Re: [time-nuts] Commercial software defined radio for clock metrology

[Kevin Rosenberg]

Hi Bob,

You have a good point. That leads to the question is what is the “best” 
measurement technique when you are sampling at a more smaller interval than the 
desired tau?

SDRs sample at high rates. The slowest the USRP N2x0 can sample is just under 
200Ksps. For easy math, let’s assume we sample at 1Msps but we want to record 
only 1sps for a long-term measurement. What’s best way to handle the 1e6 to 1 
ratio of available samples to desired samples? One method is to discard 999,999 
samples and just record the phase difference with a true tau of 1 sec. The 
other is to take a window of 1e6 samples and output the average phase 
difference over that 1 second window. Is your point that averaging samples that 
are more frequent than the tau will overestimate stability at the tau? If using 
averaged data, would it be “less lying” to multiply the ADEV by the sqrt of the 
length of the averaging window?

I’d appreciate your thoughts on the subject,

Kevin

> On Jul 29, 2016, at 6:51 PM, Bob Camp  wrote:
> 
> HI
> 
> Keep in mind that if you apply pre-filtering, an ADEV plot is lying to you ….
> 
> Bob
> 
>> On Jul 29, 2016, at 6:58 PM, Kevin Rosenberg  wrote:
>> 
>> Jeff,
>> 
>> Thanks for your very useful paper Oscillator Metrology with SDRs[1]. I
>> created a C++ program and checked residuals using a 10 MHz clock split
>> to the A and B channels of a LFRX and BasicRX boards and sampled at 1
>> Mhz. Using boxcar averaging of 1000 samples at 1 kHz, I was impressed
>> by the low noise floor approaching that of my Timepod which was
>> several times the cost. I included the Allan Deviation without
>> averaging showing the sqrt(1000) increase in noise floor without the
>> averaging[2].
>> 
>> I had a question about your experience. You mentioned using a input
>> signal near the maximum of the USRP’s ADC to get the best SNR. I
>> reviewed the schematics and application notes. I found a maximum Vpp
>> mentioned of 3.3V. I was wondering what voltage you were using to
>> drive the USRPs. When I go above 1.5-2 Vpp, I start getting signal
>> distortions and not much increase in the amplitude.
>> 
>> Many thanks for publishing your work in this area.
>> 
>> Kevin
>> 
>> [1]
>> https://arxiv.org/abs/1605.03505
>> 
>> [2]
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Re: [time-nuts] Very Accurate Delta Time RF Pulse

[Jerome Blaha]

Thank you all who responded including Bob, Attila, Vlad, Brooke, and Chris for 
some great suggestions.

This is a fun side project of mine to passively detect RF emitters based upon 
strongest nearby signal using ToA pulses from cheap log power sensors or 
perhaps the Watson-Watt method.  The hope is to use it in a vehicle with 
sufficient antenna spacing and time pulse accuracy to create a neighborhood 
plot with strongest TX locations.  

Yes, there are major issues to be overcome.  The super wide band input has no 
tuner and will pickup massive noise from many near-field sources, such as 
wi-fi, Bluetooth, or phones, however some can be filtered as noise.  
Additionally, very few omni antennas cover such a large input range and I don't 
think CW signals will be detected properly, as they don't use a distinct 
rising-edge pulse.
 
I'm leaning toward what Bob suggested with a single shot Ghz counter possibly 
with some type of pulse start/stop timer or a double input A/D with GS/s 
buffers that can be stopped and momentarily read off whenever a new strong 
signal is detected or after a set time each second.  Vlad mentioned a phase 
comparator AD8302, which would also be interesting and allow for analog or 
possibly digital wideband multi-frequency comparison using phase.  The AD8302 
apparently comes with its own internal double log power RF input, which could 
save on purchasing additional power sensor ICs as well.

Best Regards,

-Jerome 
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Re: [time-nuts] Commercial software defined radio for clock metrology

[Bob Camp]

HI

Keep in mind that if you apply pre-filtering, an ADEV plot is lying to you ….

Bob

> On Jul 29, 2016, at 6:58 PM, Kevin Rosenberg  wrote:
> 
> Jeff,
> 
> Thanks for your very useful paper Oscillator Metrology with SDRs[1]. I
> created a C++ program and checked residuals using a 10 MHz clock split
> to the A and B channels of a LFRX and BasicRX boards and sampled at 1
> Mhz. Using boxcar averaging of 1000 samples at 1 kHz, I was impressed
> by the low noise floor approaching that of my Timepod which was
> several times the cost. I included the Allan Deviation without
> averaging showing the sqrt(1000) increase in noise floor without the
> averaging[2].
> 
> I had a question about your experience. You mentioned using a input
> signal near the maximum of the USRP’s ADC to get the best SNR. I
> reviewed the schematics and application notes. I found a maximum Vpp
> mentioned of 3.3V. I was wondering what voltage you were using to
> drive the USRPs. When I go above 1.5-2 Vpp, I start getting signal
> distortions and not much increase in the amplitude.
> 
> Many thanks for publishing your work in this area.
> 
> Kevin
> 
> [1]
> https://arxiv.org/abs/1605.03505
> 
> [2]
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Re: [time-nuts] Q/noise of Earth as an oscillator

[Jim Palfreyman]

> What about an ADEV/TDEV plot of the pulsar J0437-4715?

