[time-nuts] Adafruit Ultimate GPS timing message arrival times
Yes, I find it confusing also. I've been reporting the value that Lady Heather uses to do most of her evil internal message off machinations with... For those, the negative offset value is the "natural" polarity. I'm probably going to change it around to something humans (including me) find more natural to interpret. - > Thanks, Mark. I'd missed that in the post. I still find it confusing to plot > positive times as negative ones. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Adafruit Ultimate GPS timing message arrival times
From: Mark Sims As mentioned in the post the times reported are the time stamp in the receiver packet minus the system clock time when it was received... negative value indicate the message arrives after the PPS. The polarity of the reported value is consistent with how Lady Heather makes use of the value... === Thanks, Mark. I'd missed that in the post. I still find it confusing to plot positive times as negative ones. From your data and my own measurements, I feel that using the serial NMEA stream would, today, be a last resort, as an Internet sync would be considerably better. Would you agree with that? Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk Twitter: @gm8arv ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Q/noise of Earth as an oscillator
At the risk of boring everyone, here is an "Alice and Bob" thought experiment concerning linear and circular movement: Condition A: Let's say that Alice is in her spacecraft in inertial straight line travel through nearly free space containing a thin gas which creates a slight friction to movement. She is traveling at 628 meters per 24 hours adjacent to a distance scale with markers every 628 meters on the space highway. Passing a marker results in a tick. So she can check her atomic clock every 24 hours at the tick. The thin gas causes a slight reduction of her velocity (about a 2 millisecond increase in tick interval every century). Question: Does the movement of Alice exhibit Q? If so, how can we compute the value? If there a resonant frequency? Condition B: Bob is in his spacecraft, which is identical to Alice's model. A rod 200 meters long connects Alice's craft and Bob's craft. Bob is moving at 628 meters per 24 hours in the opposite direction of Alice, so that the midpoint of the rod is fixed and unmoving with regards to the distant stars. Alice will return to the same point in space every 24 hours and pass a marker, generating a tick so she can check her atomic clock once a day at the tick. Her linear motion has been constrained to circular motion due to the stiff rod. The same thin gas is present, resulting in a 2 millisecond increase in tick interval every century. Question: Now does the movement of Alice exhibit Q? If so, how can we compute the value? If there a resonant frequency? Consider that in either Condition A or Condition B Alice (and Bob) can increase or decrease their velocity to receive timing ticks at a faster or slower rate. But there is no tendency for the velocity to return to the one tick per day rate (628 meters per 24 hours), as there would be with a harmonic oscillator. Due to Newton's First Law, the velocity remains constant unless slowed by friction or affected by external forces. We could have started with a rod which was in the limit very long, so the motion of Alice was only slightly diverted from a straight line during a 24 hour interval. We could still measure the motion in 628 meter distance intervals on a circular or angular scale. Note that nothing is fundamentally different if the rod is the exact length which causes one rotation every 24 hours. The distance traveled and the inertia resisting change in velocity is the same if the motion is linear or circular, isn't it? -- Bill Byrom N5BB On Sun, Jul 31, 2016, at 10:27 PM, Bill Byrom wrote: > I still claim that there is no natural frequency associated with the > rotation of a body. The periodic nature of the rotating body motion is > confusing you. The choice of a coordinate system is what is confusing. > > As I pointed out, what's the difference between an inertial > body moving > in a straight line and a rotating body? Let's say you take a > body moving > in free space with a small energy loss due to interactions with thin > interstellar gas. You measure it on a ruler with marks every > 628 meters > (to use my example of a point on the Earth 100 meters from the > pole as a > comparison). That's the same as making an astronomical measurement on > the Earth at a distant star which is overhead every 24 hours. In both > cases the point moves 628 meters every 24 hours (measured with > an atomic > clock). We generate a tick when the Earth has rotated to the same > relative position and when the body moving in a straight line reaches > the next 628 meter mark. Both objects generate a tick every 24 hours, > but the velocity is each case (angular or linear) is unconstrained by > any periodic physical processes. > > What makes the rotating body (Earth) suitable for study as a harmonic > oscillator with Q in this case? There is no energy transfer > during each > rotation. Should we establish a Q value for the body in free space > straight line motion? Both bodies have mass, inertia, a nearly > constant > velocity (linear and angular), and a slight loss. Each > generates a tick > every 24 hours (using the atomic clock as a reference). If we > unwrap the > polar coordinates and view the Earth rotation angle as increasing > monotonically (or make marks every 628 meters on the scale > measuring the > free space body with straight line travel) they are identical. > > The geometry of the rotating body (Earth) is fooling you into thinking > it's a periodic oscillator. Just because the position is similar after > 24 hours doesn't mean anything, since there is no energy storage and > transfer during each rotation. The Earth is reasonably symmetric (for > this discussion), and it has no field which matters for this > discussion > which is rotating. It's just matter moving in a constrained circular > fashion due to the geometry and constraints of a rigid body. > Change the > coordinate scale to linear (628 meters for each rotation at 100 meters > from the axis) and compare it to the free space object moving in a > straight l
