Re: [time-nuts] Seeking Toyocom or NDK through hole oscillator information

[jimlux]

On 6/14/18 4:27 AM, Tim Shoppa wrote:

Quoting Wikipedia; 16.368 MHz is 16 times the 1.023 MHz C/A GPS signal chipping 
rate; multiplied by 96.25 to get the 1575.42 MHz L1 frequency and multiplied by 
75 to get the 1227.60 MHz L2 frequency.


Possibly something Trimble significant with the 16.368 MHz
frequency that I'm not yet aware of... if anyone would care
to speculate, please do.





A typical direct sampling receiver would sample the RF at 16.368, and 
that puts the L1 received signal nicely at fs/4.  The P code would 
overlap the sampling bandwidth of 8.184 MHz, but the C/A code fits well 
within that range. And, since it's not at "zero", any doppler just moves 
it from the center, but it's still "positive" frequency.



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Re: [time-nuts] Bodnar "Precision Frequency Reference (GPS Clock)" AND LeoNTP Networked Time NTP Server Questions

[jimlux]

On 5/18/18 6:09 AM, Clint Jay wrote:

Interested to know how much noise would be from USB signalling and how much
is " machine noise"  from the PC as my understanding of USB signalling is
that it's differential so such should be low noise?


Every device I've worked with that had a USB interface has radiated 
significant power around 12 or 24 MHz. (I've not worked much with 
devices that support 480Mbps USB3..)


Indeed, the data wires are twisted pair (although the "twist rate" in 
most cables is pretty sketchy), but the signaling is voltage mode, not 
switched balanced current like LVDS.  So I think you get significant 
current spikes on the power wires as you charge and discharge the 
capacitance/inductance of the (unterminated) data lines.



The shielding is, in a lot of consumer devices, common to the power 
supply negative lead.  So the shield carries part of the power supply 
current, and then radiates.


In theory, USB devices sold in the United States should meet FCC Part 15 
(and the similar requirements in the EU and elsewhere) - but I'll bet 
there's a LOT of stuff out there that isn't tested, nor would it pass.



High Speed USB might be better for EMI/EMC - you're just not going to 
push 480Mbps through an unterminated system with crummy noise properties.


TI has an application note
https://www.ti.com/sc/docs/apps/msp/intrface/usb/emitest.pdf

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

[jimlux]

On 5/14/18 1:00 PM, ed breya wrote:
I don't know what sort of scientific level this contest is geared for, 
but would guess that for middle-school level, extreme numbers-oriented 
analysis of esoteric, time-nutty things may not dazzle, but bore the 
participants, judges, and audience.


Even at the middle school level, science fairs can be quite competitive 
- The California Science Fair draws hundreds of projects at that grade 
level (Grade 6-9) selected from fairs at the county level, which in turn 
draw from school fairs.


The standard of judging is quite rigorous - a "demo" won't generally be 
competitive at the state level, although it could make it through the 
county level - depending on the county.




It may be best to relate to more hands-on, everyday experience and 
observations of "normal" people. I like the suggestions about GPS and 
stroboscopic and lasery stuff, where one can maybe appreciate how modern 
everyday things work (like GPS, or how it's possible to talk to or send 
a picture to anyone in the world on your cell phone, and how these could 
not happen without precise time), or something visual and physical.


Virtually all science fairs prohibit lasers in a display - too many "bad 
things" happening with remarkably high powered lasers available online. 
You'll need to show it cannot be operated, or that it cannot present a 
hazard (i.e. if it's built into a piece of hardware that cannot be 
modified on site to allow exposure).


Even laser pointers are not allowed (because how is the display review 
committee to know whether it's 1 mW or 100 mW)





Some of the props should be "ordinary" things, like the a cell phone or 
GPS receiver, for example. Lasers are always good as long as there's a 
direct visual component to the observation. Strobe type stuff is 
particularly easy, because it's doable with mechanical and acoustical 
props, and signal measurement times are in reach of common lab equipment 
like generators, scopes, and counters, and of course there's a big 
visual experience component.


Small power visible lasers are common nowadays, so easy to use. Strobe 
lights are fairly common too, but maybe not so much as the other items. 
You can build (or buy) quite a nice strobe light nowadays using 
high-powered LEDs - the kind used for replacing incandescent and other 
illumination. This is quite easy and much safer than dealing with flash 
tubes, and is much more versatile. In fact, maybe this could even be a 
science fair project. The time element is in the stroboscopic effects 
and ability to slow or freeze apparent motion - almost everyone has 
observed this and can relate.


A strobe is a fine display, and there's probably interesting time-nuts 
kinds of experiments one can do using it - the combination of a short 
duration strobe with a modern cellphone camera running at, say, 240 fps, 
might be a good way to instrumentally measure a mechanical vibration.


But you need to have some set of experiments designed to confirm or 
reject a hypothesis. You could have a hypothesis about synchronization 
of vibrating rods on a common base, for instance.




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[time-nuts] lecture on PLL and phase noise and verilog

[jimlux]

If you're in California southern Central Coast area (Ventura, Santa 
Barbara, Thousand Oaks, etc.) the local IEEE chapter is sponsoring a 
talk on phase noise and Verilog


https://events.vtools.ieee.org/m/172159

PLL'S AND PHASE NOISE MODELING IN VERILOG
Verilog is the accepted language of choice for modeling and simulating 
digital designs. For analog blocks the tool choice is a low level 
circuit simulator like HSPICE or Spectre. For PLL’s a common 
misconception is that you can use Verilog to model a PLL if you don't 
care about accuracy, but if you do care about precision, you'll need an 
analog circuit simulator like HSPICE or Spectre. Various options like 
Verilog-A and Verilog-AMS are attempts to achieve the best of both 
worlds, but in this talk, we propose that the tool of choice for 
modeling and studying PLL’s and is plain “digital” Verilog. It's the 
right tool, but almost always used the wrong way for modeling PLL's. 
Understanding how the underlying simulation engine in Verilog works 
enables us to set up our models in a very precise, yet very simple 
manner. The efficiency and speed of Verilog allows us to literally watch 
our PLL designs come alive in the time domain with timing accuracy that 
can't be achieved in an analog circuit simulator. Watching designs 
operate in the time domain crystalizes our understanding of them, and 
enables us to study and quantify transient and other non-linear phenomena.



Biography:

Greg Warwar received a master’s degree in electrical engineering from 
Rice University in 1989. Following graduation, he joined Texas 
Instruments in Dallas, TX as a member of the technical staff where he 
worked on ΣΔ analog to digital converters for precision audio 
applications. In 1992, he joined Vitesse Semiconductor in Camarillo, CA 
where he worked for 23 years on high speed serial communications IC’s, 
focusing on many areas of analog and mixed-signal design including 
VCO’s, phase locked loops, clock recovery, frequency synthesizers, and 
adaptive equalization. Since 2015, Greg has been a principal engineer in 
the mixed-signal ASICs design group at Teradyne, Inc. in Agoura Hills, 
CA. Greg holds six U.S. patents in the area of CMOS mixed-signal IC design.

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

[jimlux]

On 5/12/18 5:01 PM, Adrian Godwin wrote:

How about a demonstration of how GPS works, substituting sound waves for
radio ?

Maybe three sound sources with harmonically-related frequencies, then
measure their phase difference on an oscilloscope.

Cheat a bit : you don't need to do cdma acquisition. Have one reference at
a low frequency, switch two more on alternately at a higher frequency.
Measure the phase difference between one pair at a time and calculate your
location relative to the stationary sources.




In science fairs that are judged, the rubric really demands something 
that can be cast into the classic "literature search, hypothesis, 
experiment, data reduction, conclusion" form.  Even straight up 
engineering is sometimes knocked down - the International Fair (being 
held this week, as it happens) does have separate rubric for engineering 
projects.


So what you want to do is cast this as an experiment or engineering 
project.  For the latter: "Performance characterization of acoustic 
multilateration"


For a more "sciencey" approach, you'd postulate some theory/hypothesis:
"air temperature measurement can be used to compensate for speed of 
sound variation in acoustic multilateration"



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

[jimlux]

On 5/11/18 9:08 PM, Jeff Woolsey wrote:

David.vanhorn wrote:


Measuring the speed of light (Fizeau or Michelson method? Other ways)


I saw a great demo of this at the Exploratorium in SF.  They had a long spool 
of fiber optic, a disc with holes, and a light source.  When static, if the 
light shines through the hole in the disc into the fiber, then you can see the 
light coming out the other end of the fiber through a different hole.   When 
rotating, you increase speed and the fiber output gets dimmer and dimmer till 
it's gone.   At that point, the light going into the fiber arrives when the 
other end is blocked, and vice versa.  High tech, but simple.


My favorite exhibit that we never see anymore.   IIRC it was a quarter
mile of fiber and a green laser.  And ISTR that the disc had one hole on
one arm and two radially on the other, but I can't remember why.  I
thought that the light would pass through the same hole twice, once on
the way in and on the way out when that same hole rotated 180 degrees to
the other end of the fiber.  The disk spun somewhere around 50 rps (60
with an AC motor?).




1km in free space would be 6 microseconds round trip. I'm not sure a 
disk spinning at 3600 rpm would work.  you'd need to have the "hole 
spacing" be on the order of 6 microseconds - and at 100 rps (6000 RPM), 
10 ms/rev, you'd need the sending and receiving hole 6/1 of a rev 
apart (about 0.2 degrees).


if you had 10 km of fiber, it would be a bit easier.
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Re: [time-nuts] Anybody have suggestions for time related science fair projects?

[jimlux]

On 5/11/18 7:07 AM, Philip Gladstone wrote:

On 11/05/2018 07:23, jimlux wrote:

On 5/10/18 9:55 PM, Hal Murray wrote:


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.




The whole area of celestial nav is time related and uses very simple 
equipment -


Telling time by measuring the sun in some way.  Occultation of stars 
by the moon.  Positions of jupiter's big 4 moons.


Pendulum experiments.  If the student has a way to change their 
altitude, can they measure changes in g.  Driving a pendulum.


Coupled resonators  (spring/mass, pendulum, vibrating rods)

Measuring the speed of light (Fizeau or Michelson method? Other ways)

Water clock, sand hour glass, etc.  Measuring performance variation 
over environmental variations.



the trick with good science projects is finding something that's not 
just a "lab demo" - where there's some engineering component to 
figuring out how to execute the demo with unusual or improvised 
equipment, or where you're measuring something that's not been done 
before.
The advice that we got when doing a middle school science project was 
that you wanted an experiment with only one variable (altitude or 
temperature etc) and a  measurement of a single variable (maybe over time).




and with multiple measurements possible - most middle school projects 
tend to be a "one and done" - you get big kudos if you show even basic 
statistical analysis - a simple significance test is a big deal, 
assuming you're not doing it with some cookbook calculator.  You'd need 
to be able to explain what it means to the judges.


And something where you show an appreciation of measurement precision 
and any curve fit.  I used to mark down projects where they used Excel 
to do a regression curve, and then reported the coefficients with 5 
digits of precision, on measurements with at most 2 digits. (and no, not 
thousands of measurements to get a sqrt(N) improvement)


AVAR is a kind of sophisticated concept - I think it would be hard for a 
middle schooler to adequately explain what it is (heck, there's enough 
trouble for people who do it for a living).



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

[jimlux]

On 5/10/18 9:55 PM, Hal Murray wrote:


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.



The whole area of celestial nav is time related and uses very simple 
equipment -


Telling time by measuring the sun in some way.  Occultation of stars by 
the moon.  Positions of jupiter's big 4 moons.


Pendulum experiments.  If the student has a way to change their 
altitude, can they measure changes in g.  Driving a pendulum.


Coupled resonators  (spring/mass, pendulum, vibrating rods)

Measuring the speed of light (Fizeau or Michelson method? Other ways)

Water clock, sand hour glass, etc.  Measuring performance variation over 
environmental variations.



the trick with good science projects is finding something that's not 
just a "lab demo" - where there's some engineering component to figuring 
out how to execute the demo with unusual or improvised equipment, or 
where you're measuring something that's not been done before.


For instance, measuring time with Jupiter's moons has been done for 
centuries, but has it been done by taking cell phone pictures through a 
telescope and then measuring the distances on the resulting images?
Can you make a sundial with a webcam pointed at a spherical reflector 
(to make an "all-sky camera")


Other experiments play off a old joke - there's one about "how to you 
tell how tall a building is using a barometer"  - take it to the top of 
the building drop it, and time how long it takes til it hits the ground. 
 Build a pendulum the height of the building, using the barometer as a 
pendulum bob.



Characterizing a clock is a good one -
a) there's well developed analytical tools for doing the data reduction 
(AVAR, etc.)
b) the experiment lends itself to collecting multiple data sets from 
multiple instances of the clock in question
c) clock performance is affected by environment, so there's lots of 
potential experiments.








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[time-nuts] NIST time and frequency seminar - 12-18 June in Boulder

[jimlux]

I didn't see a mention in the archives, so here it is

https://www.nist.gov/news-events/events/2018/06/2018-nist-time-and-frequency-seminar

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

[jimlux]

On 5/3/18 8:28 AM, Bob kb8tq wrote:

Hi

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.

Indeed this does get a bit far from the world of timing …… The distances 
involved are nasty
small. Even for the location of your telescope when doing astronomical timing 
observations,
they are unlikely to matter on a yearly basis. At some point the error is “to 
small to matter” ….

Bob



Hit send too quick..

But more realistically, this is kind of a time-nutty sort of goal - to 
be able to make measurements to a precision where you can match your 
measurements to a nearby geodetic station with "official" measurements.


All the usual time measurement with GPS issues come into it - multipath, 
the diurnal variations, solid earth tides.


It's what everyone says - getting to meters or 10s of ns - easy - 
getting to tenths of ns or cm, significantly harder.

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

[jimlux]

On 5/3/18 8:28 AM, Bob kb8tq wrote:

Hi

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.

Indeed this does get a bit far from the world of timing …… The distances 
involved are nasty
small. Even for the location of your telescope when doing astronomical timing 
observations,
they are unlikely to matter on a yearly basis. At some point the error is “to 
small to matter” ….

Bob



Unless you live on a plate boundary and have to keep repairing your 
fences and foundations 


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

[jimlux]

On 5/3/18 8:09 AM, Bob kb8tq wrote:

Hi

The sites are aimed at improving position information. To the degree that 
having an
accurate location for your antenna improves timing, simply doing that is a step 
forward
for your GPSDO.

Most sites also will give you information that shows the timing solution at a 
given point
in time. To the degree that you can connect that to prior data it could be 
useful. There
are more than a few steps involved in getting this to work.




The JPL processing chain gives not only more accurate positions vs time, 
but also estimates of clock error vs time, if that's in the data stream 
being processed.

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[time-nuts] Want a student to do some experiment on timetnuts - Re: nuts about position

[jimlux]

On 4/25/18 10:16 PM, Peter Monta wrote:


But this is a bit of a dicey science project; I'd suggest that the
researcher borrow a survey receiver for a few days (mild learning curve for
the online solver tools) or hire a surveyor (no learning curve).



If anyone knows a student at any of the following colleges who would be 
interested in doing this, I just got a (small) bucket of money to spend 
on it, but I have to get the details turned in today.


(actually any sort of time-nuts project, if it can be done for around 
$20-30k to the institution, is fine).


Has to be one of those schools, and I need a contact name to call to set 
up the details.



Florida A
Howard University
Morgan State University
North Carolina Central University
Southern University
Tennessee State University
Tuskegee University-College of Engineering
UC Riverside
University of Nevada Las Vegas (UNLV)
The University of Texas at El Paso


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Re: [time-nuts] nuts about position

[jimlux]

On 4/25/18 7:46 PM, Brooke Clarke wrote:

Hi J:

I had a number of survey stakes I placed using a manual transit and tape 
measure and hired a local surveyor to tell me where they were and also 
tell me where my GPS antenna was located.


He setup a GPS antenna on one tripod and a (Trimble?) combined GPS-total 
station on another tripod and ran a cable between the two.  After some 
time (tens of minutes or ??) he used the theodolite to sight my stakes 
and the GPS antenna.  I got a report back in a week or so.  Total cost a 
few hundred dollars.


I'm in the process of looking at how accurate the GPS is in my new LG G6 
phone.




Yep - A typical total station is good to "a few seconds" (some single 
digit mm at 100 meters) in angle. Distance is usually pretty accurate 
1.5 mm + 2ppm.


So over a typical 100m sort of size (several acres) a total station can 
provide relative positions to better than a cm, but probably not better 
than a mm.


