Re: [time-nuts] a newbie question: where can I purchase 794.7nm VCSEL for building CPT rubidium clock?

[Hal Murray]

k8yumdoo...@gmail.com said:
> I've been told that CD player type diodes can be successfully modulated up to
> about 600 MHz, but that going much further is either difficult or perhaps
> impossible.

Are DVD lasers faster?


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Re: [time-nuts] Affordable PoE 6-digit time displays?

[Hal Murray]

bow...@gmail.com said:
> I’m still hunting for something that will take NTP in and put IRIG out. 
> There
> is probably someone doing it with a Pi or an Arduino.  

There is a module in the ntp package/collection that puts out IRIG from the 
system clock.  You can use NTP if you want to keep your clock sane.  I forget 
the name.  I'll fish it out if you can't find it.


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Re: [time-nuts] nuts about position

[Hal Murray]

hol...@hotmail.com said:
> A 5 hour 1Hz run was sent to CSRS-PPP and the lat/lon/alt error ellipses
> were in the 250/250/700 mm range...

Does the position agree with other chip sets?


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[time-nuts] Sawtooth correction: next or previous PPS

[Hal Murray]

hol...@hotmail.com said:
> One thing to look out for when messing with sawtooth messages is the
> question of does the message come out before or after the PPS pulse...  good
> look finding the answer in the receiver documentation... 

Has anybody asked the manufacturers?

This should be easy to see if you record the PPS offset referenced to a good 
clock and compare that to the reported offset.  If the frequency is stable 
and you are getting a sawtooth (rather than a bridge) then a point on a 
corrected graph next to the jump in the sawtooth will look good if you have 
it right or be off by a clock cycle if you have it wrong.


hol...@hotmail.com said:
> "After" seems to be the most common answer.  That makes hardware/delay line
> compensation rather tricky.  ...

The slides from Tom Clark and Rick Hambly's VLBI talk (page 29) show a before 
setup.
  http://www.gpstime.com/files/TOW/tow-time2015.pdf

You said "most common".  That implies there are both types.  (or 
documentation errors)  We should make a list of which GPS modules do it which 
way.


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Re: [time-nuts] ˜NEO-M8N vs. NEO-M8T

[Hal Murray]

See Marks recent message about whether the offset applies to the next or 
previous PPS.  For the rest of this, I'll assume next since it's simpler to 
describe.  We can discuss the other/harder case if you agree that the rest of 
this makes sense.

g...@rellim.com said:
> Your concept of 'real time' does not match mine.

The correction message arrives before the PPS.  What's not real-time about 
that?  You don't need any data from the future.

> Also, how does that get me to the gola of a good PPS to feed into the Linux
> PPS kernel module?  I doubt Linux would accept a patch to put gpsd, and
> more, into the kernel to read GPS and adjust the PPS.

You don't fix the PPS, you fix the software processing the PPS to use the 
offset.

Assuming you are using gpsd, you fix the serial side of gpsd to save the 
offset and the PPS side uses that offset to correct the PPS offset and then 
pass the corrected value to ntpd rather than the raw value.

Linux/ntpd actually has two modes of PPS processing.  The normal mode is that 
ntpd tells the kernel how to adjust the drift and offset.  In that case, the 
gpsd processing described above would work.

There is another mode where the PLL is done in the kernal and ntpd sits off 
to the side and watches, mostly doing a sanity check.  This option, NTP_PPS, 
is not included in most kernels since it conflicts with NO_HZ_COMMON which 
saves power.

I haven't checked the code.  ntpd has a refclock config option for the 
offset.  If that works for the kernel PLL, then the latest sawtooth 
correction could be passed in each second.  If that doesn't work yet, it 
would be a small kernel mod to fix.



Another option would build some hardware to apply the correction.  See Mark's 
recent message and/or the archives.  There are chips that do the adjustable 
delays.


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Re: [time-nuts] ✘NEO-M8N vs. NEO-M8T

[Hal Murray]

g...@rellim.com said:
> Yeah, which does me zero good real time.  I'm putting the PPS into a TICC.
> My TICC has not way to accept real time corrections.  So that does me no
> good, except as a post processing step. 

Yes, but that post processing step can be done in real time.  Assuming you 
are writing the TICC data to a log file:
  Read the TICC data.
  Read the sawtooth info.
  Apply the sawtooth correction.
  Write out the updated TICC data.

I'd actually write out the raw TICC and sawtooth info and do the correction 
later on but the above recipe will drop into your current work flow for 
making your graphs.


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Re: [time-nuts] ✘NEO-M8N vs. NEO-M8T

[Hal Murray]

g...@rellim.com said:
> The results were disappointing.  See attached.  For 8x the price all I see
> is a slightly flatter ADEV curve. 

What were you expecting?

How good is your antenna?  Can you insert an attenuator and compare them 
again?  It would also be interesting to see the NEO-M8N with good vs bad 
antenna.

As Bob suggests, it will be interesting to see what happens after you apply 
sawtooth correction.


g...@rellim.com said:
> The M8T also support raw data, so I can try to use it for RINEX files. 

It would be interesting to see how well the RINEX location compares with the 
surveyed location and/or if using the RINEX location improves the timing 
output.


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Re: [time-nuts] TruePosition GPSDO Holdover Issues

[Hal Murray]

> It's not hard to make your own plots.  This is from 66 38' north.
>   http://users.megapathdsl.net/~hmurray/time-nuts/Arctic/Polar-A.png
> If anybody wants to play, I'll put the code on the web. 

Code is on:
  http://users.megapathdsl.net/~hmurray/time-nuts/Arctic/code/


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Re: [time-nuts] TruePosition GPSDO Holdover Issues

[Hal Murray]

kb...@n1k.org said:
> One thing to consider - if you get far enough north, the “hole” closes and
> you can get sat tracks from the other side of the north pole. Yes they are a
> *long* ways away. It’s no worse than a lot of tracks that GPS thinks are
> perfectly fine to use. For timing they aren’t going to do much good. They
> will improve a navigation

Neat.  Thanks.  That raises several questions.
  How high do satellites get if you are at a pole?
  What is the best or worst latitude for timing?
  What is the best/worst latitude for doing a survey?


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Re: [time-nuts] TruePosition GPSDO Holdover Issues

[Hal Murray]

> Web sites such as "In The Sky.org" can generate useful plots for any
> specified location and time but I don't know if there's anything that will
> allow building a projected map over a period, and I don't suppose there's
> going to be anything anyway that allows experimatation with antenna angle
> etc, so that really leaves using lady H to generate the plots in real time,
> which she does do really well but for something like this might be akin to
> watching grass grow:-)

If you are far enough north, you are in the hole, but you can see the other 
side of the hole over the pole.

It's not hard to make your own plots.  This is from 66 38' north.
  http://users.megapathdsl.net/~hmurray/time-nuts/Arctic/Polar-A.png

If anybody wants to play, I'll put the code on the web.

There are several steps.  First is to collect the data.  I have a python 
script that grabs everything from a NMEA device and logs each line with a 
time stamp.  The GPS orbit period is 12 hours so you need 12 hours of data to 
see everything.  But there are 30 satellites, so a few hours will show the 
hole.

The next step is to extract the data into a useful format.  That's another 
python script.  Then, just feed that to gunplot.


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Re: [time-nuts] GPS Timing Antenna Failure - Long

[Hal Murray]

>  I can't count the number of times flux and whisker  growth has caused
> problems in circuitry and connectors.

A whisker might explain things.  Would that also show up as over-current?


> So there are 3D quadrifiliar GPS antennas..

This photo is from 2009:
  http://users.megapathdsl.net/~hmurray/time-nuts/Lucent-Antenna.jpg

That's from a Lucent KS-24019L112A.

A Maxrad antenna, PN: Z3001, has the same shape, tan top with similar insides.

Another one from, Pctel, GPS-TMG-HR-26N, has a slightly larger cylinder.
It has a metal base plate.

Motorla, AN25090031, shorter and wider has a patch.
NAIS, CCAH32ST04, has a patch.








