[time-nuts] Vintage Frequency Measurement

[Scott Stobbe]

I was inspired recently coming across a Lampkin 105 frequency meter, as to
how  frequency measurement was done before counters.

Certainly zero-beating a dial calibrated oscillator, would be one approach.

Is there a standout methodology or instrument predating counters?
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Re: [time-nuts] how many seconds out does GPS discipline being to improve Rubidium stability?

[Bob Camp]

Hi

Using ADEV as an example (the other stuff will have it’s own curves, but the 
result is the same):

A typical Rb should have a stability at short tau that goes as 1/ square 
root(Tau). If you are at 2x10^-11 at 1 second, you 
will be at 2x10^-12 at 100 seconds and 2x10^-13 at 1,000 seconds. Somewhere in 
the parts in 10^-13 that relation will
start to diverge from reality. 

A fairly normal low frequency OCXO has a stability that is fairly flat with tau 
in the 1 to 100 second range. If they have been
on power constantly that “flat zone" may extend to 1,000 seconds. Floors should 
be in the low parts in 10^-12 to mid parts
in 10^-13 range. 

A good OCXO *may* beat a normal Rb at 1,000 seconds. That may or may not be an 
issue in your case. It depends a lot 
on what you are trying to do.

Simple solutions: 

1) Run something better than an Rb. A hydrogen maser is one alternative (simple 
if you don’t have to pay for it).
2) Do all your measurements as three corner hats. You run two references and 
one DUT into gear that will do that sort of test.
3) Segment the measurements and use carefully selected references for those 
ranges. 

None of those are actually simple. Number 3 sounds cool until you realize that 
you are switching test setups around a lot and
the devices you are using still need a setup like 2 to figure out which ones to 
use. 

So do you need a GPS? What are the limits on your MTIE tests? (MTIE on an OCXO 
is highly dependent on several 
things so there is no simple number there). A very normal quartz based GPSDO 
might be a fine reference for your test. 

How much shorter are the other tests? Is ADEV at 1,000 seconds even of 
interest? If the answer is < 1,000 seconds a
Rb may not do you much good at all. 

Lots of twists and turns. 

Bob





> On Feb 11, 2017, at 5:52 PM, gkk gb  wrote:
> 
> Thanks Bob,
> 
> 
> 
> I should clarify the MTIE measurement extends 10 seconds (the others are 
> less time). Is it a reasonable question to ask if GPS is needed? Or are there 
> other variables that are involved?
> 
> 
> 
> Good point about the temperature stability, I hadn't considered that. Can I 
> place in a temperature chamber to provide a better thermal environment, or 
> does that cause other issues (vibration from blowers, EMI noise, etc.)? Other 
> ways to mitigate temperature changes?
> 
> 
> 
> It seems a Rubidium is good after a timescale of 100 s. What do people do 
> below 100 s to characterize quartz oscillators. Do they simply try to find 
> the most stable parts they can afford and break the x-axis (tau) into two 
> regions using difference references for each? If so, are there generally 
> accepted "gold" standards anyone can recommend for crystal products with the 
> best stability to use as a reference between 0.1 and 100 seconds, for 
> example? 
> 
> 
> 
> On February 11, 2017 at 6:29 AM Bob Camp  wrote:
> 
> Hi
> 
> Backing up a bit here.
> 
> On Feb 10, 2017, at 7:35 PM, gkk gb  wrote:
> 
> Hello experts, I need a Rubidium frequency reference for my company, and 
> wonder if I also need to GPS discipline it.
> 
> I characterize crystal-based OCXOs for ADEV, MTIE, and TDEV, and my longest 
> measurement time is 100,000 seconds (28 hours).
> 
> If your longest measurement is a 100,000 second ADEV, then your measurement 
> time will be out in the
> 1,000,000 to 10,000,000 second range. Is that really what you are doing?
> 
> If 100,000 seconds ADEV is your longest measurement, what is the shortest tau 
> you are interested in?
> A Rb is not going to be much use for testing a good OCXO at shorter tau. 
> Where the crossover happens
> depends a lot on the grade of OCXO you are working with. By the time you get 
> to 1 second
> most OCXO’s will be noticeably better than most Rb’s.
> 
> I'm looking at this graph from SRS for PRS10,
> 
> http://www.thinksrs.com/assets/instr/PRS10/PRS10diag2LG.gif
> 
> I would suggest that plot is probably not the best one to depend on for GPS 
> performance. In a GPSDO setting
> the cut over points are all over the place depending on which design you look 
> at.
> 
> and thinking that as long as I calibrate a Rubidium source annually, there's 
> no need for a GPS (since it only appears to degrade stability). Is this true 
> in general, or is the graph misleading me because it may be true here, but 
> not always.
> 
> The big issue is going to be temperature stability. If you have a Rb that is 
> (say) 5x10^-10 over 0 to 50C, that is likely 1x10^-11 / C (or maybe more). A 
> 2C delta in
> your lab as the HVAC cycles will give you a 2x10^-11 “hump” in your ADEV plot.
> 
> Also consider that if you want an “easy” measurement of the devices you are 
> testing, the reference source probably should be
> 5X better than what you expect out of the DUT. You probably will not have 
> that luxury in this case. That gets you into multiple
> references and things like three corner hat testing.
> 

Re: [time-nuts] Neoprene rubber drops GPS multipath signals to zero

[jimlux]

On 2/11/17 10:22 AM, Poul-Henning Kamp wrote:


In message <589f4a79.3050...@rogers.com>, MLewis writes:


Late yesterday I placed old neoprene rubber mouse pads, rubber side
outwards, up the metal blinds between the blinds and the antenna.