A good optical theodolite can do *maybe* an order of magnitude better, 
in terms of the basic measurement, but then there's other confounding 
factors that might dominate.


For instance, are you sure you're holding the prism/target *precisely* 
over the mark? And just what *is* that mark.


Precision metrology in any field is fascinating, but a rabbit hole down 
which one can fall very, very deep.



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Re: [time-nuts] nuts about position

[jimlux]

On 4/25/18 11:18 AM, Brooke Clarke wrote:

Hi Tom:

As part of a FireWise community mapping process I'd like to get GPS 
coordinates of the fire hydrants (Lat, Lon, Ele). Is there a civilian 
GPS receiver that makes use of WAAS and/or DGPS corrections?


I think almost all handheld receivers these days use WAAS for improved 
performance.  WAAS should give you 1 meter kind of accuracy, 
particularly if you compare a known location in the area.


DGPS was a thing back in the 90s (I fooled with a Trimble Scout with a 
pod that received corrections over FM broadcast SCA) - I'm not sure it's 
widely used today.


The USCG DGPS transmits corrections on MF beacons, but is being 
decommissioned.  Most of the inland stations have been shutdown.



If you're a surveyor, you get corrections from a network (CORS or 
something similar), or you're primarily interested in "relative" 
position - you set up your base station and your RTK rover tells you 
where it is within 1 mm + 1ppm of distance from base.


http://www.xyht.com/ has regular features on the latest GPS survey gear.

You might be able to convince the local survey equipment rental house to 
come out and demo the gear (or give you a good price on a rental)


Or, why not just do the survey optically (!) - none of this new fangled 
GPS stuff.  Rod, level, theodolite.  If Everest could do it in the 19th 
century in India, you can do it too.


If you can find a couple benchmarks to work from, you can get accuracy 
of 1 part in 1000 with a decent 200 foot tape measure and something to 
sight with (a cheap laser level at night works pretty good to keep your 
line straight).  You're doing a series of triangles - SSS completely 
defines it, so no angles need be measured.


With decent survey gear 1 part in 10,000 or so is straightforward.

1 ppm is hot stuff with conventional optical gear - you're going to be 
making multiple measurements, compensating for refraction, etc. It's 
like GPS at 10cm accuracy - lots of things cause errors of that magnitude.


A nice theodolite (like a Wild T2) is readable to 1 second of arc. 
That's about 5 microradian.  At 100 meters, the horizontal uncertainty 
would be 0.5mm.   Yeah, not quite 1ppm, although you could probably do 
multiple setups and average in on 1ppm.


Of course, you'll then need to go out and get a decent tripod, a rod and 
target, and a rod person to wave the rod, etc.


But another poster did comment on "why not use the telescope" you could 
precision point to a series of stars and calculate using celestial nav 
where you are.  Although, that might be painful to the 1 meter sort of 
accuracy - the "tables" probably don't really account for deviations 
from ellipsoid and so forth.


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

[jimlux]

On 4/22/18 9:19 AM, Poul-Henning Kamp wrote:

Silicon comes in a number of isotopes but 95% of it is Silicon-28.

When you make pure mono-crystaline silicon, you get 50-60% better
thermal conductivity if you only use Silicon-28 atoms.

Yes, you read that right:  50-60% improvement for removing the
remaining 5% other silicon isotopes, and for this and other reasons,
sorting silicon atoms by isotope is now a thing, which amongst other
side effects have made the Advogardo Project possible.

I can't help wonder if there may be similar interesting effects in
quartz crystals, if they were monoisotopic ?

Several relevant mechanisms can be imagined, lower internal damping,
higher stiffness etc. etc.

We know a LOT about quartz and have a very good theory for its
behaviours, but i find no signs anybody has ever touched monoisotopic
Quartz.

The obvious experiment is not rocket-science, nor does it demand
inordinate resources for amateurs, see for instance from 03:35:

https://archive.org/details/59554KrystallosCF




A note the cigarette in the guy's hand - trace contaminants probably 
increase the yield 


I've looked into "garage manufacture" of crystals, although I was 
looking more at Cr and Ti doped alumina. The movie looks like it's using 
the "solution" approach (which has also been used to grow synthetic 
emeralds) which is similar to how it happens in nature.  These days, I 
wonder whether  continuous pulling from a melt like silicon boules might 
not be a better strategy.




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[time-nuts] lady heather on headless linux box

[jimlux]

Looking over the readme, it looks like LH uses X11.
Does that mean that if I build it, and run an Xserver on a box, I can 
run LH on another (headless) box via ssh?


I'm not sure I want to start down this path, so just curious if that's 
how it works.

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Re: [time-nuts] suggestions on getting 24 Mhz ?

[jimlux]

On 4/16/18 3:45 AM, Pete Lancashire wrote:

Access to " the xtal" is not an option the SDR is enclosed in a metal box.

Do a web search for RSP2Pro




It does have an external reference input..
There's not a lot of info on the Mirics data sheets (or on the sdrplay 
website)


It sort of looks like this is a somewhat enhanced version of the parts 
used in the RTL-SDR dongles.

(10 bit ADC, instead of 8 bits in the RTL2832)

And of course it needs 24MHz because it has to run the USB interface.

10 bit ADC means that you probably don't need *outstanding* clock 
performance - the sample and hold and all the other timing logic is 
probably designed to that sort of performance level - getting 
femtosecond jitter probably isn't worth it.



If you're just looking for a 24 MHz driver that doesn't need to be 
locked to anything, one of the SiTime modules would work, or you could 
probably order a TCXO for 24 MHz - it's a standard frequency (viz. USB), 
so it's almost certainly available from stock





On Sun, Apr 15, 2018, 6:00 AM Attila Kinali  wrote:


On Wed, 11 Apr 2018 03:00:23 -0700
Pete Lancashire  wrote:


Needed for SDR project as external clock source.


If your goal is, as Jim guessed, to get 24MHz from 10MHz and
you are using something like an RTL-SDR, then how about just
passing the 10MHz through a CMOS gate to square it up and
get nice harmonics, then pass a wire close to the crystal.
This should injection lock the crystal to right frequency.
It wont be a strong lock due to the 5:12 ratio, but for something
like a crystal that is already quite close, that should do the trick.

Alternatively, using an ADF4002 with a small uC to configure it
and a VCXO/VCO should also work.

 Attila Kinali
--
The bad part of Zurich is where the degenerates
 throw DARK chocolate at you.
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Re: [time-nuts] getting accurate timing on RTL-SDR output

[jimlux]

On 4/13/18 1:47 PM, Magnus Danielson wrote:

Hi Jim,

On 04/13/2018 06:52 PM, Jim Lux wrote:

I'm building a phased array receiver (actually, an interferometer) using
RTL-SDR pods, where the elements are isolated from each other - there's
a common WiFi network connection, and each node has a BeagleBone Green,
a uBlox OEM-7M-C, and the RTL-SDR V3 (which works down to HF, since it
has an internal bypass around the RF front end).

In general, I have the RTL-SDR set up to capture at 1 Megasample/second.
I fire off a capture, record it to a file in the BeagleBone's flash,
then retrieve it from my host computer using scp over the network.

What I'm trying to do is capture data from all the nodes at
(approximately) the same time, then be able to line it all up in post
processing. The GPS (or NTP) is good enough to get them all to start
recording within a few tenths of a second.

So now the challenge is to "line em up".  An obvious approach is to
transmit an inband pilot tone with some sync pattern, received by all,
and I'm working on that too.

But right now, I have the idea of capacitively coupling the 1pps pulse
from the GPS to the antenna input - the fast rising and falling edge are
broad band and show up in the sampled data.

The attached pulses1.png shows the integrated power in 1 ms chunks (i.e.
I sum the power from 1000 samples for each chunk) and it's easy to see
the GPS edges.  And it's easy to create a estimate of the coarse timing
(to 1 millisecond) - shown as the red trace.

But then, I want to get better.  So for the 20 edges in my 10 second
example, I plotted  (drift1.png) the raw I/Q output of the RTL.  The
pulse isn't too huge (maybe 10 DN out of the ADC's -128 to +128 range),
but is visible. Bottom trace is the first, and they're stacked up
0, 0.1, 1.0, 1.1, 2.0, 2.1, etc.

And you can see, no surprise, that the sample clock in the RTL isn't
dead on - over the 10 seconds, it looks like it drifts about 30- 50
microseconds - that is, the RTL clock is slow by 3-5 ppm.

SO here's the question for the time-nuts hive-mind...
What's a good (or not so good) way to develop an estimator of the
timing/frequency error. Post processing minutes of data is just fine..

I'm not sure what the actual "waveform" that is being sampled is (and it
will be perturbed by the quantization of the ADC, and probably not be
the same depending on where the RTL is tuned).  That is there's some
sort of LPF in the front of the RTL, the edge is AC coupled, and then it
goes into some sort of digital down converter in the RTL running at 28.8
MHz sample rate.

But it seems that there might be some way to "stack" a series of samples
and optimize some parameters to estimate the instantaneous time error-
given that the frequency vs time varies fairly slowly (over a minute or
so).  It's fairly obvious from the plot that if one looked at the
"single" sample when the edge comes in, not only does the time shift
with each pulse, but the phase rotates as well (totally expected)

this is one of those things where you could probably lay a ruler on it
and estimate it by eye pretty well, but I'd like an automated algorithm.

It would be nice to be able to estimate the timing to, say, a few
nanoseconds over a minute or so ( - that would allow a phase estimation
of 1/10th of a wavelength of a 20 MHz signal (e.g. Jupiter's RF noise,
or WWVH's transmissions)


Ideas???


Cross-correlate. Hug your Fourier transform as you do it.

Assume that you have a rough idea where the pulse occurs for each SDR.
FFT with a suitable window function each record.
Using one as reference, you then multiply the complex response with the
reference conjugated response.
Ether compare in the frequency domain or do inverse FFT and search the > 
time-domain for peak response.



That's the sort of strategy I'm looking at.. find a set of samples where 
the transient occurs, zero pad it out (so that when I do peak picking 
later, I've effectively got interpolation), then run the correlation


ifft(fft(a).*conj(fft(b))) in matlab





This is how modern GPS receivers to quick lockup of phase, and it works
very well. Using an FFT library i could code it in relative little C
code and setup my classic channel decoder this way.

Now, use this to compare your SDR clocks compared to the reference. As
they drift over time the windown need to shift, but you can keep track
of the number of samples shifts to keep full track of it. This should
give you enough phase and frequency information. Toss in a least square
or Kalman if you think it would help.

Cheers,
Magnus
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Re: [time-nuts] getting accurate timing on RTL-SDR output

[jimlux]

On 4/13/18 1:39 PM, Achim Gratz wrote:

Jim Lux writes:

So now the challenge is to "line em up".  An obvious approach is to
transmit an inband pilot tone with some sync pattern, received by all,
and I'm working on that too.


A maybe not-so obvious approach would be to use RTL-SDR that have been
modified for direct sampling (usually via the Q branch) and inject your
timing pulse there.  That would limit the disturbance of the actual
signal while still relatively easy to extract from the data stream.


That's where it's being injected.. I'm using the RTL-SDR V.3, which has 
the RF input fed right to the Q input.






But right now, I have the idea of capacitively coupling the 1pps pulse
from the GPS to the antenna input - the fast rising and falling edge
are broad band and show up in the sampled data.


The trouble is that you are going to impair the already low dynamic
range.  The ENOB on the I/Q ADC is around 7bit only.


Well, so far, after DDC, it's coming out about 1/5th of the dynamic 
range, and I can always adjust the size of the capacitor.







And you can see, no surprise, that the sample clock in the RTL isn't
dead on - over the 10 seconds, it looks like it drifts about 30- 50
microseconds - that is, the RTL clock is slow by 3-5 ppm.


Not all of these are created equal.  Several manufacturers claim to
factory calibrate their TCXO to better than 0.5ppm.  I have currently
two RTL-SDR that certainly are within 1ppm.  These things get quite hot,
so it definitely takes some time before they stabilize even if they do
have a TCXO in them.


Could well be.. I just turned it on, waited for the beagle to boot, 
captured the data, and moved on.







SO here's the question for the time-nuts hive-mind...
What's a good (or not so good) way to develop an estimator of the
timing/frequency error. Post processing minutes of data is just fine..


There is a program called rtl_test that just checks how many samples it
gets in a certain amount of time.  Let it run for a few hours on a PC
with a GPS-disciplined PC clock and it'll give you a pretty accurate
estimate of the mean sampling clock deviation.

The other method is to tune to a signal of known frequency and check
what it reads as.  There is a program floating around that uses a GSM
station for that purpose.


I'm not so concerned about the frequency measurement - that's "easy".. 
What I'm interested is figuring out the precise timing (in absolute 
terms) of the samples.



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Re: [time-nuts] getting accurate timing on RTL-SDR output

[jimlux]

On 4/13/18 10:33 AM, Dana Whitlow wrote:

Jim,

I'm curious:In what RF bandwidth will you be recording?


1 MHz for now.. the RTL-SDR isn't a super flexible device - there are 
apparently good and bad rates - it does a DDC with 28.8 MHz I/Q NCO 
(with who knows what kind of performance), and then filter and decimate. 
There's a set of taps published for a FIR filter in the thing.


Ultimately, it comes out as 8 bit I and 8 bit Q, so I figure if I do 
some more decimation on the 1MHz stream, I can get a few more effective 
bits.


It will run at 2 MHz sample rate without dropping samples.. I could 
probably modify the rtl utility to run at a higher rate and do a first 
software filter/downsample to get the data rate down..


I'm really only interested in fairly narrow detection bandwidth.

For telescope use, Jupiter is pretty bright.
For "phase array to listen to HF signals" 20kHz is probably plenty (it's 
not like I'm going to be developing a 3D CWSkimmer, yet)


Mostly it's because I'm managing a project at JPL where we're flying an 
interferometer to look at CMEs from the Sun

http://adsabs.harvard.edu/abs/2017EGUGA..19.5580L
and I'm intrigued by whether I can do it in the backyard..






My first thought would be to search for a cross-correlation peak
between the two antenna outputs, but quickly realized that this
does not tell you anything about the timing differences between
the two receivers.   I think you need to determine that independently
(else why bother with the interferometry in the first place?)


That's a clever idea..

Each node has its own GPS receiver, but they should all (within the 
tolerance of the receiver) be "ticking" at the same time.






The receive bandwidth in conjunction with your S/N on the PPS
spikes will conspire to limit your timing accuracy, although you
can improve on that by averaging over a few minutes as you
plan.

Dana




On Fri, Apr 13, 2018 at 11:52 AM, Jim Lux  wrote:


I'm building a phased array receiver (actually, an interferometer) using
RTL-SDR pods, where the elements are isolated from each other - there's a
common WiFi network connection, and each node has a BeagleBone Green, a
uBlox OEM-7M-C, and the RTL-SDR V3 (which works down to HF, since it has an
internal bypass around the RF front end).

In general, I have the RTL-SDR set up to capture at 1 Megasample/second. I
fire off a capture, record it to a file in the BeagleBone's flash, then
retrieve it from my host computer using scp over the network.

What I'm trying to do is capture data from all the nodes at
(approximately) the same time, then be able to line it all up in post
processing. The GPS (or NTP) is good enough to get them all to start
recording within a few tenths of a second.

So now the challenge is to "line em up".  An obvious approach is to
transmit an inband pilot tone with some sync pattern, received by all, and
I'm working on that too.

But right now, I have the idea of capacitively coupling the 1pps pulse
from the GPS to the antenna input - the fast rising and falling edge are
broad band and show up in the sampled data.

The attached pulses1.png shows the integrated power in 1 ms chunks (i.e. I
sum the power from 1000 samples for each chunk) and it's easy to see the
GPS edges.  And it's easy to create a estimate of the coarse timing (to 1
millisecond) - shown as the red trace.

But then, I want to get better.  So for the 20 edges in my 10 second
example, I plotted  (drift1.png) the raw I/Q output of the RTL.  The pulse
isn't too huge (maybe 10 DN out of the ADC's -128 to +128 range), but is
visible. Bottom trace is the first, and they're stacked up
0, 0.1, 1.0, 1.1, 2.0, 2.1, etc.

And you can see, no surprise, that the sample clock in the RTL isn't dead
on - over the 10 seconds, it looks like it drifts about 30- 50 microseconds
- that is, the RTL clock is slow by 3-5 ppm.