Re: [time-nuts] Commercial software defined radio for clockmetrology
Hi Kevin, Sorry for jumping into the thread somewhat late, but I am away on a music festival, spending my vacation working. I think some of what I would like to point out has already been covered, somewhat indirectly. When you measure ADEV, white phase modulation and flicker phase modulation both depend on the bandwidth of the input channel. This is known already from David Allan's article in Feb 1966. One peculiarity in there, that I discussed with him as I met him at the IFCS 2016, is that the white phase modulation is assumed to be a block filter, and he said that it reflects the counters that they had at that time. Anyway, any averaging you will do will affect the white and flicker phase modulations, but not white and flicker frequency modulations. When you filter, you will inflict a bias in the values, but the bandwidth is the main cause of bias for white and flicker phase modulation. It turns out that also the frequency modulations is affected by filtering, which comes as no surprise. This makes ADEV a tricky business as you get biases to "true ADEV". What is "true ADEV"? Well, ADEV is a method to estimate noise amplitudes using counters, simply because at the time, phase noise systems simply did not have enough frequency resolution to be useful for atomic clocks. The definition gives the relationship between the noise level and the ADEV value for that particular noise-type. Any number of reasons to deviate from the ADEV values cause biases, and this in itself is not a problem if the bias can be characterized and compensated for, which is what the bias functions do. The pre-filtering that MDEV does is just a tau-long phase sample average prior to the ADEV step, and this causes a bias between the MDEV and ADEV functions, different between the different noise-types, but the bias functions is known. The use of bias functions is usually where most people fail. Now, it was known in the beginning that ADEV values should always be given with the channel bandwidth, and the assumed assumption there is that it is a brick-wall filter as expected from time interval counters, delivering phase samples, or possibly frequency samples which is just a post-processing of the phase samples. The annotation of bandwidth got lost over time, and we can assume that it is f_h=1/(2T) due to Nyquist. Let's now consider two averaging methods, one where we average all samples over a second and another when we use a classic one-pole low-pass filter and sample the output. The average will have the assumed brick-wall property, as if the counter measured at 1 s tau, but obviously the white phase modulation noise is being averaged down and so will flicker phase modulation noise be to some degree, which is already in their formulas. For the low-pass filter, you will get the bandwidth aspect, which will behave similar, but as the slope behaves, it will sum up the noise differently as you integrate over frequency, so it will provide a different answer, in fact, the ADEV response and hence bias function has not been established in published work, and as I have asked around fellow researchers, only one has made some scrap note calculations during the PhD thesis time and David Allan knows that Fred Walls was working on it, as they had their offices next to each other at NBS/NIST in Boulder, but it is not known if the notes every survived. What we do know is what was hinted before, if you produce samples at high enough rate compared to your lowest analysis tau, then the bias will be small enough to not be a practical matter. For telecom measurements for instance, the highest sample tau is 1/30 of the lowest analysis tau in order to avoid this bias. The standard is very well-written in this regard, as it then provides a practical solution while allowing for many different types of implementation of the measurement, while keeping the implementation type from coloring the result too much, as the comparability of results is important. Another aspect of box-car averaging or any form of averaging is also that sub-sampling can suffer from aliasing problems, and neither box-car averaging or single-pole filters have very good anti-aliasing properties, so higher degree filters is needed, it's just that well, we don't have their bias functions. A fascinating set of additional biases can be found in counters using various averaging techniques, and then output data which may or may not be overlapping. Not all off them can be used to produce proper ADEV or MDEV, some may be used to produce proper values, but only if their overlapping output is treated like overlapping for the tau they average over and processed properly, but when not it produces biases. I see this regularly enough in poster sessions among others. Several tools fail to handle such overlapping output properly. In the end "true ADEV" values is tricky business, and mostly because it is not very well understood. I
Re: [time-nuts] Q/noise of Earth as an oscillator
t...@radio.sent.com said: > As I pointed out, what's the difference between an inertial body moving in a > straight line and a rotating body? The rotating body has a natural unit of time so there is a convenient way to make Q dimensionless. For linear motion, the natural unit of decay would be the time constant. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Another arrival time histogram: SiRF III
It was setup to only send GPRMC sentences. http://users.megapathdsl.net/~hmurray/time-nuts/RMC-hist.png Here is what it looks like over time: http://users.megapathdsl.net/~hmurray/time-nuts/RMC-offset.png There are interesting glitches at 3 hours and 23 hours. Anybody have any ideas about what would cause that? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Q/noise of Earth as an oscillator
I still claim that there is no natural frequency associated with the
rotation of a body. The periodic nature of the rotating body motion is
confusing you. The choice of a coordinate system is what is confusing.