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Re: [time-nuts] GPS Timing Antenna Failure - Long

[Hal Murray]

lmcda...@lmceng.com said:
> To make this very long story into a short one, I learned that the  HP/
> Symmetricom 58532A GPS Reference (timing) antennas use a simple patch
> antenna instead of a quadrafilar antenna and that old solder flux  residue
> will attenuate the even amplified GPS signal out of this antenna. 

Flux seems unlikely to produce a sudden failure.

If flux was the problem, I'd expect it to work poorly when first installed, 
or maybe decay slowly over time as something changed.




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[time-nuts] Anybody have suggestions for time related science fair projects?

[Hal Murray]

A few months ago, I was a judge for the county level middle school science 
fair.  (I'm not very good at what they wanted, but that's a different 
problem.)

What sort of interesting time related experiments can a middle school geek do?

Borrowing serious gear may not be off scale as long as a youngster can run it.

-

An alternat meaning to the "nut" part of time-nuts:  ")
  https://www.snopes.com/fact-check/schools-removing-analog-clocks/


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[time-nuts] Simon Winchester: The Perfectionists

[Hal Murray]

In 'The Perfectionists' Simon Winchester Looks At History Of Precision 
Engineering

https://www.npr.org/2018/05/07/608590826/in-the-perfectionists-simon-wincheste
r-looks-at-history-of-precision-engineering

KELLY: You write about that in such a personal way in the book. You include 
the detail of your Sunday morning ritual, of walking room to room in this old 
farmhouse you live in and correcting all the clocks, you know, pushing one 
hand forward a little bit and another hand back, and that you love the 
inaccuracy of that, that they're all chiming totally out of sync by midway 
through the next week.

WINCHESTER: Yes, a lovely description in Dorothy L. Sayers' book "Gaudy 
Night" about the clocks in Oxford chiming midnight in friendly disagreement. 
Well, I like clocks having friendly disagreement. I loathe digital watches 
with, I mean, the one I dare say you're looking at in the studio now, with 
microsecond countdowns. Let's take it a bit easier. Let's be a bit fuzzy in 
our needs and desires and wishes.

---

I don't know if the book discusses time.  If you aren't familiar with his 
work, he's good.



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[time-nuts] WWVB: measuring local 60 KHz noise

[Hal Murray]

Review/background:  I have an UltraLink 333 WWVB receiver.  It didn't work.  
Several weeks ago. a discussion here mentioned that the phone cable between 
the main box and antenna needs to be straight through rather than the typical 
reversed.  That was my problem.  With the correct cable, the meter shows 
signal and bounces around such that with practice, I could probably read the 
bit pattern.  But it didn't lock up.

That was several weeks ago.  I left it running.  When I looked last night, it 
had figured out that it is 2018.  I wasn't watching or monitoring, so I don't 
know how long it took.

I assume the problem is noise.  Is there any simple way to measure the noise 
around 60 KHz?  How about not so simple?

Extra credit for a way that others nuts can reproduce so we can compare the 
noise at my location with other locations.

Can any audio cards be pushed that high?  I see sample rates of 192K, but I 
don't know if that is useful.

I'd also like to measure the propagation delays on WWV so a setup for HF that 
also works down to 60 KHz would be interesting.

--

The UltraLink documentation says the display has a slot for a C or H.  The C is 
for Colorado and the H is for Hawaii.  Did WWVH have a low frequency 
transmitter many years ago?  The NIST history of WWVH doesn't mention it.

My guess is a cut+paste from a version that listened to WWV/WWVH.



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Re: [time-nuts] nuts about position (cheap receiver)

[Hal Murray]

kb...@n1k.org said:
> If you have a very good survey grade receiver and take a long enough data
> set, yes you can  watch your location drift in some parts of the world. In
> most locations, fixes a few years apart would be a better bet. 

I'm in Silicon Valley.  The San Andreas fault is a few miles from here.  A 
map of the bay area will show a dozen major faults.  A neighborhood map may 
have several smaller lines.
  https://earthquake.usgs.gov/earthquakes/events/1906calif/virtualtour/bayarea
.php

The USGS has good GPS receivers sprinkled around the area.  You can see 
occasional
antenna domes on a post alongside the highway.
  http://www.quake.geo.berkeley.edu/usgs-gps/
(Time sink warning.)

The fault moves about as fast as your fingernails grow, an inch per year.  
That's one side relative to the other.  I don't know how fast the pair is 
moving.



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Re: [time-nuts] nuts about position

[Hal Murray]

kb...@n1k.org said:
> One important qualifier to re-state. L1 post processing is very dependent on
> the distance to an “open” source of correction data. The spacing of those
> sites over the US is highly variable. If you get outside the US it is very
> much a “that depends” sort of thing. Some countries apparently don’t 
> have
> the same sort of open site network

Is there a map of the available locations?

Do the RINEX processors tell you which ones they used?  With maybe a note if 
the one they would like to use is not working properly.



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Re: [time-nuts] Question about frequency counter testing

[Hal Murray]

olegsky...@gmail.com said:
> No, it is much simpler. The hardware saves time-stamps to the memory at each
> (event) rise of the input signal (let's consider we have digital logic input
> signal for simplicity). So after some time we have many pairs of {event
> number, time-stamp}. We can plot those pairs with event number on X-axis and
> time on Y-axis, now if we fit the line on that dataset the inverse slope of
> the line will correspond to the estimated frequency. 

I like it.  Thanks.

If you flip the X-Y axis, then you don't have to invert the slope.

That might be an interesting way to analyze TICC data.  It would work 
better/faster if you used a custom divider to trigger the TICC as fast as it 
can print rather than using the typical PPS.

--

Another way to look at things is that you have a fast 1 bit A/D.

If you need results in a second, FFTing that might fit into memory.  (Or you 
could rent a big-memory cloud server.  A quick sample found 128GB for 
$1/hour.)  That's with 1 second of data.  I don't know how long it would take 
to process.

What's the clock frequency?  Handwave.  At 1 GHz, 1 second of samples fits 
into a 4 byte integer even if all the energy ends up in one bin.  4 bytes, *2 
for complex, *2 for input and output is 16 GB.


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Re: [time-nuts] Question about frequency counter testing

[Hal Murray]

olegsky...@gmail.com said:
> The plots I showed were made with approx. 5*10^6 timestamps  per second, so
> theoretically I should get approx. 4ps equivalent  resolution (or 11+
> significant digits in one second). 

Is there a term for what I think you are doing?

If I understand (big if), you are doing the digital version of magic 
down-conversion with an A/D.  I can't even think of the name for that.

If I have a bunch of digital samples and count the transitions I can conpute 
a frequency.  But I would get the same results if the input frequency was X 
plus the sampling frequency.  Or 2X.  ...  The digital stream is the beat 
between the input and the sampling frequency.

That technique depends on having a low jitter clock.  There should be some 
good math in there, but I don't see it.

A related trick is getting the time from something that ticks slowly, like 
the RTC/CMOS clocks on PCs.   They only tick once per second, but you can get 
the time with (much) higher resolution if you poll until it ticks.

Don't forget about metastability.


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Re: [time-nuts] nuts about position

[Hal Murray]

> How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D 
> position?

Elevation gets interesting.  Earth has tides in solid rock that are ballpark 
of that scale peak-peak.

It would be interesting to see if you could see the tides with low cost gear.


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Re: [time-nuts] Better quartz crystals with single isotope ?

[Hal Murray]

bro...@pacific.net said:
> Isotopes of an element differ in the number of neutrons.  The chemical
> reactions of an element are governed by the  electrons, which are the same
> for all isotopes, so chemical means can not be used to separate the
> isotopes. 

That needs a qualification, maybe inserting something like "easily".

Some chemical reactions depend slightly on mass.  I was at a talk recently 
where the speaker was using isotope ratios to investigate the source of lead 
and mercury as pollutants.  The key is that the technology for measuring 
isotope ratios in now very good.  1E4 is common, at least in research labs 
focusing on this area.



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Re: [time-nuts] Holdover: Z3801A vs KS-24361

[Hal Murray]

kb...@n1k.org said:
>> A  KS-24361 says:
>>  Predict  394.1 us/initial 24 hrs
> That would suggest the unit is unlocked. It should be below 10 us. Just as
> with the 3801, the estimate is a bit fuzzy. You should be able to see issues
> in the data on the Z3809/Z3810. 