Very boring. It's a straight line from top left to bottom right. :-)

See page 5 of this: http://arxiv.org/pdf/1004.0115.pdf

Jim Palfreyman


On 29 July 2016 at 17:33, Azelio Boriani  wrote:

> What about an ADEV/TDEV plot of the pulsar J0437-4715?
>
> On Fri, Jul 29, 2016 at 12:39 AM, Jim Palfreyman 
> wrote:
> > Hi All,
> >
> > Tom gave me a nudge to look here - I hadn't been following this thread.
> >
> > For those that don't know, I study pulsars and so the way we measure what
> > pulsars do could be relevant to this discussion.
> >
> > First, I have never heard of a Q measure when referencing a pulsar. I
> think
> > the key here is that it's not resonating as such. Rotating yes,
> resonating
> > no.
> >
> > Pulsars spin and slow down due to giving off energy (magnetic dipole
> > radiation). So in the pulsar world we mainly refer to spin frequency (F0)
> > and frequency derivative (F1). With some of the younger and more
> "erratic"
> > pulsars, F2 (and further) can be modelled.
> >
> > Here's some data on the Vela pulsar (hot off the presses - measured just
> > now):
> >
> > F0  11.1867488542579
> > F1  -1.55859177352837e-11
> > F2  1.23776878287221e-21
> >
> > Vela is young and erratic. Millisecond pulsars are outstanding clocks.
> > Here's the data for J0437-4715 - one of the most stable pulsars we know
> > about:
> >
> > F0  173.6879458121843
> > F1  -1.728361E-15
> >
> > I'm sure the "Q" of Vela would be pretty decent - but I can tell you now,
> > as a time-keeper, she's useless.
> >
> >
> > Jim Palfreyman
> >
> >
> >
> > On 28 July 2016 at 20:50, Tony Finch  wrote:
> >
> >> Neville Michie  wrote:
> >>
> >> > The conical pendulum has a simple form of a weight on a string,
> instead
> >> > of oscillating in one plane as a conventional pendulum, it swings
> around
> >> > in a circular orbit in the horizontal plane. It has a definite
> resonant
> >> > frequency.
> >>
> >> I don't think it does have a resonant frequency, any more than the Earth
> >> does: the angular velocity of the pendulum is sqrt(g/h) where h is the
> >> height of the pendulum; give it more energy, it swings higher, so h is
> >> smaller, so the frequency is higher.
> >>
> >> Tony.
> >> --
> >> f.anthony.n.finch    http://dotat.at/  -  I xn--zr8h
> >> punycode
> >> South Thames, Dover: Southwesterly 5 or 6. Slight or moderate. Rain or
> >> showers. Good, occasionally poor.
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[time-nuts] Histogram of T2 arrival times

[Mark Sims]

Easy,  I have a 4 value array.  It keeps count of the number of times each 
0.1 msec step between -2000 .. 2000 msecs was seen.  If two or more bins wind 
up with the same max count,  I report the average of those bin times, otherwise 
it's the bin with the highest count.   I also dump the counts to a file for 
later plotting.


-


>  How do you determine the bin size?
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Re: [time-nuts] Histogram of T2 arrival times

[Hal Murray]

hol...@hotmail.com said:
> te a histogram of the values (along with the average and standard
> deviation).   I'm now using the peak histogram bin(s) to determine the
> message offset time.   The histogram technique has the advantage of ignoring
> outlier points that can be caused by the system being tied up / interrupted
> doing other things (like shoving a Windows 10 upgrade up your systems' rear
> I/O port  ;-()

How do you determine the bin size?

ntpd has an interesting filter in that area.  For refclocks where it has many 
samples, it sorts them, then discards roughly 1/3 of them as outliers.  The 
code is simple.  Compute the average then check the first and last samples to 
see which is farther away.  Drop it, iterate.

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Re: [time-nuts] Q/noise of Earth as an oscillator

[Dave Brown]

The main issue has been deemed to be safety- or lack of it, due to the ring 
lasers location in an underground cavern that cannot continue to be used 
because of a high risk of additional ground/rock failure. For the present 
there has been no further ring laser work at canterbury university since the 
2010/2011 quakes and cave access is not permitted.

DaveB,
Christchurch, NZ


- Original Message - 
From: ""Björn Gabrielsson"" 
To: "Discussion of precise time and frequency measurement" 


Sent: Saturday, July 30, 2016 8:48 AM
Subject: Re: [time-nuts] Q/noise of Earth as an oscillator



I'am  not sure how the big ring lasers have progressed over the past
years. It seems the big New Zeeland earthquake messed up the nice ring
lasers over there.

http://www.fs.wettzell.de/LKREISEL/G/LaserGyros.html
http://www.phys.canterbury.ac.nz/ringlaser/about_us.shtml

--

   Björn

I believe a phase noise plot deep into the uHz or lower would apply to 
the

rotation rate of the earth.

On Saturday, 23 July 2016, Hal Murray  wrote:



t...@leapsecond.com said:
> Earth is a very noisy, wandering, drifting,
incredibly-expensive-to-measure,
> low-precision (though high-Q) clock.