As I pointed out, what's the difference between an inertial body moving
in a straight line and a rotating body? Let's say you take a body moving
in free space with a small energy loss due to interactions with thin
interstellar gas. You measure it on a ruler with marks every 628 meters
(to use my example of a point on the Earth 100 meters from the pole as a
comparison). That's the same as making an astronomical measurement on
the Earth at a distant star which is overhead every 24 hours. In both
cases the point moves 628 meters every 24 hours (measured with an atomic
clock). We generate a tick when the Earth has rotated to the same
relative position and when the body moving in a straight line reaches
the next 628 meter mark. Both objects generate a tick every 24 hours,
but the velocity is each case (angular or linear) is unconstrained by
any periodic physical processes.
What makes the rotating body (Earth) suitable for study as a harmonic
oscillator with Q in this case? There is no energy transfer during each
rotation. Should we establish a Q value for the body in free space
straight line motion? Both bodies have mass, inertia, a nearly constant
velocity (linear and angular), and a slight loss. Each generates a tick
every 24 hours (using the atomic clock as a reference). If we unwrap the
polar coordinates and view the Earth rotation angle as increasing
monotonically (or make marks every 628 meters on the scale measuring the
free space body with straight line travel) they are identical.
The geometry of the rotating body (Earth) is fooling you into thinking
it's a periodic oscillator. Just because the position is similar after
24 hours doesn't mean anything, since there is no energy storage and
transfer during each rotation. The Earth is reasonably symmetric (for
this discussion), and it has no field which matters for this discussion
which is rotating. It's just matter moving in a constrained circular
fashion due to the geometry and constraints of a rigid body. Change the
coordinate scale to linear (628 meters for each rotation at 100 meters
from the axis) and compare it to the free space object moving in a
straight line. What's the difference?
--
Bill Byrom N5BB
On Sun, Jul 31, 2016, at 09:16 PM, Tom Van Baak wrote:
> Hal:
>> Is there a term other than Q that is used to describe the rate of
>> energy loss
>> for things that aren't oscillators?
>
> Jim:
>> cooling (as in hot things)
>> discharge (as in capacitors and batteries)
>> leakage (as in pressure vessels)
>> loss
>
> Scott:
>> An irreversible process would be a better description versus
>> energy loss.
>> Like joule heating (resistance, friction).
>
> Notice that these are all energy losses over time; gradual
> processes with
> perhaps an exponential time constant, but without cycles or
> periods. We
> know not to apply Q in these scenarios.
>
> But when you have an oscillator, or a resonator, or (as I suggest) a
> "rotator", it seems to make sense to use Q to describe the normalized
> rate of decay. So three keys to Q: you need energy; you need
> energy loss;
> you need cycles over which that loss repeatedly occurs.
>
> We use units of time (for example, SI seconds) when we describe a
> rate.
> But here's why Q is unitless -- you normalize the energy (using E /
> dE)
> **and** you also normalize the time (by cycle). No Joules. No
> seconds. So
> having period is fundamental to Q. It's this unitless character
> of Q (in
> both energy and time) that makes it portable from one branch of
> science
> to another. And if you measure in radians you can even get rid of the
> 2*pi factor ;-)
>
> Without controversy, lots of articles define Q as 2*pi times {total
> energy} / {energy lost per cycle}. To me, a slowly decaying spinning
> Earth meets the three criteria. It appears to follow both the
> letter and
> the spirit of Q.
>
> Bob:
>> ummm…. Q is the general term of rate of energy loss and we just
>> happen to apply
>> it to oscillators in a very elegant fashion….
>
> Oh, no. Now we have both quality factor and elegance factor!
>
> /tvb
> _
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Re: [time-nuts] Commercial software defined radio for clockmetrology
Hi Tom, Thanks for your thoughts. I had looked at your helpful page when I started researching the effects of averaging. Currently, I’m experimenting with the dual receivers in the SDR using cross-correlation to reduce the noise floor. Kevin > On Jul 30, 2016, at 5:08 PM, Tom Van Baak wrote: > >> SDRs sample at high rates. The slowest the USRP N2x0 can sample is just >> under 200Ksps. > > Hi Kevin, > > I don't have an easy answer for you. BobC / BruceG / MagnusD / JohnM / > EnricoR can shed light on this. But I support your effort to figure out how > to obtain real truth from a massive oversampled data set. > > If you feel uneasy that ADEV statistics might lie, see: > http://leapsecond.com/pages/adev-avg/ > > ADEV is always a tricky, since the measurement bandwidth is not always > specified, or how that bandwidth is implemented. Both the front-end h/w > design and any embedded s/w manipulation of raw data will distort (bias) the > statistics. Distortion itself is not a show-stopper, as long as you can > properly model it and back it out. But it seems the challenge is knowing how > valid the model is, and if model itself depends on the noise type. > > /tvb > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Q/noise of Earth as an oscillator
Hi Tom,
You said: "you need energy; you need energy loss; you need cycles over
which that loss repeatedly occurs."