SO here's the question for the time-nuts hive-mind...
What's a good (or not so good) way to develop an estimator of the
timing/frequency error. Post processing minutes of data is just fine..

I'm not sure what the actual "waveform" that is being sampled is (and it
will be perturbed by the quantization of the ADC, and probably not be the
same depending on where the RTL is tuned).  That is there's some sort of
LPF in the front of the RTL, the edge is AC coupled, and then it goes into
some sort of digital down converter in the RTL running at 28.8 MHz sample
rate.

But it seems that there might be some way to "stack" a series of samples
and optimize some parameters to estimate the instantaneous time error-
given that the frequency vs time varies fairly slowly (over a minute or
so).  It's fairly obvious from the plot that if one looked at the "single"
sample when the edge comes in, not only does the time shift with each
pulse, but the phase rotates as well (totally expected)

this is one of those things where you could probably lay a ruler on it and
estimate it by eye pretty well, but I'd like 

Re: [time-nuts] RINEX for Android

[jimlux]

On 4/12/18 1:29 PM, Björn wrote:

Hi Jim,

Teqc is not a Windows-only program.  There are actually several ARM/Debian 
compilations. I assume some receiver protocols have been implemented with NDAs 
attached (hey Trimble...) and that might be one reason not to distribute source 
code. However if JPL would have a long term need for a specific build - Perhaps 
Unavco would consider supporting that.

https://www.unavco.org/software/data-processing/teqc/teqc.html

Teqc does translation (binary to Rinex conversion), editing of rinex and 
quality control of rinex data.

Not sure if that is something you want/need to do at your Beaglebone or what 
post processing package you intend to use.  Some post processing softwares 
might eat uBlox binary natively - all likely support rinex.

—




interesting.. there's Rpi builds which *might* work, at least it's ARM.

This is for my backyard, not for JPL, but that doesn't stop me from 
poking the JPL people and having them ask UNAVCO.


So now I just need to get some binary files out of my GPS receivers.


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Re: [time-nuts] RINEX for Android

[jimlux]

On 4/12/18 6:57 AM, Ole Petter Rønningen wrote:

I think teqc.exe can read ubx-files directly

Ole


12. apr. 2018 kl. 12:46 skrev jimlux <jim...@earthlink.net>:

It turns out that some of the newer Android phones support an API which returns 
raw GNSS data and that can be logged to a file in RINEX format. There's a few 
apps out there that do this although I've not tried it (my Samsung S6 doesn't 
have the right hardware).

In any case, it might be interesting, if you have one of these devices, to let 
it log for a while, with the phone in a fixed place, and then post process the 
data.

I ran across this when looking for software to generate RINEX files from data 
from NEO-7 GPS modules (which I'm still looking for)

_



I'm working in a Beaglebone environment - ARM, Debian- so the Windows 
tools don't work.  Before I go out and write python code to push 
characters out the serial port and get the output, I was hoping that 
someone had done some of this before.. I can do the conversion from a 
binary file to RINEX somewhere else.


rtklib might do the trick, but might also be overkill.  It seems that 
all I need to do is send the right strings to the GPS and it will start 
spitting out the right binary messages, which I then capture and post 
process. (perhaps using rtklib's utility to do binary to RINEX).




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[time-nuts] RINEX for Android

[jimlux]

It turns out that some of the newer Android phones support an API which 
returns raw GNSS data and that can be logged to a file in RINEX format. 
There's a few apps out there that do this although I've not tried it (my 
Samsung S6 doesn't have the right hardware).


In any case, it might be interesting, if you have one of these devices, 
to let it log for a while, with the phone in a fixed place, and then 
post process the data.


I ran across this when looking for software to generate RINEX files from 
data from NEO-7 GPS modules (which I'm still looking for)


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Re: [time-nuts] suggestions on getting 24 Mhz ?

[jimlux]

On 4/11/18 3:00 AM, Pete Lancashire wrote:

Needed for SDR project as external clock source.

-pete


I assume you mean derived from a high quality 10 MHz.

some sort of discrete divide multiply?   divide by 5 multiply by 12?
A PLL with VCXO with good far out noise?  (sort of like "clean up loops" 
used for distributing 10 or 100 MHz )

A DDS (with internal multiplier)


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

[jimlux]

On 4/9/18 5:20 AM, Dave Daniel wrote:
Responding to Jim's post ( I can't find his original post), a 
significant advantage to owning "vintage" instruments is that, in 
general, they may be repaired more easily than later model instruments. 
This fact was my guiding principle when setting up my lab, and that was 
based on Jim Williams' "There's No Place Like Home" article that appears 
as chapter 17 in his book entitled "The Art and Science of Analog 
Circuit Design". The more recent the design of the instrument, the more 
highly integrate is it's circuitry. In many cases, that integration 
manifests itself in the use of VLSI ASICs of one form or another that 
cannot be found, and if one is able to find one to replace a failed 
component, the techniques and tools required to swap it out are 
advanced, perhaps quite advanced. For a corporate enterprise, these 
facilities may be /de rigeur/, but for the home lab, they are, for one 
or more reasons, not feasible and the home lab owner must ship the 
instrument off to some company which can perform the repair or 
calibration at significant cost. I can repair a Tektronix 7104 
oscilloscope. I'm pretty sure I can't repair a Tektronix TDS7104.





This comes up on time-nuts a lot...
(and at work at JPL, because for the most part, we buy equipment, not 
rent it, and the original project ate the whole cost - there's no 
concept of "amortization and depreciaton" - it's just how the govt works)


Yes, the ability to repair is useful, and I'll not deny the pedagogical 
value of older, less "automated" instruments - nothing beats a slotted 
line  (or lecher wires) to understand VSWR, etc.


At JPL we have piles of HP8663 signal generators - a fine piece of gear, 
but all more than 20-25 years old - and they're all slowly dying off. 
Likewise, we have tons of HP portable spectrum analyzers, all with 
screens that are hardly readable. But that creates a problem - we have 
racks of equipment that *depend* on the idiosyncracies of those 8663s, 
and because no project wants to redesign the entire test campaign, we 
keep scrounging to find the last few working ones.


If your time is "free", then the hours it takes to track down a 
replacement transistor with the right properties, solder it in, etc. 
makes it a good deal - *if and only if* you didn't have something else 
more interesting to work on.


I'm fairly busy these days, and while resurrecting test gear was 
something I did when I was younger and poorer, today, I don't think I'd 
make that choice.   I am more interested in making the measurement, than 
in learning more about the innards of 30 year old test equipment.  And 
I'd rather spend my time learning the idiosyncracies of modern 
inexpensive equipment - that $900 SignalHound is a pretty nifty piece of 
gear, even if it is "Windows only" and I have to run a VM to talk to it. 
 Likewise, my $500 Ten-Tec VNA won't go to 50 GHz like the 8510 I used 
to use at work (the one where the sweeper hiccups periodically and locks 
up, and is "not economically repairable), but it's a lot cheaper than a 
FieldFox and serves the need I had for it at the time (measuring mutual 
Z between antennas).

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

[jimlux]

On 4/8/18 8:20 PM, Glenn Little WB4UIV wrote:
The USB stuff has no front end and stability and calibration is highly 
questionable..
I'm thinking here of the $1K sort of device - traceable cal, quite 
stable, etc.


Not the $20 RTL-SDR


How can you discriminate between mixes within the USB device and the 
signal of interest?


The same way you can distinguish on a full up analyzer - you change the 
input attenuator and see if the relative heights of the peaks change.





I will take my 141T or my 8566 over USB every time.
Rather lug a little weight around and know what I am seeing on the 
display is what is really out there.


A little?

There is a reason that usable SAs have weight to them and USB devices do 
not.


Monolithic RF ICs have made it possible to get very good performance in 
a smaller package.
Your 141T or 8566 have a fair bit of size and mass to run the CRT and 
user interface.


To be fair, one should take the size of the computer you're running 
the USB pod with and add that.


One thing where the USB pods don't necessarily do as well is on the 
tunable preselector filters or on the number of attenuator steps.



I'd have to go look at something like a Keysight/Agilent FieldFox or the 
Anritsu equivalent to see what sort of front end design they use - for 
all intents and purposes these are a tablet computer and 2 port 
VNA/Spectrum Analyzer in one (two)hand-held device.








Glenn


On 4/8/2018 6:58 PM, Andy ZL3AG via time-nuts wrote:

On 9/04/2018, at 3:52 AM, jimlux wrote:

Test equipment tends to be aged - Unless you have a particular need 
for a HP 600 series microwave signal generator, there are probably 
better sources available much cheaper that use more modern 
components. In this day and age, I don't think people should suffer 
through 141T spectrum analyzers or even a 8568- Spend your money an a 
nice USB unit instead.



Blasphemy!


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

[jimlux]

On 4/8/18 7:36 AM, paul swed wrote:

Thanks
It has to have been Apex that I visited. The back areas were a mix of open
sky and sort of sheds.


Don't want to be there in an earthquake.  After the Northridge quake, 
they had to rearrange their outdoor maze to improve safety somewhat.




The air was typically pretty dry so the stuff held up well. There were
things I would have liked to have grabbed.
Could easily see a day digging around.


Indeed - the only problem I have with Apex is that if what you're 
looking at is junk, but would look good on a set, they can make more 
money renting it to a production than selling it - and it's priced 
accordingly.  Anything with a rack full of blinky-lights panels has 
likely been rewired to be "blinky lights".


They have (or used to, haven't been there in about 5-6 years) an 
excellent selection of multi pin circular connectors at reasonable 
prices - very handy if you've got some surplus gear with no cables.


Test equipment tends to be aged - Unless you have a particular need for 
a HP 600 series microwave signal generator, there are probably better 
sources available much cheaper that use more modern components. In this 
day and age, I don't think people should suffer through 141T spectrum 
analyzers or even a 8568- Spend your money an a nice USB unit instead.





Inside its stacked to the 20 ft ceilings and they have ladders like you see
in home depot to get to the top.
There was a genrad admittance bridge on the top shelf. In good condition
and in the nice wood box.
I did not go to C as I simply ran out of time. Pretty good?
Regards
Paul
WB8TSL

On Sun, Apr 8, 2018 at 12:18 AM, Jeff Woolsey  wrote:


Geez.  The Agilent IEEE-1588 units I mentioned a month or two ago were
the last things I bought there.



There is one crazy place down in northern LA. Some what hard to get to

but

my god the stuff. Overwhelming. They dicker also. Nothing like a tough
bargain was there 3 years ago.


I happen to have returned from a family spring break in LA/SD just
today.  Yesterday I visted C surplus in Duarte and picked up a couple
items, one was way-underpriced.  This morning I was at APEX Electronics
in Sun Valley.  Overwhelming is right.  Being where they are in LA they
have a fair amount of prop business.   Imagine the backroom at
WeirdStuff. Now imagine ther same thing, only open to the sky, out
back.  I inquired about a couple items near the front, but didn't have
room in the car (or my wallet) for them.  The Yelp reviews are accurate.

--
Jeff Woolsey {{woolsey,jlw}@jlw,first.last@{gmail,jlw}}.com
Nature abhors straight antennas, clean lenses, and empty storage
"Delete! Delete! OK!" -Dr. Bronner on disk space management
Card-sorting, Joel.  -Crow on solitaire

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[time-nuts] NEO-7 GPS default 1pps width?

[jimlux]

I've got some NEO-7Ms here, and without an oscilloscope handy - what's 
the factory default 1pps pulse width?


The manual says pulseLenRatio is zero and pulseLenRatioLock is 100,000 (us)
flags-lockedOtherSet is 1, so I think that means "only generate 100ms 
pulses when locked"



Does that align with anyone else's experience?

Tnx
Jim
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[time-nuts] Harrison's birthday

[jimlux]

Google reminds us that 3 April is Harrison's birthday..

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

Interesting he (depending on your calendar) was born and died on the 
same day.  And, interesting he died in 1776, which is of some 
significance in the US.

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Re: [time-nuts] quartz / liquid nitrogen

[jimlux]

On 4/2/18 1:39 PM, Hal Murray wrote:

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.





CTE mismatch in packages will be a significant problem - you might find 
that your ICs don't work because bond wires have been ripped off the 
die. Parts might have popped off the board too.


But if you have one, and it's sacrificable, give it a try - a cooler 
with some dry ice, and put the circuit above the dry ice, and it will 
cool slowly

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Re: [time-nuts] GPS ANTENNA

[jimlux]

On 4/1/18 3:29 PM, Azelio Boriani wrote:

An unusual attenuator with a DC pass.



A few feet of RG-174 (or any 0.1" diameter coax) would probably work.





On Sun, Apr 1, 2018 at 10:21 PM, David C. Partridge
 wrote:

Or use a choke ring survey antenna and an attenuator :)

Dave

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob kb8tq
Sent: 01 April 2018 14:43
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] GPS ANTENNA

Hi

Indeed, it is *very* easy to put to much gain in front of a timing GNSS 
receiver. These beasts are trying to dig out a signal that you can’t even see 
with a spectrum analyzer.
It’s way to far below the noise floor to detect that way. They optimize things 
pretty tightly to get that done (and to hit a price target ….). Put to much 
gain in front of them and they get unhappy.

Making this even more crazy, the survey industry standard antenna *does* have a 
lot of gain. Survey receivers need way more gain in front of them than timing 
receivers. Put a survey antenna directly on a timing device and trouble will 
likely be the outcome. Equally, a survey instrument probably will not be happy 
with a timing receiver.

Why all this nonsense? As far as I can tell, it goes back to how the very early 
L1 / L2 survey boxes were designed back in the 1980’s and early 1990’s. They 
made a basic decision to put a lot of gain at the antenna. Motorola came along 
with their GPS modules later on. They made a *very* different decision about 
how to distribute the gain. There are very good arguments on both sides for why 
they did it this way.
The bottom line is still - you need to match things up …

Bob


On Apr 1, 2018, at 2:36 AM, cfo  wrote:

On Sat, 31 Mar 2018 10:58:19 -0500,
donandarline-Re5JQEeQqe8AvxtiuMwx3w
wrote:


I found a supplier for high quality GPS antennas at a very reasonable
price. PCTEL GPSL1-TMG-SPI-40NCB.


*** SNIP ***

I had one of those on 25m cable, and it worked fine on a Tbolt , until
i got an active antenna splitter that also had some gain.
Then i had to replace it w. a 26dB version of same type, else the
"Jackson Lite" was loosing sync.

What i mean here, is that you can get too much gain too.

Btw: Good price.

CFO
Denmark

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

[jimlux]

On 3/30/18 10:43 PM, Hal Murray wrote:

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.


Maybe locked, but probably not in a 'integer number of cycles per 
symbol' sense, more in the "derived from the same master 10 MHz 
reference" sense.


All stations use the same data rates, but have different carrier 
frequencies, and the carrier frequencies are the same ones we've always 
had, which don't necessarily have nice ratios between them.


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

[jimlux]

On 3/30/18 5:52 PM, Bob kb8tq wrote:

Hi



On Mar 30, 2018, at 6:13 PM, Hal Murray  wrote:


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?


Anything from a crystal oscillator to a Cs standard. It’s very much a “that 
depends”
sort of thing. If Crazy Bob is the chief engineer it might be a hydrogen maser 
….


And Crazy Bob can convince the owner of the station that it's needed




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


As noted earlier, color burst references were a big deal a long time ago. 
Depending
on how they do what they do it might still be a good bet. The big risk is that 
it could
be a good bet “most of the time”.





I wonder how stable the underlying timing of ATSC or DVB-T is?  You 
could recover the carrier or bit clock from an over the air signal, 
should you be lucky enough to live where the signal exists.   It's non 
trivial - all modern receivers do it as part of a single cheap 
monolithic chip - but maybe you could find some SDR code to run on a 
PLUTO or other cheap SDR that lets you "see" that level of the signal.


There's no inherent reason why it should be controlled well, at least 
for ATSC - the receivers are designed to tolerate multipath, Doppler, 
and other impairments.


But for simulcasting, the various transmitter carriers need to be 
matched fairly well.

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Re: [time-nuts] WWV/CHU

[jimlux]

On 3/29/18 3:49 AM, Attila Kinali wrote:

On Thu, 29 Mar 2018 03:12:24 -0700
Hal Murray  wrote:


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)


I think the easiest is GnuRadio... A quick googling lead
to https://github.com/jasonabele/gr-wwvb
I don't know anything about it so use at own risk :)
But at least it seems like something that can be done easily
on a rainy evening.

