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

[Hal Murray]

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

Flux seems unlikely to produce a sudden failure.

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




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Re: [time-nuts] Datametrics SP-100 Time Code Generator

[Dave ZL3FJ]

Correct, Dan- nothing received-still interested though, if something pops up. 
Unit is still here and a friend has a sidereal version but no data.
DaveB, NZ

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Dan Veeneman
Sent: Saturday, May 12, 2018 11:38
To: time-nuts@febo.com
Subject: [time-nuts] Datametrics SP-100 Time Code Generator

Hello,

I'm looking for a schematic and/or service manual for a Datametrics SP-100, a 
1970s-era rack-mount IRIG time code generator.  According to the Time Nuts 
archives, Dave Brown (ZL3FJ) was looking for this information back in 2005 but 
as far as I can see received no reply.  I have found references to its use in a 
timing distribution system but haven't found service information that would 
allow component level repair.

Does anyone have, or know of a source for, technical information on this unit?


Thanks!


Cheers,

Dan



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[time-nuts] Possibly interesting book

[lstosk...@cox.net lstosk...@cox.net]

WSJ had review of The Perfectionists by Simon Winchester May 5-6( Books).  
Sounds right up this group's alley.  As the reviewer states, it: corrals a 
large cast of eccentric individuals."  Many of which it might have been fun to 
spend time with.   I've read a few of his other 29 books and most are an 
interesting ride.  I have one on order.  N0UU
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Re: [time-nuts] Anybody have suggestions for time related science fair projects?

[Brooke Clarke]

Hi:

Here's some great ideas from Clifford Stoll:
https://www.ted.com/talks/clifford_stoll_on_everything?language=en
The transcript is available in 27 languages.

PS He has an on line business selling Klein Bottles (some with calibration 
certificates:)
http://www.kleinbottle.com/

I got a Chinese Spouting Bowl from him.
http://www.prc68.com/I/ChineseSpoutingBowl.shtml

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html


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

[Larry McDavid]

Thanks, Dave, for reporting your failed GPS antenna; at least, I am not 
alone in having this failure.


It will be interesting to understand what you find when you open your 
failed 58532A. Removing the radome is very easy, just 4 screws and some 
wiggling or gentle prying. If yours does not have the metal shield-can 
over the coax termination, a quick look at the coax solder joints for 
old flux will confirm or refute that as the likely failure cause. If 
your antenna has the shield-can and you see no flux around its soldered 
tabs, there likely is no flux problem.


Perhaps 1-2 years ago Symmetricom offered here a deep discount on this 
antenna, clearing their stock; presumably they have something newer. The 
antennas with the shield-can are from my purchase from Symmetricom of 
several of these antennas. The 58532A that failed is at least 10 years 
old so they must have made an in-line design change without changing the 
part number.


If you do remove the PWB, you will find the RF circuit rather obvious 
and even rectilinear in layout. All the parts are SMT. Two of the three 
amplifier chips are the same, as are two of the three bandpass filters. 
The first amplifier and the first bandpass filter are unique.


My primary goal in writing this narrative was to help someone who also 
had a similar antenna failure. I've heard now from several who have. If 
the fix is as simple as old flux removal, the antennas can probably be 
salvaged.


When I first tested the repaired antenna, I used a 5 vdc GPS device and 
that was successful. Later, I used another GPS device that puts only 3.3 
vdc to the antenna and that worked ok also, with no noticeable 
difference in performance. Note that the Symmetricom spec rates the 
antenna at 5 vdc input.


Larry W6FUB


On 5/12/2018 3:17 PM, Artek Manuals wrote:

Larry
Thanks for the analysis... I too have a failed 58532A which died  a year 
ago . which I had not bothered to disassemble yet..The weather guessers 
are predicting rain all week net week so maybe I will find an 
opportunity to comp[are my findings to yours


Do you have a schematic for the board or is the layout so simple that it 
is self evident once you look at the board?