With regard to the earth, where is the first one? Sure it was there at the
start when the solar system formed, but where is it now?
Jim
On 1 August 2016 at 12:16, Tom Van Baak wrote:
> Hal:
> > Is there a term other than Q that is used to describe the rate of energy
> loss
> > for things that aren't oscillators?
>
> Jim:
> > cooling (as in hot things)
> > discharge (as in capacitors and batteries)
> > leakage (as in pressure vessels)
> > loss
>
> Scott:
> > An irreversible process would be a better description versus energy loss.
> > Like joule heating (resistance, friction).
>
> Notice that these are all energy losses over time; gradual processes with
> perhaps an exponential time constant, but without cycles or periods. We
> know not to apply Q in these scenarios.
>
> But when you have an oscillator, or a resonator, or (as I suggest) a
> "rotator", it seems to make sense to use Q to describe the normalized rate
> of decay. So three keys to Q: you need energy; you need energy loss; you
> need cycles over which that loss repeatedly occurs.
>
> We use units of time (for example, SI seconds) when we describe a rate.
> But here's why Q is unitless -- you normalize the energy (using E / dE)
> *and* you also normalize the time (by cycle). No Joules. No seconds. So
> having period is fundamental to Q. It's this unitless character of Q (in
> both energy and time) that makes it portable from one branch of science to
> another. And if you measure in radians you can even get rid of the 2*pi
> factor ;-)
>
> Without controversy, lots of articles define Q as 2*pi times {total
> energy} / {energy lost per cycle}. To me, a slowly decaying spinning Earth
> meets the three criteria. It appears to follow both the letter and the
> spirit of Q.
>
> Bob:
> > ummm…. Q is the general term of rate of energy loss and we just happen
> to apply
> > it to oscillators in a very elegant fashion….
>
> Oh, no. Now we have both quality factor and elegance factor!
>
> /tvb
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
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Re: [time-nuts] Q/noise of Earth as an oscillator
Hal:
> Is there a term other than Q that is used to describe the rate of energy loss
> for things that aren't oscillators?
Jim:
> cooling (as in hot things)
> discharge (as in capacitors and batteries)
> leakage (as in pressure vessels)
> loss
Scott:
> An irreversible process would be a better description versus energy loss.
> Like joule heating (resistance, friction).
Notice that these are all energy losses over time; gradual processes with
perhaps an exponential time constant, but without cycles or periods. We know
not to apply Q in these scenarios.
But when you have an oscillator, or a resonator, or (as I suggest) a "rotator",
it seems to make sense to use Q to describe the normalized rate of decay. So
three keys to Q: you need energy; you need energy loss; you need cycles over
which that loss repeatedly occurs.
We use units of time (for example, SI seconds) when we describe a rate. But
here's why Q is unitless -- you normalize the energy (using E / dE) *and* you
also normalize the time (by cycle). No Joules. No seconds. So having period is
fundamental to Q. It's this unitless character of Q (in both energy and time)
that makes it portable from one branch of science to another. And if you
measure in radians you can even get rid of the 2*pi factor ;-)
Without controversy, lots of articles define Q as 2*pi times {total energy} /
{energy lost per cycle}. To me, a slowly decaying spinning Earth meets the
three criteria. It appears to follow both the letter and the spirit of Q.
Bob:
> ummm…. Q is the general term of rate of energy loss and we just happen to
> apply
> it to oscillators in a very elegant fashion….
Oh, no. Now we have both quality factor and elegance factor!
