>> Bob-
>>
>> As a rank amateur e astronomer, I am a  lurker. I am amazed at what I have
>> learned here. I know that there are differences between the meaning of
>> precision and accuracy, but please correct my understanding if I am
>> imprecise.
>>
>> I have a need for precise time, as all sorts of calculations are dependent
>> on precise geocentric position, and of course time to convert to other times
>> e.g. sidereal, utc, etc., as related to the motion control of a large
>> telescope.
>>
>> I have an old hp z3805a; seems to be really precise, agreeing with my
>> location (surveyed). Other gps's that I have seem to wander more.
> I suspect that is a function of how the 3805 presents the data. 
>
>> My question is thus: It seems that procuring a more precise PPS/time output
>> unit is quite a bit more costly than what I have; even more costly is a unit
>> that has both more precise PPS/time output, and a really stable 10 Mhz
>> output ( I might add that I am a Ham, where 1 uhz  error is detrimental).
> Sub ns *jitter* is doing well at 1 second with GPS. Accuracy is different 
> than jitter. Since the GPS clock is not a direct expression of UTC from 
> BIH ( nothing is … sorry about that …) there is some back tracking to get
> *very* accurate time. 
>
>> Assuming I can afford an upgrade, would  getting a more precise PPS/time
>> unit then and feed that data into separate OCXO? Getting both seems out of
>> my league.
> If you have the $300 to $2000 for a multi band GNSS timing receiver, it will 
> indeed help a bit. How much will depend a lot on the state of the ionosphere 
> and the correction process. Troposphere also gets into things. I don’t know of
> any receiver that directly estimates Tropo delay. 

There is means to infer Tropo-delay with single receivers, but it is not
very accurate that I've seen. However, the usual way is to use nearby
receivers as reference. Eventually as the actual position is known,
tropo errors can be inferred more directly for a fixed receiver.

It is worth noting that you do not only want a good multi band GNSS
timing receiver, you also want a good phase-stable and multi-path
rejecting antenna to go with it, such as choke-ring or pin-wheel. Much
of carrier-phase properties is lost in a bad antenna.

Another aspect is that if you care about very accurate time, you need
the antenna, cable and receiver calibrated, as the delay through these
is not fully cancelled in the reception processing. In precise
positioning processing, the antenna should be of known type and properly
orienter such that the phase center calibration is compensated actively.

If you do not need a paper to show how good you are, you can do pretty
good guestimates to roughly your delays and compensate those. At some
point you end up wanting to do a real calibration anyway, if you try to
push the limit downwards.

>
>> Seems that  could the best of both worlds.
> Best would team the fancy receiver with a fancy standard. An OCXO is better
> than a TCXO. Most Rb's beats the OCXO long term. A Cs will beat them both
> if you run out long enough. You then get into things like GNSS disciplined 
> Passive Hydrogen Masers. Properly done they should perform quite well. A
> disciplined Active Maser would / could beat a Passive Maser …..
>
> The better the “flywheel” the better the result, at least for frequency / 
> stability. 
> It will count off seconds quite nicely. Just how far off from “right” those 
> seconds
> are is a bit unclear. ( = you still are not accurate)
>
> For accuracy you need a path back to BIH and the “official” definition of UTC.
> That’s true even with the brand new fresh from the factory disciplined Active
> Maser that you sold the house to buy ….. There are lots of nasty little delays
> that creep into the mix …. All of them need to be taken care of to below your
> target error level. If you are after < 10 ns accuracy, this could get pretty 
> exciting. 

BIPM these days, not BIH. There is plenty of things and thorns. I've
touched on some.

I've seen some crazy stuff. Temperature stabilized concrete pillars,
temperature stabilized coax. All depends on how deep your pockets goes
and crazyness.

I have yet to go that crazy, but at times I wonder.

Cheers,
Magnus


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Re: [time-nuts] World's most precise.... wall clock

[Bob kb8tq]

Hi

> On Mar 10, 2021, at 9:39 AM, Charlie  wrote:
> 
> Bob-
> 
> As a rank amateur e astronomer, I am a  lurker. I am amazed at what I have
> learned here. I know that there are differences between the meaning of
> precision and accuracy, but please correct my understanding if I am
> imprecise.
> 
> I have a need for precise time, as all sorts of calculations are dependent
> on precise geocentric position, and of course time to convert to other times
> e.g. sidereal, utc, etc., as related to the motion control of a large
> telescope.
> 
> I have an old hp z3805a; seems to be really precise, agreeing with my
> location (surveyed). Other gps's that I have seem to wander more.