Stay tuned for film at 11

-DC
de NR1DX
manu...@artekmanuals.com

On 5/12/2018 4:07 PM, Larry McDavid wrote:
I recently had an unexpected failure of a white-conical-dome 
HP/Symmetricom 58532A GPS antenna..


--
Best wishes,

Larry McDavid W6FUB
Anaheim, California  (SE of Los Angeles, near Disneyland)
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Re: [time-nuts] Anybody have suggestions for time related science fair projects?

[Wayne Holder]

Using a pendulum to measure gravity requires precision timekeeping.
Wikipedia has a nice discussion of this at
https://en.wikipedia.org/wiki/Pendulum#Gravity_measurement

There are number of very clever techniques developed long ago, such as
Henry Kater's design for a reversible, dual pivot pendulum that made it
possible to get quite precise measurements starting about the 1820s.  Then,
around 1835 Friedrich Bessel found ways to simplify calibration of Kater's
design and even cancel out errors due to air drag.  More interestingly,
gravity measuring pendulums became not of the earliest ways used to
standardize the measure of length, which shows how nearly all efforts at
standardization ultimately rely on accurate timekeeping.

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

[Bruce Griffiths]

At telecom wavelengths GDD can be quite low.
Laser source spectral widths can also be low.
At visible wavelengths an fiber length imbalance of 1m with a 1nm bandwidth 
light source makes interferometry impossible/difficult without GDD compensation 
even if delays are matched.
The moodulation bandwidth isnt an issue for this application but with a long 
enough fiber the source spectral bandwidth may be.
Polarisation locked single transverse mode VCSELs are inexpensive and typically 
have spectral bandwidths of 100MHz or so.


Bruce
> On 13 May 2018 at 11:31 Dana Whitlow  wrote:
> 
> 
> Indeed; however, with single mode fiber the limit is not too bad.  At
> Arecibo we routinely ran bandwidths in
> excess of 1 GHz through fibers of about 1500 ft length with no problems.
> For the science fair project a
> bandwidth of a few MHz should suffice for lengths of, say, 500 ft.  It's
> just that I don't know how bad the
> multimode dispersion problem would be when using shorter wavelengths, and
> I'm sure not equipped to
> make any measurements at home now that I'm retired and far away from the
> observatory.
> 
> Dana
> 
> 
> On Sat, May 12, 2018 at 5:44 PM, Bruce Griffiths  > wrote:
> 
> > Even with single mode fiber its finite group delay dispersion will likely
> > restrict the usable light source bandwidth.
> >
> > Bruce
> > > On 13 May 2018 at 03:38 Dana Whitlow  wrote:
> > >
> > >
> > > It may  be that a nicely-written request to Corning could yield the loan
> > of
> > > a big spool of fiber
> > > for the duration of a science fair project.
> > >
> > > Another alternative, perhaps easier to implement, might be an
> > > electrically-driven light modulator
> > > at the detector end.  For the source, an LED or diode laser is easy to
> > > modulate at respectable
> > > rates.  This approach should allow use of such high frequencies that an
> > > open optical path using
> > > mirrors might even suffice.
> > >
> > > Or here's an intermediate scheme:
> > > If one were to use two modulated sources (or one with a beamsplitter),
> > with
> > > one path delayed
> > > by the long(ish) fiber and the other by a minimal-length local fiber,
> > > something resembling a streak
> > > camera (implemented with a rotating mirror) might permit use of
> > > substantially higher pulse rates
> > > than with a rotating disk, without incurring the need for anything very
> > > fancy in the way of mechanics.
> > > Only the modulated source should require a reasonably accurate drive
> > > frequency- the "detector"
> > > would be essentially self-calibrating.  A small mirror, say of cm size,
> > > could probably be safely
> > > rotated at Dremel speeds approaching 500 rev/s, and if 1 mrad angular
> > > resolution is attained,
> > > this would yield a resolution of ~160 ns.  So a fiber length of 500 ft
> > > (approx 750 ns one-way delay)
> > > should yield an angular separation of nearly five "dots" between delayed
> > > and undelayed dots.
> > > And if the sources are modulated at a rate such that a few pulse
> > > repetitions are visible in the
> > > field of view, the scheme is self-calibrating as long as the PRF and the
> > > velocity factor in the fiber
> > > are known.  Probably the only precision work would be the optics required
> > > to focus a reasonable
> > > amount of light from the source(s) onto the two fibers., and I believe
> > this
> > > requirement could be
> > > adequately met with microscope objectives borrowed from one's school's
> > > biology lab.
> > >
> > > A fly in the ointment is that if ordinary (read, inexpensive) IR fiber is
> > > used at convenient visible
> > > wavelengths, propagation will occur in more than one spatial mode, with
> > > different modes propagating
> > > at different speeds.   I don't know how much of a problem this would
> > > raise.  But it may be that if
> > > tweaking of the transmitting end illumination is done, both in angle and
> > > transverse position, most
> > > of the propagating light could be confined to a single mode.  I speak of
> > > visible wavelengths simply
> > > because using these avoids the cost of electronic detectors,
> > oscilloscopes,
> > > etc, potentially saving
> > > a lot on the cost of the experiment as well as making for a more
> > satisfying
> > > presentation.
> > >
> > > Dana
> > >
> > >
> > > On Sat, May 12, 2018 at 9:45 AM, Bob kb8tq  wrote:
> > >
> > > > Hi
> > > >
> > > >
> > > >
> > > > > On May 12, 2018, at 7:01 AM, jimlux  wrote:
> > > > >
> > > > > 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 