/tvb
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Re: [time-nuts] Q/noise of Earth as an oscillator
On Sat, Jul 30, 2016 at 1:19 AM, Tom Van Baak wrote: > 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 > On Mon, Aug 1, 2016 at 6:50 AM, Bill Byrom wrote: > My final argument is that the rotation frequency of the Earth is > affected by tidal friction, but the amplitude of the motion of that > point 100 meters from the axis is unaffected. The amplitude of a > harmonic oscillator is directly affected by friction or other losses, > but the effect on resonant frequency is tiny. So loss effects frequency > in one situation and amplitude in the other. How can Q relate to both > situations? > -- > Bill Byrom N5BB > I'll try to answer both. Apologies for mistakes or shortcuts, I will correct or provide details in future posts if needed. If we consider this definition: Q = 2*pi * energy stored / energy lost per cycle, we can write it as Q = 2*pi * E / (-dE/d(cycle)) = E / (-dE/d(theta)) => E = E0*exp(-theta/Q). The energy decays exponentially if the frequency is constant. The impulse response of an RLC circuit is an exponentially decaying sinusoid with a fixed frequency, so Q naturally describes the decay of an RLC circuit and other resonant systems that behave similarly. Suppose we want to use Q for a rotating object that gradually slows down. When a rotating object loses energy, the period increases. From the definition, the energy of a rotating object with constant Q decays exponentially when we are counting cycles. But each cycle gets stretched over time, so the energy decay is slower than exponential over time. Omitting the derivation, a rotating object with constant Q behaves like this: E0 = energy at t = 0 I = moment of inertia k1 = sqrt(E0/I) k2 = E0*I theta = 2*Q*log(k1*t/(Q*sqrt(2)) + 1) rad omega = k1*2*Q / (k1*t + Q*sqrt(2)) rad/s(1) energy = k2*Q^2 / (E0/2*t^2 + sqrt(2*k2)*Q*t + I*Q^2) Consider the Earth with an LOD increase of 2 ms/century (6.338e-13 s/s). Suppose LOD = 0 at t = 0. Then k3 = 6.338e-13/(86400 s) omega0 = 72921151.467064e-12 rad/s omega = omega0 * (1 - t*k3) rad/s.(2) ( from http://hpiers.obspm.fr/eop-pc/earthor/ut1lod/UT1.html ) The frequency linearly decreases over time, which is different from the angular frequency of a rotating object with constant Q (1). Again omitting the derivation, the changing Q of the Earth over time is Q = omega0 * (1 - t*k3)^2 / (2*k3).(3) The Q is around 4.97e12 and decreases very slowly to 4.74e12 after 100 million years, assuming a constant 2 ms/century for that duration. If the period linearly increases over time, the angular frequency is omega = 2*pi / (T0 + k4*t) rad/s(4) where T0 is the period at t = 0 and k4 is the change in period per second. This looks like the angular frequency with constant Q (1). Let's make (4) look like (1): omega = k1*2*(pi/k4) / (k1*t + T0*k1/k4) so we set Q = pi/k4 and set k4 equal to the change in the period of (2) at t = 0. Then we get Q = omega0 / (2*k3)(5) which is the same as (3) when t = 0. If we approximate omega0 = 2*pi/86400 (1 cycle = 1 solar day), (5) is the same as tvb's formula pi * (86400 * 365 * 100 / 0.002). To recap: 1. An oscillation with fixed frequency and exponential decay has constant Q. 2. A rotating object with linearly decreasing frequency (2) has decreasing Q (3). 3. A rotating object with linearly increasing period (4) has constant Q (5). 4. Over short time scales or when Q is very large, (3) is almost equal to (5). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Q/noise of Earth as an oscillator
Hal Murray wrote: > It's energy loss in both cases. > > Is there a term other than Q that is used to describe the rate of energy loss > for things that aren't oscillators? I've seen "energy dissipation" or "energy decrement". Before Q was used to describe line width of atomic and optical clocks, before Q was used to describe performance of simple harmonic oscillators and quartz crystals, before or while Q was used to describe the ratio of reactance to resistance in a coil, horologists that worked with precision pendulum clocks needed a way to characterize the amount of energy lost per period. This was very important because the energy lost each swing (due to all forms of friction) had to be replaced in order to keep the pendulum oscillator running. And the timekeeping performance seemed to be related to how small or how consistent this energy was. I'm sure "decrement" was used before then, but I'm not well-read enough in science history to have any idea. Still... What I do know is this abstract from a 1938 paper [1], written by an early time nut: THE DISSIPATION OF ENERGY BY A PENDULUM SWINGING IN AIR, By E. C. ATKINSON -- ABSTRACT. The decrement of a pendulum falls slowly with the amplitude: hence the need for determinations based on small changes of angle. The resulting errors of observation lead to erratic values but not to systematic error. The result of measurements with a seconds pendulum enclosed in a case is shown by a smoothed curve, the departure from observed times being expressed by smoothing fractions, and a smoothing figure is a measure of this departure for the whole or part of the experiment. From the decrement the rate of loss of energy is calculated. This 7 kg. pendulum with amplitude 53' dissipates a Board of Trade Unit (which serves a 70 w. lamp for 14 hours) in rather over 100,000 years. Experiments with different pendulums are described by which the component losses due to suspension, rod, and bob are found. Suspension springs made from thin strip clamped in chaps dissipate large and variable amounts of energy compared with springs made from thick strip ground thin in the middle. The variable losses are associated with variable rates of the pendulum. The cylindrical case adds considerably to the air resistance. The measured loss due to a gravity impulse lever is little in excess of the computed loss from collision with the pendulum: for a seconds pendulum 1/2000 part of the free pendulum loss. -- This article is also a favorite of mine because it talks about a "root mean square of a series of such fractions may be called the smoothing figure for the series, and its smallness is an indication of the confidence which may be placed in the result." -- a 1938 precursor of the two-sample variance, or Allan deviation. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Q/noise of Earth as an oscillator