I can guarantee you that it is not the neoprene itself which does it.

It could be residual ZnO, used to catalyze polymerisation of the neoprene,
but more likely it is metal deliberately added to the neoprene to
change the RF impedance of the material.


Or to make it heavy, so it lays on the table better.  They could just 
load it with sand or iron oxide or scrap whatever.









Polymers with varying metal content offer a handy range of
electromagnetic impedances between "short" and "open"[1], and it
is used a fair bit in various niche markets.

See for instance the first document here;

http://www.eccosorb.com/resource-white-papers.htm

It is not inconceiveable that off-spec or scrap materials from
the production might end up as mousemats.


I don't know if the production volume is high enough.. one never knows..
Eccosorb and related RF elastomers are sufficiently expensive that they 
must do something with it.



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Re: [time-nuts] Neoprene rubber drops GPS multipath signals to zero

[Bob Camp]

Hi

For any microwave material, the good old “toss it in a microwave” test is a 
quick
and dirty one. If the material heats up, it’s lossy. Yes, there are other 
fairly exciting 
things that can happen other than it warming a bit …. 

Bob

> On Feb 11, 2017, at 5:51 PM, MLewis  wrote:
> 
> Interesting.
> My guess wasn't a material made for RF but a carbon added to give a decent 
> black colour.
> 
> "It is not inconceiveable that off-spec or scrap materials from the 
> production might end up as mousemats."  and "stealth material".
> Very interesting.
> At an airshow many years ago, these mouse pads were a promotional give-away 
> by the Department of National Defence in Canada...
> 
> I'm now seeing some multipath signals sneak through, usually in the single 
> digital strength but for brief moments as high as 15 dBs. Coming from 
> elevation 5 to 10 degrees, between azimuth 300 to 330 and also azimuth 30 and 
> 60. I'm suspecting the office tower at 135 that sticks up above the bank of 
> buildings. I'll have to add a 1" strip up to 3" high in LOS to that building 
> to see what that does.
> The other multipath signals remain at 0.0.
> 
> Michael
> 
> On 11/02/2017 1:22 PM, Poul-Henning Kamp wrote:
> > 
> >
> > I can guarantee you that it is not the neoprene itself which does it.
> >
> > It could be residual ZnO, used to catalyze polymerisation of the neoprene,
> > but more likely it is metal deliberately added to the neoprene to
> > change the RF impedance of the material.
> >
> > ...
> >
> > [1] If you arrange for the imperance to ramp from open to short you
> > have a "stealth material".
> >
> 
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Re: [time-nuts] Line Frequency standard change - Possible ?

[Poul-Henning Kamp]

In message <344e0d5f-e79f-fcfa-eba5-4cf50e047...@comcast.net>, Peter Reilley 
writes:

>If a solar farm also included a battery bank then they would be able to supply
>VAs along with Watts just like a conventional generator.

The large MW size solar farms can already do that but with capacitors rather
than batteries.

I belive Germany has started to change regulations so future solar farms will
have to offer both VA and W to the grid, but I don't know the exact details.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] Neoprene rubber drops GPS multipath signals to zero

[MLewis]

Interesting.
My guess wasn't a material made for RF but a carbon added to give a 
decent black colour.


"It is not inconceiveable that off-spec or scrap materials from the 
production might end up as mousemats."  and "stealth material".

Very interesting.
At an airshow many years ago, these mouse pads were a promotional 
give-away by the Department of National Defence in Canada...


I'm now seeing some multipath signals sneak through, usually in the 
single digital strength but for brief moments as high as 15 dBs. Coming 
from elevation 5 to 10 degrees, between azimuth 300 to 330 and also 
azimuth 30 and 60. I'm suspecting the office tower at 135 that sticks up 
above the bank of buildings. I'll have to add a 1" strip up to 3" high 
in LOS to that building to see what that does.

The other multipath signals remain at 0.0.

Michael

On 11/02/2017 1:22 PM, Poul-Henning Kamp wrote:
> 
>
> I can guarantee you that it is not the neoprene itself which does it.
>
> It could be residual ZnO, used to catalyze polymerisation of the 
neoprene,

> but more likely it is metal deliberately added to the neoprene to
> change the RF impedance of the material.
>
> ...
>
> [1] If you arrange for the imperance to ramp from open to short you
> have a "stealth material".
>

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Re: [time-nuts] how many seconds out does GPS discipline being to improve Rubidium stability?

[gkk gb]

Thanks Bob,


I should clarify the MTIE measurement extends 10 seconds (the others are 
less time). Is it a reasonable question to ask if GPS is needed? Or are there 
other variables that are involved?


Good point about the temperature stability, I hadn't considered that. Can I 
place in a temperature chamber to provide a better thermal environment, or does 
that cause other issues (vibration from blowers, EMI noise, etc.)? Other ways 
to mitigate temperature changes?


It seems a Rubidium is good after a timescale of 100 s. What do people do below 
100 s to characterize quartz oscillators. Do they simply try to find the most 
stable parts they can afford and break the x-axis (tau) into two regions using 
difference references for each? If so, are there generally accepted "gold" 
standards anyone can recommend for crystal products with the best stability to 
use as a reference between 0.1 and 100 seconds, for example? 