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

[Adrian Godwin]

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.


On Sun, May 13, 2018 at 12:31 AM, Dana Whitlow 
wrote:

> Indeed; however, with single mode fiber the limit is not too bad.  At
> Arecibo we routinely ran bandwidths in
> excess of 1 GHz through fibers of about 1500 ft length with no problems.
> For the science fair project a
> bandwidth of a few MHz should suffice for lengths of, say, 500 ft.  It's
> just that I don't know how bad the
> multimode dispersion problem would be when using shorter wavelengths, and
> I'm sure not equipped to
> make any measurements at home now that I'm retired and far away from the
> observatory.
>
> Dana
>
>
> On Sat, May 12, 2018 at 5:44 PM, Bruce Griffiths <
> bruce.griffi...@xtra.co.nz
> > wrote:
>
> > Even with single mode fiber its finite group delay dispersion will likely
> > restrict the usable light source bandwidth.
> >
> > Bruce
> > > On 13 May 2018 at 03:38 Dana Whitlow  wrote:
> > >
> > >
> > > It may  be that a nicely-written request to Corning could yield the
> loan
> > of
> > > a big spool of fiber
> > > for the duration of a science fair project.
> > >
> > > Another alternative, perhaps easier to implement, might be an
> > > electrically-driven light modulator
> > > at the detector end.  For the source, an LED or diode laser is easy to
> > > modulate at respectable
> > > rates.  This approach should allow use of such high frequencies that an
> > > open optical path using
> > > mirrors might even suffice.
> > >
> > > Or here's an intermediate scheme:
> > > If one were to use two modulated sources (or one with a beamsplitter),
> > with
> > > one path delayed
> > > by the long(ish) fiber and the other by a minimal-length local fiber,
> > > something resembling a streak
> > > camera (implemented with a rotating mirror) might permit use of
> > > substantially higher pulse rates
> > > than with a rotating disk, without incurring the need for anything very
> > > fancy in the way of mechanics.
> > > Only the modulated source should require a reasonably accurate drive
> > > frequency- the "detector"
> > > would be essentially self-calibrating.  A small mirror, say of cm size,
> > > could probably be safely
> > > rotated at Dremel speeds approaching 500 rev/s, and if 1 mrad angular
> > > resolution is attained,
> > > this would yield a resolution of ~160 ns.  So a fiber length of 500 ft
> > > (approx 750 ns one-way delay)
> > > should yield an angular separation of nearly five "dots" between
> delayed
> > > and undelayed dots.
> > > And if the sources are modulated at a rate such that a few pulse
> > > repetitions are visible in the
> > > field of view, the scheme is self-calibrating as long as the PRF and
> the
> > > velocity factor in the fiber
> > > are known.  Probably the only precision work would be the optics
> required
> > > to focus a reasonable
> > > amount of light from the source(s) onto the two fibers., and I believe
> > this
> > > requirement could be
> > > adequately met with microscope objectives borrowed from one's school's
> > > biology lab.
> > >
> > > A fly in the ointment is that if ordinary (read, inexpensive) IR fiber
> is
> > > used at convenient visible
> > > wavelengths, propagation will occur in more than one spatial mode, with
> > > different modes propagating
> > > at different speeds.   I don't know how much of a problem this would
> > > raise.  But it may be that if
> > > tweaking of the transmitting end illumination is done, both in angle
> and
> > > transverse position, most
> > > of the propagating light could be confined to a single mode.  I speak
> of
> > > visible wavelengths simply
> > > because using these avoids the cost of electronic detectors,
> > oscilloscopes,
> > > etc, potentially saving
> > > a lot on the cost of the experiment as well as making for a more
> > satisfying
> > > presentation.
> > >
> > > Dana
> > >
> > >
> > > On Sat, May 12, 2018 at 9:45 AM, Bob kb8tq  wrote:
> > >
> > > > Hi
> > > >
> > > >
> > > >
> > > > > On May 12, 2018, at 7:01 AM, jimlux  wrote:
> > > > >
> > > > > 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 