Hi > On Jul 31, 2016, at 8:19 PM, Hal Murray wrote: > > > t...@radio.sent.com said: >> So loss effects frequency in one situation and amplitude in the other. How >> can Q relate to both situations? > > It's energy loss in both cases. > > Is there a term other than Q that is used to describe the rate of energy loss > for things that aren't oscillators? ummm…. Q is the general term of rate of energy loss and we just happen to apply it to oscillators in a very elegant fashion…. Bob > > > -- > These are my opinions. I hate spam. > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Q/noise of Earth as an oscillator
An irreversible process would be a better description versus energy loss. Like joule heating (resistance, friction). On Sunday, 31 July 2016, Hal Murray wrote: > > t...@radio.sent.com said: > > So loss effects frequency in one situation and amplitude in the other. > How > > can Q relate to both situations? > > It's energy loss in both cases. > > Is there a term other than Q that is used to describe the rate of energy > loss > for things that aren't oscillators? > > > -- > These are my opinions. I hate spam. > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Q/noise of Earth as an oscillator
On 7/31/16 5:19 PM, Hal Murray wrote: t...@radio.sent.com said: So loss effects frequency in one situation and amplitude in the other. How can Q relate to both situations? It's energy loss in both cases. Is there a term other than Q that is used to describe the rate of energy loss for things that aren't oscillators? cooling (as in hot things) discharge (as in capacitors and batteries) leakage (as in pressure vessels) loss ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Q/noise of Earth as an oscillator
t...@radio.sent.com said: > So loss effects frequency in one situation and amplitude in the other. How > can Q relate to both situations? It's energy loss in both cases. Is there a term other than Q that is used to describe the rate of energy loss for things that aren't oscillators? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Q/noise of Earth as an oscillator
Ron Ott wrote: > There might be two Qs: one relating to the axil rotation and another > concerning the volume behavior Hi Ron, Chris, and now also Bill, I was thinking this tangent wouldn't come up, but yes, in the fields of Seismology or Earth Science, you will also see "quality factor" and the letter Q used. In their case it refers to the attenuation of seismic waves traversing through the earth and bouncing back. It's a clever way to explore the composition of the earth, from the inner core outwards. It's an ironic (in the Fe sense) way to make large earthquakes a wonderful tool of science in addition to a dreadful threat to property and life. Here's a few links that mention this type of Earth Q: "Deep Earth Structure – Q of the Earth from Crust to Core" in Treatise on Geophysics, Seismology and structure of the Earth, 2008 http://indico.ictp.it/event/a07174/session/116/contribution/64/material/0/0.pdf "Anisotropy of Earth’s inner core intrinsic attenuation from seismic normal mode models" in Earth and Planetary Science Letters, 2014 http://www.geo.uu.nl/~seismain/pdf/Earth_Planet_Sc_Lett_2014_Makinen.pdf "Wide-band coupling of Earth’s normal modes due to anisotropic inner core structure" in Geophysical Journal International, 2008 https://www.princeton.edu/geosciences/people/irving/publications/pdfs/Irving-2008-GJI-WideBand.pdf "Tidal dissipation compared to seismic dissipation: in small bodies, in earths, and in superearths" in The Astrophysical Journal, 2012 https://arxiv.org/pdf/1105.3936.pdf Any you're right. The "vibrating planet jello" Q is unrelated to the "rotating planet timekeeping" Q that I mentioned. The jello Q is a couple of hundred. The rotation/clock Q is a couple of trillion. That's why we define the second from the rotation of the earth and not the sound of the earth. Just in case readers think there can't ever be more than one Q, I refer you to pendulum clocks. The main Q, the one that is related to timekeeping, is derived from the periodic decay of the swing of the pendulum. Especially for precision pendulum clocks, there are other Q's as well: the rod/bob combination lends itself to many unwanted modes of physical vibration, up/down, front/back, left/right, twist, "violin modes", etc. Each of these modes have amplitude, period, and decay. They all interact with each other and with the main swinging of the pendulum in nasty ways. And yes, they all have their own Q. /tvb - Original Message - From: "Ron Ott" To: ; "Discussion of precise time and frequency measurement" Sent: Wednesday, July 27, 2016 9:57 AM Subject: Re: [time-nuts] Q/noise of Earth as an oscillator There might be two Qs: one relating to the axil rotation and another concerning the volume behavior of the earth as a giant bowl of Jello. But you'd have to figure out how to really slam the planet to excite the entire