It says it is locked and has been locked for days.
  >> Locked to GPS  TFOM 3  FFOM 0

I used this as a learning exercise for my new TICC.  Something is clearly 
fishy.

The reference for the TICC is the crystal in a HP 5334B with the good-crystal 
option.  It's not calibrated, but there isn't any GPS logic to jerk it 
around.  I assume the swing is due to temperature.  I corrected the slope of 
the graph by hand.

Here is a day+ of data:
  http://users.megapathdsl.net/~hmurray/time-nuts/TICC/TICC-KS.png

Here is a zoomed in chunk:
  http://users.megapathdsl.net/~hmurray/time-nuts/TICC/TICC-KS-2.png


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Re: [time-nuts] TCVCXO Adjustment

[Hal Murray]

kb...@n1k.org said:
> The gotcha is that you do not have a calibrated adjustment. Put another way,
> there isn’t a perfect correlation between DAC bits and ppm. Each adjustment
> you make is subject to a bit of error. When you are trying to get within a
> ppm,  your measurements are quicker, so the larger error ( percentage of
> step) may not be as big a deal. When you get close, it is likely to become a
> big deal.  

Interesting.  Thanks.

How much does it vary from unit to unit?  How non-linear is it likely to be?  
How much does it change with temperature?

Anybody have data?

Are fancy OCXOs more linear?


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Re: [time-nuts] TCVCXO Adjustment

[Hal Murray]

kb...@n1k.org said:
> The alternative is to plug a USB GPS into the mac and do a bit of code to
> compare things. If you want to pass the gizmo around to your friends …. that
> can be done. Pretty good ones are “sub $10” delivered.  

USB GPS gizmos generally don't have a PPS and the timing on the NMEA 
sentences is generally crappy.  (I may be biased by a few bad examples.)

Does anybody have a list of ones known to work well?

There is at least one GPS-USB with PPS, the Navisys GR-601W/GR-701W/GR-801W,  
They were hard to get retail.  Looks like idealez sells them Taiwan for $47 
for the 701W (Ublox 7), $50 for the 801W (Ublox 8) (plus shipping).  I 
haven't tried ordering through them.  Gary and/or Mark may have some for sale.

--

Plan B is a GPS breakout and a USB-serial breakout and a few wires.  4x less 
USB jitter if your USB-Serial chip is full-speed.

I got mine from SparkFun:
Venus GPS with SMA Connector
  https://www.sparkfun.com/products/11058
USB to Serial Breakout - FT232RL
  https://www.sparkfun.com/products/12731

--

Google found this.  I don't know anything more:
  https://www.zti-communications.com/z050-gps-dongle/


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Re: [time-nuts] TCVCXO Adjustment

[Hal Murray]

wayne.hol...@gmail.com said:
> I believe that the "precision" of -20 value on the 4th line is supposed to
> be interpreted as 2^-20 seconds which, if my math is correct, works out to
> be a precision of about 1 PPM. Is that correct?

That's the time between ticks or the time it takes to read the clock.  It 
doesn't tell you anything about how correct the clock is.


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Re: [time-nuts] Ultralink

[Hal Murray]

j...@febo.com said:
> The modular cable connecting the receiver to the decoder is wired  straight
> through, not reversed as most telephone cables are.  My fear is  that
> someone (like me) might at one point have used a reverse cable and  thus put
> reverse polarity on the board; I don't see any reverse power  protection. 

Many thanks for that comment.  I hadn't checked that before.

My cable was reversed.  A new/correct one arrived today.  The meter is 
working.  With a bit of practice, I'll bet I could read the data pattern off 
the wiggles.

But after an hour, the LCD still shows time-since-power-up rather than date 
and time.


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Re: [time-nuts] WWVB information

[Hal Murray]

The month recently changed from 3 to 4.  A while ago, the bottom digit of the 
year changed from 8 to 7.  I think the out-of-phase time is shorter for a 0 
than for a 1.  Would a few more 0 bits be enough to push it into sync?

Is there "goodness" parameter that you can monitor?  It might be interesting 
to see if that correlates with day, hour, minute encoding?


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[time-nuts] Holdover: Z3801A vs KS-24361

[Hal Murray]

On that Status page, A Z3801A says:
  Predict  2.5 us/initial 24 hrs

A  KS-24361 says:
  Predict  394.1 us/initial 24 hrs

Both have been running for weeks.

Is anybody seeing similar?


Also, the Satellite Status area has a header of SS on the Z3801A and C/N on 
the KS.  Does anybody know the units and/or what that is actually measuring?

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Re: [time-nuts] Cheap jitter measurements

[Hal Murray]

kb...@n1k.org said:
> Except that’s not the way most timers run. The silicon needed to get a
> programable  divider to work at 2.4 GHz is expensive. If you dig into the
> hardware descriptions,  the clock tree feeds something much slower to the
> “top end” of the typical timer in a CPU or MCU. The exception is the high
> perf timers in some of the Intel chips.  There the issue is getting them to
> relate to anything “outside” the chip.

I think I got started in this area back in the early DEC Alpha days.  They 
had a register that counted raw clock cycles.  Simple.  I got stuck thinking 
that was the obvious/clean way to do things.

Many thanks for giving me a poke to go learn more about this area.

That was back before battery operation was as interesting as it is today.  I 
suspect power is more likely the critical factor.  Half the power goes into 
the low order bit, so counting by 4 every 4th cycle rather than 1 every cycle 
saves 3/4 of the power.


> That may be what the kernel does, but it implements the result as a drop /
> add to a counter.  

If the source of time is a register counting CPU clock ticks, and the CPU 
clock (2 or 3 GHz) is faster than the resolution of the clock (1 ns) it will 
be hard to see any drop/add.  However, if the time register is significantly 
slower, then the drop/add is easy to spot.  But all that is lost in the noise 
of cache misses and such.

Here is a histogram from an Intel Atom running at 1.6 GHz.

First pass, using rpcc.
cycles  Hits
24 86932
36904825
48  8011
60   122
72 1
   14411
...
So it looks like the cycle counter gets bumped by 12.  That's a strange 
number.  I suspect it's tangled up with changing the clock speed to save 
power.  There are conflicting interests in this area.  If you want to keep 
time, you need a register than ticks at a constant rate as you change speed.  
If you are doing performance analysis, you want a register than counts cycles 
at whatever speed the CPU is running.  Or maybe I'm confused.

Second pass, using clock_gettime.
  nSec  Hits
   698 2
   768 5
   769 2
   838 3
   908 2
   977 1
   978 3
  1047237102
  1048383246
  1117204072
  1118172490
  1187   275
  1188   135
  1257   263
  125847
  1326 7
  1327   216
...
The clock seems to be ticking in 70ns steps.  That doesn't match 12 clock 
cycles so I assume they are using something else.

>From another system:
Second pass, using clock_gettime.
  nSec  Hits
19 45693
20347538
21591129
22 15284
2363
2434
2532
...
Note that this is 50 times faster than the previous example.

I haven't figured out the kernel and library software for reading the clock.  
There is a special path for some functions like reading the clock that avoids 
the overhead of getting in/out of the kernel.  I assume there is some shared 
memory.
  https://en.wikipedia.org/wiki/VDSO

Again, thanks Bob.

TICC arrived today.


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Re: [time-nuts] Any guesses as to how Citizen is claiming ±1 second/year with using this AT-cut 8.4MHz XTAL?

[Hal Murray]

kb...@n1k.org said:
> Before you say it can’t be done, the whole “average out” thing is how 
> time
> pieces have been done for hundreds of years. The device may swing this  way
> and that …. done properly it eventually averages out. How well it works for
> you … that depends.  

There is a wonderful message in the archives someplace that describes how to 
adjust a watch.  The recipe is roughly:
  Adjust watch to run correctly in the shop.
  Give it to customer.  Tell him to come back after a week of normal use.
  Measure offset.
  Adjust watch to compensate for that offset.

That probably doesn't work very well if your watch spends the night on the 
stand and your room temperature changes a lot from summer to winter.