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

[Dana Whitlow]

Indeed; however, with single mode fiber the limit is not too bad.  At
Arecibo we routinely ran bandwidths in
excess of 1 GHz through fibers of about 1500 ft length with no problems.
For the science fair project a
bandwidth of a few MHz should suffice for lengths of, say, 500 ft.  It's
just that I don't know how bad the
multimode dispersion problem would be when using shorter wavelengths, and
I'm sure not equipped to
make any measurements at home now that I'm retired and far away from the
observatory.

Dana


On Sat, May 12, 2018 at 5:44 PM, Bruce Griffiths  wrote:

> Even with single mode fiber its finite group delay dispersion will likely
> restrict the usable light source bandwidth.
>
> Bruce
> > On 13 May 2018 at 03:38 Dana Whitlow  wrote:
> >
> >
> > It may  be that a nicely-written request to Corning could yield the loan
> of
> > a big spool of fiber
> > for the duration of a science fair project.
> >
> > Another alternative, perhaps easier to implement, might be an
> > electrically-driven light modulator
> > at the detector end.  For the source, an LED or diode laser is easy to
> > modulate at respectable
> > rates.  This approach should allow use of such high frequencies that an
> > open optical path using
> > mirrors might even suffice.
> >
> > Or here's an intermediate scheme:
> > If one were to use two modulated sources (or one with a beamsplitter),
> with
> > one path delayed
> > by the long(ish) fiber and the other by a minimal-length local fiber,
> > something resembling a streak
> > camera (implemented with a rotating mirror) might permit use of
> > substantially higher pulse rates
> > than with a rotating disk, without incurring the need for anything very
> > fancy in the way of mechanics.
> > Only the modulated source should require a reasonably accurate drive
> > frequency- the "detector"
> > would be essentially self-calibrating.  A small mirror, say of cm size,
> > could probably be safely
> > rotated at Dremel speeds approaching 500 rev/s, and if 1 mrad angular
> > resolution is attained,
> > this would yield a resolution of ~160 ns.  So a fiber length of 500 ft
> > (approx 750 ns one-way delay)
> > should yield an angular separation of nearly five "dots" between delayed
> > and undelayed dots.
> > And if the sources are modulated at a rate such that a few pulse
> > repetitions are visible in the
> > field of view, the scheme is self-calibrating as long as the PRF and the
> > velocity factor in the fiber
> > are known.  Probably the only precision work would be the optics required
> > to focus a reasonable
> > amount of light from the source(s) onto the two fibers., and I believe
> this
> > requirement could be
> > adequately met with microscope objectives borrowed from one's school's
> > biology lab.
> >
> > A fly in the ointment is that if ordinary (read, inexpensive) IR fiber is
> > used at convenient visible
> > wavelengths, propagation will occur in more than one spatial mode, with
> > different modes propagating
> > at different speeds.   I don't know how much of a problem this would
> > raise.  But it may be that if
> > tweaking of the transmitting end illumination is done, both in angle and
> > transverse position, most
> > of the propagating light could be confined to a single mode.  I speak of
> > visible wavelengths simply
> > because using these avoids the cost of electronic detectors,
> oscilloscopes,
> > etc, potentially saving
> > a lot on the cost of the experiment as well as making for a more
> satisfying
> > presentation.
> >
> > Dana
> >
> >
> > On Sat, May 12, 2018 at 9:45 AM, Bob kb8tq  wrote:
> >
> > > Hi
> > >
> > >
> > >
> > > > On May 12, 2018, at 7:01 AM, jimlux  wrote:
> > > >
> > > > 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 