> 
> On February 11, 2017 at 6:29 AM Bob Camp  wrote:
> 
> Hi
> 
> Backing up a bit here.
> 
> > > 
> > On Feb 10, 2017, at 7:35 PM, gkk gb  wrote:
> > 
> > Hello experts, I need a Rubidium frequency reference for my 
> > company, and wonder if I also need to GPS discipline it.
> > 
> > I characterize crystal-based OCXOs for ADEV, MTIE, and TDEV, and my 
> > longest measurement time is 100,000 seconds (28 hours).
> > 
> > > 
> If your longest measurement is a 100,000 second ADEV, then your 
> measurement time will be out in the
> 1,000,000 to 10,000,000 second range. Is that really what you are doing?
> 
> If 100,000 seconds ADEV is your longest measurement, what is the shortest 
> tau you are interested in?
> A Rb is not going to be much use for testing a good OCXO at shorter tau. 
> Where the crossover happens
> depends a lot on the grade of OCXO you are working with. By the time you 
> get to 1 second
> most OCXO’s will be noticeably better than most Rb’s.
> 
> > > 
> > I'm looking at this graph from SRS for PRS10,
> > 
> > http://www.thinksrs.com/assets/instr/PRS10/PRS10diag2LG.gif
> > 
> > > 
> I would suggest that plot is probably not the best one to depend on for 
> GPS performance. In a GPSDO setting
> the cut over points are all over the place depending on which design you 
> look at.
> 
> > > 
> > and thinking that as long as I calibrate a Rubidium source 
> > annually, there's no need for a GPS (since it only appears to degrade 
> > stability). Is this true in general, or is the graph misleading me because 
> > it may be true here, but not always.
> > 
> > > 
> The big issue is going to be temperature stability. If you have a Rb that 
> is (say) 5x10^-10 over 0 to 50C, that is likely 1x10^-11 / C (or maybe more). 
> A 2C delta in
> your lab as the HVAC cycles will give you a 2x10^-11 “hump” in your ADEV 
> plot.
> 
> Also consider that if you want an “easy” measurement of the devices you 
> are testing, the reference source probably should be
> 5X better than what you expect out of the DUT. You probably will not have 
> that luxury in this case. That gets you into multiple
> references and things like three corner hat testing.
> 
> > > 
> > So my question, is a GPS necessary to discipline a Rubidium 
> > standard to characterize the best crystal oscillators for stability, or can 
> > I do without it (and just calibrate the Rubidium annually to maintain 
> > accuracy) and actually get better stability?
> > 
> > How many seconds out is a GPS generally needed to improve accuracy 
> > from a Rubidium standard?
> > 
> > > 
> If you really are running 1,000,000 to 10,000,000 second long tests, you 
> need the GPS.
> 
> Lots of variables
> 
> Bob
> 
> > > 
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> > 
> > > 
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Re: [time-nuts] Line Frequency standard change - Possible ?

[Poul-Henning Kamp]

In message <006a1c6a-0b2f-16fd-5fef-64352ff14...@earthlink.net>, jimlux writes:
>On 2/9/17 4:03 PM, Poul-Henning Kamp wrote:
>> 
>> In message <63beea7a-f9fc-6e1d-b855-2c7056de3...@earthlink.net>, jimlux 
>> writes:
>>
>>> I think also of the issues from distributed generation - consider a
>>> rooftop solar installation with 20 or so MicroInverters, all "slaved" to
>>> the line.  Just from manufacturing variations, I suspect each
>>> microinverter is a little bit different than the others.
>>
>> Surprising there is almost no variation, because it hurts badly on
>> both your nameplate efficiency and thermal design.
>
>I was thinking about phase stability and "matching" to the grid.. each 
>microinverter (in a short time sense) might have a different phase 
>relationship (which turns into power factor), essentially introducing 
>some "noise" into the system.

At least here in Europe, the eletricity grids were very hostile
to solar initially and therefore the electrical requirements
for approval ended up being very strict, so basically no:  Solar
inverters had to be model citizens noisewise to get installed.

>HV AC lines have exactly the same problem, the switches carry enough 
>energy that "quenching" the arc is by no means assured through the zero 
>crossing.

It is not by any means *assured*, but at least it is *possible*.

Not so with HVDC.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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Re: [time-nuts] Line Frequency standard change - Possible ?

[Peter Reilley]

They may well be willing to pay for more expensive equipment because they
can make money from it.   large industrial electricity users pay for the VAs
that they use.   Even though they are not energy the utility has to 
supply them.

The utility charges for this service.

If a solar farm also included a battery bank then they would be able to 
supply
VAs along with Watts just like a conventional generator.   With 
batteries solar

farms could contribute to grid stability just like other suppliers.

Pete.



On 2/10/2017 7:43 AM, David wrote:

On Thu, 09 Feb 2017 23:39:24 +, you wrote:


It is harder than it sounds.

Small solar inverters are the best, they an regulate down at milliseconds
notice, and many jurisdictions impose asymetric frequency bands on
them to exploit this.

Big inverters, no matter what you put behind them, get quite a bit
more expensive if they are designed to provide "non-VA" power,
because you suddenly have to run the current both ways in the same
half-cycle.

Nobody wants to pay for that voluntarily, and nobody are particular
keen to cause the first explosion/fire while they get the control-law
debugged.

Imagine how they will scream if they have to pay for fields of big
synchronous motors to be connected.

https://en.wikipedia.org/wiki/Synchronous_condenser
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Re: [time-nuts] Line Frequency standard change - Possible ?

[Didier Juges]

One issue with power factor corrected power supplies is that in the short
term (as a minimum, at the line frequency), they do behave like resistors
(current goes up when voltage goes up) but as they have a slow voltage
regulation loop to provide regulated output, they do behave like constant
power loads to the grid in the long term. The transition between the two
modes of operation is not always smooth and can lead to instabilities when
combined with the generator's response and the line impedance.
I had this particular problem with a 5kW PFC corrected power supply that
was working fine by itself but caused line oscillations when 16 of them
were running in parallel.