I suspect that is a function of how the 3805 presents the data. 

> 
> My question is thus: It seems that procuring a more precise PPS/time output
> unit is quite a bit more costly than what I have; even more costly is a unit
> that has both more precise PPS/time output, and a really stable 10 Mhz
> output ( I might add that I am a Ham, where 1 uhz  error is detrimental).

Sub ns *jitter* is doing well at 1 second with GPS. Accuracy is different 
than jitter. Since the GPS clock is not a direct expression of UTC from 
BIH ( nothing is … sorry about that …) there is some back tracking to get
*very* accurate time. 

> 
> Assuming I can afford an upgrade, would  getting a more precise PPS/time
> unit then and feed that data into separate OCXO? Getting both seems out of
> my league.

If you have the $300 to $2000 for a multi band GNSS timing receiver, it will 
indeed help a bit. How much will depend a lot on the state of the ionosphere 
and the correction process. Troposphere also gets into things. I don’t know of
any receiver that directly estimates Tropo delay. 

> 
> Seems that  could the best of both worlds.

Best would team the fancy receiver with a fancy standard. An OCXO is better
than a TCXO. Most Rb's beats the OCXO long term. A Cs will beat them both
if you run out long enough. You then get into things like GNSS disciplined 
Passive Hydrogen Masers. Properly done they should perform quite well. A
disciplined Active Maser would / could beat a Passive Maser …..

The better the “flywheel” the better the result, at least for frequency / 
stability. 
It will count off seconds quite nicely. Just how far off from “right” those 
seconds
are is a bit unclear. ( = you still are not accurate)

For accuracy you need a path back to BIH and the “official” definition of UTC.
That’s true even with the brand new fresh from the factory disciplined Active
Maser that you sold the house to buy ….. There are lots of nasty little delays
that creep into the mix …. All of them need to be taken care of to below your
target error level. If you are after < 10 ns accuracy, this could get pretty 
exciting. 


Bob

> 
> All advise welcome; it's how we learn
> 
> Thank you,
> 
> Charlie
> N6CFH
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@lists.febo.com] On Behalf Of Bob
> kb8tq
> Sent: Wednesday, March 10, 2021 5:24 AM
> To: Discussion of precise time and frequency measurement
> 
> Cc: hmur...@megapathdsl.net
> Subject: Re: [time-nuts] World's most precise wall clock
> 
> Hi
> 
>> On Mar 10, 2021, at 6:04 AM, Hal Murray  wrote:
>> 
>> 
>> kb...@n1k.org said:
>>> The gotcha here is that if you want accurate *time*, you are better off
> using
>>> the sawtooth corrected output from a (good) GPS module rather than a
> GPSDO. 
>> 
>> Why is that?
> 
> The controller gets in the way. If you want good frequency stability you
> have long
> time constants. The local reference is free to (and does) wander inside that
> time
> constant. 
> 
>> 
>> I would have guessed that a GPSDO would average over many GPS pulses thus 
>> reducing the noise.
> 
> It does and it does. However that does not help the accuracy of your 1
> second
> time tick. A good GPS module *with* sawtooth. can get you down to a fraction
> of a nanosecond (ADEV) on your 1 PPS. There is no need to average that noise
> down any further. 
> 
>> 
>> Is it something like GPSDOs are normally designed for good frequency
> rather 
>> than good time, so when they find the time is off, they use a small
> frequency 
>> offset for a long time to correct rather than a big frequency offset for a
> 
>> short time?
>> 
>> Are there any GPSDOs designed for good time?  Or any with parameters that
> can 
>> be tweaked to provide good time?
> 
> There are a few. They steer the 1 PPS so it follows the PPS output of the
> module. 
> If all you want is time, j

Re: [time-nuts] World's most precise.... wall clock

[Peter Reilley]

I was thinking about the discussion on synchronizing a grandfather clock
using a magnet and coil.   Most methods for doing this use an external
power supply or a battery.

What about powering the synchronizing circuit from energy harvested
from the pendulum.   Consider that you can get a quartz watch that will
run for 5 years on a minuscule battery.   Surely there is enough excess
energy to be harvested from the pendulum to exceed the energy available
from such a small battery.

The circuit could use a capacitor for energy storage and eliminate the
battery.   Of course the clock would be only as accurate as the 32KHz
crystal but that should satisfy anyone but a time nut. ;-)

You might have to adjust the pendulum to run a little fast so as to
provide the excess energy for the circuit.   The coil would act to slow
the pendulum each cycle thereby absorbing energy which would be
available to power the circuit.