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

[MLewis]

Would it be too simple a project to have a GPS demonstration:

 * GPS time, leap seconds (need for)
 * UTC time
 * Local Time Zone time (rise, set, noon)
 * Solar Time (rise, set, noon)
 * Solid Earth Tides
 * and a custom sun dial, marked for solar time and local time (a lamp
   can simulate solar noon and other angles)


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

[Bruce Griffiths]

Even with single mode fiber its finite group delay dispersion will likely 
restrict the usable light source bandwidth.

Bruce
> On 13 May 2018 at 03:38 Dana Whitlow  wrote:
> 
> 
> It may  be that a nicely-written request to Corning could yield the loan of
> a big spool of fiber 
> for the duration of a science fair project.
> 
> Another alternative, perhaps easier to implement, might be an
> electrically-driven light modulator
> at the detector end.  For the source, an LED or diode laser is easy to
> modulate at respectable
> rates.  This approach should allow use of such high frequencies that an
> open optical path using
> mirrors might even suffice.
> 
> Or here's an intermediate scheme:
> If one were to use two modulated sources (or one with a beamsplitter), with
> one path delayed
> by the long(ish) fiber and the other by a minimal-length local fiber,
> something resembling a streak
> camera (implemented with a rotating mirror) might permit use of
> substantially higher pulse rates
> than with a rotating disk, without incurring the need for anything very
> fancy in the way of mechanics.
> Only the modulated source should require a reasonably accurate drive
> frequency- the "detector"
> would be essentially self-calibrating.  A small mirror, say of cm size,
> could probably be safely
> rotated at Dremel speeds approaching 500 rev/s, and if 1 mrad angular
> resolution is attained,
> this would yield a resolution of ~160 ns.  So a fiber length of 500 ft
> (approx 750 ns one-way delay)
> should yield an angular separation of nearly five "dots" between delayed
> and undelayed dots.
> And if the sources are modulated at a rate such that a few pulse
> repetitions are visible in the
> field of view, the scheme is self-calibrating as long as the PRF and the
> velocity factor in the fiber
> are known.  Probably the only precision work would be the optics required
> to focus a reasonable
> amount of light from the source(s) onto the two fibers., and I believe this
> requirement could be
> adequately met with microscope objectives borrowed from one's school's
> biology lab.
> 
> A fly in the ointment is that if ordinary (read, inexpensive) IR fiber is
> used at convenient visible
> wavelengths, propagation will occur in more than one spatial mode, with
> different modes propagating
> at different speeds.   I don't know how much of a problem this would
> raise.  But it may be that if
> tweaking of the transmitting end illumination is done, both in angle and
> transverse position, most
> of the propagating light could be confined to a single mode.  I speak of
> visible wavelengths simply
> because using these avoids the cost of electronic detectors, oscilloscopes,
> etc, potentially saving
> a lot on the cost of the experiment as well as making for a more satisfying
> presentation.
> 
> Dana
> 
> 
> On Sat, May 12, 2018 at 9:45 AM, Bob kb8tq  wrote:
> 
> > Hi
> >
> >
> >
> > > On May 12, 2018, at 7:01 AM, jimlux  wrote:
> > >
> > > 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.
> >
> > I think the term “long fiber” in this case should really be “very very
> > long”.  Exactly how the typical student
> > funds the acquisition of something in the “many miles” range, I have no
> > idea.
> >
> > You could use an optical grating of some sort as your “spinning disk”. The
> > end of the fiber is going to be