Normal RTL-SDR's do not work for WWVB as they have a lower cut of
frequency in the range of 20-50MHz...unless you bypass the tuner
chip and feed the signal directly to the ADC. As IIRC all RTL-SDR
give you something like 2Msps, that should be more than plenty to
decode WWVB and related signals. If you feed the RTL-SDR from an
external frequency source, you should be able to related that
frequency source to WWV.


The RTL-SDR is an interesting device - I'm putting together a hobby HF 
interferometer with GPS to provide time tags.


Yes, most of the newer parts (RTL-SDR v3, for instance) provide a 
programmable bypass of the front end downconverter (the part is actually 
designed to tune TV signals and the L-band output of a consumer dish LNB)
The backend chip (RTL2832U) is a digital downconverter which mixes and 
filters the nominal 3.5 MHz IF which is sampled at 28.8 MHz


You can actually adjust the output sample rate - something around 2 
Msample/second is the default, but there's lots of other rates 
available.  For WWV you could crank it down, but..

The ADC is 8 bits (7 ENOB) and the output is 8 bit I/8 bit Q.

Folks have modified the RTL-SDR to accept an external frequency 
reference, so you could take the output from your ensemble of Cesium 
references to discipline a hydrogen maser (so your close in phase noise 
is better),then use that to drive a 28.8 MHz discrete divide/multiply 
chain, and run that into your $30 receiver to improve the frequency 
accuracy.  (not for nothing are we called time-nuts)







Attila Kinali



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Re: [time-nuts] WWV/CHU

[jimlux]

On 3/29/18 3:12 AM, Hal Murray wrote:


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)



Hal,
you should know better than to have a question like "get time" on this 
list without specify the precision and accuracy .


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



The little HF dongle receivers will certainly receive HF WWV or WWVH, if 
propagation supports it, and you can listen to the dulcet tones of the 
appropriately gendered announcer ("at the tone, the time will be twelve 
hours thirty four minutes coordinated universal time") - you could 
probably track and decode the tone/ticks.  I would think that if you can 
hear the voice, you can decode the 100 Hz subcarrier, but I've not tried 
it. You can see the 100 Hz on a spectrum analysis display.


I would think that you can get propagation limited accuracy with the 
RTL-SDR type receiver.


Antenna is going to be the big challenge - the little whip antenna for 
the dongle won't usually cut it.



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Re: [time-nuts] Putting the clock forward at Avebury Stone Circle

[jimlux]

On 3/15/18 11:38 AM, Brooke Clarke wrote:

Hi:

The DST adjustment in the UK:
http://www.ntsouthwest.co.uk/2014/04/putting-the-clock-forward-at-avebury-stone-circle/ 



“Obviously Stone Age man didn’t have daylight saving, so twice a year we 
have to move one of the stones.” said Hilary Makins, National Trust Head 
Ranger.




note carefully the date on the story..

(but I did use the picture and caption earlier this week - since the US 
and other parts of the world don't change at the same time, some of my 
regular teleconferences didn't go quite as planned)


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Re: [time-nuts] Mechanical Precision Clocks

[jimlux]

On 3/6/18 5:12 PM, Tom Van Baak wrote:

Hi Adrian,

FYI -- Bill's also a long-time member of time-nuts. And he's also one of the reasons there is 
a time-nuts group. In the mid 90's I met Bill (and also Corby) through classified ads in Nuts 
& Volts magazine. Long story, but it was then that I learned it was "ok" to be 
interested in both vintage mechanical / pendulum clocks and also modern quartz / atomic 
clocks. His pendulum clocks are world-class masterpieces and his home atomic time lab was the 
inspiration for mine.

 From my perspective most historical, horological, mechanical watch & clock 
people are shy (or even dismissive) of anything electronic. Similarly, most 
electronic timekeeping people are ignorant (or even dismissive) of the wonderful 
world of precision mechanical timekeeping. So there's only a small subset of people 
who bridge that gap. Bill is one of them. If you're interested in modern mechanical 
timekeeping, please subscribe to HSN (Horological Science Newsletter) via 
http://www.hsn161.com

If you have any questions for Bill, I'm sure he'd be happy to answer them.




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

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

[jimlux]

On 3/5/18 10:26 AM, Mark Sims wrote:


Besides those clocks Heather has alarm clock and egg timer alarms.



because doesn't everyone time their soft boiled eggs to the microsecond? 
 (hmm, my Z3801 GPSDO is probably good to 1E-11 at tau of 300 seconds, 
so that's a potential error of 3ns ) 

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Re: [time-nuts] HP 5065A super

[jimlux]

On 2/23/18 1:33 PM, Bob kb8tq wrote:

Hi


On Feb 23, 2018, at 4:23 PM, Attila Kinali  wrote:

Hoi Bob,

On Thu, 22 Feb 2018 21:58:09 -0500
Bob kb8tq  wrote:


The same nickel plating effect gets into a lot of things. If you are shopping 
for very
low IMD connectors, nickel plating is out. Things get non-linear (to a very 
slight
degree) when it is present. If -180 db is the goal for those spurs, you might 
only
hit -120 db with the nickel connectors …..


Interesting. About what frequency range are you talking?


UHF up into microwaves. It was part of a lecture back when I was in school … I
assume the basic physics hasn’t changed since then :)




Passive intermodulation distortion? What is the physics... hysteresis 
curves in the magnetization of the nickel is what I would suspect.


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Re: [time-nuts] HP 5065A super

[jimlux]

On 2/22/18 12:29 PM, Leo Bodnar wrote:

Here is ENIG fact that is not widely known at the moment but which some might 
find useful.

I could not understand why I get better TDR and insertion loss results from 
solder-mask covered microstrip transmission lines than from otherwise identical 
microstrips on the same substrate with soldermask removed and, therefore, 
covered with ENIG.

Gold can't be bad, right? As it turns out, even gold coin has two sides to it.

I have found that Shlepnev and McMorrow conducted extensive research and 
published data, some of which is presented here 
http://www.simberian.com/Presentations/NickelCharacterizationPresentation_emc2011.pdf



the ever useful http://www.microwaves101.com/ site has an excellent 
discussion of this under the "skin effect" heading.



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Re: [time-nuts] eBay GPS antennas

[jimlux]

On 2/16/18 10:47 AM, Bob kb8tq wrote:

Hi

Well, the interesting point about Glonass timing is that it is independent of 
the
GPS empire. Galileo is another independent time source. Running a GPSDO
linked to each one would let you inter-compare the time from each of them.
Indeed I would *guess* that Galileo would do pretty well. Reports to date on
Glonass have not been encouraging. It still might be interesting to do. Once
Furuno releases the Galileo firmware, one of the Opus 7 based devices should
be able to run each of them. uBlox or some of the others would also do the
same thing.



However, if you're going to post process data using something like 
Gipsy-X, they have "better estimates" of the time base for all the 
systems, so you can get a combination. I suppose when you process you 
tell it which one is your favorite base, and it adjusts to that.


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Re: [time-nuts] eBay GPS antenna test results.

[jimlux]

On 2/15/18 6:04 AM, Bob kb8tq wrote:

Hi

There are a number of reasons to believe that these antennas are worse
than the typical “telecom GPS” antenna for L1 only duty driving a TBolt.
If you are going to do L1 / L2 work with something like a NetRS, then indeed
you will need a dual band antenna. These (the $99 ones)  are the lowest cost
“new in box” L1 / L2 antennas that I have seen. One would *guess* that their
close to horizon multi path rejection is not quite as good as a Trimble Zephyr,
a Novatel Pinwheel, or a choke ring. The ones from China
  also don’t cost $1800 to $6000 when new either …




one could probably improvise something that serves as a choke ring, or 
elevation fence.  The infamous JPL Helibowl is pretty simple, and has 
pretty good rejection of signals near the horizon.


See, e.g. Page 143 in GPS/GNSS Antennas, by Rao.  (I found it on google

https://books.google.com/books?id=nL-YFWLQrPIC=PA143=PA143=helibowl+antenna=bl=U-7Y3TMIQw=D4xZVMmv73XkCAH_8KkMegMnxX4=en=X=0ahUKEwjbjLGTjKjZAhVM7WMKHdYPC5sQ6AEIMTAB#v=onepage=helibowl%20antenna=false

Oddly, it cites to C.Y Cheng, Numerical Electromagnetic Modeling of a 
Small Aperture Helical-Fed Reflector Antenna, Masters thesis, Ohio 
University, Aug 1998.


Good luck finding that one on-line
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Re: [time-nuts] Team of physicists repeats tvb Project GREAT

[jimlux]

On 2/14/18 6:51 PM, Tim Lister wrote:

On Feb 14, 2018 19:47, "Chris Caudle" <ch...@chriscaudle.org> wrote:

On Wed, February 14, 2018 7:06 pm, jimlux wrote:

At substantially more expense, and with an experimental lattice clock,


Does that schematic figure in the paper imply that the "transportable"
strontium and ytterbium clocks are built into trailers instead of the
traditional rack enclosure?
Actually now that I look more closely it looks like maybe two trailers.
Doesn't seem like something that Jim is going to be flying any time soon.


Yes. From the Nature article text:
"The transportable 87Sr lattice clock is (compared with laboratory clocks)
designed to be compact, with robust optical parts12
<https://www.nature.com/articles/s41567-017-0042-3#ref-CR12>. The physics
package is less than 0.6 m3 in size, and we use laser breadboards with
mechanical stress-resistant fibre couplers21
<https://www.nature.com/articles/s41567-017-0042-3#ref-CR21>. All
components except the reference cavity of the interrogation laser are
rigidly mounted in a car trailer (size 2.2 m × 3 m × 2.2 m), and vibration
isolation is provided by rubber dampers. The trailer interior is
temperature stabilized, while the small volume of the trailer hinders air
exchange and generates hot spots with more than 10 K temperature rise.
However, the optics and the physics package are placed apart and shielded
from these and are stable to within 0.4 K after an initial temperature rise
of about 1 K. The transportable ultrastable reference cavity for the clock
interrogation lasers is rigidly mounted to endure transport12
<https://www.nature.com/articles/s41567-017-0042-3#ref-CR12>. It was placed
next to the trailer to avoid its performance being degraded by vibrations
induced in the trailer’s air conditioning system. The vibration amplitudes
in the trailer are a factor of ten larger than under typical laboratory
conditions, leading to a corresponding increase in clock instability. A
reference resonator with lower acceleration sensitivity or an active
feed-forward system may in the future remedy this inconvenience22
<https://www.nature.com/articles/s41567-017-0042-3#ref-CR22>."




We have discussed the desirability of suitable caves for operation of 
high quality clocks many times on this list.

Clearly this is another instance.

With respect to flying such things in space - this is the continual 
challenge - DSAC (the trapped mercury ion clock) was a couple of benches 
in a special time keeping lab when I first saw it, oh, a decade ago?. 
It will fly later this year and it's probably about the size of an 
airplane carry-on.

https://www.jpl.nasa.gov/missions/deep-space-atomic-clock-dsac/

Cold Atom Laboratory basically takes several optical benches operated by 
a team of post-docs that makes Bose Einstein Condensates (BEC) and turns 
it into a box the size of a dorm refrigerator that goes "ping" when you 
press a button and makes a BEC (in either Rb or K, as you choose).


https://coldatomlab.jpl.nasa.gov/mission/

Just as a rule of thumb, I've found that it takes about 10-20 times the 
cost to get from "benchtop prototype"(TRL 5) to "flyable unit" (TRL 6), 
as it cost to get from idea to benchtop prototype.


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Re: [time-nuts] Team of physicists repeats tvb Project GREAT

[jimlux]

On 2/14/18 6:46 PM, Chris Caudle wrote:

On Wed, February 14, 2018 7:06 pm, jimlux wrote:

At substantially more expense, and with an experimental lattice clock,


Does that schematic figure in the paper imply that the "transportable"
strontium and ytterbium clocks are built into trailers instead of the
traditional rack enclosure?
Actually now that I look more closely it looks like maybe two trailers.
Doesn't seem like something that Jim is going to be flying any time soon.


nor will tvb's brother-in-law be wearing it as a wristwatch
http://www.leapsecond.com/pages/atomic-bill/
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[time-nuts] Team of physicists repeats tvb Project GREAT

[jimlux]

https://www.nature.com/articles/s41567-017-0042-3

At substantially more expense, and with an experimental lattice clock, 
and a lot more references..

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Re: [time-nuts] True Time Nut Mission: NASA's Deep Space Atomic Clock (DSAC)

[jimlux]

On 2/8/18 8:55 PM, Bill Byrom wrote:

After the successful Falcon Heavy launch earlier this week, it appears that the 
Deep Space Atomic Clock (DSAC) is now scheduled to go up in June 2018 on a 
Falcon Heavy carrying the US Air Force STP-2 test payloads.
https://www.nasa.gov/feature/goddard/2018/nasa-tests-atomic-clock-for-deep-space-navigation

For a fun video about this project suitable for non-time-nuts, see:
https://www.nasa.gov/mission_pages/tdm/clock/sammy-the-second.html



"The Deep Space Atomic Clock is being readied for flight next year. 
Moving hardware from the laboratory to space meant conquering a number 
of technological challenges."


A number of really hard technological challenges. Aside from taking a 
bench full of gear and squeezing it down to a few liters.


Note the date on an earlier note:
"DSAC is scheduled for launch in mid-2016"





Date: Tue, 12 Jan 2016 17:31:26 -0600

Upcoming Event: Deep Space Atomic Clock
Jan. 14, 2016, at 7 p.m. PT (10 p.m. ET, 0300 UTC)
You can watch this event via USTREAM:  http://www.ustream.tv/NASAJPL2

Speakers:
Todd Ely, DSAC Principal Investigator, JPL
Allen H. Farrington, DSAC Project Manager, JPL
http://www.nasa.gov/mission_pages/tdm/clock/clock_overview.html#.VpWMgK9OKK0
Atomic clocks are an integral, yet almost invisible component of modern
life.
For space exploration, they have been the foundational frequency
standard for NASA's Deep Space Network. NASA's Deep Space Atomic Clock
(DSAC) Technology Demonstration Mission, led by the Jet Propulsion
Laboratory, has been maturing the latest Atomic Clock technologies into
a smaller package, suitable for installation on a variety of deep space
probes to enhance navigation precision and gravity science across the
solar system.

DSAC is scheduled for launch in mid-2016.
Satellite being built by Surrey Satellite Technologies USA, Englewood,
CO



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Re: [time-nuts] Vanguard TCXO

[jimlux]

On 2/8/18 11:49 AM, Mark Goldberg wrote:

On Thu, Feb 8, 2018 at 10:51 AM, jimlux <jim...@earthlink.net> wrote:


On 2/8/18 5:34 AM, Mark Goldberg wrote:


What is the phase noise like on the cheap TCXO?Vectron




VT-702 (the first one in the list online)
-99 at 10Hz
-123 at 100Hz
-143 at 1kHz

going to Mouser and looking for the cheapest 10MHz TCXO
FOX924 (about $2) - no data
SiT5000 (about ) - -140 dBc@1kHz, -150 dBcfrom 10k to 100k, -160 @ 1M (no
price)
ECS -TXO-3225-100-TR ($2.71 each) - -135dBc @ 1 kHz
ASTX-H11 ($3.16) -130dBc @ 1 kHz, -158dBc @100k

FOX922CE at 16.369 MHz, -145 @ 10kHz




Can you provide a link to the "list online"?


I just went to digikey and searched for TCXO and 10 MHz




I am always wary when no or few specifications are provided. If you look at
manufacturer;s like Vectron, they provide lots of data, phase noise at many
frequencies, aging, etc.



it's what you pay for - if the spec says -135 at 10kHz, and that's all, 
then that's what they test. - that's cheaper.


A $100 oscillator will tend to have a lot more data than a $2 one 

At some point, you just BUY a batch of oscillators and test them yourself.

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Re: [time-nuts] Vanguard TCXO

[jimlux]

On 2/8/18 5:34 AM, Mark Goldberg wrote:

What is the phase noise like on the cheap TCXO? Being on frequency is far
from the only characteristic that matters. I did some research on cheap
TCXOs for Kenwood radios and found truly awful phase noise and lots of
spurs above and below the oscillator frequency. I don't know if these
characteristics are important for your unit.

One eBay source says -125 dBc/1kHz. (Should be stated as -125 dBc/Hz @ 1
kHz). That is not very good. I found the cheap TCXOs I tested actually had
worse phase noise at 15 - 20 kHz offset.