On 3/10/2021 9:26 AM, Dana Whitlow wrote:

Hal,

The older (and probably the newer models, too) Trimble Thunderbolt GPSDOs
have
a user-adjustable time constant accessible via the serial port using a
program like
"Tboltmon.exe" (from Trimble).  I suspect that  "Lady Heather"  may also do
this.  I
am fortunate in owning a still functioning PC with an actual hardware RS232
port
and a usable O/S (Win XP), so running Tboltmon is a trivial exercise for me.

In addition to time constant, tboltmon also lets one examine (and set,
where appropriate)
a large number of other items, and it's reasonably intuitive to use.  I've
never had to resort
to a manual. (if there even is one) to do what I needed.

My own experience is that a time constant around 50 sec works best in my
environment,
providing the best compromise between filtering PPS jitter from out of the
unit's GPS
receiver and tamping down OCXO wanderings due to my home HVAC system's
cycling.
Setting a far longer time constant value (say, much longer than 500 sec)
tends to lead
to "funny business" so I just don't go there.

I have convinced myself that the PPS output from my Tbolt is derived from
the produced
10 MHz output, because if I trigger an o'scope from the PPS output, the 10
MHz sinewave
shows very little time jitter, perhaps 1 or 2 nsec.  So, I'm pretty happy
with the T'bolt, with
two (minor) exceptions:


  Its RF sensitivity seems rather poor compared to that of "modern"

receivers (my unit
 was apparently made in the early 2000s).


  In tboltmon, the signal "strength" indications are displayed in units

called 'AMU',
 for which I've been unable to find a definition.

Dana


On Wed, Mar 10, 2021 at 6:53 AM Hal Murray  wrote:


kb...@n1k.org said:

The gotcha here is that if you want accurate *time*, you are better off

using

the sawtooth corrected output from a (good) GPS module rather than a

GPSDO.

Why is that?

I would have guessed that a GPSDO would average over many GPS pulses thus
reducing the noise.

Is it something like GPSDOs are normally designed for good frequency
rather
than good time, so when they find the time is off, they use a small
frequency
offset for a long time to correct rather than a big frequency offset for a
short time?

Are there any GPSDOs designed for good time?  Or any with parameters that
can
be tweaked to provide good time?


--
These are my opinions.  I hate spam.




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Re: [time-nuts] World's most precise.... wall clock

[Charlie]

Bob-

As a rank amateur e astronomer, I am a  lurker. I am amazed at what I have
learned here. I know that there are differences between the meaning of
precision and accuracy, but please correct my understanding if I am
imprecise.

I have a need for precise time, as all sorts of calculations are dependent
on precise geocentric position, and of course time to convert to other times
e.g. sidereal, utc, etc., as related to the motion control of a large
telescope.

I have an old hp z3805a; seems to be really precise, agreeing with my
location (surveyed). Other gps's that I have seem to wander more.

My question is thus: It seems that procuring a more precise PPS/time output
unit is quite a bit more costly than what I have; even more costly is a unit
that has both more precise PPS/time output, and a really stable 10 Mhz
output ( I might add that I am a Ham, where 1 uhz  error is detrimental).

Assuming I can afford an upgrade, would  getting a more precise PPS/time
unit then and feed that data into separate OCXO? Getting both seems out of
my league.

Seems that  could the best of both worlds.

All advise welcome; it's how we learn

Thank you,

Charlie
N6CFH












-Original Message-
From: time-nuts [mailto:time-nuts-boun...@lists.febo.com] On Behalf Of Bob
kb8tq
Sent: Wednesday, March 10, 2021 5:24 AM
To: Discussion of precise time and frequency measurement

Cc: hmur...@megapathdsl.net
Subject: Re: [time-nuts] World's most precise wall clock

Hi

> On Mar 10, 2021, at 6:04 AM, Hal Murray  wrote:
> 
> 
> kb...@n1k.org said:
>> The gotcha here is that if you want accurate *time*, you are better off
using
>> the sawtooth corrected output from a (good) GPS module rather than a
GPSDO. 
> 
> Why is that?

The controller gets in the way. If you want good frequency stability you
have long
time constants. The local reference is free to (and does) wander inside that
time
constant. 

> 
> I would have guessed that a GPSDO would average over many GPS pulses thus 
> reducing the noise.

It does and it does. However that does not help the accuracy of your 1
second
time tick. A good GPS module *with* sawtooth. can get you down to a fraction
of a nanosecond (ADEV) on your 1 PPS. There is no need to average that noise
down any further. 