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Re: [time-nuts] TCVCXO Adjustment

[Hal Murray]

wayne.hol...@gmail.com said:
> Since the TCVCXO includes a voltage control input, my plan is to also add a
> 12-Bit Digital-to-Analog Converter ...

What's the temperature stability of the D/A?

How does that compare with a 10 turn pot?  I remember a comment about pots 
aging.  It was somewhat recently.  I don't remember the details.  I think it 
was something like the wiper wore a small groove which made it hard to make 
tiny adjustments.  I don't know how long it takes for the groove to form.

A possible option is to just measure the osc and do the adjustment in 
software.


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Re: [time-nuts] Cheap jitter measurements

[Hal Murray]

g...@rellim.com said:
> It tests the time to do two back to back clock_gettime().

That's the time it takes to read the clock.  That's not what I mean by 
granularity but I think I see how you might use that word.  The comment at 
the top of the code says "latency".

When I hear "granularity", I think of the tick size of the clock.  It's easy to 
measure a big tick size, read the clock, spin reading until it changes, 
subtract.

Things get interesting if the tick size is less than the time it takes to read 
the clock.  In that case, you may be able see the tick size with a histograms 
of the times to read the clock.

With calibration, I can correct for the duration of time it takes to read the 
clock.  I'm not sure how to do the calibration.  In some cases it cancels out.  
Cache misses may be more significant.


PS: Try running that code on an ARM.  And consider reading the clock 3 times 
and collecting 2 sets of data.  The idea is that the first read takes all the 
cache misses so the time for the second read should be faster and cleaner.

I see a tick size of 1 microsecond on a Pi 1, and 52 ns on a Pi 2 and Pi 3.

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Re: [time-nuts] Cheap jitter measurements

[Hal Murray]

Gary said:
>> The API  for the kernel clock can be read to a ns.  I don't see ntpd
>> having much use for finer grain than that.  I should look at the
>> source to see what the internal details look like.

> Yeah, but the granularity is much worse.

Do you have code that demonstrates that?  (or tell me how and I'll try it)

I think most modern kernels derive time from a cycle-count register.  So the 
basic clock should be accurate to a cycle.  Yes, that's worse than a ns on 
slow CPUs.

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Re: [time-nuts] Cheap jitter measurements

[Hal Murray]

kb...@n1k.org said:
> Yes, but looping back to the start of this thread, the intent is to actually
> measure the jitter directly.  That’s where the whole need for a stamped
> pulse comes from. To paraphrase the earlier comments, the intent is to get
> away from a “self reported” result and actually do a direct measurement.  

I think that should be a reasonable project.

1) Write some code to grab the time, send a pulse, grab the time.  Log that.
2) Use a time-stamp counter to log the time of the pulse.
3) Write the software to merge the two log files.


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Re: [time-nuts] Cheap jitter measurements

[Hal Murray]

kb...@n1k.org said:
> The kernel clock comes from the CPU clock. That CPU clock is phase locked to
> a crystal. If you have a CPU that is driven by a VCXO that is a *very*
> unusual CPU board.  The crystal runs at an arbitrary frequency. That gives
> you edges that are unlikely to happen “right on the second”.  

I was assuming the CPU clock was fast enough that reading a cycle-count 
register and converting to ns would be within a ns which is the resolution of 
the clock.

That's obviously not true for low end SOC type setups.  A Pi-1 runs at 700 
MHz.  The Pi 3 is up to 1.4 GHz.


> And the kernel does the “adjust” by dropping or adding clock cycles to the
> count.

I was expecting the kernel to do the clock arithmetic with lots of fractional 
bits.
You get things like:
  This is a 2.4 GHz system.  That's 0.41666 ns per cycle
  But the crystal is 12 ppm fast, so we actually use 0.416661666
  It's been 123456 cycles since we last checked.
  That's 51439.382637696 ns
Internally, the current time has to remember the fractional bits.

If anybody is looking carefully, most PC clocks are spread spectrum.  We 
should do some back-of-envelope work on how significant that is.


> Being able to read the kernel time is only part of the process. You need to
> generate an edge. That gets you into timers and (likely) a different set of
> limitations as the 

If you want an output pulse, I was thinking of generating it from userland at 
roughly the right time but recording the actual time.  That would require a 
fixup pass in software before analyzing the data recorded by traditional 
hardware approaches.



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Re: [time-nuts] Cheap jitter measurements

[Hal Murray]

kb...@n1k.org said:
> Somewhere in the NTP algorithm, there is a “zero error” estimate. GPS
> modules have the same thing buried in them. A GPS module (like NTP as
> described above) can only *express* a PPS modulo some clock rate. GPS
> modules get around this with a firmware hack. They simply tell you what the
> error was. It is a simple way to get out of the “I need a 10 GHz clock
> source” problem. No need for FPGA’s or any other guck. You just do an
> estimate and report it. It then would work on any hardware and let you do
> the sort of measurements we’re talking about.

The GPS offset is a kludge to work around not being able to control the local 
oscillator.

> Now - *can* that be done with NTP??  Who knows…. 

The kernel clock has a knob so the same concept doesn't apply.

The API  for the kernel clock can be read to a ns.  I don't see ntpd having 
much use for finer grain than that.  I should look at the source to see what 
the internal details look like.

If ntpd decides the clock needs correcting, it tells the kernel to do the 
work.  The kernel offsets the clock rate knob by 500 PPM, so it takes 2000 
microseconds to adjust the clock by 1 microsecond.  It would be possible to 
read the correction-left and adjust the time by that amount.

I think it would be possible to make similar adjustments by post processing 
the data.  I'd have to double check to make sure I understand what is in 
loopstats.  If now, we could fix it.


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Re: [time-nuts] Weird Stuff WareHouse shutting down

[Hal Murray]

drkir...@kirkbymicrowave.co.uk said:
> I think people learn more with old test equipment.  I know someone who has a
> 1 GHz LeCroy scope,  as well as a high end Agilent, but can't seem to
> measure the simplest of signals, that I could easily measure with a 50 year
> old scope. 

With modern scopes, you just push the button.  1/2 :), but the one on my 
Rigol scope is labeled "Auto".


Many years ago, my boss used to use a scope when interviewing technicians: 
scramble the knobs, then watch how they sort things out.


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Re: [time-nuts] Cheap jitter measurements

[Hal Murray]

kb...@n1k.org said:
> In both cases (pulse in and pulse out) the first step is to ask NTP “when
> was that?”. You still have a pretty big chunk of NTP in the  middle of the
> process …. If NTP only “knows” what is happening (or can control what is
> happening)  to +/- 300 ns. The guts of  your data will be limited to the
> same  300 ns.  

NTP itself doesn't actually do any timing measurements.  That is done by the 
OS.

I'm not familiar with Windows.  All my OS comments apply to Linux and *BSD.  
Windows is probably similar is most respects but may be missing details.

The system clock runs off the CPU crystal.  The kernel has a knob for fine 
tuning the clock speed.  There is another knob that says bump the clock speed 
a bit (500 PPM) long enough to adjust the time by X seconds.  ntpd uses both.

[Many years ago, most kernels used an interrupt from the battery backed clock 
(RTC or TOY) for the main timing and interpolated using the CPU clock.]


The kernel can capture a time stamp on a PPS pulse and on packet arrivals.  I 
don't know of anything similar for packet departure.

The kernel can support more than one PPS so you could feed a GPSDO in on one 
for NTP and use another for general timing measurements.  Those measurements 
are using the kernel clock as a reference.  You can turn ntpd off so the 
system time will have more long term drift but less short term wobble as ntpd 
corrects for errors.]


I don't know of a good way to get a pulse out at a specified time.  You can 
measure the time that user code sends a pulse out and setup a timer to go off 
every second.  I don't know how to adjust or specify the offset from 
timer-going-off to system clock ticking to another second.

The Linux kernel PPS code has an option to send a pulse out when one comes 
in.  I haven't played with it.  I think it could help with measuring the 
interrupt response delays.

tvb: If I send you some data, can you turn it into pretty graphs?





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Re: [time-nuts] Cheap jitter measurements

[Hal Murray]

>> What do you mean by "jitter" and what do you really want to do?
> I mean jitter as NTP defines jitter.  Whatever that is.