Vectron
VT-702 (the first one in the list online)
-99 at 10Hz
-123 at 100Hz
-143 at 1kHz

going to Mouser and looking for the cheapest 10MHz TCXO
FOX924 (about $2) - no data
SiT5000 (about ) - -140 dBc@1kHz, -150 dBcfrom 10k to 100k, -160 @ 1M 
(no price)

ECS -TXO-3225-100-TR ($2.71 each) - -135dBc @ 1 kHz
ASTX-H11 ($3.16) -130dBc @ 1 kHz, -158dBc @100k

FOX922CE at 16.369 MHz, -145 @ 10kHz
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Re: [time-nuts] Etching of quartz crystals

[jimlux]

On 2/5/18 5:54 AM, Attila Kinali wrote:

On Sun, 4 Feb 2018 09:21:54 -0500
Bob kb8tq  wrote:


The images on this page gives a good impression about the current
skill-level in that area:

https://www.azonano.com/article.aspx?ArticleID=2740 



The gotcha is shown in the pictures. First point is that they are etching *very*
small features. A 5 MHz 3rd overtone blank is way thicker than what they are
playing with. The second issue is that even at small scale the walls are going
non-parallel.


That's exactly the issue here. While SAW resonators benefit quite a lot
from the processing skills learned from semiconductor fabrication, these
skills do not translate into BAW manufacturing. SAW resonators are built
etching or depositing small features ontop of a SiO2 wafer that is supposed
to be as flat as possible. On the other hand BAW oscillators are 3D structures
by themselves. They are lens shaped (thus not flat) to keep the oscillation
energy trapped in the center of the slap, thus allowing the edges to be used
for mounting/contacting, with minimal damping of the oscillation.

Yes, the shapes are simple. But not only because that's the only shapes
we know how to build, but also because these shapes allow us to calculate
how the crystal will oscialate and because the simpler the structure the
easier it is to build it with high precision and accuracy.

It would be possible to use edging of surface structures into the
crystal to form a Bragg reflector (instead of the lense shape).
But I have no idea how well it works. Considering that it is easier
to build a slap that is flat and then etching structures on it, than
to form a 3D structure, I wonder why I have not read about anyone
doing exactly that (beside for SAW structures).



Follow the money - or lack thereof - Folks are happy with the existing 
technology - If I'm flying a science mission that needs a space 
qualified Ultra Stable Oscillator - I've already budgeted my several 
million dollars, claiming that I'll just use what we already know how to 
build, and I spend no more proposal pages talking about it.  I certainly 
am not going to say "instead of spending $1M/oscillator for my 2 
oscillators, I'm going to spend $5M on an experimental process to change 
how the resonator is made, and by the way, it might not work"


Would using ion milling and other modern fabrication techniques lead to 
an oscillator with *significantly* better performance or *significantly* 
lower cost?


For those users for whom this is important, research focuses on looking 
for another qualitatively different way to get there - That's sort of 
what the CSAC and the Deep Space Atomic Clock (DSAC) are about - the ion 
trap clock for DSAC gives you long term performance BETTER than a USO. 
Although probably not at a lower cost, yet, there is potential for it to 
be so.
The CSAC gives you "good accuracy at low power", compared to an OCXO - 
less than 1/10th the power.



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Re: [time-nuts] Rakon HSO-14

[jimlux]

On 2/3/18 3:31 PM, Poul-Henning Kamp wrote:


In message <31183984-ed9d-60e1-6528-76dfde5f3...@rubidium.dyndns.org>, Magnus D
anielson writes:


The slots and thus the remaining bridges seems to have been a relatively
simple stage of the process. Orientation of the blank seems to have been
simple. The shapes for the electrodes seems to have been worse.






I have no idea if the result would actually work and be on frequency,
or for that matter, where I can borrow one of those machines, but...


with increased use of very high performance DDS and PLLs, the precise 
frequency may not be as important as it was when you were limited to 
straight up multiplication/mixing synthesis.


I suspect that a "10 MHz +/- 100kHz" might be a higher yield requirement 
than 10 MHz +/- 1ppm or +/- 1 ppb.


You could focus more on aging behavior.





The prices mentioned were not prohibitive in the context, you would
break even well before a thousand units at the prices mentioned.

Poul-Henning

[1] Surprising to me is that modern dentists are highly kitted for
CNC-ing very hard ceramic materials at high precision.


But, small "tooth sized" pieces - how big is your crystal.






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Re: [time-nuts] More on SiLabs 5340

[jimlux]

On 1/29/18 3:37 PM, Mark Goldberg wrote:

Reference my earlier postings titled "SI532X Chips Close In Spurs (Somewhat
Long)". There are many sets of register values that will get you the same
output frequency and the clock builder may not give you an optimal set for
phase noise and spurs. I created a spreadsheet to calculate other sets of
values and chose one that worked the best. I just did it through trial and
error of the different sets of values I came up with until I found one with
low spurs.




We've experienced that here with other PLL chips - For the ADF4108 
integer-N PLL, sometimes there's a big difference between R odd and R 
even (the R is the reference divisor in the fout = fin * (M*B+A)/R


So you wind up fooling around with various combinations of A, B, and R 
to get the spurs where you want them (or, more commonly, to move them 
from where you don't want them)


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Re: [time-nuts] Microsemi 3120A sold on eBay

[jimlux]

On 1/27/18 3:33 PM, Bruce Griffiths wrote:

http://www.chronos.co.uk/files/pdfs/mic/3120a.pdf

Bruce



 On 28 January 2018 at 11:57 "Dr. Ulrich L. Rohde via time-nuts" 
 wrote:

 What are the specs ? 73 de N1UL

 Sent from my iPhone

 > >

 On Jan 27, 2018, at 5:38 PM, John Miles  wrote:

 So, who's the lucky winner? Anyone on here? That's the first one of 
these
 I've seen in the "secondary market," so to speak.

 https://www.ebay.com/itm/332531180078

 -- john





More importantly what license keys does it include:
"The base model of the 3120A allows customers to measure phase noise and 
ADEV. Upgradeable software options for customers to measure AM noise, 
HDEV, MDEV, TDEV, and jitter, along with the ability to set test mask 
limits or to use ...




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Re: [time-nuts] CSAC Project(was CSAC purchase)

[jimlux]

On 1/27/18 8:10 AM, Bob kb8tq wrote:

Hi

“Included software” on the CSAC is a pretty short list …. There
is not much past the “stuff” to set it on frequency and read out
a few alarms.


There's a half dozen serial ascii commands to the CSAC, and a 
corresponding number of output messages. None are particularly "special" 
- I can't imagine needing a "display" for the telemetry, except perhaps 
as a novelty.


You'd want to periodically check the heater power, maybe?

I'd just expose a "diagnostic interface" on a CSAC based clock, and if 
you want to fool with it (or change the frequency, etc.), you hook up 
your external whatever.

LE Bluetooth Serial port perhaps?

You could write an App for a phone to talk to it, and I'm sure it will 
be in the top10 on the iStore and GooglePlay within weeks. Your 
retirement funding is assured. 




One thing that gets into a lot of these projects:

We are Time Nuts and spec things in terms of time. This error
over that period is some specific number. Maybe we look at
temperature rather than sit it on the shelf for a year. The number
is still a time error.






Very much so. Even here on "time-nuts" we discuss more about "frequency" 
- ADEV is a frequency error measure, after all.

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

[jimlux]

On 1/25/18 7:17 PM, Joseph Gwinn wrote:

On Thu, 25 Jan 2018 21:13:44 -0500, time-nuts-requ...@febo.com wrote:


Message: 2
Date: Thu, 25 Jan 2018 16:16:59 -0500
From: John Ackermann N8UR 
To: time-nuts@febo.com
Subject: Re: [time-nuts] Slightly OT: interest in a four-output,
ultra-low jitter, synthesizer block?
Message-ID: 
Content-Type: text/plain; charset=utf-8; format=flowed

Yes, I was planning to include bypasses, and I've been convinced to put
at least the 1.8V regulator on the board as well.  And to think about
the interconnects.


What I've seen widely done in circuits requiring low phase noise is to
have a cascade of regulators, all but the last one (that feeds the RF
component in question) beings switchers of different switching
frequency, with simple low-pass filters between the regulators, and
between the last regulator and the RF component being powered.
   Between the filtration due to the regulators and that due to the
LPFs, one can achieve very large ripple and noise attenuations.




What we've done is switcher from wide range bus (9-24V) to 8V, 60 dB 
ultimate attenuation low pass, switcher 8V to 5V(e.g.), 60 db low pass, 
linear with great HF rejection (i.e. the LT3042) to 3V


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Re: [time-nuts] CSAC Project(was CSAC purchase)

[jimlux]

On 1/25/18 3:28 PM, Ronald Held wrote:

Jim;
No need to order in the spring or fall anymore?   Looking forward
to your data.
Ronald



you and me, and a bunch of other folks as well

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

[jimlux]

On 1/25/18 1:18 PM, Hal Murray wrote:


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.


usually, it's so that noise coupled back from the part doesn't back in 
through the 1.8V.


If you have a (say) 5V supply and you generate 3.3Vdd with one regulator 
and 1.8V with another regulator, you (should) have better isolation. 
Trees rather than cascades.





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

[jimlux]

On 1/25/18 12:12 PM, wb6bnq wrote:

Hi John,

Thanks for the response.  Here is my 2 cents:

Well, due to the level of difficulty in chip mounting, I would prefer to 
see a complete project. I.E., power supply for a single input of 12 
volts and regulators the necessary chip values, proper input protection 
for the 10 MHz input level and single ended outputs of the appropriate 
levels (I am assuming more than 3 volts) or an amplifier stage for 
arriving at such.  Equally have RF connectors (SMA would be good) on the 
board perhaps.


The eval board for $200 might be a solution for that need: SMA 
connectors all around, runs off 5V from USB.







Of course as cheap as possible, hi hi.


Oh, well, $200 might be cheaper than cobbling together 
packaged/connectorized parts though.




  A carrier board arrangement
would be useless to me.  My application would be to provide signals for 
things like my Quicksilver SDR receiver, among other uses.


If you are interested, I can show you a nice little ABS (I think) box 
that has EMI built-in that I used for a project that should be more than 
large enough for your needs.


Than

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Re: [time-nuts] CSAC Project(was CSAC purchase)

[jimlux]

On 1/25/18 11:20 AM, Bob kb8tq wrote:

Hi

One of the unique features of underwater timing is that the sea bottom 
temperature
(once you get well away from a coastline) is *very* stable. In some 
deployments, the “random”
nature of ambient temperature that we fight all the time in the rest of the 
world, simply is not
present. The device sits at 2.345 C and that’s it …..




It helps that water density has a maximum at a particular temperature - 
water that is warmer or colder tends to float up above it. I was just 
looking it up and found apparently that does vary with salinity, too... 
oh no, another miniscule factor to account for - is there a "seawater 
density nuts" list...


Let's see, the bottom of Lake Tahoe (fresh water, so no salinity 
variation) is probably fairly stable at 4C. Or any other freshwater 
later that actually gets cold enough, and doesn't freeze to the bottom - 
so the deeper Great Lakes would probably work.  How warm does the bottom 
of Lake Superior get in late summer?







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Re: [time-nuts] CSAC Project(was CSAC purchase)

[jimlux]

On 1/25/18 9:39 AM, gandalfg8--- via time-nuts wrote:



At the time of writing a copy is available here

www.obsip.org/documents/Gardner_IEEE_Oceans_2016.pdf




"While results from an early batch of CSACs have been largely positive, 
later units have not performed as well. The CSAC specifications have 
changed, reflecting a decrease in reliability and accuracy of more 
recent units."


no kidding - there's a well known issue when MicroSemi took over 
building CSACs from Symmetricom, these things (like many precision 
timing widgets) have a "recipe" and it's easy to "lose the recipe" or 
find that there's unexpected and unknown components to the recipe.


Take a look at data sheet revs for the CSAC.. full temp range, then all 
of a sudden around rev G or H, temperature range is quoted at 0-35C 
operating, *0-40C non-op*.  I asked the sales rep if they ship them with 
icepacks in styrofoam like mail order cheese in the summer - that UPS 
truck gets way over 40C inside.


As always, this was discussed on the list and is in the archives.

That being said, I have no complaints about Microsemi being forthcoming 
about the issue and helping us to understand the nature of the problem. 
And they claim to have fixed the problem.


Hopefully, this summer, I'll have some data from a "narrow temp range" 
CSAC against GPS 1pps in an environment where there's no gravitational 
effects, and fairly small temperature fluctuations.


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Re: [time-nuts] RE CSAC Project(was CSAC purchase)

[jimlux]

On 1/23/18 12:36 PM, Ronald Held wrote:

Bob:
   What is you idea of portable in terms of size and mass for RbXO?
 Ronald
Jim
I suppose I am try to do "better' and my TCXO watches which at best
run around a second/year.


1 second/year is quite good - about 30 ppb. It's a bit tricky (like all 
things time-nutty) - the "aging" on a TCXO could be that good - but the 
instantaneous frequency control might not be that good.  1ppm is pretty 
vanilla for a TCXO over a fairly wide temperature range, so 30 ppb at 
"constant skin temp" (say, 5 C range) is probably reasonable.


I've got some test data here for some fancy TCXOs intended for space 
with a spec of 2ppm aging first year and then 1ppm/year after that.  The 
actual aging in the first year was 0.08 ppm, at 70C. Some of the other 
oscillators in the lot were 0.02ppm, 0.05ppm.


So, I think the spec here is "covers all the things that can go wrong", 
but by cherry  picking, you could do better.


(or, our system design could tolerate several ppm aging over years, and 
"run of the mill" for Vectron was actually a lot better)








 OCXO and TCXO are both available smaller than the CSAC (particularly
  tcxo).  I'm using a vectron EX-421 OCXO and it's about 1cm on a side,
  the OX205 is about 1" square and maybe 0.60" tall.

  TCXOs are available in "cellphone" form factors (e.g. tiny SMT packages)



Bob:
   Long term, maybe a year, sounds like a reasonable goal. Maybe I am
just chasing the next zero, if I have the metaphor correct?
 Ronald



Hi

  I’m guessing there was a question to me that somehow got lost in the world of
  ones and zeros ….

My comment was in terms of temperature stability. The CSAC has a temp stability
  specification of +/-4x10^-10 over -10 to +70C. There are TCXO’s that
will get below
  5x10^-9 over that range and use far less power. There are OCXO’s that will get
  to better temperature stability numbers over that range.  Neither one
will do the long
  term aging that a Rb will.

  Bob
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Re: [time-nuts] CSAC purchase

[jimlux]

On 1/22/18 12:05 PM, Ronald Held wrote:



Bob:
OCXO and TCXO are larger then the CSAC?  How much more power would
they need to get within a factor of ten to the 1.5s/1000 years?
  Ronald



OCXO and TCXO are both available smaller than the CSAC (particularly 
tcxo).  I'm using a vectron EX-421 OCXO and it's about 1cm on a side, 
the OX205 is about 1" square and maybe 0.60" tall.


TCXOs are available in "cellphone" form factors (e.g. tiny SMT packages)

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Re: [time-nuts] CSAC purchase

[jimlux]

On 1/20/18 5:05 PM, Ronald Held wrote:

I am thinking of buying a CSAC plus evaluation board.
Eventually I might want to make it portable. Any suggestions including
where to buy it?




MicroSemi is the manufacturer - Find a distributor and order it.

For instance, Digikey has the CSAC ($5312.50) and the eval board ($928.75)

portable isn't a problem - just run it off batteries.

It's pretty easy to hook up - power, 1pps in and out and 10 MHz out 
(they have versions that put out 5, 10.24, and 16.384 MHz too).


A serial port to control the device

The eval board has SMA connectors, a sub-d for the serial port, and 
comes with a wall wart to run it.


Download the Microsemi CSAC UserGuide for more info

you can fool with the disciplining algorithm, etc.
It's a low power device compared to a OCXO (<120mW)

They're a pretty nifty device, even if the price more than tripled in 
the last couple years.



Jackson Labs makes some integrated systems using CSAC, I believe.


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Re: [time-nuts] minimalist sine to square

[jimlux]

On 1/19/18 12:54 PM, Poul-Henning Kamp wrote:


In message <898171c2-0e9a-6a2a-dcfc-b7d893f89...@earthlink.net>, jimlux writes:


What about the plethora of LVDS receivers - they're basically a
differential input thresholder, with deliberate hysteresis, looking for
a 300 mV shift across a 100 ohm resistor.