> 
> Is it something like GPSDOs are normally designed for good frequency
rather 
> than good time, so when they find the time is off, they use a small
frequency 
> offset for a long time to correct rather than a big frequency offset for a

> short time?
> 
> Are there any GPSDOs designed for good time?  Or any with parameters that
can 
> be tweaked to provide good time?

There are a few. They steer the 1 PPS so it follows the PPS output of the
module. 
If all you want is time, just use the module PPS and save on the electric
bill. 

Bob

> 
> 
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> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] World's most precise.... wall clock

[Dana Whitlow]

Hal,

The older (and probably the newer models, too) Trimble Thunderbolt GPSDOs
have
a user-adjustable time constant accessible via the serial port using a
program like
"Tboltmon.exe" (from Trimble).  I suspect that  "Lady Heather"  may also do
this.  I
am fortunate in owning a still functioning PC with an actual hardware RS232
port
and a usable O/S (Win XP), so running Tboltmon is a trivial exercise for me.

In addition to time constant, tboltmon also lets one examine (and set,
where appropriate)
a large number of other items, and it's reasonably intuitive to use.  I've
never had to resort
to a manual. (if there even is one) to do what I needed.

My own experience is that a time constant around 50 sec works best in my
environment,
providing the best compromise between filtering PPS jitter from out of the
unit's GPS
receiver and tamping down OCXO wanderings due to my home HVAC system's
cycling.
Setting a far longer time constant value (say, much longer than 500 sec)
tends to lead
to "funny business" so I just don't go there.

I have convinced myself that the PPS output from my Tbolt is derived from
the produced
10 MHz output, because if I trigger an o'scope from the PPS output, the 10
MHz sinewave
shows very little time jitter, perhaps 1 or 2 nsec.  So, I'm pretty happy
with the T'bolt, with
two (minor) exceptions:

>  Its RF sensitivity seems rather poor compared to that of "modern"
receivers (my unit
was apparently made in the early 2000s).

>  In tboltmon, the signal "strength" indications are displayed in units
called 'AMU',
for which I've been unable to find a definition.

Dana


On Wed, Mar 10, 2021 at 6:53 AM Hal Murray  wrote:

>
> kb...@n1k.org said:
> > The gotcha here is that if you want accurate *time*, you are better off
> using
> > the sawtooth corrected output from a (good) GPS module rather than a
> GPSDO.
>
> Why is that?
>
> I would have guessed that a GPSDO would average over many GPS pulses thus
> reducing the noise.
>
> Is it something like GPSDOs are normally designed for good frequency
> rather
> than good time, so when they find the time is off, they use a small
> frequency
> offset for a long time to correct rather than a big frequency offset for a
> short time?
>
> Are there any GPSDOs designed for good time?  Or any with parameters that
> can
> be tweaked to provide good time?
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
>
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Re: [time-nuts] World's most precise.... wall clock

[Magnus Danielson]

Hi,

On 2021-03-10 14:23, Bob kb8tq wrote:
> Hi
>
>> On Mar 10, 2021, at 6:04 AM, Hal Murray  wrote:
>>
>>
>> kb...@n1k.org said:
>>> The gotcha here is that if you want accurate *time*, you are better off 
>>> using
>>> the sawtooth corrected output from a (good) GPS module rather than a GPSDO. 
>> Why is that?
> The controller gets in the way. If you want good frequency stability you have 
> long
> time constants. The local reference is free to (and does) wander inside that 
> time
> constant. 

Indeed. It is different to optimize for ADEV or TDEV performance.

However, even when phase/time is interesting, a frequency optimization
has benefits when it comes to hold-over performance, i.e. how stable it
will be after loosing tracking. You very quickly come to a situation
where frequency error dominates the phase error, and only later does
drift and environment start to kick in.

>
>> I would have guessed that a GPSDO would average over many GPS pulses thus 
>> reducing the noise.
> It does and it does. However that does not help the accuracy of your 1 second
> time tick. A good GPS module *with* sawtooth. can get you down to a fraction
> of a nanosecond (ADEV) on your 1 PPS. There is no need to average that noise
> down any further. 
Actually, you go below that if you average long enough, but the sawtooth
for sure helps. There is enough of noise and systematics to make things
move around. It's still not very good thought, so you end up with a
fuzzy border about there. As always, it depends. :)
>
>> Is it something like GPSDOs are normally designed for good frequency rather 
>> than good time, so when they find the time is off, they use a small 
>> frequency 
>> offset for a long time to correct rather than a big frequency offset for a 
>> short time?
>>
>> Are there any GPSDOs designed for good time?  Or any with parameters that 
>> can 
>> be tweaked to provide good time?
> There are a few. They steer the 1 PPS so it follows the PPS output of the 
> module. 
> If all you want is time, just use the module PPS and save on the electric 
> bill. 