On Feb 11, 2017 4:04 AM, "David"  wrote:

> On Thu, 9 Feb 2017 19:06:51 -0500, you wrote:
>
> >One simplistic way to look at all this is that a switcher presents a
> “negative
> >resistance” load. If you drop voltage, current goes up. OCXO’s happen
> >to share this issue. Negative resistances are *not* what most power source
> >guys want in their control loop.
> >
> >Bob
>
> People working with emitter/source followers do not like it either and
> I cannot see the folks using inverters wanting to pay to put big
> resistive heaters across the grid to compensate.
>
> Adding power factor correction to switching power supplies was cheap
> compared adding "negative resistance" correction.
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Re: [time-nuts] Neoprene rubber drops GPS multipath signals to zero

[Poul-Henning Kamp]

In message <589f4a79.3050...@rogers.com>, MLewis writes:

>Late yesterday I placed old neoprene rubber mouse pads, rubber side 
>outwards, up the metal blinds between the blinds and the antenna.

I can guarantee you that it is not the neoprene itself which does it.

It could be residual ZnO, used to catalyze polymerisation of the neoprene,
but more likely it is metal deliberately added to the neoprene to
change the RF impedance of the material.

Polymers with varying metal content offer a handy range of
electromagnetic impedances between "short" and "open"[1], and it
is used a fair bit in various niche markets.

See for instance the first document here;

http://www.eccosorb.com/resource-white-papers.htm

It is not inconceiveable that off-spec or scrap materials from
the production might end up as mousemats.

Here is an interesting article about other things you can do with
such materials:

https://archive.org/details/bstj27-1-58

Poul-Henning


[1] If you arrange for the imperance to ramp from open to short you
have a "stealth material".

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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[time-nuts] Neoprene rubber drops GPS multipath signals to zero

[MLewis]

My TW4722 GNSS active antenna is on a 100 mm stainless ground-plane, 
placed on 2" of wood on a window sill behind two panes of glass, between 
metal blinds and the glass, almost touching the glass. Feeds a NEO-M8T.


Late yesterday I placed old neoprene rubber mouse pads, rubber side 
outwards, up the metal blinds between the blinds and the antenna.
All signal levels dropped, many around 3 to 5 dBs, a few as much as 15 
dBs. Seemed to equally affect LOS and multipath signals.


After running the night with that to see the affect, I stripped the 
neoprene rubber off another mouse pad and placed the resulting neoprene 
rubber pad under the antenna's 100 mm stainless circular ground-plane 
(left resting on the pad), with the front of the pad folded upwards 
extending an arbitrary 2" up the glass window pane. Pad is 8.75" wide.


Multipath signals reflecting from the bank of buildings opposite the 
window were as high as 24 dBs. After placing the neoprene rubber pad 
under the ground-plane and up the glass, they dropped down to zero.

Zero.
0.0
(screen shot from LH attached)
(Skyview is somewhat less than azimuth ~60 degrees to ~240 degrees. 
Everything outside of that is multipath.)


Mouse pads were the earlier thin bottom-textured pads of denser neoprene 
rubber, not the later thick smooth air-foamed pads (which I've not tried).


Hope this info can help someone as much as it's helped me.

Michael

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Re: [time-nuts] Line Frequency standard change - Possible ?

[Magnus Danielson]

Hi,

I know. In practice many of the operators in the US is working together 
to get smarter, share experiences and learn from each other and others.

Good folks.

Cheers,
Magnus

On 02/11/2017 04:08 PM, Bob Camp wrote:

Hi

To be fair to these guys, they have a number of challenges that have nothing to
do with technology. They cross link to other companies and have little control
over how each one operates. Here in the US, we have multiple regulatory
agencies (it happens at the state, federal, and international level).  they all 
are involved
in any change. That makes for a very long and drawn out dance when you fiddle
with this or that. Also, in many cases are the shareholders in the company
who seem to have goals as well ….

Not an easy thing.

Bob


On Feb 11, 2017, at 5:22 AM, Magnus Danielson  
wrote:

Work is already underway to improve the relicense of power grid operations. 
They is smarting up quickly. The PMU/synchrophasor measurements depend on UTC 
and before it can be used full-blown for operation the single point of failure 
needs to be handled.

Cheers,
Magnus

On 02/09/2017 11:19 PM, Peter Reilley wrote:

Isn't this "hard" lock to UTC creating a single point of failure? A
solar burst, an EMP, or
a software error could leave us all in the dark.   After all, smart
inverters could be
programmed to act like big lumps of rotating iron and be compatible with
the current
system.

Pete.

On 2/9/2017 4:31 PM, Poul-Henning Kamp wrote:


In message
<4fbdd81ddf04fc46870db1b9a747269202916...@mbx032-e1-va-8.exch032.ser
verpod.net>, "Thomas D. Erb" writes:


I was wondering if anyone was familiar with this proposal, is this
a uncoupling of line frequency from a time standard ?

The interesting thing about this is that all research and experiments
(for instance on the danish island Bornholm) indicates that the only
way we stand any chance of keeping future AC grids under control in the
medium term is to lock the frequency *hard* to UTC.

Its a very interesting topic.

In the traditional AC grid power is produced by big heavy lumps of
rotating iron.  This couples the grid frequency tightly to the
power-balance of the grid:  If the load increases, the generators
magnetic field drags harder slowing the rotor, lowering the frequency
and vice versa.