I think you need to figure out what you want to do so you don't fool yourself.

ntpd is a PLL.  There is a low pass filter in the control loop.  It will 
track the low frequency wander of the source.

Assume you have a stable Rb reference.

Assume your GPSDO has a (small) day/night shift.

If you collect data with a TICC referenced to that Rb, that shift will show 
up.  If you collect data with ntpd, you will get the filtered version of that 
shift.  I'd expect small bumps at the day/night changes.

Ballpark for the time constant on the filter is the polling interval.  You 
can see the results of the filter by introducing a "bump" with ntpfrob.

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Re: [time-nuts] Environmental sensor recommendations

[Hal Murray]

> Are there any recommendations for other off-the-shelf sensors=
>  worth looking at?

Consider the TEMPer USB units from eBay.  Their main advantage is low cost.  
They have a temperature sensor in a thumb drive size USB module.  At least 
one model comes with a slightly bulky sensor on the end of a 3ft cable.

Most of the low cost units have a fairly coarse step size.  Please let me/us 
know if you find (or build) a good high resolution setup.  I assume that will 
be a thermistor and good DAC.

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Re: [time-nuts] Cheap jitter measurements

[Hal Murray]

g...@rellim.com said:
> With care I can measure GPS jitter on a RasPi to a bit over 300 nano sec
> resolution.  That is the smallest increment of the RasPi 3B clock with a
> 64-bit kernel.  That is clearly not time-nuts accuracy.

> What would you guys suggest as the cheapest way to see jitter down to around
> 1 nano second?   

What do you mean by "jitter" and what do you really want to do?

Jitter usually needs a reference.  Do you have one?


> I'm thinking maybe something like a rubidium standard (FE-5680A) and a
> TICC-TAPR?  But that would put me out around $400. 

Do you have a scope?

The Rigol DS1102E is/was quite popular and is good for close to a ns.  I got 
mine several years ago for $400.  Looks like the going price is closer to 
$300 now.  It's got a USB port.  You can read the data and decode it in 
software.

They make lots of similar scopes.  The middle 2 digits are the bandwidth: 5=>
50MHz, 10=>100MHz.  The last digit is the number of channels.)

The chip in the BeagleBone series boards has extra CPUs that help with things 
like this.  I don't know how fast they go.  I haven't seen 64 bit versions or 
a lot of software activity.

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Re: [time-nuts] quartz / liquid nitrogen

[Hal Murray]

> If not Nitrogen, how about dry ice (-109F -78C)?

Dry ice is relatively easy to get.  It wouldn't be hard to try a quick 
experiment.


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Re: [time-nuts] New GNSS chipsets

[Hal Murray]

mag...@rubidium.dyndns.org said:
> I have advocated for receivers able to handle multiple frequencies and
> multiple GNSS for some time, sneaking it into documents, so there should be
> some preparations for this now.

How well do various GNSS track UTC and/or eachother?


> The benefit is naturally redundancy, but also higher precision. 

I've been assuming the cheap GPS jammers will kill the others too.  Are there 
any signals far enough away from L1 that they might get through?


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Re: [time-nuts] Timestamping audio waveforms

[Hal Murray]

tsho...@gmail.com said:
> Or should I, say, take the PPS from a GPS, and feed it into channel 2, with
> the audio going into channel 1, and make a stereo recording?  ...

I assume the audio API is for a batch of samples.  If you get time stamps on 
a stream of batches, you can work out the frequency of the crystal the audio 
A/D is using.

I think you will need the PPS approach to calibrate the delay through the 
system.  If it's low enough, you can drop it.

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Re: [time-nuts] TV Signals as a frequency reference

[Hal Murray]

> As noted earlier, color burst references were a big deal a long time ago.

Thanks.  I was fishing for something modern, maybe a bit clock out of the 
digital receiver.

I'm assuming that the digital stream is locked to the carrier.  That may not 
be correct.


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Re: [time-nuts] TV Signals as a frequency reference

[Hal Murray]

fgr...@otiengineering.com said:
>   Now that analog TV has gone away, so
>   have these signals. 

What do the local TV stations use for a frequency reference?

Are there low cost receivers that also produce a good reference frequency?


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Re: [time-nuts] WWV/CHU

[Hal Murray]

t...@leapsecond.com said:
> In general, if the author or paper is related to NIST, the original
> copyright-free PDF will be available in the NIST Time and Frequency
> Publication Database. That easily searchable database, and the thousands of
> papers it contains, is probably the greatest asset we time nuts have. For
> those of you that don't know it yet, check it out:

> https://tf.nist.gov/general/publications.htm 

Thanks.

Another other great resource (non time-nut) is NIH Pubmed.

I think the deal is that they get to distribute a copy of any paper from 
research that they finance.  I think the publisher gets 6 months or a year 
before the NIH free version goes online.

I assume the publishers freaked out when the idea was first announced.  
Anybody know of a paper discussing that issue?



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Re: [time-nuts] Ultralink

[Hal Murray]

t...@leapsecond.com said:
> I updated http://leapsecond.com/museum/ulio/ with more manuals, and many
> exterior / interior photos of the 301 module. 

Thanks. My 301 says it is a 30TH Rev-A - mostly through hole parts.  Same 
layout.


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Re: [time-nuts] WWV/CHU

[Hal Murray]

jim...@earthlink.net said:
> Hal, you should know better than to have a question like "get time" on this
> list without specify the precision and accuracy . 

I was thinking of measuring the results, and maybe comparing various 
receivers if I get that far.

"Good enough" for me would be to see the change in prop delay from night to 
day.


> I was in a meeting yesterday with a lot of technical people, discussing
> testing an HF receiver, and I mentioned WWV as a source, and there were  a
> combination of blank looks and amused/amazed looks (at the blank  looks) -
> OK, so now we know who in the room are the computer only people  (WWV? is
> that some sort of NTP protocol?) and who  are the radio people 

I listened to WWV as a kid.  I think my father told me about it.  (We had a 
good collection of old tube radios.)

Roughly 40 years ago, a friend showed me a NBS booklet describing a scheme 
for distributing time via TV.  I forget the details.  It was a cooperative 
project with one of the major networks.  NBS published the propagation delays 
which changed occasionally as the phone companies providing the underlying 
links rerouted things.

This is an IEEE article from 1972 that looks like a good fit:
  Nationwide Precise Time and Frequency
  Distribution Utilizing an Active Code Within
   Network Television Broadcasts
DAVID A. HOWE
https://www.researchgate.net/publication/3092613



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[time-nuts] Ultralink

[Hal Murray]

I have a 333 box with 301 antenna.  It was a gift several years ago.  The 
display updates, but the meter never gets off 0.  At the time, I thought the 
new modulation scheme had killed it and didn't investigate.  But tvb 
suggested it should still work, so I took the cover off.

Anybody know anything about the innards?  I see a 20 pin DIP that says Atmel. 
 I assume that's the CPU.  The display updates, so it's obviously mostly 
working.  There are also 2 8 pin DIPs and a transistor.

There are 3 pots in one corner, labeled: LCD, AGC, and A/D.

I haven't opened the antenna box yet.

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Re: [time-nuts] Ultralink WWVB receiver manuals?

[Hal Murray]

>From info for a 332A, YMMV, etc...

>  (a) is the 6P6C modular cable 
> connecting the receiver and decoder straight, or reversed

Receiver/decoder cable RJ11-4/6 wired pin 1 to pin 1 - 500
   feet maximum length

> (b) what are the four DIP switches on the back of the 333 used for?

Option switches - 4 position dip switch provides installed
option selection as follows:
1Battery backup - ON is enabled
2Report time each second - ON is enabled
3,4  Reserved

Backup Battery Enable
Upon power up, place Option Switch 1 in the ON
position to enable RTC battery backup. During ship-
ment and periods of no use, set this switch to OFF to
avoid battery cell reversal.

Reset
The decoder may be reset by removing power and
setting Option Switch 1 to OFF for a few seconds.


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[time-nuts] WWV/CHU

[Hal Murray]

What do I need in in order to get time from WWV or CHU?

Do I need a fancy receiver as a front end?  Do I have a chance with one of 
the low cost USB thumb drive size receivers?