volume. Earthquakes are probably too wimpy. Ron From: Chris Caudle To: time-nuts@febo.com Sent: Wednesday, July 27, 2016 8:50 AM Subject: Re: [time-nuts] Q/noise of Earth as an oscillator On Wed, July 27, 2016 10:33 am, Chris Caudle wrote: > Does that imply that this value is not constant: >>> And if you take the classic definition >>> Q = 2 pi * total energy /energy lost per cycle >>> then it would seem earth has a Q factor. After re-reading "The Story of Q" I agree that Q of a rotating body could be non-constant, but also consistent with the original definition of Q as the ratio of reactance to resistance of an inductor, which of course would vary almost completely linearly over a wide frequency range where the resistive dissipation was not frequency dependent (i.e. where skin effect was negligible). Perhaps a more useful question is whether that is still a useful definition compared to how the term is more typically used now to refer to resonance bandwidth. -- Chris Caudle ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] GPSDO design articles
Finally for today, I posted two white papers from PTF, Inc. that discuss the basics of GPSDO design. These are the best accessible discussions of "how it's done" at the professional level that I'm aware of, and (IMO) should be required reading for anyone attempting a DIY GPSDO design. Note that some of the ADEV graphs show the use of local oscillators that are less stable at short tau than most time-nuts would use, so the corresponding crossover frequencies are lower (PLL bandwidths are higher) than would be appropriate for a time-nuts grade GPSDO by a factor of ~10. The file names are: Basics_of_GPS_discipline_PTF_AN_APP-29 Optimizing_stability_in_GPSDO_design_PTF (Didier's system will convert the underscore characters to spaces for indexing.) Once again, these are still in quarantine, but will be searchable when Didier moves them into the general population (which could take several weeks). When that happens, "PTF" will be a good search term. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Q/noise of Earth as an oscillator
I agree with those who repudiate the use of "Q" with respect to the length of an Earth day, and I feel that the statement about the Earth near the end of "The Story of Q" is incorrect when viewed from a modern perspective. I base my arguments on: (1) The existing use of Q to describe the tidal dissipation in a body for over 50 years. This has nothing to do directly with the stability of the rotation rate. See "Q in the Solar System" for a discussion of how Q refers to tidal dissipation: http://www.es.ucsc.edu/~pkoch/EART_206/09-0127/Goldreich%20&%20Soter%2066%20Icarus%205-375.pdf (2) The fact that the Earth is not a harmonic oscillator with a periodic forcing function or natural resonance. The length of a day is an accident of history. Let's consider the rotation of a body in a near-vacuum. First note that there is no sinusoidal physical quality of the rotating body which stands out. For harmonic oscillators we are familiar with periodic position, velocity, voltage, current, electric field, and magnetic field values which have a natural period based on physical characteristics. Harmonic oscillators transfer energy every cycle between fields. But if you correct for the spacetime distortion due to the mass of the Earth and the electromagnetic forces holding the surface from the center of our planet, an object on the surface of the Earth is moving each 24 hours in a manner constrained by geometry and similar to the free motion of a body in space far from gravitational fields. In other words, the motion of an object on the surface is similar to that of a satellite in free-fall. The motion does not involve any periodic change of kinetic and potential energy as in a pendulum, flexing quartz crystal, L-C resonant circuit, cavity, or the similar quantum mechanical constraints which cause resonance lines in the exchange of energy between electromagnetic fields and electrons in atoms. I would describe the rotation rate of the Earth in a similar manner to a rigid object (which is not spinning) in inertial movement in free space (away from gravitation and other fields) with respect to an arbitrary distance scale. For example, consider a point on Earth which is 100 meters from the north axis, and an object in free space moving inertially at a rate of 628 meters per 24 hours (described in atomic clock seconds, of course). Either the point on the Earth or the object in free space can't be described as in motion without reference to some external scale (due to relativity). The point on Earth (and the object in free space) can be described in motion at a rate of 628 meters per 24 hours with respect to our Sun or to the distant stars (cosmic microwave radiation, as in Mach's principle). Both the Earth and the object in free space have inertia due to their mass, but in neither case does the size, mass, composition, or other characteristics of the body cause a preferred velocity. The velocity of that point 100 meters from the north axis (assuming the axis hadn't moved over time) was quite different several million years ago (due to tidal effects), and there is no preferred velocity for that point on the Earth, just as there is no preferred velocity for the object in free space. If a comet strikes either one the velocity will change to any arbitrary value imparted by the kinetic energy of the impacting object. A point on the Earth's surface is constrained by the geometry of the spinning body to be in motion at a certain rate relative to other points on the body, and due to the body being reasonably rigid we consider there to be a "rotation rate" for the