I played with that, I used a small transformer to balance the signal
and then into LVDS receiver through a voltage divider.  Worked well,
but I didn't measure the jitter, it was just for a micro-controller.



You can also do it with capacitive dc block to one side, and some 
resistors - the ap notes describe it.  The receivers are a fairly high Z 
input, so you pick the voltage divider resistors to make the termination 
resistance right for the incoming signal.

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Re: [time-nuts] minimalist sine to square

[jimlux]

On 1/19/18 11:31 AM, Tom Van Baak wrote:

John's TADD-2-mini [1] uses the Wenzel sine-to-square converter. It performs 
very well but requires +10 V.

I'm looking for a solution that works at 5 V (e.g., USB powered) and also uses 
fewer parts. Wenzel also mentions using a differential line receiver [2]. That 
would be an ideal single-chip 5 V solution for me but the two parts he 
mentions, MC1489 [3] and SN55182 [4], don't appear fast enough for a 10 MHz 
input.



There are tons of LVDS that run on 3.3 or 5V, Maxim, TI both have parts.

The first Maxim part google turned up with "LVDS receiver" was a quad, 
esd protected unit good to 400 MHz, 2ns prop delay, 50mV hysteresis.


You do want to watch the common mode voltages - some of the parts are 
not good about having the signals swing near the rails (or beyond).

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Re: [time-nuts] minimalist sine to square

[jimlux]

On 1/19/18 11:31 AM, Tom Van Baak wrote:

John's TADD-2-mini [1] uses the Wenzel sine-to-square converter. It performs 
very well but requires +10 V.

I'm looking for a solution that works at 5 V (e.g., USB powered) and also uses 
fewer parts. Wenzel also mentions using a differential line receiver [2]. That 
would be an ideal single-chip 5 V solution for me but the two parts he 
mentions, MC1489 [3] and SN55182 [4], don't appear fast enough for a 10 MHz 
input.

Can any of you circuit experts suggest some line receivers that would work? 
Maybe DS9637 [5]? This isn't for cesium work so it doesn't have to be quite as 
good as the TADD-2.



What about the plethora of LVDS receivers - they're basically a 
differential input thresholder, with deliberate hysteresis, looking for 
a 300 mV shift across a 100 ohm resistor.


Plenty fast (GHz)






Thanks,
/tvb

[1] http://www.tapr.org/~n8ur/T2_Mini_Manual.pdf
[2] http://www.wenzel.com/documents/waveform.html
[3] https://www.onsemi.com/pub/Collateral/MC1489-D.PDF
[4] http://www.ti.com/lit/ds/slls092d/slls092d.pdf
[5] http://www.ti.com/lit/ds/symlink/ds9637a.pdf


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Re: [time-nuts] Reference input on HP counters

[jimlux]

On 1/7/18 9:55 AM, Jerry Hancock wrote:

As far as lazy, I will check my equipment.

When the others that replied using the term “lock” or “locked”, what do you 
mean by that?  That for instance, the external reference is multiplied up 
directly to the internal frequency (IF I suppose) or is it phase locked, for 
instance?  I’m sure there are other cases.

I’m trying to differentiate between two cases:

1) I apply an external reference at 10Mhz (assumed all the devices require 
10Mhz at a certain level) and using a switch of some type (electronic or 
manual) the reference is now multiplied and manipulated directly to feed stages 
of the device.  In this way, the phase noise of the device is very much 
dependent on the external reference.  So if a noisy external is used it impacts 
the device across all time values.

2) I apply an external reference and another oscillator, maybe the default or 
supplied internal 10Mhz (like a 10811, etc) is now EFC adjusted to phase lock 
to the external reference.  In this way, I would think the phase noise of the 
device would have been impacted less by the external reference (under the time 
constant of the PLL or EFC loop.

Either way, an oscillator with phase issues used as the external reference is 
going to have some impact on the device, correct?  I’m thinking of in the case 
where you use a GPSDO that doesn’t have a very good master oscillator.

Thanks,


I think #1 is the more common traditional approach - the external 
reference "substitutes" for the internal reference. This leads to all 
kinds of discussions about "should I use the counter's internal 
oscillator as the external reference for the spectrum analyzer or vice 
versa" - since counters usually have good AVAR and drift, but don't 
worry as much about close in phase noise, while spectrum analyzers are 
the opposite.


#2 is similar to what's going on inside the 33622, I think.


The differences in ultimate performance depend on what the various 
synthesis schemes are, whether loop based with a PLL or direct synthesis 
with dividers and multipliers.


And even if you know the scheme used in a particular piece of gear, the 
actual behavior is something you basically have to find by 
experimentation (or asking people who have tried it), since 
implementations are always "non-ideal".


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Re: [time-nuts] AM vs PM noise of signal sources

[jimlux]

On 1/7/18 8:05 AM, Arnold Tibus wrote:

Am 07.01.2018 um 16:33 schrieb jimlux:

On 1/6/18 6:12 PM, Dana Whitlow wrote:
One point about oscillator design I've not yet seen mentioned is 
this: the

limiter
must not degrade the resonator Q when in action.  Hence, a pair of 
diodes
connected in parallel back to back, across a shunt resonator, would 
be a bad

thing to do from the perspective of low phase noise. A differential
amplifier
that limits by running out of current on peaks, driving a shunt 
resonator,

is
a much better way even though one pays a price in having more transistor
noise in the circuit.

I've long wondered if a very slow AGC might avoid the nonlinear 
mechanisms

issue except, of course, for things happening within the AGC loop's
bandwidth.






That's the Wein bridge stabilized by a light bulb, popularized by 
Messrs Hewlett and Packard a while ago.

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Hello everybody, excuse me please,

but I see quite often mentioned the 'Wein bridge'. (Wein in german is 
'vino' or 'wine' ;-)
Not of real technical importance, but shouldn't this not be correctly 
called a 'Wien bridge'?

As I know that this tricky circuit was developed by Max Wien in 1891.
Max Karl Werner Wien was a German physicist and the director of the 
Institute of Physics at the University of Jena at that time.

  (sorry, I am a nut ;-)  )







Ah yes. And I imagine then that the pronounciation should be in english 
"veen"

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Re: [time-nuts] Reference input on HP counters

[jimlux]

On 1/7/18 7:21 AM, Jerry Hancock wrote:

I’m being a little lazy as I can check the schematics, but in the general case, 
do HP counters, frequency generators, etc, switch to the external reference 
when one is available or discipline the internal oscillator?  Are there brands 
of test equipment that generally discipline vs switch?



By the each.

Particularly for newer equipment it can be somewhat of a hybrid - the 
Keysight 33622, for instance, seems to have some sort of frequency 
locked loop (according to the manual and emails from Keysight).  It 
stays on the internal reference, but the frequency is adjusted to match 
the external reference (whether they adjust the oscillator, or reprogram 
a DDS, I'm not sure).


I've seen test data, though, that seems to imply there's something else 
going on - the phase noise is reduced when fed from a quiet external 
source, and if it was a simple frequency locked loop, I don't think that 
would happen.





Third question, again generally, when you discipline an oscillator, what impact 
does this have on the oscillator's phase noise?  I assume this third question 
depends on the discipline loop (if I’m using the correct term).

Thanks
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Re: [time-nuts] AM vs PM noise of signal sources

[jimlux]

On 1/6/18 6:12 PM, Dana Whitlow wrote:

One point about oscillator design I've not yet seen mentioned is this: the
limiter
must not degrade the resonator Q when in action.  Hence, a pair of diodes
connected in parallel back to back, across a shunt resonator, would be a bad
thing to do from the perspective of low phase noise. A differential
amplifier
that limits by running out of current on peaks, driving a shunt resonator,
is
a much better way even though one pays a price in having more transistor
noise in the circuit.

I've long wondered if a very slow AGC might avoid the nonlinear mechanisms
issue except, of course, for things happening within the AGC loop's
bandwidth.






That's the Wein bridge stabilized by a light bulb, popularized by Messrs 
Hewlett and Packard a while ago.

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

[jimlux]

On 12/13/17 1:28 PM, Jerry Hancock wrote:

Well, if you haven’t selected a DDS and you need I/Q, I would go with the tried 
and true 9854 as it has I/Q outputs and I thought a 12bit DAC so the resulting 
spurs and sfdr are lower than other chips, or were, as I think they have 14bit 
DACs on other chips now.  It also depends on the highest frequency range needed 
and power requirements as they all seem to run hot.  There is a new DDS, a 9910 
I think, that uses a 14bit DAC but it is a single output and would need to sync 
clocks if you need I/Q.  I have used the 9854 with PIC, Arduino and STM32 and 
assuming the frequency range is ok, I found it to be the better of the chips.  
I don’t think they have a replacement for it (I/Q with 14bit DAC would be 
great) but I haven’t looked lately.

The language is C but I think it has C++ and C# compilers out there.  Also, 
once you have the code tested on the Arduino you can just run it on the 
equivalent AVR chip and build your own board.  I don’t think there is a license 
or runtime compiler issue and if there is, I remember seeing a GNU compiler for 
the AVRs and Arduino.  My only point is that for prototyping and testing, the 
Arduino seems to be the easiest with tons of support and many, many adapters 
and I/O,  The STM32 boards are faster but the learning curve is just 
unbelievable.  It took me months to master those boards compared to minutes for 
the Arduino.




I agree - $20 for a Teensy, some jumper wires from solder holes on the 
Teensy to your breadboard, load up the Teensyduino libraries into the 
Arduino IDE and your SPI/I2C/serial interface is done.  I did this to 
write arduino code to drive a Silabs part.


If it takes an hour, I'd be surprised (or you have an incredibly slow 
download connection, like doing it on an airplane in the back rows where 
the WiFi is clunky - which I have done).  The hard part when going to a 
standalone design is picking the right pins on the microcontroller 
(since so many have multiple functions, you want to be careful about 
accidentally using something that has another useful function).



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

[jimlux]

On 12/13/17 12:56 PM, Richard (Rick) Karlquist wrote:

I should have said AD9832.  But that was just an example
that would work.  I may choose a different one for whatever
reason.

Regarding the Arduino board:  that is what I would call
a "daughter" board, which I can't have.  Is the Arduino
board open source, so that I can just copy the schematic
of it to my own board?  Is the Arduino software also
open source?



yes to both.

There's also a fair amount of "non arduino" software that runs on the 
arduino hardware platform (whether ATMEGA or Freescale or some other ARM 
processor).


The pjrc.com teensy is available with pins sticking out, so you can 
mount it like a sort of thicker than normal wide DIP.


I've built standalone designs inheriting the processor schematic from 
the pjrc.com Teensy series (which use the Freescale parts which have a 
built in USB interface, useful for me).


If you're used to cross compilers using the usual GCC toolsets, and 
such, then you don't need the Arduino IDE environment (although it *is* 
easy, and gives you a nice prototyping platform).  You can program most 
of these chips using the JTAG interface, assuming you have a JTAG pod of 
some sort.  That gives you a single chip solution that still has a 
fairly clean development environment.









Rick

On 12/13/2017 12:47 PM, Clint Jay wrote:

I think maybe you might have meant the AD9835 ?

Anyway, there are plenty of code examples out there, do you have a
processor in mind or are you free to use whatever is suggested?



On 13 Dec 2017 20:03, "Richard (Rick) Karlquist" 
wrote:


I need a very simple controller to tune a DDS with up/down
switches (imagine setting the time on a clock).  A DDS
chip, such as an AD9836 would go on a PC board and a couple
of pushbuttons would tell the controller to tune up or
down.

Before reinventing this wheel, I thought I would see if
anyone knows of a similar solution that can be leveraged.
What I would like is both hardware and software, where
the software could be edited to accommodate the up/down
buttons.  A last resort would be to write software from
scratch.  My software skills are extremely limited.
Cutting and pasting code might work for me.

I need to be able to embed this onto an existing PC board.
I can't use a preexisting "daughter" card, other than
to copy the design of the card.

Rick Karlquist
N6RK



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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[jimlux]

On 12/9/17 11:14 AM, Mark Sims wrote:

In the standards definitions that include "at sea level", the question these days is "which 
sea level?".  As ocean temperature changes sea level will change (except maybe in Washington DC).  Will 
the standards be amended to include something like "at sea level in 1990" or will the value being 
defined drift around with the changing sea level?


Sea Level is arbitrary anyway - what is usually meant is "zero elevation 
relative to some specified geoid".


 The Pacific and Atlantic oceans have different mean heights relative 
to the geoid


In the United States, for a long time it was the North American Datum 
(NAD) that was the reference, but now, it's probably WGS84 (I'm too lazy 
to go look it up).


WGS84 has a very precise definition in terms of the semiaxes lengths, 
and their orientation relative to stellar references.  WGS 84 uses the 
IERS reference meridian for longitude.


Flattening of 1/298.257,223,563
equatorial radius of 6,378,137 m
so polar radius of 6,356,752.3142 m

The Earth Grav Model (EGM96) defines the geoid, last revised in 2004. 
*that* model defines the nominal sea surface with spherical harmonics. 
There's something like 100,000 specific terms in that gravity model.


Sourceforge has a program that will tell you geoid height for a given 
lat lon.


https://geographiclib.sourceforge.io/cgi-bin/GeoidEval

Near my house (34N, 119W), it appears that the EGM96 height is -37.17 m, 
relative to the ellipsoid defined above.


It so happens that due to crustal movement, my house is gradually rising 
about 1 cm/year, but I don't know if the local sea level also rises to 
match, or if the beach is getting farther away.



One can measure this, in theory
https://www.unavco.org/education/resources/modules-and-activities/gps-california-plate-motion/gps-california-plate-motion.html










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Re: [time-nuts] End-of-Range: Oscilloquartz OCXO 8600-3

[jimlux]

On 12/8/17 9:29 AM, Magnus Danielson wrote:

Hi,

The unloaded Q is above 3 million, which is another way to measure how 
unusual these are.


If I had schematics I would be more inclined to do something.






However, the value for me is not to have it as sharp 5 MHz source, 
but very low phase noise and high stability source as reference for 
measurement. The offset error is less of a concern then, so that is 
why I have not spent quality time to fix it.





Don't people *want* a nice quiet oscillator with a slight offset, that 
way you're already set up for the DMTD measurement.


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[time-nuts] TDEV or phase Dev for a GPSDO?

[jimlux]

Has someone already done the work and plotted TDEV or phase Dev for a 
run of the mill GPSDO.
Particularly for a GPSDO with a non-exotic oscillator.. Or, perhaps the 
USRP flavor?


There's a fair number of Modified ADEV plots out there from time-nuts 
and others, so I can calculate it, but hey, if someone has done the work 
for me, I'm lazy.


http://www.leapsecond.com/museum/manyadev.gif for instance, tells me 
that at 1000 seconds, a  TCXO has MDEV of around 1E-9, so TDEV of about 
0.6 microseconds, and a Z3801 (MDEV 0.5E-11) has a TDEV of 3ns.


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

[jimlux]

On 12/7/17 1:29 PM, Bill Hawkins wrote:





So yes, this could be interesting for a hobbyist, but it won't add
anything to Science.
A MASER is overkill. Heck, so are Rubidium and Caesium.
A naked crystal will be rock solid compared to received WWV.

OTOH, NTP has marvelous mathematical tricks to reduce Internet
propagation delay.
A scheme to reduce varying atmospheric delay would be useful, if there
weren't much better ways to get a standard frequency.



What you are talking about is "better ionosphere modeling", which is 
something that a lot of people have spent a lot of time and effort on, 
without a lot of success.  That said, there are some real time ionograms 
out there that are fascinating to watch.  It doesn't take a very 
sophisticated receiver to receive the signals from a variety of 
ionosonde transmitters.


Juha Vierinen has a variety of interesting software:
http://www.sgo.fi/~j/gnu_chirp_sounder/

Juha also has done stuff with measuring the frequency of beacon satellites

http://www.sgo.fi/~j/jitter/web/



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Re: [time-nuts] Propagation delay within analog radio, (Radio Shack Timecube) and an SDR, at HF

[jimlux]

On 12/2/17 12:57 PM, Patrick Barthelow wrote:

Just about to go across town to pick up TWO  Radio Shack Timecube radios,
that someone will sell cheap.  Been 35 years since I have seen one.   Used
one in College to bring time to astronomy instruments in the field.
 From a newbie: Has anyone measured or does anyone have an idea of the
propagation delay between an audio tick signal on the RF carrier at the
antenna port, to an audio waveform on the demodulator/audio amp?
  Microseconds?  more? less?
If I hang a scope on the speaker audio out, and RF modulated input signal,
how much delay would there be? Same question for  an SDR.