Is there an obvious software package to start with?  (Linux)


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Re: [time-nuts] Odetics Telecom CommSync - GPS Rollover Problem.

[Hal Murray]

> Anyone else on the list have Odetics CommSync's and can report on their 
> status?

Most software like ntpd can "fix" offsets like that.  From ntp.conf on a 
KS-24361 that I haven't managed to get started correctly:
  fudge  127.127.26.0 time1 619315199.0453
(That's about a second short of 1024 weeks.  It normally needs -0.9547)

Of course, that doesn't help if the device has a built-in display that you 
want to use.


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Re: [time-nuts] WWVB Antenna revisited/Spectracom 8182

[Hal Murray]

organli...@pacbell.net said:
> One would think inexpensive products would be sacrificed verses the more
> expensive equipment. 

There are many many the low cost units and only a few of the expensive ones.

It would be interesting to see how many of the expensive WWVB boxes were 
still running when they made the switch in transmission format.  I expect 
most of the places that needed good time had already switched to GPS.


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Re: [time-nuts] Use the LT3042 for retrofit?

[Hal Murray]

kb...@n1k.org said:
[context is EFC control voltage]
> Generally, the biggest factor is the voltage drop from the oven current
> getting into the EFC “loop”. Its actually pretty hard to keep them 
> separate.

Is there a fundamental problem, or is it just that everybody uses historical 
footprints that don't have separate ground pins?

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Re: [time-nuts] Recommendations for Mains Power Monitor / Logger

[Hal Murray]

I know of two ways to monitor frequency.  One is to use one of tvb's PICs.  
That needs a good frequency reference, probably a GPSDO.

The other is to use the PPS input on a Linux box.  That uses the system clock 
so you meed a good NTP setup.

Some of the APS family of UPS boxes will monitor the voltage.  You can ask 
what was the min/max since the last time I asked?  (as well as what is the 
current voltage)  That's good enough to catch glitches.

If you want to measure current, I'd start with a current transformer.  I 
don't know of anybody using them for long term measurements.  I've used them 
with a scope to look at startup transients.

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Re: [time-nuts] Frequency deviations in Europe affect clocks

[Hal Murray]

If you don't pay your bills, the guy who was sending you power stops sending 
it so your zone starts running without enough power.

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Re: [time-nuts] TymServe TS2100 dead power supply

[Hal Murray]

k6...@comcast.net said:
> RANDOM QUESTION -- does anybody know of software to *generate* IRIG time
> code? Something in C that's adaptable to a modern micro would be good. In
> something like a Raspberry Pi 3, IRIG generation would make a nice addition
> to Lady Heather... 

Look at util/tg.c or util/tg2.c in the ntp package.

Download here:
  http://support.ntp.org/bin/view/Main/SoftwareDownloads


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Re: [time-nuts] WWV or Net Clock controlled oscillator

[Hal Murray]

hol...@hotmail.com said:
> The university that I hang out at has a clock tower with a full set of
> bells.   ...

Stanford has a clock tower.

Searching YouTube for >Stanford Clock Tower< will find several short videos.

It's in a roughly 10 ft square room with big windows on all 4 sides.  I stop 
to admire it when I'm in the area with spare time.   It's all mechanical.  A 
wonderful contraption.  Somebody winds it each day or two.  The mechanism is 
down at ground level where it is easy to see.  Cables go up to the bells.


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[time-nuts] ADEV data for mechanical clocks

[Hal Murray]

> So, where's the ADEV plot for Bill's Q1,Q2, and Q3?

Does anybody have any ADEV data for mechanical clocks?  (I didn't find any by 
google, but there was a lot of noise so maybe I missed something.)

I'd expect a watch to slow down slightly as the spring unwinds.  That 
probably doesn't apply to clocks driven by weights.

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Re: [time-nuts] Z3801A OCXO manual trimming

[Hal Murray]

n...@npgcable.com said:
> Does the oscillator have an adjustment?  If so, is this somewhat accessible
> without destroying the assembly?  Are there pictures of the oscillator
> assembly? 

https://www.realhamradio.com/GPS-oven-journey.htm

https://www.realhamradio.com/z3801a-turning-point.htm


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Re: [time-nuts] While we are talking about Z3801's

[Hal Murray]

kb...@n1k.org said:
> If still nothing, put a scope on the RX output of the serial chip in the
> 3801. Do the same  for the TX input of the same chip.  

I think the Z3801A prints out a version string at power up.  Sometimes that 
helps debug the transmit path.


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Re: [time-nuts] While we are talking about Z3801's

[Hal Murray]

wpxs...@gmail.com said:
> Hal, I can't communicate with it. That has been gone for a while now. 

I assume it worked at some point.  Did talking to it stop working at the same 
time the frequency stopped tracking?  If so, I'd guess the CPU inside has 
stopped working and isn't setting the DAC correctly.


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Re: [time-nuts] LT1016 as a pulse shaper...

[Hal Murray]

Bruce Griffiths  said:
> If I had a suitable PCB board for it I would do the measurement properly.

What would a suitable board look like and/or what sort of gear do you need to 
measure PN?


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Re: [time-nuts] While we are talking about Z3801's

[Hal Murray]

> Mine has quit achieving lock.
...
> After reading about someone else's trouble, i wonder if my OCXO has aged
> out.

Have you checked the status page?  Is the GPS unit seeing satellites?


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Re: [time-nuts] Microsemi up for sale?

[Hal Murray]

Thanks.


rich...@karlquist.com said:
> 2.  Magnetic state selection, as used in the 5071A, would be replaced by
> optical pumping.  Len Cutler was heartbroken that HP/Agilent management
> wouldn't fund this effort. 

> It turns out that, even now in 2018, optical pumping is not ready for prime
> time in a working standard because the lasers drift over time.

Is there something fundamental in there, or is the lack of products because 
nobody has made the big investment required to figure out how to do it.

What is the bandwidth of the laser?  What happens if it drifts slightly?  Can 
it be servoed?  ...



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Re: [time-nuts] Setting Z3801 date

[Hal Murray]

> Setting the date should update the EEPROM.

Interesting.  It's not working that way on mine.  If I power cycle, it both 
T2 and Status page come up in Jul 1998.

Is my EEPROM worn out?  Older version of firmware?   ??

  HEWLETT-PACKARD,Z3801A,3542A01377,3543-A


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Re: [time-nuts] Setting Z3801 date

[Hal Murray]

> My Z3801A happily accepted a recent year (2016?) when it rolled over.   You
> have to do the power-down,   disconnect antenna, send corrected date, power
> down, connect antenna, power up sequence.   I don't think the updated date
> appears until the unit starts tracking satellites again. 

I think the second power down in there resets the date.

I'm using a python hack that shows both the T2 time string and the status 
page.  When I set the date, the status page shows the new date.  The T2 date 
doesn't change.  When the GPS gets synced up, the T2 date and status page 
date both jump to goodness.


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Re: [time-nuts] Setting Z3801 date

[Hal Murray]

Thorbjørn Pedersen said:
> Try this:
> Disconnect antenna.
> Power off / power on.
> Set date correctly. (You have the commands?)
> Connect antenna.
> Let it survey and stabilize

That's what I remember.

The first problem is that the Z3801 doesn't accept dates after 2007.  It 
gives an E-222 error.  (I forget the text, it's something like out-of-range.) 
 I didn't search for the exact cutoff.  I just edited the year and tried 
again, so it's somewhere in 2007 or 2008.

The second problem is that I'm using an "antenna challenged" setup.  So it 
takes a while to latch on to the satellites.

But I tried again.  This time, I set it to 2007 and after waiting long 
enough, GPS got synced and time jumped to the correct time.

Thanks for the poke.

---

Then I shifted to the KS-24361

It doesn't complain about the dates it doesn't like.  It just doesn't do 
anything with them.

It takes dates after 2007.  I forget the exact break point.

But when the GPS syncs up, it jumps to 1998.  ??  Sigh.




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[time-nuts] Setting time on Z3801A and KS24361

[Hal Murray]

I currently have one each that think it is 13 Jul 1998.  That's ballpark of 
20 years ago.  I assume it's 1024 weeks.  The time of day is good.