This makes the grid frequency a "proxy signal" for the power balance,
and very usefully so, because it travels well and noiselessly through
the entire AC grid.

The only other possible "balance signal" is the voltage, and it
suffers from a host of noise mechanisms, from bad contacts and
lightning strikes to temperature, but worst of all, it takes double
hit when you start big induction motors, thus oversignalling the
power deficit.

Where the frequency as "proxy" for grid balance reacts and can
be used to steering on a 100msec timescale, you need to average
a voltage "proxy" signal for upwards of 20 seconds to get the
noise down to level where you don't introduce instability.

The big picture problem is that we are rapidly retiring the rotating
iron, replacing it with switch-mode converters which do not "couple"
the frequency to power balance.

For instance HVDC/AC converters, solar panel farms, and increasingly
wind generators, do not try to drag down the frequency when they
cannot produce more or drag the frequency up when they can produce
more power, they just faithfully track whatever frequency all the
rotating lumps of iron have agreed on.

As more and more rotating iron gets retired, the grid frequency
eventually becomes useless as a "proxy-signal" for grid balance.

Informal and usually undocumented experiments have already shown
that areas of grids which previously were able to run in "island"
mode, are no longer able to do so, due to shortage of rotating iron.

One way we have found to make the voltage a usable fast-reacting
proxy for grid power-balance, is to lock the frequency to GNSS at
1e-5 s level at all major producers, which is trivial for all the
switch-mode kit, and incredibly hard and energy-inefficient for the
rotating iron producers.

The other way is to cut the big grids into smaller grids with HVDC
connections to decouple the frequencies, which allows us to relax
the frequency tolerance for each of these subgrids substantially.

This solution gets even better if you load the HVDC up with capacitance
to act as a short time buffers, but the consequences in terms of
short circuit energy are ... spectacular?

(It is already bad enough with cable capacitance in long HVDC
connections, do the math on 15nF/Km and 100.000 kV yourself.)

All these issues are compounded by the fact that the "50/60Hz or
bust" mentality has been tatooed on the nose of five generations
of HV engineers, to such an extent that many of them are totally
incapable of even imagining anything else, and they all just "know"
that DC is "impossible".

In the long term, HVDC is going to take over, because it beats HVAC
big time on long 

[time-nuts] u-blox NEO-M8T GPS initial tracking test

[Mark Sims]

I don't have an M8T, only an M8.

Heather defaults to showing up to 14 satellites.  You can specify more sats or 
a dual column display using the SI or GCT commands or you can click the mouse 
on the satellite info table.

You can also use the SG command to set the GNSS configuration, but version 5.0 
has some issues and does not work for most settings.  
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Re: [time-nuts] Line Frequency standard change - Possible ?

[Poul-Henning Kamp]

In message <9fd9beca-832a-4c38-9799-4a31625f7...@n1k.org>, Bob Camp writes:

>Not an easy thing.

Not even close, which is precisely why the "50/60 Hz or bust" mindset
doesn't work any longer.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] The USFS Frequency Standard...

[Poul-Henning Kamp]

In message <2126b261-3e4e-46d4-9181-1fb368244...@n1k.org>, Bob Camp writes:

>One *could* make a WWVB “new modulation” receiver with some sort
>of MCU demo board and a handful of parts. It would be fine for a basement
>lab / learning sort of project.

With reasonable OCXO as timebase, it would do much more than that.

SRS sold the SR700 Loran receiver as a "Cesium replacement".

>the longer you wait to start that project, the better a board you will have
>as the base of the project. 

Current boards are more than capable of this, a 12 ADC at 1MSPS is plenty.

>How many people want to spend more than a year on that sort of thing

Unless you're a total programming beginner, you will have carrier lock in
a week:

* Configure ADC for 1MSPS

* Interrupt routine: exponentially average the samples into a 50[1]
  bucket circular buffer

* Control-Loop (not time-critical):

  * Multiply 50 buckets with synthetic sine/cos function,

  * Average the 2x50 results to get I/Q phase signal.

  * Feed phase into PLL to steer OCXO.

  * Bonus: Decode timegram.

I did that with Loran-C, which is a *much* harder signal, I did it
8 years ago, and I did it in two weeks.

Poul-Henning

[1] If you use a platform with enough memory, for instance a BBB,
use a one million (=full second) buffer instead, you will be
able to pull any and all VLF signals out of it.  For instance
the US navy runs a couple of stations with frequency stability
comparable to WWV.  On a BBB you could even add a FRI length
buffer also, to receive the Wildwood Loran-C.



-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] The USFS Frequency Standard...

[Bob Camp]

Hi

One *could* make a WWVB “new modulation” receiver with some sort
of MCU demo board and a handful of parts. It would be fine for a basement
lab / learning sort of project. Given the way the semiconductor world works,
the longer you wait to start that project, the better a board you will have
as the base of the project. 

At the end of the project with everything working fine, you still have WWVB
as the “source”. Propagation issues still limit what you can achieve. 
MSF (as far as I know) is still on the air. That still is going to cause issues
if you are in the New England area. Miami is still a long way from Colorado.
If you happen to live in Denver, not much of a problem at all. 

How many people want to spend more than a year on that sort of thing when
a < $10 GPS USB dongle would do as good a job? It’s a back burner project
here. There isn’t a real big push to get it onto the front burner. Yes, 
following 
the masses like that is a bit sad. There are things that would be learned doing
this sort of thing. Some of them would be about WWVB. A few of the learnings
would be about GPS. As others have very correctly pointed out, diverse sources 
of time
are a good thing. We are headed towards a GPS monoculture. 