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

[Bruce Griffiths]

Like this so called star target?:
https://www.edmundoptics.com/test-targets/resolution-test-targets/1-black-1-white-glass-star-target-5deg-wedge-pair-angle/

Bruce
> On 13 May 2018 at 02:45 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> 
> 
> > On May 12, 2018, at 7:01 AM, jimlux  wrote:
> > 
> > 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.
> 
> I think the term “long fiber” in this case should really be “very very long”. 
>  Exactly how the typical student
> funds the acquisition of something in the “many miles” range, I have no idea. 
> 
> You could use an optical grating of some sort as your “spinning disk”. The 
> end of the fiber is going to be 
> mighty small. The spacing on the grating could be quite tight. Where you get 
> a circular part like that ….
> again no idea. 
> 
> Bob
> 
> 
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> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> 
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Re: [time-nuts] Question about frequency counter testing

[Magnus Danielson]

On 05/12/2018 09:41 PM, Bob kb8tq wrote:
> Hi
> 
> 
>> On May 12, 2018, at 1:20 PM, Oleg Skydan  wrote:
>>
>> Hi!
>>
>> From: "Bob kb8tq" 
>>> There is still the problem that the first post on the graph is different 
>>> depending
>>> on the technique.
>>
>> The leftmost tau values are skipped and they "stay" inside the counter. If I 
>> setup counter to generate lets say 1s stamps (ADEV starts at 1s) it will 
>> generate internally 1/8sec averaged measurements, but export combined data 
>> for 1s stamps. The result will be strictly speaking different, but the 
>> difference should be insignificant.
> 
> Except here are a *lot* of papers where they demonstrate that the difference 
> may be *very* significant. I would
> suggest that the “is significant’ group is actually larger than the “is not” 
> group. 

There is no reason to treat it light-handed as about the same, as they
become different measures, where there is a measurement bias. Depending
on what you do, there might be a bias function to compensate the bias
with... or not. Even when there is, most people forget to apply it.

Stay clear of it and do it properly.

Averaging prior to ADEV does nothing really useful unless it is
well-founded, and then we call it MDEV and PDEV, and then you have to be
careful about the details to do it proper. Otherwise you just waste your
time to get "improved numbers" which does not actually help you to give
proper measures.

>>
>>> The other side of all this is that ADEV is really not a very good way to 
>>> test a counter.
>>
>> Counter testing was not a main reason to dig into statistics details last 
>> days. Initially I used ADEV when tried to test the idea of making the 
>> counter with very simple HW and good resolution (BTW, it appeared later it 
>> was not ADEV in reality :). Then I saw it worked, so I decided to make a 
>> "normal" useful counter (I liked the HW/SW concept). The HW has enough power 
>> to compute various statistics onboard in real time, and while it is not 
>> requisite feature of the project now, I think it will be good if the counter 
>> will be able to do it (or at least if it will export data suitable to do it 
>> in post process). The rest of the story you know :)
> 
> Again, ADEV is tricky and sensitive to various odd things. This whole debate 
> about it being sensitive goes 
> back to the original papers in the late 1960’s and 1970’s. At every paper I 
> attended the issue of averaging
> and bandwidth came up in the questions after the paper. The conversation has 
> been going on for a *long*
> time. 