Best, 73,   Pat Barthelow AA6EG
apol lo...@gmail.com





Milliseconds - mostly from the audio processing chain.  For analog 
systems, the delay is inversely proportional to bandwidth and 
proportional to number of sections.


In SDR implementations (obviously not the Timecube) the latency can be 
quite long, and can be variable. Most SDR implementations don't pay much 
attention to RF/Baseband delays as long as the pipeline doesn't run dry.



This was a big, big deal in the early days of the Flexradio, because it 
used a half duplex processing chain with buffers - Tx/Rx turnaround 
could only occur on a buffer boundary, and if you cranked the bandwidth 
down (for CW), the buffer had to be fairly big.



Gnuradio and Pothos (two popular frameworks for SDR) don't really have 
any provision for accurate timing - they're basically "signal flow 
graph" based systems, and the latency through a block is whatever the 
software gives you.


The USRP, in the usual "RF up/downconverter from digital samples" mode 
is also noncoherent between RF and digital side - there's buffering in 
the USB or Ethernet interfaces.


The RTL-SDR pod is "coherent within a stream" - that is, once you're 
streaming, there aren't any dropped samples, but the absolute timing 
between RF sample and a particular USB data packet is uncertain (due to 
USB device driver stuff).


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Re: [time-nuts] Trimble Mini-T Timing Glitches

[jimlux]

On 11/30/17 3:05 PM, Leo Bodnar wrote:

Completely off-topic comment while on the subject:

I can't see how randomly selected 1ms of data can contain unambiguously 
detectable start of C/A code.
If NAV data bit phase flip occurred within this 1ms of data then correlation 
search will most probably fail.
Yes, the probability of this is only 5% (assuming equal number of 1s and 0s in 
NAV message) but still not zero.


I believe that Nav bits only flip at code epoch boundaries (actually, 
every 20 code epochs), it can't change in the middle of a 1023 chip 
sequence.  You use the epoch sync signal to run your symbol integrator.




Perhaps the quote should have added "carefully chosen 1ms of data"
At the minimum, one would typically select 2ms of sampled data when they are 
doing a correlation search and then they are guaranteed a full PRN sequence 
somewhere in there.

Leo


From: Tom Van Baak Thu, 30 Nov 2017 14:43:02 -0800
In order to find the beginning of a C/A code in the received signal only a
very limited data record is needed such as 1 ms. If there is no Doppler effect
on the received signal, then one millisecond of data contains all the 1,023
chips.


Doppler does make it harder (ask the folks who did the Huygens probe)





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Re: [time-nuts] Trimble Mini-T Timing Glitches

[jimlux]

On 11/30/17 1:31 PM, Leo Bodnar wrote:

Bob, this is quite an unorthodox description of how GPS works.
You probably want to rephrase that before it gets ripped to shreds.
Leo

From: Bob kb8tq 

GPS extracts time and location by locking on to various codes in the 
transmissions.

One of them happens to run at about a 1 KHz clock rate. A slip on that part of 
the
process gives you a (modulo) 1 ms clock jump. Certain types of interference may
“help” the receiver make these sorts of mistakes.


I thought it was fairly accurate - the primary thing from which you get 
your time reference is the C/A code epoch, which is a 1 millisecond sort 
of thing.  The Nav message is on top of that at 50 bps, but "GPS time" 
is reckoned in "weeks and milliseconds of week"  (e.g. that's what you 
get out of a variety of small Novatel single board receivers).


So a lot of receivers have a basic "cycle" that runs at the epoch rate.
To generate a 1pps, you take your current nav solution to figure out how 
far from the "epoch time for spacecraft #N" the "top of the second" is 
at, and then jam that into a counter of some sort that delays the epoch 
timing signal some number of clock ticks until the 1pps gets generated.


I suppose you could have some fancy system that takes the 1kHz ticks 
from ALL currently tracked satellites, and forms some sort of average to 
generate the 1pps signal.


But it's easier to take the "PN epoch sync" line, delay it by some 
number of processor clocks, and generate the 1pps.  Pick the strongest 
signal, since the epoch sync is probably "best".


It's also likely that the "epoch sync" is latched by the processor clock 
- hence hanging bridges, etc.


And all sorts of implementation idiosyncracies could confuse the "1pps 
logic" into putting the wrong delay count in.


BTW, it could well be a multimillisecond delay from "epoch sync" to 
"1pps"   For the purposes of illustration, let's say the range to the SV 
can vary by +/- 10,000km  - that's 30 milliseconds light time.


So I could be tracking SV1 at the horizon, calculate my delay, and then 
hiccup and now track SV2, directly overhead, but use the delay from SV1 
(until the next 1pps cycle comes around).


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

[jimlux]

On 11/29/17 5:53 PM, Bob kb8tq wrote:

HI




On Nov 29, 2017, at 8:41 PM, jimlux <jim...@earthlink.net> wrote:

On 11/29/17 3:41 PM, Bob kb8tq wrote:

Hi
Needless to say *demonstrating* this 0.001 db sort of gain flatness on a 
repeater
out to crazy low frequencies is a bit involved. It *is* a great gig if you 
happen to be
a consultant …
Bob




demonstrating 0.001 dB (or would that really be 0.1 mB or 100 microBels) 
precision in *any* application is a bit involved.  That's 0.03%



Yup, now do it at some silly low frequency ( 0.(some number of zeros)1 Hz …. 
great way to waste a lot of time.




That's a volt meter

It's the "do it at 1 Hz and 10 MHz and every 1 Hz in between" that is 
the challenge.

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

[jimlux]

On 11/29/17 3:41 PM, Bob kb8tq wrote:

Hi

Needless to say *demonstrating* this 0.001 db sort of gain flatness on a 
repeater
out to crazy low frequencies is a bit involved. It *is* a great gig if you 
happen to be
a consultant …

Bob




demonstrating 0.001 dB (or would that really be 0.1 mB or 100 microBels) 
precision in *any* application is a bit involved.  That's 0.03%



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Re: [time-nuts] Allan variance by sine-wave fitting

[jimlux]

On 11/27/17 2:45 PM, Magnus Danielson wrote:



There is nothing wrong about attempting new approaches, or even just 
test and idea and see how it pans out. You should then compare it to a 
number of other approaches, and as you test things, you should analyze 
the same data with different methods. Prototyping that in Python is 
fine, but in order to analyze it, you need to be careful about the details.


I would consider one just doing the measurements and then try different 
post-processings and see how those vary.
Another paper then takes up on that and attempts analysis that matches 
the numbers from actual measurements.


So, we might provide tough love, but there is a bit of experience behind 
it, so it should be listened to carefully.





It is tough to come up with good artificial test data - the literature 
on generating "noise samples" is significantly thinner than the 
literature on measuring the noise.


When it comes to measuring actual signals with actual ADCs, there's also 
a number of traps - you can design a nice approach, using the SNR/ENOB 
data from the data sheet, and get seemingly good data.


The challenge is really in coming up with good *tests* of your 
measurement technique that show that it really is giving you what you 
think it is.


A trivial example is this (not a noise measuring problem, per se) -

You need to measure the power of a received signal - if the signal is 
narrow band, and high SNR, then the bandwidth of the measuring system 
(be it a FFT or conventional spectrum analyzer) doesn't make a lot of 
difference - the precise filter shape is non-critical.  The noise power 
that winds up in the measurement bandwidth is small, for instance.


But now, let's say that the signal is a bit wider band or lower SNR or 
you're uncertain of its exact frequency, then the shape of the filter 
starts to make a big difference.


Now, let’s look at a system where there’s some decimation involved - any 
decimation raises the prospect of “out of band signals” aliasing into 
the post decimation passband.  Now, all of a sudden, the filtering 
before the decimator starts to become more important. And the number of 
bits you have to carry starts being more important.


It actually took a fair amount of work to *prove* that a system I was 
working on

a) accurately measured the signal (in the presence of other large signals)
b) that there weren’t numerical issues causing the strong signal to show 
up in the low level signal filter bins

c) that the measured noise floor matched the expectation
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Re: [time-nuts] Recommendation for cheap GBIP adapter for Linux

[jimlux]

On 11/18/17 11:04 AM, Attila Kinali wrote:

Hi,

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 (Windows doesn't matter at all).
I do not mind writing my own read-out software (that's quickly and
easily done). What would people here recommend?


I use the Prologix GPIB to Ethernet converters.

Makes it "platform independent" since it's just an IP socket to the 
outside world

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

[jimlux]

On 11/17/17 5:16 PM, Hal Murray wrote:


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?



not huge.. Earth is 40,000 km circumference (thank you Napoleon and the 
Cassinis), so at the equator the velocity is on the order of 500 m/s


Doppler is about 600 Hz from earth rotation.

1ppm at mid latitudes

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Re: [time-nuts] Absolute phase

[jimlux]

On 11/17/17 11:05 AM, Jerry Hancock wrote:

Granted I expect someone on this list to reply with something that makes me 
feel stupid, if you have two GPSDO units running side by side, should the phase 
delta on the 10Mhz output be zero (ideally)?  Is there an absolute phase 
standard kept between GPSDO units as all it would take is one extra inverter in 
the chain to flip the phase, no?



I don't think so..
GPSDOs are really more of a syntonization (same frequency) rather than a 
synchronization (same phase) box.


You might have two boxes of the same kind that have some well defined 
and stable phase relationship between, say, the 10 MHz sine and the 1pps 
(if the 1pps is derived by dividing the 10 MHz, for instance)



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Re: [time-nuts] Discussion of precise time and frequency measurement

[jimlux]

On 11/13/17 9:32 AM, Gregory Beat wrote:

I grew up east of the Iowa/Missouri border, so this boundary dispute was 
well-known ... and occurred at same time Joseph Smith (Mormons) was at Nauvoo, 
IL (1839-1844).
In 2006, the Iowa-Missouri border was investigated with GPS, as much an archeology 
project as locating the historic Sullivan & Brown survey markers.
http://www.theamericansurveyor.com/PDF/TheAmericanSurveyor_MO-IABoundaryLineInvestigation_Mar-Apr2006.pdf
Iowa-Missouri Border War (1826-1849)
http://iagenweb.org/history/soi/soi32.htm

NOAA’s : National Geodetic Survey (NGS) made news in 2009 when media reported 
that the Four Corners monument was in wrong place (by 2.5 miles).
Deseret News
https://www.deseretnews.com/article/705299160/Four-Corners-Monument-is-indeed-off-mark.html
NOAA statement and clarification
https://www.ngs.noaa.gov/INFO/fourcorners.shtml
==
I’m in France and I don’t think that any borders in Europe were defined by 
astronomical observation, but in the US I believe that at least some of the 
state borders were thus fixed. As a second’s error in time will be about a 
nautical mile in US latitudes, I wonder if anyone has measured with GPS, how 
good the original surveys were?





Googling "cadastral survey" would be how you'd find out.

There's also a famous case of the border between New Mexico and Colorado 
being crooked because of poor surveying, but the monuments define the 
border not the words in the laws defining the border.

http://www.denverpost.com/2007/08/02/were-not-so-square-after-all/
https://supreme.justia.com/cases/federal/us/267/30/case.html

Same with the border between Utah and Colorado.

The increased use of GPS has made it trivial to go out and find a 
particular position - but remember - it's the monument that controls the 
location and boundary, not the coordinates.  My house sits on a lot 
where the corners are defined relative to some physical monumentation (a 
brass disk nailed to the sidewalk typically,with a dimple in the nail 
head) - so as my house gradually drifts north a few cm/year, I don't 
have to worry about the line shifting.


Sometimes this "tied to the monument" thing breaks down - and that's 
what court cases are made of.



In any case, most of the state boundaries in the western United States 
were done with astronomical measurements.  Probably using a chronometer 
for time, as opposed to using lunar occultation of stars.


The Commissioner of the General Land Office employed Ehud N. Darling, a 
surveyor and astronomer, to make this survey. He made the survey in 
1868, and filed his field notes in the Land Office. In accordance with 
his instructions, he adopted as the northeast corner of New Mexico a 
stone monument that had been established by Capt. J. N. Macomb, an Army 
Engineer, in 1859, to mark the intersection of the 37th parallel with 
the 103d meridian, and, taking this as his beginning point, surveyed and 
marked the line of the parallel, as determined by astronomical 
observations and calculations for latitude, westwardly to the 109th 
meridian, a distance of over 331 miles. ...


Several years later, the Commissioner of the General Land Office 
employed John J. Major, a surveyor and astronomer, to survey and mark 
the remaining portion of the southern boundary of the Territory of 
Colorado, extending along the 37th parallel to the 102d meridian. Major 
made this survey in 1874, and marked the line of the parallel between 
the Macomb monument and that meridian. The field notes of this survey 
were filed in the Land Office and approved by the Commissioner.


and so on over the next 20-30 years

This kind of surveying was hard work: hostile native americans attacking 
survey parties, wildlife (lions, bears, etc.).  The wildlife problem 
wasn't quite as bad as tigers eating surveyors in India doing the Great 
Trigonometric Survey.




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Re: [time-nuts] GPS III

[jimlux]

On 11/12/17 10:22 PM, Magnus Danielson wrote:

Hi Don,

Hardly. As long as you do GPS L1 C/A code only, chanses you get any 
useful improvement isn't all that great. SBAS may help you some thought.





the new L1C code plus increase in radiated power might help

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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[jimlux]

On 11/7/17 8:39 PM, Gary E. Miller wrote:

Yo Tom!

On Tue, 7 Nov 2017 20:16:09 -0800
"Tom Van Baak"  wrote:


Which is small compared to the published GPS time resolution
(IS_GPS_200H, page 54) of 90 ns.


Correct. GPS performs far better than the original spec. Like the
Mars rovers...


Of course, but then you are on a wing and a prayer, not engineering.


Not really - the original spec for GPS was based on being able to track 
to a single chip of the PN code at 1 MHz, or about 300m position error, 
and 30m for the precise code at 10MHz.


And that was the limit of the technology back in the late 70s early 80s
A fancy multichannel correlator was literally a rack of equipment, and 
things like RAKE receivers to deal with multipath were the subject of 
papers in IEEE transactions - hardly a "buy it at the hardware store"


What has changed, and what's sort of amazing, given that the GPS signal 
hasn't really changed much is that technology has made substantial 
advances,  both in terms of silicon and in terms of the algorithms.


It is easy now to have a 64 simultaneous channel correlator that 
trivially tracks to a fraction of a chip and also recovers the carrier 
phase.  Codeless receivers allow tracking of the higher rate code, and 
today, a L1 only receiver is sort of a legacy oddity - perhaps because 
it has some peculiarity for a particular system, or a "drive every tenth 
of a penny out of the system cost" item.


Back in "30 m CEP" days who cared about the fact that the receive 
antenna phase center wasn't the same for all look angles.  Today, folks 
go out and extensively calibrate these things, and build antennas where 
the phase center is "stable" to 1 mm or better.



We've got much, much better analytical tools to process the data - folks 
regularly process long collections of data from inexpensive receivers 
where one has to account for things like solid earth tides, not to 
mention continental drift.  My house in Southern CA is steadily heading 
north a few cm/year. That's actually measureable with equipment you 
could reasonably buy for under $1000 (I think.. you might be able to do 
it for under $100)



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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[jimlux]

On 11/7/17 1:44 PM, MLewis wrote:

Yo Gary!

With a strictly SSE skyview, I still regularly get signals from sats to 
my NW. When they're at the right elevation and heading, their signals 
pass over me and reflect back at me from a tall building. When running 
my M8T with the position unlocked, and those NW sats are getting a 
reflection and reporting in, (although the reflecting building is 
further away to the SE) my GPS position drifts up to 300' to my south (S 
of SSE). (reported position goes for a walk, staggering across the 
parking lot, wanders through a park with an occasional loop, across a 
road, then sits down for a while, before wandering back)


Is it reasonable to use the 9" ~= 1 ns for:
running with a fixed & correct survey position, and NW sats reflecting a 
signal to me, that 300' drift would equate to a (300' x 12") /  9" = 
400, for a ballpark 400 ns error?




No.. in free space it's about a foot per nanosecond.. 9" is 0.75 
velocity factor, reasonable for coax, for instance, depending on the 
dielectric.





Thanks,

Michael

On 07/11/2017 3:40 PM, Gary E. Miller wrote:

Yo Lars!