What is the Q of the Earth?  It might be on one of your web pages, but I
don't remember seeing it.  Google found a few mentions, but I didn't
find a
number.

I did find an interesting list of damping mechanisms in a geology book.
Geology-nuts are as nutty as time-nuts.  Many were discussing damping of
seismic waves rather than rotation.

I've seen mention that the rotation rate of the Earth changed by a few
microseconds per day as a result of the 2011 earthquake in Japan.  Does
that
show up in any data?  Your recent graph doesn't go back that far and
it's
got
a full scale of 2000 microseconds so a few is going to be hard to see.



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[time-nuts] Histogram of T2 arrival times

[Mark Sims]

I have added some code to my message time offset measurement routine to 
calculate a histogram of the values (along with the average and standard 
deviation).   I'm now using the peak histogram bin(s) to determine the message 
offset time.   The histogram technique has the advantage of ignoring outlier 
points that can be caused by the system being tied up / interrupted  doing 
other things (like shoving a Windows 10 upgrade up your systems' rear I/O port  
;-()
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Re: [time-nuts] Histogram of T2 arrival times

[Rick Jones]

Yup.  I have some USB thermometers that are good for such things.


Model?  URL?


Might be over-spec'ed or simply reflect a lack of broad evaluation on 
their part, but the SPEC folks have an accepted device list for 
temperature sensors to be used for measuring ambient temps for 
SPECpower(tm) benchmarks:


https://www.spec.org/power/docs/SPECpower-Device_List.html#mozTocId276706

rick jones

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Re: [time-nuts] Commercial software defined radio for clock metrology

[Kevin Rosenberg]

Jeff,

Thanks for your very useful paper Oscillator Metrology with SDRs[1]. I created 
a C++ program and checked residuals using a 10 MHz clock split to the A and B 
channels of a LFRX and BasicRX boards and sampled at 1 Mhz. Using boxcar 
averaging of 1000 samples at 1 kHz, I was impressed by the low noise floor 
approaching that of my Timepod which was several times the cost. I included the 
Allan Deviation without averaging showing the sqrt(1000) increase in noise 
floor without the averaging[2].

I had a question about your experience. You mentioned using a input signal near 
the maximum of the USRP’s ADC to get the best SNR. I reviewed the schematics 
and application notes. I found a maximum Vpp mentioned of 3.3V. I was wondering 
what voltage you were using to drive the USRPs. When I go above 1.5-2 Vpp, I 
start getting signal distortions and not much increase in the amplitude. 

Many thanks for publishing your work in this area.

Kevin

[1]
https://arxiv.org/abs/1605.03505

[2]
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Re: [time-nuts] Histogram of T2 arrival times

[Gary E. Miller]

Yo Hal!

On Fri, 29 Jul 2016 02:50:59 -0700
Hal Murray  wrote:

> > So, you have plotted offset versus temp?  Can we see that?  
> 
> I don't have offset vs temperature.  This is what I work with:
>   http://users.megapathdsl.net/~hmurray/time-nuts/LAN-clock.png
>   http://users.megapathdsl.net/~hmurray/time-nuts/LAN-temp.png

150F to 170F on the CPU temps?  And your house temp is a sinusoid?

Weird...

> > Yup.  I have some USB thermometers that are good for such things.   
> 
> Model?  URL?

They're all Chinese random stuff.  You'll never find the same model when
you reorder.  This one has the same model number as one of mine, totally
different case:

http://pcsensor.com/usb-thermometer/temper2.html

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com  Tel:+1 541 382 8588


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Re: [time-nuts] Histogram of T2 arrival times

[Hal Murray]

> So, you have plotted offset versus temp?  Can we see that?

I don't have offset vs temperature.  This is what I work with:
  http://users.megapathdsl.net/~hmurray/time-nuts/LAN-clock.png
  http://users.megapathdsl.net/~hmurray/time-nuts/LAN-temp.png

Scan the wiki page for PID controllers:
  https://en.wikipedia.org/wiki/PID_controller

Consider the simple case (no I, no D).  If you have a constant rate of 
temperature change, there is a stable point with a constant offset.  The 
offset keeps adjusting the frequency (drift in ntp speak) to track the 
temperature.  The offset and temp derivative are related by the gain.

The graphs aren't great, but when the temperature is going up the offset is 
positive and the reverse.


> I would not be surprised if temp was dominant here.  But I can think of a
> few other things that may be dominant instead. 

Such as?


> I would only consider CPU temp a very rough proxy for XTAL temp.  Room
> ambient would be much closer to XTAL temp.

That box is fanless.  (There is actually a tiny fan under the disk.)  Mostly, 
it's not doing any work.

Room temp tracks CPU temp.

> Yup.  I have some USB thermometers that are good for such things. 

Model?  URL?


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Re: [time-nuts] Histogram of T2 arrival times

[Gary E. Miller]

Yo Hal!

On Thu, 28 Jul 2016 17:26:40 -0700
Hal Murray  wrote:

> g...@rellim.com said:
> >> The systems collecting the data have 200-300 microsec peak-peak of
> >> clock offset, mostly tracking daily temperature swings.  
> > How do you know that?   
> 
> Which "that"?

The thing just previous to "that": temp swings.