Indeed, unless you need hold-over capability, that's when an OCXO or
Telecom Rubidium may kick in and be relevant. As time-nuts, we do it
regardless, because it is fun, but that is a different account. :)

Cheers,
Magnus

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Re: [time-nuts] World's most precise.... wall clock

[Bob kb8tq]

Hi

> On Mar 10, 2021, at 6:04 AM, Hal Murray  wrote:
> 
> 
> kb...@n1k.org said:
>> The gotcha here is that if you want accurate *time*, you are better off using
>> the sawtooth corrected output from a (good) GPS module rather than a GPSDO. 
> 
> Why is that?

The controller gets in the way. If you want good frequency stability you have 
long
time constants. The local reference is free to (and does) wander inside that 
time
constant. 

> 
> I would have guessed that a GPSDO would average over many GPS pulses thus 
> reducing the noise.

It does and it does. However that does not help the accuracy of your 1 second
time tick. A good GPS module *with* sawtooth. can get you down to a fraction
of a nanosecond (ADEV) on your 1 PPS. There is no need to average that noise
down any further. 

> 
> Is it something like GPSDOs are normally designed for good frequency rather 
> than good time, so when they find the time is off, they use a small frequency 
> offset for a long time to correct rather than a big frequency offset for a 
> short time?
> 
> Are there any GPSDOs designed for good time?  Or any with parameters that can 
> be tweaked to provide good time?

There are a few. They steer the 1 PPS so it follows the PPS output of the 
module. 
If all you want is time, just use the module PPS and save on the electric bill. 

Bob

> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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Re: [time-nuts] World's most precise.... wall clock

[Hal Murray]

kb...@n1k.org said:
> The gotcha here is that if you want accurate *time*, you are better off using
> the sawtooth corrected output from a (good) GPS module rather than a GPSDO. 

Why is that?

I would have guessed that a GPSDO would average over many GPS pulses thus 
reducing the noise.

Is it something like GPSDOs are normally designed for good frequency rather 
than good time, so when they find the time is off, they use a small frequency 
offset for a long time to correct rather than a big frequency offset for a 
short time?

Are there any GPSDOs designed for good time?  Or any with parameters that can 
be tweaked to provide good time?


-- 
These are my opinions.  I hate spam.




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Re: [time-nuts] World's most precise.... wall clock

[Bob kb8tq]

Hi

The gotcha here is that if you want accurate *time*, you are better off using
the sawtooth corrected output from a (good) GPS module rather than a GPSDO.

Bob

> On Mar 3, 2021, at 6:20 PM, djl  wrote:
> 
> Hi John:   What's the cost of the CSAC GPSDO? I'd ask directly, but the exact 
> device specification seems a bit murky.
> Thanks
> 
> On 2021-03-03 10:34, John Sloan wrote:
>> I’ve built several small home-brew NTP servers using a Raspberry Pi,
>> a GPS receiver, and an LCD display. Most of them are desk clocks.
>> My favorite one (and the biggest money sink) is a mantle clock in my
>> living room that incorporates a chip-scale cesium “atomic clock”.
>> Photo: https://flic.kr/p/2kqoHC7
>> Blog article:
>> https://coverclock.blogspot.com/2017/05/my-stratum-0-atomic-clock_9.html
>> Git repo: https://github.com/coverclock/com-diag-astrolabe
>> --
>> J. L. SloanDigital Aggregates Corp.
>> +1 303 940 9064 (O)3440 Youngfield St. #209
>> +1 303 489 5178 (M)Wheat Ridge CO 80033 USA
>> jsl...@diag.comhttp://www.diag.com 
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> 
> -- 
> 
> The whole world is a straight man.
> --
> Dr. Don Latham  AJ7LL
> PO Box 404, Frenchtown, MT, 59834
> VOX: 406-626-4304
> 
> 
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Re: [time-nuts] World's most precise.... wall clock

[djl]

Hi John:   What's the cost of the CSAC GPSDO? I'd ask directly, but the 
exact device specification seems a bit murky.

Thanks

On 2021-03-03 10:34, John Sloan wrote:

I’ve built several small home-brew NTP servers using a Raspberry Pi,
a GPS receiver, and an LCD display. Most of them are desk clocks.
My favorite one (and the biggest money sink) is a mantle clock in my
living room that incorporates a chip-scale cesium “atomic clock”.