Earth. Similarly, different points on the body in free space are constrained by geometry and the rigid nature of that body so that they are moving at the same rate with respect to the Sun or the distant stars. In either case, if there are no outside influences (gravity, tidal friction, radiation pressure, solar or interstellar wind pressure, etc.) the body will remain in constant motion. That's Newton's First Law. The periodicity of the rotation of a spherical object is a geometric illusion, not a material property. The only reason some think of the Earth as a periodic oscillator is that geometry and gravity causes the motion of a point on the surface to be a helix in space-time. This causes an apparent periodicity constrained by geometry which is unrelated to the exchange in energy between fields which characterizes harmonic oscillators. Consider an artificial satellite which is rotating. Just as with the Earth, the rotation rate can take any value when kinetic energy is added from external interactions (constrained by relativistic effects and breakup of the body). There is no natural resonant frequency related to rotation (or linear motion of the body I earlier described moving in free space). The one Earth rotation per 24 hours rate is just a constraint of geometry and the accidental rotational inertia at a specific moment in our history, and is no
[time-nuts] Diophantine frequency synthesis articles
I also posted six files pertaining to Diophantine frequency synthesis on Didier's site. Four are papers dating to 2006-2007 by Sotiriadis, one is a paper of the same era by Stork, and one is a patent granted to Wilke in 1993. These are also still in quarantine, but will be searchable when Didier moves them into the general population (which could take several weeks). "Diophantine" will be a good search term. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Adafruit Ultimate GPS timing message arrival times
As mentioned in the post the times reported are the time stamp in the receiver packet minus the system clock time when it was received... negative value indicate the message arrives after the PPS. The polarity of the reported value is consistent with how Lady Heather makes use of the value... --- > Are you sure that the arrival time is negative? In my experience, the NMEA > message is /after/ the PPS, and not before it. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Short-term frequency stability symposium 1964
On 7/31/16 3:40 AM, Charles Steinmetz wrote: I was looking through my files and found a 1965 NASA publication that contains the papers presented at a 1964 IEEE-NASA symposium on the short-term stability of oscillators. It's a wonderful collection of seminal papers by most of the usual suspects of the era (see attached table of contents). I posted it to Didier's site. It's still in quarantine, but will be searchable when Didier moves it into the general population (which could take several weeks). The file name is: "Short-Term Frequency Stability IEEE-NASA symposium NASA SP-80 1965" Good to have it on Didier's site.. For now, it seems to be available at http://www.ieee-uffc.org/main/history/short-term_f_stab.pdf However, IEEE could decide at any time to put it behind a paywall. In theory, you could find it at some NASA NTRS server, but not everything is there, and those servers come and go as people freak out more or less about export controls, etc. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Short-term frequency stability symposium 1964
That NASA SP-80 is a classic! Your upload looks like the 17.5 MB version at: https://archive.org/details/nasa_techdoc_19660001092 There's also a (cleaner?) 9.7 MB copy here: http://www.ieee-uffc.org/main/history/short-term_f_stab.pdf which is part of the excellent collection of historical documents: http://www.ieee-uffc.org/main/history.asp Warning - that uffc history site is a real time sink! /tvb - Original Message - From: "Charles Steinmetz" To: Sent: Sunday, July 31, 2016 3:40 AM Subject: [time-nuts] Short-term frequency stability symposium 1964 > I was looking through my files and found a 1965 NASA publication that > contains the papers presented at a 1964 IEEE-NASA symposium on the > short-term stability of oscillators. It's a wonderful collection of > seminal papers by most of the usual suspects of the era (see attached > table of contents). > > I posted it to Didier's site. It's still in quarantine, but will be > searchable when Didier moves it into the general population (which could > take several weeks). The file name is: > >"Short-Term Frequency Stability IEEE-NASA symposium NASA SP-80 1965" > > Best regards, > > Charles > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Adafruit Ultimate GPS timing message arrival times
From: Mark Sims A couple of people have asked about the poor message arrival time performance of the popular Adafruit Ultimate GPS receiver. I modified Lady Heather to analyze the message arrival times using a histogram instead of a simple average. When I looked at the histogram data (.01 msec resolution), I was rather shocked... With an hour of data, most receivers have maybe a couple dozen bins hit, with the peak bin several hundred counts above the next lower peak. The Adafruit had over 1800 bins hit, with the peak bin having six hits. Attached is the histogram... you probably don't want to use this receiver to drive a clock based upon message arrival times... == Mark, Are you sure that the arrival time is negative? In my experience, the NMEA message is /after/ the PPS, and not before it. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk Twitter: @gm8arv ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