> You can get the temperature connection by plotting offset and
> temperature over 24-48 hours.  You can get confirmation by plotting
> the drift.

So, you have plotted offset versus temp?  Can we see that?

> Crystals are well known to have a temperature effect so the
> drift-temp connection shouldn't be surprising.

I would not be surprised if temp was dominant here.  But I can think
of a few other things that may be dominant instead.

If you have data, I'd love to see it, but conjecture is not very
useful, except to design a new experiment.

> On Linux, you can get the temperature from
>   /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
> or similar. 

I would only consider CPU temp a very rough proxy for XTAL temp.  Room  
ambient would be much closer to XTAL temp.

> You would really like to measure the temperature at the crystal.  I
> haven't gone that far.

Yup.  I have some USB thermometers that are good for such things.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com  Tel:+1 541 382 8588


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Re: [time-nuts] Histogram of T2 arrival times

[Hal Murray]

g...@rellim.com said:
>> The systems collecting the data have 200-300 microsec peak-peak of
>> clock offset, mostly tracking daily temperature swings.
> How do you know that? 

Which "that"?

I don't have a formal proof, just a collection of data that all fits together.

You can get the clock offset from loopstats.  That can lie, for example by 
using a PPS over USB without fudging to correct for the USB polling delay or 
getting the time from the net with asymmetric delays due to routing or 
last-mile link speeds.

You can confirm things by using a good NTP system to monitor your targets.  
That's somewhat circular since you have to ask how good is the clock on your 
"good" system.

You can get the temperature connection by plotting offset and temperature over 
24-48 hours.  You can get confirmation by plotting the drift.

Crystals are well known to have a temperature effect so the drift-temp 
connection shouldn't be surprising.

On Linux, you can get the temperature from
  /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
or similar.  The filename depends slightly on the version of the kernel you are 
using.

You can get confirmation of the temperature from the disk using hddtemp or 
smartd and/or by monitoring your room temperature.  (That works better if the 
disk is in the same box.)

You would really like to measure the temperature at the crystal.  I haven't 
gone that far.



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Re: [time-nuts] Histogram of T2 arrival times

[Gary E. Miller]

Yo Hal!

On Thu, 28 Jul 2016 13:55:32 -0700
Hal Murray  wrote:

> http://users.megapathdsl.net/~hmurray/time-nuts/T2-hist.png

Cool!

> The systems collecting the data have 200-300 microsec peak-peak of
> clock offset, mostly tracking daily temperature swings.

How do you know that?

RGDS
GARY
---
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Re: [time-nuts] Q/noise of Earth as an oscillator

[Björn Gabrielsson]

I'am  not sure how the big ring lasers have progressed over the past
years. It seems the big New Zeeland earthquake messed up the nice ring
lasers over there.

http://www.fs.wettzell.de/LKREISEL/G/LaserGyros.html
http://www.phys.canterbury.ac.nz/ringlaser/about_us.shtml

--

Björn

> I believe a phase noise plot deep into the uHz or lower would apply to the
> rotation rate of the earth.
>
> On Saturday, 23 July 2016, Hal Murray  wrote:
>
>>
>> t...@leapsecond.com said:
>> > Earth is a very noisy, wandering, drifting,
>> incredibly-expensive-to-measure,
>> > low-precision (though high-Q) clock.
>>
>> What is the Q of the Earth?  It might be on one of your web pages, but I
>> don't remember seeing it.  Google found a few mentions, but I didn't
>> find a
>> number.
>>
>> I did find an interesting list of damping mechanisms in a geology book.
>> Geology-nuts are as nutty as time-nuts.  Many were discussing damping of
>> seismic waves rather than rotation.
>>
>> I've seen mention that the rotation rate of the Earth changed by a few
>> microseconds per day as a result of the 2011 earthquake in Japan.  Does
>> that
>> show up in any data?  Your recent graph doesn't go back that far and
>> it's
>> got
>> a full scale of 2000 microseconds so a few is going to be hard to see.
>>
>>
>>
>> --
>> These are my opinions.  I hate spam.
>>
>>
>>
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Re: [time-nuts] Q/noise of Earth as an oscillator

[Tom Van Baak]

Scott Stobbe wrote:
> I believe a phase noise plot deep into the uHz or lower would apply to the
> rotation rate of the earth.

Yup. You'll see lots of uHz to Hz noise plots by people working with seismic 
noise, for example. My introduction to the subject were the many plots and 
papers that describe the heroic effort LIGO goes through to measure tidal and 
seismic noise in order to keep their gravity wave servos locked. Short-term, 
the surface of the earth is a very noisy place. But if you can model or measure 
it before it hits the mirrors, you can mostly back it out.

One can use PN and ADEV statistics on earth rotation, just like any other clock 
or oscillator. And it seems we can also compute Q for the earth, as if it were 
a mechanical oscillator.

The remaining question in this thread is if earth Q measurement has actual 
meaning, that is, if the concept of Q is valid for a slowly decaying rotating 
object, as it is for a slowly decaying simple harmonic oscillator. And that's 
were get into the history and definition(s) and applicability of Q to non 
harmonic oscillators, such as coils, capacitors, atomic clocks, planets, 
pulsars, etc.