Bob


> On Feb 10, 2017, at 8:02 PM, paul swed  wrote:
> 
> Burt you missed nothing. It would appear that all good intentions did not
> lead to new business. So there you go the old receivers useless and no new
> ones made.
> Certainly all of the old ones can be made to work using the cheatn dpskr
> shared with time nuts. But boy compared to the gpsdo's this lazy time nut
> likes the simplicity and economics. Sure I can't say I am the first kid on
> the block with a USFS but that hasn't been much of a topic lately.
> 
> I do fire up the old wwvb receivers just to make sure the cheatn dpskr
> works and that they still do. But 99.9% of the time its the gpsdo these
> days. Its there until it isn't.
> Regards
> Paul
> WB8TSL
> 
> On Fri, Feb 10, 2017 at 3:47 PM, Burt I. Weiner  wrote:
> 
>> Technically speaking, the United State Frequency Standard (USFS) is still
>> considered to be transmitted via WWVB on 60 kHz, essentially making WWVB
>> the USFS.  But is WWVB still a usable frequency standard reference since
>> they've gone to phase shifting their signal for time keeping purposes?
>> Will GPS become the "official" USFS reference signal?
>> 
>> Is there a 60 kHz WWVB receiver out there that can still be used as
>> reference?  Is there a commercially made receiver out there that now uses
>> the phase shifting technique of WWVB for accurate time keeping?
>> 
>> Have I missed something?
>> 
>> Burt, K6OQK
>> 
>> Burt I. Weiner Associates
>> Broadcast Technical Services
>> Glendale, California U.S.A.
>> b...@att.net
>> K6OQK
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Re: [time-nuts] how many seconds out does GPS discipline being to improve Rubidium stability?

[Bob Camp]

Hi

Backing up a bit here.


> On Feb 10, 2017, at 7:35 PM, gkk gb  wrote:
> 
> Hello experts, I need a Rubidium frequency reference for my company, and 
> wonder if I also need to GPS discipline it.
> 
> 
> I characterize crystal-based OCXOs for ADEV, MTIE, and TDEV, and my longest 
> measurement time is 100,000 seconds (28 hours). 

If your longest measurement is a 100,000 second ADEV, then your measurement 
time will be out in the 
1,000,000 to 10,000,000 second range. Is that really what you are doing? 

If 100,000 seconds ADEV is your longest measurement, what is the shortest tau 
you are interested in?
A Rb is not going to be much use for testing a good OCXO at shorter tau. Where 
the crossover happens
depends a lot on the grade of OCXO you are working with. By the time you get to 
1 second 
most OCXO’s will be noticeably better than most Rb’s.

> 
> 
> I'm looking at this graph from SRS for PRS10,
> 
> 
> http://www.thinksrs.com/assets/instr/PRS10/PRS10diag2LG.gif

I would suggest that plot is probably not the best one to depend on for GPS 
performance.  In a GPSDO setting 
the cut over points are all over the place depending on which design you look 
at. 

> 
> 
> and thinking that as long as I calibrate a Rubidium source annually, there's 
> no need for a GPS (since it only appears to degrade stability). Is this true 
> in general, or is the graph misleading me because it may be true here, but 
> not always.

The big issue is going to be temperature stability. If you have a Rb that is 
(say) 5x10^-10 over 0 to 50C, that is likely 1x10^-11 / C (or maybe more). A 2C 
delta in 
your lab as the HVAC cycles will give you a 2x10^-11 “hump” in your ADEV plot. 

Also consider that if you want an “easy” measurement of the devices you are 
testing, the reference source probably should be 
5X better than what you expect out of the DUT. You probably will not have that 
luxury in this case. That gets you into multiple
references and things like three corner hat testing. 

> 
> 
> So my question, is a GPS necessary to discipline a Rubidium standard to 
> characterize the best crystal oscillators for stability, or can I do without 
> it (and just calibrate the Rubidium annually to maintain accuracy) and 
> actually get better stability?
> 
> 
> How many seconds out is a GPS generally needed to improve accuracy from a 
> Rubidium standard?

If you really are running 1,000,000 to 10,000,000 second long tests, you need 
the GPS.

Lots of variables 

Bob


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Re: [time-nuts] Line Frequency standard change - Possible ?

[Bob Camp]

Hi

To be fair to these guys, they have a number of challenges that have nothing to
do with technology. They cross link to other companies and have little control 
over how each one operates. Here in the US, we have multiple regulatory 
agencies (it happens at the state, federal, and international level).  they all 
are involved 
in any change. That makes for a very long and drawn out dance when you fiddle
with this or that. Also, in many cases are the shareholders in the company 
who seem to have goals as well ….

Not an easy thing.