Has anybody set their time recently?

I thought I knew how to set the time, but the last time I tried, it didn't 
work.  I have done it in the past, but that was several/many years ago.  I 
think a recent date was rejected.  I'll dig out the exact error message if 
anybody is curious.

I also have a Z3801A that is working correctly.  I assume it has not lost 
internal power since before the magic date and the date-check is on the 
set-path rather than the current-time path.

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Re: [time-nuts] Symmetricom 58532A GPS Antenna : Launch3 Surplus

[Hal Murray]

li...@philpem.me.uk said:
> Generally speaking, you can seal most RF connectors quite nicely with a few
> layers of self-amalgamating tape and a layer of PVC tape over the top of
> that (to protect from UV). 

Many years ago, I picked up a chunk of scrap the local cable TV installer had 
left on the ground underneath the utility pole out in front of my house.  It 
was a chunk of industrial strength shrink wrap with a layer of goop on the 
inside.

Is that stuff available in small quantities?  Would the antenna withstand the 
necessary heat?

How do hams seal antenna connectors?


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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Hal Murray]

deirdre@gmail.com said:
> MSF disciplined oscillator?! I don't trust these receivers to any better
> than about the 20ms mark, so such a disciplined oscillator would have quite
> a long integration time! 

It would be interesting to see if you can find any pattern in your histogram 
plots.  Say, time of day.

What happens if you average over 10 or 100 samples?


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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Hal Murray]

> Since MSF *is* on 60 KHz, you do indeed get dead spots.

If the two signals are not encoded identically, there should be an 
interesting signal when one of the transmitters is off and the other is on.  
Has anybody looked for that sort of pattern?

Is there a map of the dead spots?  Any time-nuts live in/near one?



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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Hal Murray]

rnabioul...@gmail.com said:
> How difficult would it be to complete these modules and integrate them with
> the rest of NTP, as NTP decoder modules?  So instead of an AM HF receiver,
> the setup for these signals would be: 

The simple way to do that is to use the shared-memory interface.  No changes 
to ntpd required.


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Re: [time-nuts] Rakon HSO-14

[Hal Murray]

kb...@n1k.org said:
> Unfortunately ( at the rates you must use) the “blast it with a fire hose”
> approach is not very fast….. 

How fast to laser blasters work and/or how much do they damage the crystal?


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Re: [time-nuts] Slightly OT: interest in a four-output, ultra-low jitter, synthesizer block?

[Hal Murray]

lajeune...@mail.com said:
> Any non-zero output impedance and the digital load changes enter back in as
> noise on what should be the quiet VDDA. 

Thanks.   I missed the "A" on the VDDA.


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Re: [time-nuts] Slightly OT: interest in a four-output, ultra-low jitter, synthesizer block?

[Hal Murray]

j...@febo.com said:
> The challenge is that the chip is a 7x7 mm 44-QFN package and really  wants
> to be put on a six-layer circuit board.  That's doable, but  challenging,
> for home assembly. 

Can anybody comment on the toaster oven approach?

Is it practical for things like this?  How much does a solder mask cost?  How 
much other stuff do I need?  Does the solder paste need to be refrigerated 
and other quirks like that?

What are the chances of a newbie getting a 44-QFN right on the first try?


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Re: [time-nuts] Slightly OT: interest in a four-output, ultra-low jitter, synthesizer block?

[Hal Murray]

lajeune...@mail.com said:
> I'm sure you know the 1.8V supply regulators should not be fed from VDDA
> (3.3V), but I'll mention it anyway. 

Why not?

That sounds like the sort of issue I should understand but I'm coming up 
blank.


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Re: [time-nuts] Suggestion for a timing GPS receiver (Trimble / Ublox /other?)

[Hal Murray]

time-nuts@febo.com said:
> The cheapest is not a 5T there are many 6 and 7 for $ 10. T gives you
> nothing unless you  have saw tooth correctionBerrt Kehren 

Does the T firmware also support known-position mode where it can operate on 
only one satellite?


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Re: [time-nuts] SI5328

[Hal Murray]

Does anybody know what's in the DSPLL box?

It may be in the data sheet(s), but I haven't found it.


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Re: [time-nuts] Looking for information regarding Trimble 33429-00 microcentered GPS antenna.

[Hal Murray]

kb...@n1k.org said:
> If indeed dual frequency GPS is part of the intended use, the survey
> oriented gear  will be slightly happier if the “right” corner faces north.

What's in the antenna that makes North interesting?  and/or how would a 
receiver take advantage of it?



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[time-nuts] PBS, Tue evening, The Secret of Tuxedo Park

[Hal Murray]

(Sorry for the clutter to those of you outside the US.)

http://www.pbs.org/wgbh/americanexperience/films/secret-tuxedo-park/
Two of the shorts mentions time.

Many thanks for the Tuxedo Park book suggestion many years ago.


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Re: [time-nuts] SI532X Chips Close In Spurs (Somewhat Long)

[Hal Murray]

marklgoldb...@gmail.com said:
> I was hoping someone who knows these devices might have some insight into
> what the issue is and how to determine which plans will not provide close in
> spurs, without requiring testing. Any suggestions are appreciated. 

If you look at the binary of the word that goes into a DDS adder, the ones 
with more low order bits have closer in spurs.  Think of that word as a 
fraction, binary point on the left rather than right.

If your adder word is 0.001 (binary) it will divide by 8, no spurs.
If you have 0.0011, it will divide by a little less than 8 and have spurs.



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Re: [time-nuts] On the IETF leap-seconds.list SHA1

[Hal Murray]

> I am still unable to access the NIST ftp-site linked earlier in this thread.

There have been several URLs mentioned.

If you want:
  ftp://time.nist.gov/pub/leap-seconds.list
Try 
  ftp://ftp.nist.gov/pub/time/leap-seconds.list

Any attempts at web/ftp-ing to time.nist.gov are very likely to not work.
Don't waste your time trying.  That's their rotating DNS for NTP servers.

I think the original plan was to have all the NTP sites mirror the FTP info 
but it didn't work out.


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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Hal Murray]

t...@leapsecond.com said:
> For GPS and OCXO the choice of time constant is fairly obvious. But the
> ADEV for mains frequency isn't quite as pretty. So I'm not sure several
> hours would work; maybe more like days or weeks? Here's a sample ADEV for
> power line frequency: 

Has anybody investigated what the ADEV looks like if you plot something like 
one hour samples over a day?  That is is the ADEV in the morning when the 
temperature is warming up the same as the ADEV in the evening when the 
temperature is cooling off?



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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Hal Murray]

apollo...@gmail.com said:
> Want to provide an accurate  (relatively accurate) 60 hz reference to the
> chip.   Some room inside for custom modifications.  Does a TCXO or similar
> exist in a small package that provides 60 hz ticks? 

I doubt if you will find a TCXO that puts out 60 Hz.  But it's only one chip 
to make a divider.  The trick is to do it in software rather than hardware.

The real question is what sort of error pattern are you interested in.  The 
power company has good long term stability.  How good is your TCXO?  It would 
be fun to play with the numbers.  On the other hand, can you derive your 60 
Hz from a GPSDO?

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Re: [time-nuts] Simple open source microcontroller solution to tune DDS needed

[Hal Murray]

> ... is in bascom, whatever that is.

I had to look it up.

https://en.wikipedia.org/wiki/MBASIC#BASCOM

> Microsoft sold a CP/M BASIC compiler (known as BASCOM)
> which used a similar source language to MBASIC.


> Developers welcomed BASCOM as an alternative to the popular but slow and
> clumsy CBASIC. Unlike CBASIC, BASCOM did not need a preprocessor for MBASIC
> source code so could be debugged interactively.[2] A disadvantage was
> Microsoft's requirement of a 9% royalty for each compiled copy of a
> program[3] and $40 for hardware-software combinations.

???




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Re: [time-nuts] Pendulum clock suspension

[Hal Murray]

> This puzzled me since yesterday as I discovered how the suspension of
> pendulum clocks is made, that is a springy plate.

There is less loss in a suspension like that than there would be in a pivot 
bearing.

The spring doesn't change parameters as it gets dirty or the oil dries out.