/tvb

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Re: [time-nuts] Q/noise of Earth as an oscillator

[Alex Pummer]

the Q factor could be derived from the modulation bandwidth of an 
oscillator [ the "old way" of measuring the Q of resonator of the 
running oscillator's ], therefore if we look the fluctuation spectrum of 
the frequency of an oscillator we could determine the Q. Any circular 
movement could be seen as the source of a harmonic oscillation.


73
KJ6UHN
Alex



On 7/29/2016 9:28 AM, Attila Kinali wrote:

On Fri, 29 Jul 2016 03:29:27 -0500
David  wrote:


Capacitors and inductors have an associated Q while lacking a resonate
frequency except for parasitic elements.  Their Q increases with
frequency up to a point; does that apply to a spinning body?  I guess
it depends on the loss mechanism.

The Q of an inductor (or capacitor) is defined at a specific frequency.
You can see it as the Q factor that would be achieved, if the inductor
(capacitor) would be paired up with an ideal capacitor (inductor) with
a value such, that it would result in the specified frequency.

Hence, if you increase the frequency, the Q factor increases for an inductor. 
Conversly, the Q factor of an capacitor decreases with increasing  frequency.

See also:
https://en.wikipedia.org/wiki/Inductor#Q_factor
https://en.wikipedia.org/wiki/Capacitor#Q_factor


Attila Kinali



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Re: [time-nuts] Very Accurate Delta Time RF Pulse Measurements

[Attila Kinali]

On Fri, 29 Jul 2016 09:23:02 -0700
Chris Albertson  wrote:

> Sounds like you want to build something rather then use some
> instruments you can buy.   I've thought a little about this too as I
> want to make a LIDAR to measure distance using a laser pulse.  In my
> case I want both low cost and for the device to be very small and
> light and run off a battery

For this kind of application I would recommend looking into
chips like the TDC1000 (there are multiple in this family, and
other manufacturers have similar chips). They are made exactly for
that kind of application, though with ultrasonic flow measurement
in mind. The timing resolution is high enough that you can build a LIDAR
with <10cm resolution that does consume very litte power.

For higher resolution, I would go for a sinusoidal modulation scheme
and measure the phase difference between the transmitted and received
signal. That should easily give you resolution in the sub-cm range,
but also consumes more power.

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] NCOCXO anyone?

[Alex Pummer]

it is a way to use a carrier fc to make one SSB  signal with fm 
modulation frequency, use just the side-band, , which have a frequency 
of fc + fm = fR,  [fR/fc is a function of the SSB modulator carrier 
suppression capability,]  fm could be from less than 1/2 fc any 
frequency to zero, if it is zero fR =f c. With fm is not zero, the phase 
of fR will advance relative to  fc as long as fm is not zero if fm 
becomes zero the advance will stop.
The generation of a very small frequency offset will need fm = the 
offset frequency
To "clean up" the resulting fR, a PLL could be locked to it, which could 
look to one single frequency only [with very narrow tuning range 
oscillator, perhaps a a tunable crystal and very narrow loop filter 
[just to let pass fm ]
since oscillators are by definition amplifiers with infinite high gain 
that PLL could look  into fc!
Attila I don't know anything about any patent, but I developed that kind 
of system for video colour performance analyzing system in the "past 
century".

73
KJ6UHN
Alex

On 7/29/2016 9:23 AM, Attila Kinali wrote:

On Fri, 29 Jul 2016 00:26:07 + (UTC)
Bruce Griffiths  wrote:


Diophantine Frequency Synthesizer Design for Timekeeping Systems

I quickly went over the papers people have pointed me at. Without
having gone through all the math, the idea for choosing the PLL values
looks neat. The 2-cascaded synthesizer is also the one used by Spectratime
for their FemtoStepper, which bring us back to the question: How do they
achieve phase steps? I see how offset frequencies are generated (with
arbitrary small step sized), but I do not see how this can be turned
in fine resulution phase steps when using PLL's as the controlling elements.


Discusses a diophantine synthesiser.Note Sotiriadis' work on diophantine
numbers and frequency synthesis appears to be a rehash of an old Patent
perhaps due to a lack of competent searching for prior art.This issue was
discussed on the list some time ago,

Which patent are you refering to?

Attila Kinali


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Re: [time-nuts] Very Accurate Delta Time RF Pulse Measurements

[Brooke Clarke]

Hi Jerome:

The Vietnam era Radar Warning Systems used 4 wide band antennas (nose, tail & wing tips) and displayed the bearing, 
rough distance & threat type on a CRT.
Near the antenna was a crystal video receiver using a multi channel filter driving Schottky diode detectors.  The output 
from each detector fed a video log amp.

http://www.prc68.com/I/RWR.shtml
http://www.prc68.com/I/ALR54.shtml

The Fenwick antenna patent based on time delay beam steering is far superior to a phased array in that it's frequency 
independent.

http://www.prc68.com/I/Ant.shtml#TDBS
I think the basis of TOA.

Can you say more about the specifics of what you are trying to do?

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

 Original Message 

Hi Guys,

This is a little outside of time-nuts scope, but not by much.  I'm interested 
in finding the time between two rising edges above a set threshold with 
preferably nS or high ps timing accuracy.  Can this be simply done with a few 
programmed Microchip PICs or with a good short term OCXO clock?  The issue I 
see is that a 10Mhz timing reference with 1 cycle difference in time yields 
100ns resolution, which is far too large, so maybe a PIC can solve this.