On Tue, 7 Nov 2017 20:32:19 +
Lars Walenius  wrote:


Another question: If You have an error in the surveyed position of
say 3meters and you receive all of the available satellites in all
directions how much will this really affect your timing?

I'll oversimply a bit by repeating Adm. Grace Hoppers famous giveaway.
When asked, she handed out 9 inch long peieces of wire, and said: that
is a nanaosecond.

3m is about 118.11 inches is about 13 ns.  So worst case, skipping the
3D math, yoy get about +/13 ns.

Which is small compared to the published GPS time resolution 
(IS_GPS_200H,

page 54) of 90 ns.

RGDS
GARY
--- 


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

    Veritas liberabit vos. -- Quid est veritas?
 "If you can’t measure it, you can’t improve it." - Lord Kelvin


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[jimlux]

On 11/7/17 1:30 PM, Ole Petter Ronningen wrote:

Not knowing better, I would expect there to be diurnal effects due to the
ionospere being in the shade or not. I suspect there are people on this
list that know better.

Anyway, the effect I am seeing is also very slowly drifing, see screenshot
of about 20 days of data below. The daily variation varies quite a bit. I
am not sure this can be explained by ionospheric activity, but then again I
dont know much about what goes on up there.

As mentioned, I also have L1/L2 data from the same period, I believe it is
possible to extract or at least estimate the Total Electron Content from
that data somehow, but I do not know how - it gets pretty arcane pretty
quickly for a layman.

Ole



http://www.navipedia.net/index.php/Ionospheric_Delay
has a nice discussion with simple equations to turn TEC into delay, etc.


You might also look into seeing if you can put your data in a form to be 
processed by GIPSY at JPL - they have a service where you can upload 
your raw observables and they post process it.


https://gipsy-oasis.jpl.nasa.gov/



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Re: [time-nuts] Oscillators and Ovens

[jimlux]

On 11/1/17 1:38 PM, Hal Murray wrote:



In general, OCXOs have crystals with high Q -> low phase noise,  especially
compared to a TCXO, which *can't* have high Q, or the  temperature
compensation circuit can't do it's work.


I don't understand that.  Why can't I build a high Q TCXO?  I don't need to
change the compensation very fast.  Are good crystals high enough Q that it
would take too long?


Think of the oscillator as an amplifier and a high Q mechanical filter - 
it gets the Q from being mechanically stiff.


In order to move the frequency, you have to electrically push it, which 
is counter to the mechanical stiffness.  You just don't have the tuning 
range available.


We struggled on a project to build a high Q, but adjustable DRO, and 
that was the fundamental problem.





What's the time constant?  I'd guess it's Q/freq, maybe with factors of 2pi
or e or ???

That seems small relative to how fast temperature changes.  (but maybe fast
relative to FCC smearing or things like that)




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Re: [time-nuts] Designing an embedded precision GPS time

[jimlux]

On 11/1/17 12:13 PM, Adrian Godwin wrote:

How do those compare with vectron's part : ?

https://www.vectron.com/products/ocxo/mx-503.htm



That part is interesting, but the phase noise (-124 dBc @ 100 Hz) isn't 
particularly impressive compared to a middle of the road OCXO (-155dBc 
at 100Hz)


The frequency stability is very nice, compared to a TCXO, and at a LOT 
less power (40mW) than the OCXO (2W after warmup).




There's also this patent.

http://www.google.sr/patents/US20020005765

I don't really know if that's valid - it seems to propose something similar
to the numerically-compensated oscillator in my rather old PM frequency
counter.



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Re: [time-nuts] Oscillators and Ovens

[jimlux]

On 11/1/17 10:59 AM, Attila Kinali wrote:

Hi Jim,

On Wed, 1 Nov 2017 06:17:31 -0700
jimlux <jim...@earthlink.net> wrote:


That's why I wish they'd sell OCXOs, cheap, without the oven. Or maybe
look for regular XO (no TC).  Those might have a more "pure" (read lower
order) freq vs temp characteristic.



It feels like I have asked this before, but I cannot remember and
cannot find the mailSo: What do you mean by "OCXO without oven?"




I often have requirements for "good phase noise" but no particular 
requirement for "good temperature stability" or Allan Deviation for tau 
> 200 seconds - we get frequency knowledge from other sources (e.g. 
just like a GPSDO, or it can be inferred from the measurement)
I often have a system where the environment is pretty benign - a typical 
on-orbit temperature variation might be a degree or two over 90 minutes 
(or longer), if that - we don't know what the temperature will be (in 
advance), but once it's up there, it's pretty stable.  Maybe the temp 
changes a bit due to relative orientation to the sun and similar 
effects, so there's a annual variation.  My current spacecraft is 
expected to change maybe 5-6 degrees over the year.


For instance, in a software defined radio, the input oscillator is often 
fed into some sort of NCO or DDS for tuning - knowledge of the frequency 
is what you really want, because the ultimate requirement is on the 
frequency accuracy at the input or output of the radio - the regulators 
care not a whit what kind of oscillator is inside (well, they DO ask on 
the license application, but it's really not relevant)


THere are also systems like Doppler radars - they need good pulse to 
pulse stability, and low phase noise to avoid reciprocal mixing 
degradation of the noise floor - but they care not what the exact 
frequency is.


In general, OCXOs have crystals with high Q -> low phase noise, 
especially compared to a TCXO, which *can't* have high Q, or the 
temperature compensation circuit can't do it's work.


So, it would be nice to have a *cheap* lowish power packaged part that 
has the Q of an OCXO, but without the power consumption of the oven 
(typically measured in watts).


yeah, I'd be operating it *way* far from the optimum turnover temp, so 
the tempco might be huge (in oscillator terms), but I don't really care 
- in fact, that might give me a way to measure the temperature of the 
system.


I have gotten quotes for OCXOs with the oven disabled-  but that's 
making it a custom part and as Bob has pointed out, the moment you 
deviate from the "catalog part", the cost (and often more importantly, 
the delivery time) goes up.


I think the ideal, of course, is to get an oscillator high performance 
crystal cut with the turnover temp around 20-30C - useless for a OCXO, 
but might be real useful for GPS/temp compensated oscillator where the 
oscillator drives a DDS (or or provides an output giving the estimated 
frequency).




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Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

[jimlux]

On 11/1/17 7:37 AM, Magnus Danielson wrote:

Hi,


 Silly people
want a relative comfortable temperature and well, building A/C is 
typically bang/bang regulated so you get what you paid for.






wouldn't a true time-nut be in a basically isothermal cave at 10C far 
underground, and just follow the classic mother's advice "put on a 
sweater if you feel cold"



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Re: [time-nuts] Designing an embedded precision GPS time

[jimlux]

On 11/1/17 6:01 AM, Bob kb8tq wrote:

Hi

Unfortunately not all TCXO’s are created equal. It depends a bit on the
original intended use. I’d bet it also depends a bit on the original target
price. Perturbations  (frequency jumps) over temperature are one “feature”
that might be present. Hysteresis at half the temperature spec is another
“feature”.

Even within the same batch or same test run, some will be much better
than others. You stop the compensation process when they get “good enough”.
That will mean that a few are right at whatever the production target is and
others exceed the target by quite a bit.

While crystal curves are indeed cubic, there are higher order terms in the
curve. The “why” is something people get to write papers on.If you are trying
to compensate to tight specs, you will see all sorts of stuff. It is not at all 
uncommon
to see >9th order curves residual curves. Indeed some of that is from residuals
in the compensation circuit as well as from the crystal.

Why all this yack? A lot of people come from a background using OCXO’s. An
OCXO generally has a low order temperature characteristic. It also is rare to 
see
things like frequency perturbations in an OCXO. Moving from one to the other
can be a bit interesting.



Indeed - I was looking at algorithmically compensating some cheap TCXOs 
and there's an amazing spread in the "details" of the curves - sure, 
they all met the spec (several ppm, as I recall), but it was clear after 
very little testing that there was no "one algorithm to fit them all"


As you say, good grist for a paper or thesis project.

That's why I wish they'd sell OCXOs, cheap, without the oven. Or maybe 
look for regular XO (no TC).  Those might have a more "pure" (read lower 
order) freq vs temp characteristic.


The problem I see with regular XO is that they tend to be designed to a 
cost point and there might be more of the hysteresis and mechanical 
effects - if you're not claiming better than 100ppm, then 50 ppm of 
hysteresis isn't a problem.


A 1ppb OCXO is going to have to be a better mechanical design - so that 
it can hit that 1ppb every time when you turn the oven on and go from 
cold to hot.



Maybe this is just griping in general - why don't mass production 
manufacturers make exactly the niche part I want to buy (that is of no 
use to anyone else)for $3 each


I suppose if you were going to build little algorithmically compensated 
modules, you'd bite the bullet and design a crystal oscillator and then 
YOU get to choose what crystal in what mount etc.


When all is said and done, the production cost for a design that uses a 
crystal in a can plus half a dozen discrete devices to make an 
oscillator is probably not a lot different than the production cost for 
a design using an oscillator in a can.  it's the "other stuff" in the 
design that will add up.











Bob




On Oct 31, 2017, at 10:42 PM, jimlux <jim...@earthlink.net> wrote:

On 10/31/17 1:47 PM, Bob kb8tq wrote:

HI
TCXO is a very loosely defined term. A part that does +/- 5 ppm -40 to +85C
is a TCXO. A part that does +/- 5x10^-9 over 0 to 50C may also be a TCXO.
Dividing the total deviation of either one by the temperature range to come
up with a “delta frequency per degree” number would be a mistake. You
would get a number that is much better than the real part exhibits.
Working all this back into a holdover spec in an unknown temperature
environment is not at all easy.


Very much so - most of the TCXO curves I've seen tend to be "much" better than 
the spec over the central part of the frequency range (which makes sense, the underlying 
crystal is a cubic with temp, most likely)

Retrace and hysteresis might be your dominant uncertainty.
I've attached a typical TCXO data plot for your viewing pleasure..
(that's an expensive oscillator, because it's for space, but I don't think 
space or not changes the underlying performance)



Bob

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Re: [time-nuts] Designing an embedded precision GPS time

[jimlux]

On 10/31/17 1:47 PM, Bob kb8tq wrote:

HI

TCXO is a very loosely defined term. A part that does +/- 5 ppm -40 to +85C
is a TCXO. A part that does +/- 5x10^-9 over 0 to 50C may also be a TCXO.

Dividing the total deviation of either one by the temperature range to come
up with a “delta frequency per degree” number would be a mistake. You
would get a number that is much better than the real part exhibits.

Working all this back into a holdover spec in an unknown temperature
environment is not at all easy.



Very much so - most of the TCXO curves I've seen tend to be "much" 
better than the spec over the central part of the frequency range (which 
makes sense, the underlying crystal is a cubic with temp, most likely)


Retrace and hysteresis might be your dominant uncertainty.
I've attached a typical TCXO data plot for your viewing pleasure..
(that's an expensive oscillator, because it's for space, but I don't 
think space or not changes the underlying performance)




Bob




TCXODataVectron 47.pdf
Description: Adobe PDF document
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Re: [time-nuts] NEO-7M various modes

[jimlux]

On 10/28/17 3:24 PM, Wayne Holder wrote:

uBlox has a utility called u-center
<https://www.u-blox.com/en/product/u-center-windows> that's a free
download.  You can use it to configure the various output options (and
enable and disable different messages) and a then save this config back to
the module as the start up default.

Downloaded it, hooked up the modules, found that they won't quite get a 
fix indoors next to the window, but if I take it outside, it will. 
Oddly, the SNR on the SVs is good enough, but there's something 
preventing the fix from happening.


Maybe it's because it's a cold start, it needed to run for a while to 
acquire the almanac or something.







Wayne

On Sat, Oct 28, 2017 at 3:12 PM, jimlux <jim...@earthlink.net> wrote:


I've got 4 NEO-7M-C modules hooked up to 7 beaglebone greens, side by
side, and they're not behaving the same..

I've got gpsd running, and I'm looking at the output of cgps and/or
gpsmon, as well as ppstest


Some emit NMEA sentences, others binary (ublox?) strings?

Some get a fix and start toggling the 1pps line, others don't.

Is there some command string one can send to them to put them into a known
state (cold reset?) - the one that's working the best (I.e. has a fix AND
toggles 1pps) seems to be putting out binary strings (when viewed with
gpsmon).


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[time-nuts] NEO-7M various modes

[jimlux]

I've got 4 NEO-7M-C modules hooked up to 7 beaglebone greens, side by 
side, and they're not behaving the same..


I've got gpsd running, and I'm looking at the output of cgps and/or 
gpsmon, as well as ppstest



Some emit NMEA sentences, others binary (ublox?) strings?

Some get a fix and start toggling the 1pps line, others don't.

Is there some command string one can send to them to put them into a 
known state (cold reset?) - the one that's working the best (I.e. has a 
fix AND toggles 1pps) seems to be putting out binary strings (when 
viewed with gpsmon).



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Re: [time-nuts] chrony vs ntpd

[jimlux]

On 10/28/17 2:25 PM, djl wrote:

Would a step recovery diode be better?
for example 
http://www.mwrf.com/analog-semiconductors/designing-step-recovery-diode-based-comb-generator 



Maybe, but that's starting to increase the complexity.  I've used 
various and sundry harmonic mixers using SRDs (aka Sampling Phase 
Detectors)  The SRD has very fast transition times, so getting well up 
into microwave is easy.


For my application, I'm happy down at 15 MHz, and a reasonably fast rise 
time on a 1 microsecond pulse does it quite nicely.

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Re: [time-nuts] chrony vs ntpd

[jimlux]

On 10/28/17 10:34 AM, John Ackermann N8UR wrote:
Jim, I thought about using an RF-input sync pulse for alignment during 
the Solar Eclipse measurement experiment, but ended up running out of 
time to implement it.  But some very crude experiments indicated that 
it's not hard to generate an edge out of a PPS that creates a comb well 
past HF.  My idea was to do a divide-by-sixty to end up with 
pulse-per-minute rather than PPS.  The lower rate would be less annoying 
to filter out of the results.


I'm interested to hear if you end up doing this, and if so how.



Yes, a nice narrow pulse makes a nice comb.  I've done it for a single 
shot wideband gain calibration across the band for my space HF receiver 
(in ground test).


The tricky parts, I have found, are:
1) the rise and fall time have a big effect on the relative heights of 
the comb vs freq - perfectly square gives you a nice sin(x)/x, but if it 
starts to be not-square, then it rolls off faster.  I've been thinking 
about how to do something that measures it


2) Amplitude of the pulse - that one seems pretty straightforward - a 
good switch from a regulated voltage.


3) The effects of the antenna and receiver impedances - well - to a 
certain extent, that's what I want to measure.   So the idea is that if 
you inject a pulse through a known resistance into the receiver/antenna 
combination (at the receiver input), and, I do this at two or three 
different impedances, I should be able to back out the impedance effects 
(with some TBD uncertainty).



So far, I've been experimenting with RF tone bursts from a 33622 
function generator - Easy to detect, but I've not found a good way to 
get a nice sharp marker - you can slide a matched filter along and get a 
sort of pulse, but it's not what I want.


I'm starting to think that some sort of PN code might be the way to go - 
It makes it easy to integrate over a longer time (e.g. many edges to 
look at).






John


On 10/28/2017 12:04 PM, jimlux wrote:
Now that I have successfully connected my GPS receiver to my beagle 
and I'm getting pps ticks into the driver, etc. (thanks to info from 
several folks on this list!) the question arises of whether to use 
ntpd or chrony.


For my particular application, I'm more interested in synchronizing 
time on the local machine, not necessarily being a NTP server - all of 
my beagles have a GPS on them.  Of course, there may be times when a 
GPS doesn't work, or something else comes up where it would be useful 
for one of the machines to "get time" from somewhere else.


What I am doing is using the Beagle to capture RF samples (RTL-SDR) in 
a distributed array, with wireless connections among the nodes.  The 
processing isn't necessarily real-time (maybe later..), for now, it's 
"trigger some seconds of capture at approximately the same time" and 
post process in matlab/octave.


There's all kinds of nondeterministic latency issues with the 
USB/RTL-SDR path, so I'm under no illusion that I can capture samples 
aligned to the 1pps.  However, what I *can* do is generate a "sync 
pulse" from the 1 pps and feed it into the RTL's RF input in some 
(TBD) way.
And the 1pps might give me a clever way to calibrate the frequency 
drift of the RTLSDR's clock.


Right now, I'm interested in HF signals (so the period is 30 ns at the 
top end, and 500 ns at the bottom end)




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