Bob 

> On Feb 11, 2017, at 5:22 AM, Magnus Danielson  
> wrote:
> 
> Work is already underway to improve the relicense of power grid operations. 
> They is smarting up quickly. The PMU/synchrophasor measurements depend on UTC 
> and before it can be used full-blown for operation the single point of 
> failure needs to be handled.
> 
> Cheers,
> Magnus
> 
> On 02/09/2017 11:19 PM, Peter Reilley wrote:
>> Isn't this "hard" lock to UTC creating a single point of failure? A
>> solar burst, an EMP, or
>> a software error could leave us all in the dark.   After all, smart
>> inverters could be
>> programmed to act like big lumps of rotating iron and be compatible with
>> the current
>> system.
>> 
>> Pete.
>> 
>> On 2/9/2017 4:31 PM, Poul-Henning Kamp wrote:
>>> 
>>> In message
>>> <4fbdd81ddf04fc46870db1b9a747269202916...@mbx032-e1-va-8.exch032.ser
>>> verpod.net>, "Thomas D. Erb" writes:
>>> 
 I was wondering if anyone was familiar with this proposal, is this
 a uncoupling of line frequency from a time standard ?
>>> The interesting thing about this is that all research and experiments
>>> (for instance on the danish island Bornholm) indicates that the only
>>> way we stand any chance of keeping future AC grids under control in the
>>> medium term is to lock the frequency *hard* to UTC.
>>> 
>>> Its a very interesting topic.
>>> 
>>> In the traditional AC grid power is produced by big heavy lumps of
>>> rotating iron.  This couples the grid frequency tightly to the
>>> power-balance of the grid:  If the load increases, the generators
>>> magnetic field drags harder slowing the rotor, lowering the frequency
>>> and vice versa.
>>> 
>>> This makes the grid frequency a "proxy signal" for the power balance,
>>> and very usefully so, because it travels well and noiselessly through
>>> the entire AC grid.
>>> 
>>> The only other possible "balance signal" is the voltage, and it
>>> suffers from a host of noise mechanisms, from bad contacts and
>>> lightning strikes to temperature, but worst of all, it takes double
>>> hit when you start big induction motors, thus oversignalling the
>>> power deficit.
>>> 
>>> Where the frequency as "proxy" for grid balance reacts and can
>>> be used to steering on a 100msec timescale, you need to average
>>> a voltage "proxy" signal for upwards of 20 seconds to get the
>>> noise down to level where you don't introduce instability.
>>> 
>>> The big picture problem is that we are rapidly retiring the rotating
>>> iron, replacing it with switch-mode converters which do not "couple"
>>> the frequency to power balance.
>>> 
>>> For instance HVDC/AC converters, solar panel farms, and increasingly
>>> wind generators, do not try to drag down the frequency when they
>>> cannot produce more or drag the frequency up when they can produce
>>> more power, they just faithfully track whatever frequency all the
>>> rotating lumps of iron have agreed on.
>>> 
>>> As more and more rotating iron gets retired, the grid frequency
>>> eventually becomes useless as a "proxy-signal" for grid balance.
>>> 
>>> Informal and usually undocumented experiments have already shown
>>> that areas of grids which previously were able to run in "island"
>>> mode, are no longer able to do so, due to shortage of rotating iron.
>>> 
>>> One way we have found to make the voltage a usable fast-reacting
>>> proxy for grid power-balance, is to lock the frequency to GNSS at
>>> 1e-5 s level at all major producers, which is trivial for all the
>>> switch-mode kit, and incredibly hard and energy-inefficient for the
>>> rotating iron producers.
>>> 
>>> The other way is to cut the big grids into smaller grids with HVDC
>>> connections to decouple the frequencies, which allows us to relax
>>> the frequency tolerance for each of these subgrids substantially.
>>> 
>>> This solution gets even better if you load the HVDC up with capacitance
>>> to act as a short time buffers, but the consequences in terms of
>>> short circuit energy are ... spectacular?
>>> 
>>> (It is already bad enough with cable capacitance in long HVDC
>>> connections, do the math on 15nF/Km and 100.000 kV yourself.)
>>> 
>>> All these issues are compounded by the fact that the "50/60Hz or
>>> bust" mentality has been tatooed on the nose of five generations
>>> of HV engineers, to such an extent that many of them are totally
>>> incapable of even imagining anything else, and they all 

Re: [time-nuts] Line Frequency standard change - Possible ?

[Magnus Danielson]

Work is already underway to improve the relicense of power grid 
operations. They is smarting up quickly. The PMU/synchrophasor 
measurements depend on UTC and before it can be used full-blown for 
operation the single point of failure needs to be handled.


Cheers,
Magnus

On 02/09/2017 11:19 PM, Peter Reilley wrote:

Isn't this "hard" lock to UTC creating a single point of failure? A
solar burst, an EMP, or
a software error could leave us all in the dark.   After all, smart
inverters could be
programmed to act like big lumps of rotating iron and be compatible with
the current
system.

Pete.

On 2/9/2017 4:31 PM, Poul-Henning Kamp wrote:


In message
<4fbdd81ddf04fc46870db1b9a747269202916...@mbx032-e1-va-8.exch032.ser
verpod.net>, "Thomas D. Erb" writes:


I was wondering if anyone was familiar with this proposal, is this
a uncoupling of line frequency from a time standard ?

The interesting thing about this is that all research and experiments
(for instance on the danish island Bornholm) indicates that the only
way we stand any chance of keeping future AC grids under control in the
medium term is to lock the frequency *hard* to UTC.

Its a very interesting topic.

In the traditional AC grid power is produced by big heavy lumps of
rotating iron.  This couples the grid frequency tightly to the
power-balance of the grid:  If the load increases, the generators
magnetic field drags harder slowing the rotor, lowering the frequency
and vice versa.

This makes the grid frequency a "proxy signal" for the power balance,
and very usefully so, because it travels well and noiselessly through
the entire AC grid.

The only other possible "balance signal" is the voltage, and it
suffers from a host of noise mechanisms, from bad contacts and
lightning strikes to temperature, but worst of all, it takes double
hit when you start big induction motors, thus oversignalling the
power deficit.

Where the frequency as "proxy" for grid balance reacts and can
be used to steering on a 100msec timescale, you need to average
a voltage "proxy" signal for upwards of 20 seconds to get the
noise down to level where you don't introduce instability.

The big picture problem is that we are rapidly retiring the rotating
iron, replacing it with switch-mode converters which do not "couple"
the frequency to power balance.