This weekend project would be a multi-element antenna array, each with a 
super-fast response log peak power detector fed into several PICs for time of 
arrival.  Whenever a nearby high energy RF pulse is detected, the time of 
arrival between two antenna elements and hence the direction toward the TX 
could be roughly computed.  Some typical log peak detectors have an 8ns input 
pulse response time, so I'm hoping that rise times are similar between multiple 
detectors, negating the delayed response.

There are time of arrival/AoA systems out there with synthetic doppler, phased 
arrays, correlative interferometers, and phase comparators, but it would be 
interesting to accomplish super wideband AoA timing on two rising pulses with 
relatively cheap parts.

Thanks,

-Jerome
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Re: [time-nuts] Very Accurate Delta Time RF Pulse Measurements

[Chris Albertson]

Sounds like you want to build something rather then use some
instruments you can buy.   I've thought a little about this too as I
want to make a LIDAR to measure distance using a laser pulse.  In my
case I want both low cost and for the device to be very small and
light and run off a battery

I think the way to do this is to have a function generator that
creates a ramp function that moves from zero to some max volts in 100
ns.   Then when the pulse arrives you use that to trigger a capture of
the ramp's current voltage into a sample and hold.  Then later look at
the difference in the volts in each sample and hold.If the time
difference is longer than one ramp period then you need to also sample
the counts in a normal counter for each pulse edge.

I guess you might use a PIC to implement the above but I find it is
always easier to write software on a larger computer.  The aded cost
of using more expensive device is nothing if it saves hours or days of
effort (and you are only building one unit.)

You could use the uP internal counter to measure the rough time
interval and whatever drives that internal counter would also drive
the ramp function generator



>> This is a little outside of time-nuts scope, but not by much.  I'm
>> interested in finding the time between two rising edges above a set
>> threshold with preferably nS or high ps timing accuracy.  Can this be
>> simply done with a few programmed Microchip PICs or with a good short
>> term OCXO clock?  The issue I see is that a 10Mhz timing reference
>> with 1 cycle difference in time yields 100ns resolution, which is far
>> too large, so maybe a PIC can solve this.
>>
>> This weekend project would be a multi-element antenna array, each with
>> a super-fast response log peak power detector fed into several PICs
>> for time of arrival.  Whenever a nearby high energy RF pulse is
>> detected, the time of arrival between two antenna elements and hence
>> the direction toward the TX could be roughly computed.  Some typical
>> log peak detectors have an 8ns input pulse response time, so I'm
>> hoping that rise times are similar between multiple detectors,
>> negating the delayed response.
>>
>> There are time of arrival/AoA systems out there with synthetic
>> doppler, phased arrays, correlative interferometers, and phase
>> comparators, but it would be interesting to accomplish super wideband
>> AoA timing on two rising pulses with relatively cheap parts.
>>
>> Thanks,
>>
>> -Jerome
>> ___
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>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
>
> --
> WBW,
>
> V.P.
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-- 

Chris Albertson
Redondo Beach, California
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[time-nuts] On the path to nuclear isomer time clock?

[André Esteves]

On the path to nuclear isomer time clock?

http://www.nature.com/nature/journal/v533/n7601/full/nature17669.html

cheers,

Aife
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Re: [time-nuts] Q/noise of Earth as an oscillator

[Scott Stobbe]

I believe a phase noise plot deep into the uHz or lower would apply to the
rotation rate of the earth.

On Saturday, 23 July 2016, Hal Murray  wrote:

>
> t...@leapsecond.com said:
> > Earth is a very noisy, wandering, drifting,
> incredibly-expensive-to-measure,
> > low-precision (though high-Q) clock.
>
> What is the Q of the Earth?  It might be on one of your web pages, but I
> don't remember seeing it.  Google found a few mentions, but I didn't find a
> number.
>
> I did find an interesting list of damping mechanisms in a geology book.
> Geology-nuts are as nutty as time-nuts.  Many were discussing damping of
> seismic waves rather than rotation.
>
> I've seen mention that the rotation rate of the Earth changed by a few
> microseconds per day as a result of the 2011 earthquake in Japan.  Does
> that
> show up in any data?  Your recent graph doesn't go back that far and it's
> got
> a full scale of 2000 microseconds so a few is going to be hard to see.
>
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
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Re: [time-nuts] Q/noise of Earth as an oscillator

[Attila Kinali]

On Fri, 29 Jul 2016 03:29:27 -0500
David  wrote:

> Capacitors and inductors have an associated Q while lacking a resonate
> frequency except for parasitic elements.  Their Q increases with
> frequency up to a point; does that apply to a spinning body?  I guess
> it depends on the loss mechanism.

The Q of an inductor (or capacitor) is defined at a specific frequency.
You can see it as the Q factor that would be achieved, if the inductor
(capacitor) would be paired up with an ideal capacitor (inductor) with
a value such, that it would result in the specified frequency.

Hence, if you increase the frequency, the Q factor increases for an inductor. 
Conversly, the Q factor of an capacitor decreases with increasing  frequency.