Photo: https://flic.kr/p/2kqoHC7

Blog article:
https://coverclock.blogspot.com/2017/05/my-stratum-0-atomic-clock_9.html

Git repo: https://github.com/coverclock/com-diag-astrolabe

--
J. L. SloanDigital Aggregates Corp.
+1 303 940 9064 (O)3440 Youngfield St. #209
+1 303 489 5178 (M)Wheat Ridge CO 80033 USA
jsl...@diag.comhttp://www.diag.com 


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--

The whole world is a straight man.
--
Dr. Don Latham  AJ7LL
PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304


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Re: [time-nuts] World's most precise.... wall clock

[Ben Bradley]

This might be desirable.

https://www.ebay.com/itm/THE-AMATEUR-SCIENTIST-ON-CD-ROM-LATEST-EDITION-VERSION-4-M2071-/112117678275

On Wed, Mar 3, 2021 at 4:19 PM Chris Caudle <6807.ch...@pop.powweb.com> wrote:
>
> > On Tue, 02 Mar 2021 22:42:45 -0800
> > Hal Murray  wrote:
> >
> >> The basic idea is to mount a magnet on a stiff wire so that it sticks
> >> out to
> >> the side of the pendulum arm, then mount a coil so the magnet will
> >> swing
> >> through it.  Now pulse the coil to get the desired results.
>
> On 2021-03-03 02:54, Attila Kinali wrote:
> > This is basically injection locking of a pendulum clock.
> > Pendulum clocks are very nice for injection locking, due
> > to their relatively low Q and because a magnetic field can
> > be easily adjusted in strength.
>
>
> I don't have the reference at hand right away, but I did see an article
> in the past describing a mechanism which placed the magnet on the end of
> the pendulum, and had one coil to sense the magnet swinging past, and
> another coil to provide the impulse to the pendulum.  The timing of the
> impulse was controlled by a microcontroller, so it could provide some
> rough phase locking function by varying the time between the detection
> pulse and the driven impulse, and maybe the amplitude or length of the
> impulse.
> If there is interest I can see if I can find that article again, but
> that may be straying from the original request, which seemed to be
> looking for something with a digital display.
>
> --
> Chris Caudle
>
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Re: [time-nuts] World's most precise.... wall clock

[Chris Caudle]

On Tue, 02 Mar 2021 22:42:45 -0800
Hal Murray  wrote:

The basic idea is to mount a magnet on a stiff wire so that it sticks 
out to
the side of the pendulum arm, then mount a coil so the magnet will 
swing

through it.  Now pulse the coil to get the desired results.


On 2021-03-03 02:54, Attila Kinali wrote:

This is basically injection locking of a pendulum clock.
Pendulum clocks are very nice for injection locking, due
to their relatively low Q and because a magnetic field can
be easily adjusted in strength.



I don't have the reference at hand right away, but I did see an article 
in the past describing a mechanism which placed the magnet on the end of 
the pendulum, and had one coil to sense the magnet swinging past, and 
another coil to provide the impulse to the pendulum.  The timing of the 
impulse was controlled by a microcontroller, so it could provide some 
rough phase locking function by varying the time between the detection 
pulse and the driven impulse, and maybe the amplitude or length of the 
impulse.
If there is interest I can see if I can find that article again, but 
that may be straying from the original request, which seemed to be 
looking for something with a digital display.


--
Chris Caudle

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Re: [time-nuts] World's most precise.... wall clock

[John Sloan]

I’ve built several small home-brew NTP servers using a Raspberry Pi,
a GPS receiver, and an LCD display. Most of them are desk clocks.
My favorite one (and the biggest money sink) is a mantle clock in my
living room that incorporates a chip-scale cesium “atomic clock”.

Photo: https://flic.kr/p/2kqoHC7

Blog article: 
https://coverclock.blogspot.com/2017/05/my-stratum-0-atomic-clock_9.html

Git repo: https://github.com/coverclock/com-diag-astrolabe

--
J. L. SloanDigital Aggregates Corp.
+1 303 940 9064 (O)3440 Youngfield St. #209
+1 303 489 5178 (M)Wheat Ridge CO 80033 USA
jsl...@diag.comhttp://www.diag.com 


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Re: [time-nuts] World's most precise.... wall clock

[Edesio Costa e Silva]

Hi!