> -following the above, the lenght of the pendulum varies during a swing,

> Ok that we can neglect the above yet having an extremely good approximation,
> but is it conceptually right? 

With a constant length pendulum, there is a slight variation in the frequency 
with the height (width?) of the swing.  (I haven't done the math since 
college physics which was a long time ago.)

It would be interesting to see how much the length of a pendulum changes as 
the suspension spring bends and how much that changes the resonant frequency 
and how that compares with the length change due to temperature.  I suspect 
it's down in the noise.


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Re: [time-nuts] Helmholtz Resonator and other Maintained Oscillators

[Hal Murray]

k8yumdoo...@gmail.com said:
> The flex hose demonstration was interesting in that different regimes of
> swinging speed resulted in oscillation in different modes.  I wonder why.

It depends on the speed of the air going through the tube.

https://www.youtube.com/watch?v=4aJ36-TlPD4

http://www.exo.net/~pauld/activities/AAAS/aaas2001.html
http://www.exo.net/~pauld/summer_institute/summer_day13music/Whirly.html


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Re: [time-nuts] Helmholtz Resonator and other Maintained Oscillators

[Hal Murray]

What's the Q of a Helmholtz Resonator?  What do I do to make a high(er) Q 
version?

With a narrow band filter, it might make a neat demo/toy to pull an audio 
signal out of the noise.  With 2 at different frequencies you could demonstrate 
FSK.

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Re: [time-nuts] Test WWV timecube against Cesium, Rubidium, MASER or other precision time (UT-1) metrology

[Hal Murray]

martin.burni...@burnicki.net said:
> Hm, this file is part of the standard NTP source code package available
> here: http://support.ntp.org/bin/view/Main/SoftwareDownloads 

Argh.  Good catch.  Thanks.

I knew that it came from the ntp package.  I thought it was stand alone but 
it seems to use some of the ntp package.

If anybody is having trouble building it, let me know and I'll try to figure 
out the recipe.


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Re: [time-nuts] Test WWV timecube against Cesium, Rubidium, MASER or other precision time (UT-1) metrology

[Hal Murray]

kb...@n1k.org said:
> To get the accuracy into the 1 ms range on WWV, you would need a pretty good
> idea of the path length between you and WWV. 

Dave  Mills has a program to compute delays.

 * By default it prints out a summer (F2 average virtual height 350 km) and
 * winter (F2 average virtual height 250 km) number.  The results will be
 * quite approximate but are about as good as you can do with HF time anyway.
 * You might pick a number between the values to use, or use the summer
 * value in the summer and switch to the winter value when the static
 * above 10 MHz starts to drop off in the fall.  You can also use the
 * -h switch if you want to specify your own virtual height.

What's the height difference between night and day?

This was google's first response.
  https://opensource.apple.com/source/ntp/ntp-136/clockstuff/propdelay.c


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Re: [time-nuts] Rubidium freq standard - temperature

[Hal Murray]

je...@hanler.com said:
> I tried scoping some pins.  I see a few different levels and one pin has
> what looks like a clock signal with a period of about 4.2ms.  Other than
> that, hard to tell without a manual.

Some devices print out version info and such at power up.  If you are willing 
to power cycle one, you might learn something by putting a scope on a pin 
when you power cycle it.

You can probably tell input pins from output pins by connecting a pin to 
ground or power through a 10 K resistor.  (That's assuming that one of  the 
output pins is high so you can tell what power is.  Or just guess 5V since 
it's old enough.  Or poke around to see what you find.)

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Re: [time-nuts] Performance verification for time counters

[Hal Murray]

kb...@n1k.org said:
> The gotcha with a DDS in this case are the sawtooth spurs. To get them down
> to the 5 ps level, you would need a DDS with a clock that is well into the
> 100’s of GHz. 

I think that assumes you want to be able to generate an arbitrary frequency.

Suppose I start with 10 MHz.  It's easy to get a clean 1 MHz or 5 MHz, but 
not so easy to get 3 MHz.  But if I start with 9 MHz, I can get a clean 3 MHz.

How do I figure out how many crystals I need?

How good are PLLs relative to 5 ps?  Can I use them to make pseduo-crystals?

What's the term for PLLs where I divide the output by M and the reference by 
N?  As M and N get bigger I get more possible output frequencies but the 
output of the phase comparator gets lower in frequency and hence harder to 
filter.  How low can I go before 5 ps gets interesting?  (Is that a 
reasonable question?)

If I have an array of crystals and PLLs, I can get some more flexibility if 
the crystals are VXOs.



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Re: [time-nuts] Performance verification for time counters

[Hal Murray]

l...@leobodnar.com said:
> Now, what would be recognised procedure for sweeping external input pulse
> delay over few hundred ns in a controlled, measurable and repeatable way?  

How about using another crystal at a slightly different frequency?

Suppose you start with 10.01 MHz and divide by 1000.  That will 
slowly sweep a pulse.  All you have to do is reset the counter at the right 
time to get it started at the right phase.

I think you can do something similar with a DDS type generator starting from 
an arbitrary frequency.  It won't sweep in a simple ramp but will be a 
sawtooth pattern where the points on each tooth are at slightly different 
offsets that will fill in the whole space if you merge them together.


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Re: [time-nuts] Why discipline Rubidium oscillator?

[Hal Murray]

> aren’t too many steps after that

Your imagination is broken.

There are lots more steps.  Most of them are very expensive.


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Re: [time-nuts] Input filter for data logger

[Hal Murray]

t...@leapsecond.com said:
> Note the picPET outputs a h/w event counter along with the timestamp. This
> can be ignored but the counter helps identify noisy inputs, allows one to
> distinguish between fast and too-fast inputs, and was very useful during
> development to validate the accuracy of the device. 

The event counter also lets you catch lost events in the downstream gear that 
is capturing/logging data from the picPET.



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Re: [time-nuts] Recommendation for cheap GBIP adapter for Linux

[Hal Murray]

att...@kinali.ch said:
> I have a need for a GBIP adapter that I can use with Linux. It shouldn't be
> too expensive, but I rather spend a few bucks more for ease of use. Where
> "ease of use" means I don't have problems with weird drivers on Linux

I've been happy with the Prologix.  It may not be as low cost as you would 
like.

It uses one of the common USB-Serial chips, so there is no problem with 
drivers on Linux.

It needs hardware flow control or long-enough pauses in the right places.  
That was the only problem I had getting started.



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[time-nuts] How good is your ADEV at 10E7 seconds? :)

[Hal Murray]

Context is the what-next portion of a recent LIGO talk.  For those of you 
that missed it (or didn't pay enough attention), on Aug 17th, they got good 
data from a pair of neutron stars.  1.7 seconds later, the Fermi satellite 
got a gamma ray burst.  Within a day, the optical guys had found a new spot.  
Over the next days and weeks, they got data over the whole spectrum, radio to 
X-rays.  (There were 70 observatories lined up to pounce.  Everybody wanted 
in on the action.)

LIGO only works for roughly the audio spectrum.  At the low and high ends, 
the noise goes up.  Lots of people are working on how to build gear that will 
work at other wavelengths.

One proposal is to monitor pulsars.  There might be stuff leftover from the 
big bang with a period of a year or so.  If you can get good timing from a 
pulsar, you might be able to see it.  I suspect that will take "good" timing 
to a scale that would astonish most time-nuts.



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Re: [time-nuts] Time and frequency practical exercise 2018 late quarter; precision measure of 432mhz band Sat in Lunar Orbit

[Hal Murray]

kb...@n1k.org said:
> Ok, 1 Hz at 437.5 MHZ is roughly 2 ppb. That is pretty much “slam dunk”
> accuracy with a GPSDO. Much easier to obtain and set up in a school
> environment. The key will be orbit estimation for the +/- doppler part of
> it.  Orbit estimation is not quite a slam dunk sort of thing. The GPSDO
> would also give accurate location. Even with good orbit data, the solution
> still requires a good location estimate. 

What is the orbital period?  It would be fun to plot the Doppler over time 
and see if you can get something that looks like a big chunk of an orbit.

Ugh.   What is the Doppler due to the Earth's rotation?


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