See also:
https://en.wikipedia.org/wiki/Inductor#Q_factor
https://en.wikipedia.org/wiki/Capacitor#Q_factor


Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] NCOCXO anyone?

[Attila Kinali]

On Fri, 29 Jul 2016 00:26:07 + (UTC)
Bruce Griffiths  wrote:

> Diophantine Frequency Synthesizer Design for Timekeeping Systems

I quickly went over the papers people have pointed me at. Without
having gone through all the math, the idea for choosing the PLL values
looks neat. The 2-cascaded synthesizer is also the one used by Spectratime
for their FemtoStepper, which bring us back to the question: How do they
achieve phase steps? I see how offset frequencies are generated (with
arbitrary small step sized), but I do not see how this can be turned
in fine resulution phase steps when using PLL's as the controlling elements.

> Discusses a diophantine synthesiser.Note Sotiriadis' work on diophantine
> numbers and frequency synthesis appears to be a rehash of an old Patent
> perhaps due to a lack of competent searching for prior art.This issue was
> discussed on the list some time ago,

Which patent are you refering to?

Attila Kinali
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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[time-nuts] WTB: HP 5334a or 5334b

[Jeff AC0C]

If you have a unit in good condition, excess to your needs, kindly contact 
me off list please.


73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie


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Re: [time-nuts] Very Accurate Delta Time RF Pulse Measurements

[Vlad]

May be some more accurate alternative to AD8302 could do that. AD8302 
could measure Gain/Loss and Phase up to 2.7 GHz. I using one in my 
project and its doing its job right (I think).




On 2016-07-28 19:12, Jerome Blaha wrote:

Hi Guys,

This is a little outside of time-nuts scope, but not by much.  I'm
interested in finding the time between two rising edges above a set
threshold with preferably nS or high ps timing accuracy.  Can this be
simply done with a few programmed Microchip PICs or with a good short
term OCXO clock?  The issue I see is that a 10Mhz timing reference
with 1 cycle difference in time yields 100ns resolution, which is far
too large, so maybe a PIC can solve this.

This weekend project would be a multi-element antenna array, each with
a super-fast response log peak power detector fed into several PICs
for time of arrival.  Whenever a nearby high energy RF pulse is
detected, the time of arrival between two antenna elements and hence
the direction toward the TX could be roughly computed.  Some typical
log peak detectors have an 8ns input pulse response time, so I'm
hoping that rise times are similar between multiple detectors,
negating the delayed response.

There are time of arrival/AoA systems out there with synthetic
doppler, phased arrays, correlative interferometers, and phase
comparators, but it would be interesting to accomplish super wideband
AoA timing on two rising pulses with relatively cheap parts.

Thanks,

-Jerome
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--
WBW,

V.P.
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Re: [time-nuts] phase noise in digital divider, 2nd harmonic

[Graham / KE9H]

It is not traditional phase noise, and not a normal Nyquist filtering
problem, but, yes, presence of significant second harmonic energy in your
DDS output will shift/dither your squaring input.

It is hard, with practical filters and filter components to get much better
coverage than one-half octave per low-pass filter.  It will be set by how
much second harmonic content you can tolerate. That is, how far down the
low-pass filter slope the second harmonic needs to be to get the
performance you want.

So using the one-half octave per filter "rule of thumb" then you might need
three or more low pass filters, depending on the actual frequency span
output you are dealing with.

--- Graham

On Thu, Jul 28, 2016 at 6:39 PM, life speed via time-nuts <
time-nuts@febo.com> wrote:

> Hi,
>
> Been a while since I visited, I recall there are many, well, time nuts
> here.  I am trying to track down a source of phase noise in a frequency
> synthesizer design.  One part of the frequency reference upconverts a DDS
> and then divides it down again using a digital divider - standard technique
> for DDS angle modulation spurious reduction.
>
> The DDS tunes over more than an octave, so obviously the single low pass
> filter isn't going to cut it.  I am noticing up to 3 dB phase noise
> degradation at the output of the divider as the DDS frequency decreases and
> the 2nd harmonic is in-band to the LPF.  I suspect this is disturbing the
> threshold crossing in the high speed digital logic divider, as described in
> "The Effect of Harmonic Distortion on Phase errors in Frequency
> Distribution and Synthesis" by F.L. Walls et al at NIST.
>
> What do you think?  I should probably put in a switched filter to get my 3
> dB back  ;)
>
> - Lifespeed
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Re: [time-nuts] phase noise in digital divider, 2nd harmonic

[Attila Kinali]

On Thu, 28 Jul 2016 23:39:24 + (UTC)
life speed via time-nuts  wrote:

> The DDS tunes over more than an octave, so obviously the single low pass 
> filter isn't going to cut it.  I am noticing up to 3 dB phase noise 
> degradation at the output of the divider as the DDS frequency decreases and 
> the 2nd harmonic is in-band to the LPF.  I suspect this is disturbing the 
> threshold crossing in the high speed digital logic divider, as described in 
> "The Effect of Harmonic Distortion on Phase errors in Frequency Distribution 
> and Synthesis" by F.L. Walls et al at NIST.
> 
> What do you think?  I should probably put in a switched filter to get my 3 dB 
> back  ;)

Without being an expert in DDS and knowing your circuit, this sounds
like the most likely cause and the easiest solution. All other harmonics
reduction systems I am aware of are much more complicated.


Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Very Accurate Delta Time RF Pulse Measurements

[Attila Kinali]

On Thu, 28 Jul 2016 23:12:54 +
Jerome Blaha  wrote:

> Hi Guys,
> 
> This is a little outside of time-nuts scope, but not by much.  
> I'm interested in finding the time between two rising edges above a set
> threshold with preferably nS or high ps timing accuracy.  Can this be simply
> done with a few programmed Microchip PICs or with a good short term OCXO
> clock?  The issue I see is that a 10Mhz timing reference with 1 cycle
> difference in time yields 100ns resolution, which is far too large, so maybe
> a PIC can solve this.

I think the easiest way is to implement something like the PICTIC II [1].
That should get you into the order of 100ps with minimal effort.
With a little bit of care, you can make it go down to 20-30ps rms.
But I think, that the pulse generation itself is probably the part
that limits your precision, as the logarithmic amplifiers are usually
quite noisy.


Attila Kinali

[1] http://www.ko4bb.com/doku2015/doku.php?id=precision_timing:pictic

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Q/noise of Earth as an oscillator

[Azelio Boriani]

What about an ADEV/TDEV plot of the pulsar J0437-4715?

On Fri, Jul 29, 2016 at 12:39 AM, Jim Palfreyman  wrote:
> Hi All,
>
> Tom gave me a nudge to look here - I hadn't been following this thread.
>
> For those that don't know, I study pulsars and so the way we measure what
> pulsars do could be relevant to this discussion.
>
> First, I have never heard of a Q measure when referencing a pulsar. I think
> the key here is that it's not resonating as such. Rotating yes, resonating
> no.
>
> Pulsars spin and slow down due to giving off energy (magnetic dipole
> radiation). So in the pulsar world we mainly refer to spin frequency (F0)
> and frequency derivative (F1). With some of the younger and more "erratic"
> pulsars, F2 (and further) can be modelled.
>
> Here's some data on the Vela pulsar (hot off the presses - measured just
> now):
>
> F0  11.1867488542579
> F1  -1.55859177352837e-11
> F2  1.23776878287221e-21
>
> Vela is young and erratic. Millisecond pulsars are outstanding clocks.
> Here's the data for J0437-4715 - one of the most stable pulsars we know
> about:
>
> F0  173.6879458121843
> F1  -1.728361E-15
>
> I'm sure the "Q" of Vela would be pretty decent - but I can tell you now,
> as a time-keeper, she's useless.
>
>
> Jim Palfreyman
>
>
>
> On 28 July 2016 at 20:50, Tony Finch  wrote:
>
>> Neville Michie  wrote:
>>
>> > The conical pendulum has a simple form of a weight on a string, instead
>> > of oscillating in one plane as a conventional pendulum, it swings around
>> > in a circular orbit in the horizontal plane. It has a definite resonant
>> > frequency.
>>
>> I don't think it does have a resonant frequency, any more than the Earth
>> does: the angular velocity of the pendulum is sqrt(g/h) where h is the
>> height of the pendulum; give it more energy, it swings higher, so h is
>> smaller, so the frequency is higher.
>>
>> Tony.
>> --
>> f.anthony.n.finch    http://dotat.at/  -  I xn--zr8h
>> punycode
>> South Thames, Dover: Southwesterly 5 or 6. Slight or moderate. Rain or
>> showers. Good, occasionally poor.
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Re: [time-nuts] Q/noise of Earth as an oscillator

[David]

On Wed, 27 Jul 2016 15:15:48 -0400, you wrote:

>On 7/27/2016 10:04 AM, time-nuts-requ...@febo.com wrote:
>
>> Exciting the Earth with a new frequency (and an adeguate amount of
>> energy) sets a new rotational speed: you cannot retune a (for example)
>> quartz crystal in the same way...
>
>Sure you can. Spin it at 100 RPM, or 1000, RPM or even 25000  RPM... :)
>
>Interesting conversation. I tend to agree the earth is not a classic 
>harmonic oscillator. Energy is not exchanged between different storage 
>mechanisms. It's rotational period has no natural harmonic frequency. 
>i.e. rotational period could be anything.
>
>However I also agree it exhibits characteristics of other items that Q 
>can be calculated for. Rate of slowing, loss of energy per cycle, etc.
>And since the definition of Q is varied and used quite widely, it seems 
>Q is also appropriate here.
>
>Maybe Earth is a special case since after all it DID give us the second, 
>and we DO set our atomic clocks to IT every 6 to 12 months...
>
>...now I'll be thinking of this all night...  ...I think Tom is just 
>toying with us now...
>
>Dan

Capacitors and inductors have an associated Q while lacking a resonate
frequency except for parasitic elements.  Their Q increases with
frequency up to a point; does that apply to a spinning body?  I guess
it depends on the loss mechanism.

If you used the Earth's rotation as part of a harmonic oscillator,
what would limit the Q?  All the sloshing fluid, physical
displacement, and mechanical hysteresis add up to energy lost per
cycle.

This seems like one of those fun physics problems where you start with
a bunch of seemingly unrelated pieces of numerical data and calculate
the mass of the Milky Way.
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