For instance HVDC/AC converters, solar panel farms, and increasingly
wind generators, do not try to drag down the frequency when they
cannot produce more or drag the frequency up when they can produce
more power, they just faithfully track whatever frequency all the
rotating lumps of iron have agreed on.

As more and more rotating iron gets retired, the grid frequency
eventually becomes useless as a "proxy-signal" for grid balance.

Informal and usually undocumented experiments have already shown
that areas of grids which previously were able to run in "island"
mode, are no longer able to do so, due to shortage of rotating iron.

One way we have found to make the voltage a usable fast-reacting
proxy for grid power-balance, is to lock the frequency to GNSS at
1e-5 s level at all major producers, which is trivial for all the
switch-mode kit, and incredibly hard and energy-inefficient for the
rotating iron producers.

The other way is to cut the big grids into smaller grids with HVDC
connections to decouple the frequencies, which allows us to relax
the frequency tolerance for each of these subgrids substantially.

This solution gets even better if you load the HVDC up with capacitance
to act as a short time buffers, but the consequences in terms of
short circuit energy are ... spectacular?

(It is already bad enough with cable capacitance in long HVDC
connections, do the math on 15nF/Km and 100.000 kV yourself.)

All these issues are compounded by the fact that the "50/60Hz or
bust" mentality has been tatooed on the nose of five generations
of HV engineers, to such an extent that many of them are totally
incapable of even imagining anything else, and they all just "know"
that DC is "impossible".

In the long term, HVDC is going to take over, because it beats HVAC
big time on long connections, and it is only a matter of getting
semiconductors into shape before that happens.  That however,
is by no means a trivial task:  It's all about silicon purity.




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Re: [time-nuts] Line Frequency standard change - Possible ?

[Magnus Danielson]

Hi Jim,

On 02/09/2017 11:39 PM, jimlux wrote:

On 2/9/17 1:31 PM, Poul-Henning Kamp wrote:


In message
<4fbdd81ddf04fc46870db1b9a747269202916...@mbx032-e1-va-8.exch032.ser
verpod.net>, "Thomas D. Erb" writes:


I was wondering if anyone was familiar with this proposal, is this
a uncoupling of line frequency from a time standard ?


The interesting thing about this is that all research and experiments
(for instance on the danish island Bornholm) indicates that the only
way we stand any chance of keeping future AC grids under control in the
medium term is to lock the frequency *hard* to UTC.

Its a very interesting topic.




I think also of the issues from distributed generation - consider a
rooftop solar installation with 20 or so MicroInverters, all "slaved" to
the line.  Just from manufacturing variations, I suspect each
microinverter is a little bit different than the others.


By code these needs to feed in phase with the line, meaning they do not 
contribute with reactance as if it was rotating iron.


While trying to be "safe" is does not contribute to stability, only to 
power.


Cheers,
Magnus
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Re: [time-nuts] how many seconds out does GPS discipline being to improve Rubidium stability?

[David J Taylor]

From: gkk gb

Hello experts, I need a Rubidium frequency reference for my company, and 
wonder if I also need to GPS discipline it.


I characterize crystal-based OCXOs for ADEV, MTIE, and TDEV, and my longest 
measurement time is 100,000 seconds (28 hours).

[]


While you are waiting for your Rubidium, perhaps this little GPS box may 
help?


 http://www.leobodnar.com/shop/index.php?main_page=product_info_id=234

Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv 


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Re: [time-nuts] Line Frequency standard change - Possible ?

[David]

On Thu, 9 Feb 2017 17:19:49 -0500, you wrote:

>Isn't this "hard" lock to UTC creating a single point of failure? A 
>solar burst, an EMP, or
>a software error could leave us all in the dark.   After all, smart 
>inverters could be
>programmed to act like big lumps of rotating iron and be compatible with 
>the current
>system.
>
>Pete.

I have the same concern.  I am dubious of tying power grid reliability
to GPS reliability and doubly so in a threat environment which
includes hostile actors.  And if an alternative more reliable timing
standard was used then why use GPS at all?

Inverters lack the overload capability and resistance of rotating iron
unless they are overbuilt in which case they would be uneconomical.
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Re: [time-nuts] Line Frequency standard change - Possible ?

[David]

On Thu, 9 Feb 2017 19:06:51 -0500, you wrote:

>One simplistic way to look at all this is that a switcher presents a “negative
>resistance” load. If you drop voltage, current goes up. OCXO’s happen 
>to share this issue. Negative resistances are *not* what most power source
>guys want in their control loop.
>
>Bob

People working with emitter/source followers do not like it either and
I cannot see the folks using inverters wanting to pay to put big
resistive heaters across the grid to compensate.

Adding power factor correction to switching power supplies was cheap
compared adding "negative resistance" correction.
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Re: [time-nuts] Line Frequency standard change - Possible ?

[David]

On Thu, 09 Feb 2017 23:39:24 +, you wrote:

>It is harder than it sounds.
>
>Small solar inverters are the best, they an regulate down at milliseconds
>notice, and many jurisdictions impose asymetric frequency bands on
>them to exploit this.
>
>Big inverters, no matter what you put behind them, get quite a bit
>more expensive if they are designed to provide "non-VA" power,
>because you suddenly have to run the current both ways in the same
>half-cycle.
>
>Nobody wants to pay for that voluntarily, and nobody are particular
>keen to cause the first explosion/fire while they get the control-law
>debugged.

Imagine how they will scream if they have to pay for fields of big
synchronous motors to be connected.

https://en.wikipedia.org/wiki/Synchronous_condenser
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