I found a copy at 


Edésio

On Tue, Mar 02, 2021 at 10:42:45PM -0800, Hal Murray wrote:
> > Maybe one day I'll make this work with a grandfather clock.
>
> Many years ago, Scientific American had an article describing adding a magnet
> to the pendulum and the circuitry to drive it.
>
> The basic idea is to mount a magnet on a stiff wire so that it sticks out to
> the side of the pendulum arm, then mount a coil so the magnet will swing
> through it.  Now pulse the coil to get the desired results.
>
> Scientific American, September 1974, Amateur Scientist
> A venerable clock is made highly accurate by equipping it with quartz-crystal 
> works
>
> They want $8 for a pdf.
> https://www.scientificamerican.com/article/the-amateur-scientist-1974-09/
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
>
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Re: [time-nuts] World's most precise.... wall clock

[Attila Kinali]

On Tue, 02 Mar 2021 22:42:45 -0800
Hal Murray  wrote:

> The basic idea is to mount a magnet on a stiff wire so that it sticks out to 
> the side of the pendulum arm, then mount a coil so the magnet will swing 
> through it.  Now pulse the coil to get the desired results.

This is basically injection locking of a pendulum clock.
Pendulum clocks are very nice for injection locking, due
to their relatively low Q and because a magnetic field can
be easily adjusted in strength.

You don't need to place the magnet at any one specific position.
It is enough that it is somewhere in the path of the pendulum.
My favorite position is right beneath the center.

The injected pulses should be long enough to have an effect
with a reasonably weak magnetic field, but short enough to
be an impulse, from the point of view of the mechanical system.
I.e. the pulse length should be a fraction of the time it take
for the pendulum to pass the magnet. Somewhere between 1/2
and 1/10 should work in most cases.

Start with getting the pendulum clock as close to the right
rate as possible. Place the magnet where it suits you best.
Then adjust the current through the magnet such that you can
barely feel some resistance when you move the pendulum through
the field with your hands. Set your electronics to inject pulses
at the appropriate rate. This does not have to be at every pass,
but can be, e.g., every 10th pass. Now let the clock run and see
whether you get proper synchronization/locking. If not, increase
the current through the magnet step wise until it is strong enough
for synchronization. Test over varying temperatures, air humidity
and pressure to ensure that changes of the natural frequency of
the pendulum don't get your clock unlocked.

If you have trouble with keeping the clock locked and don't want
to increase the current any further, increase the pulse length.

For additionaly time-nuttyness, you can add a sensor somewhere in
the path of the pendulum and measure its phase versus true
time. Suitable sensors are fork light barriers and Hal sensors.


Attila Kinal
-- 
The driving force behind research is the question: "Why?"
There are things we don't understand and things we always 
wonder about. And that's why we do research.
-- Kobayashi Makoto

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Re: [time-nuts] World's most precise.... wall clock

[Hal Murray]

> Maybe one day I'll make this work with a grandfather clock.

Many years ago, Scientific American had an article describing adding a magnet 
to the pendulum and the circuitry to drive it.

The basic idea is to mount a magnet on a stiff wire so that it sticks out to 
the side of the pendulum arm, then mount a coil so the magnet will swing 
through it.  Now pulse the coil to get the desired results.

Scientific American, September 1974, Amateur Scientist
A venerable clock is made highly accurate by equipping it with quartz-crystal 
works

They want $8 for a pdf.
https://www.scientificamerican.com/article/the-amateur-scientist-1974-09/


-- 
These are my opinions.  I hate spam.




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Re: [time-nuts] World's most precise.... wall clock

[DM]

Here are a few online projects for GPS-controlled clocks. Most (all?) have a 
PIC or Arduino to run the clock and sync to GPS time. 
[ http://w8bh.net/avr/clock2.pdf | http://w8bh.net/avr/clock2.pdf ] 
https://www.elprocus.com/how-to-build-a-gps-clock-using-arduino/ 
https://learn.adafruit.com/arduino-clock 
https://www.tindie.com/products/nsayer/gps-clock/ 
https://mitxela.com/shop/clock 
https://www.sparkfun.com/tutorials/47 

DIY projects are easy to find with Google: 
The search string I used was: gps digital clock kit OR diy OR build 

There are a number of clocks with Nixie tube displays also; just add "nixie" to 
the Google search string. 

Good luck 
Dave M 




From: "Eamonn Nugent"  
To: time-nuts@lists.febo.com 
Sent: Tuesday, March 2, 2021 4:38:24 PM 
Subject: [time-nuts] World's most precise wall clock 

Hi! 

I have a perhaps silly question. I want to take an inferior medium (our 
eyes) and give it something attractively precise to look at. Is there such 
a thing as a digital (wall) clock with a 1PPS/10MHz/etc. input? I see that 
some clocks have GPS antenna inputs, but I want to take a GPSDO and hook it 
up to a digital clock. Purely for fun, as a mini project for myself while I 
build my bigger clocks. 

Maybe one day I'll make this work with a grandfather clock. 

Thanks, 

Eamonn 
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Re: [time-nuts] World's most precise.... wall clock

[Tom Van Baak]

Eamonn,

Here are a couple of ideas for you:

1) You may find some GPS / NTP / 1PPS / 10 MHz precise time friendly 
professional clocks at:


https://www.masterclock.com/

2) If you have a 50/60 Hz mains wall clock you can always use this trick:

http://leapsecond.com/pages/atomic-nixie/

3) You can convert your perfect 10 MHz into perfect 32.768 Hz and inject 
that into any cheap 32 kHz tuning fork clock. Sometimes it's as simple 
as one wire. Watch one for one problem: some newer 32 kHz clocks use 
cycle slipping in which case feeding in exactly 32768 Hz will result in 
a very slight loss of time as far as the hands show.


A $1 solution to converting 10 MHz to 32 kHz is:

http://leapsecond.com/pic/src/pd30.asm
http://leapsecond.com/pic/picdiv.htm

4) You can convert your perfect GPS/1PPS into the bipolar stepper 
signals used by the Lavet motor in almost all analog wrist / desk / wall 
clocks:


https://en.wikipedia.org/wiki/Lavet-type_stepping_motor
http://leapsecond.com/pages/32kHz/

5) If you want sidereal time, another $1 PIC solution, see PD28 and PD29 at:

http://leapsecond.com/pic/src/

This technique can be adapted to a wide range of frequencies.

6) Projects to hack / adapt display clocks to Rb or Cs or GPS/GPSDO 
timing sources is not uncommon on sites like Hackaday.com so have a look 
there as well.


/tvb

On 3/2/2021 2:38 PM, Eamonn Nugent wrote:

Hi!

I have a perhaps silly question. I want to take an inferior medium (our
eyes) and give it something attractively precise to look at. Is there such
a thing as a digital (wall) clock with a 1PPS/10MHz/etc. input? I see that
some clocks have GPS antenna inputs, but I want to take a GPSDO and hook it
up to a digital clock. Purely for fun, as a mini project for myself while I
build my bigger clocks.

Maybe one day I'll make this work with a grandfather clock.

Thanks,

Eamonn
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Re: [time-nuts] World's most precise.... wall clock

[Lux, Jim]

On 3/2/21 4:32 PM, ed breya wrote:
If you can open it up and get at and identify the crystal, you can 
synthesize its ideal frequency from a GPSDO output, then run it in 
there in place of the crystal. 




I did this for a 24hr Mars clock using a 3325 to generate 31947.2745 Hz



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Re: [time-nuts] World's most precise.... wall clock

[ed breya]

If you can open it up and get at and identify the crystal, you can 
synthesize its ideal frequency from a GPSDO output, then run it in there 
in place of the crystal.


Ed

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Re: [time-nuts] World's most precise.... wall clock

[Bill Beam]

Hi,

I had same question several years ago.

You're gonna have to roll your own.

Look here 



On Tue, 2 Mar 2021 17:38:24 -0500, Eamonn Nugent wrote:

>Hi!

>I have a perhaps silly question. I want to take an inferior medium (our
>eyes) and give it something attractively precise to look at. Is there such
>a thing as a digital (wall) clock with a 1PPS/10MHz/etc. input? I see that
>some clocks have GPS antenna inputs, but I want to take a GPSDO and hook it
>up to a digital clock. Purely for fun, as a mini project for myself while I
>build my bigger clocks.

>Maybe one day I'll make this work with a grandfather clock.

>Thanks,

>Eamonn
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Bill Beam
NL7F




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[time-nuts] World's most precise.... wall clock

[Eamonn Nugent]

Hi!

I have a perhaps silly question. I want to take an inferior medium (our
eyes) and give it something attractively precise to look at. Is there such
a thing as a digital (wall) clock with a 1PPS/10MHz/etc. input? I see that
some clocks have GPS antenna inputs, but I want to take a GPSDO and hook it
up to a digital clock. Purely for fun, as a mini project for myself while I
build my bigger clocks.

Maybe one day I'll make this work with a grandfather clock.

Thanks,

Eamonn
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