If you go back to Dr. David Allan's Feb 1966 paper, you clearly see how
white and flicker phase modulation noise depend on the bandwidth, and
then assumed to be brick-wall filter. Your ability to reflect the
amplitude of those noises properly thus depends on the bandwidth.

Any filtering reduces the bandwidth, and hence artificially reduces the
ADEV value for the same amount of actual noise, then it is not
representing the underlying noise properly. However, if you use this for
improving your frequency measurements, it's fine and the processed ADEV
will represent the counters performance with that filter. Thus, the aim
will govern if you should or should not do the pre-filtering.

>>> If you are trying specifically just to measure ADEV, then there are a lot 
>>> of ways to do that by it’s self.
>>
>> Yes, but if it can be done with only some additional code - why not to have 
>> such ability? Even if it has some known limitations it is still a useful 
>> addition. Of cause it should be done as good as it can be with the HW 
>> limitations. Also it was/is a good educational moment.
> 
> It’s only useful if it is accurate. Since you can “do code” that gives you 
> results that are better than reality,
> simply coming up with a number is not the full answer. To be useful as ADEV, 
> it needs to be correct. 

Exactly.

>>
>> Now it is period of tests/experiments to see the used technology 
>> features/limitations(of cause if those experiments can be done with the 
>> current "ugly style HW"). I have already got a lot of useful information, it 
>> should help me in the following HW/FW development. The next steps are analog 
>> front end and GPS frequency correction (I should get the GPS module next 
>> week). I have already tested the 6GHz prescaler and now wait for some parts 
>> to finish it. Hope this project will have the "happy end" :).
> 
> I’m sure it will come out to be a very cool counter. My *only* concern here 
> is creating inaccurate results
> by stretching to far with what you are trying to do. Keep it to the stuff 
> that is accurate.

Bob and I are picky, and for a reasoon. When we want our ADEV plots, we
want them done properly, or else we can improve the specs of the
oscillators by changing how fancy post-processing we do on the
counter-data. Yes, we see this in professional conferences too.

Mumble... BAD SCIENCE!

Metrology correct 

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

[Magnus Danielson]

Hi,

On 05/12/2018 08:38 PM, Oleg Skydan wrote:
> Hi!
> 
> From: "Magnus Danielson" 
>> ADEV assumes brick-wall filtering up to the Nyquist frequency as result
>> of the sample-rate. When you filter the data as you do a Linear
>> Regression / Least Square estimation, the actual bandwidth will be much
>> less, so the ADEV measures will be biased for lower taus, but for higher
>> taus less of the kernel of the ADEV will be affected by the filter and
>> thus the bias will reduce.
> 
> Thanks for clarification. Bob already pointed me to problem and after
> some reading *DEV theme seems to be clearer.

The mistake is easy to make. Back in the days, it was given that you
should always give the system bandwidth alongside a ADEV plot, a
practice that later got lost. Many people does not know what bandwidth
they have, and the effect it has on the plot. I've even heard
distinguished and knowledgeable person in the field admit of doing it
incorrect.

>>> Does the ADEV plots I got looks reasonable for the used "mid range"
>>> OCXOs (see the second plot for the long run test)?
>>
>> You probably want to find the source of the wavy response as the orange
>> and red trace.
> 
> I have already found the problem. It is HW problem related to poor
> isolation between reference OCXO signal and counter input signal clock
> line (it is also possible there are some grounding or power supply
> decoupling problems - the HW is made in "ugly construction" style). When
> the input clock frequency is very close (0.3..0.4Hz difference) to the
> OCXO subharmonic this problem become visible (it is not FW problem
> discussed before, cause counter reference is not a harmonic of the OCXO
> anymore).

Make sense. Cross-talk has been performance limit of several counters,
and care should be taken to reduce it.

> It looks like some commercial counters suffers from that
> problem too. After I connected OCXO and input feed lines with short
> pieces of the coax this effect greatly decreased, but not disappeared.

Cross talk exists for sure, but there is a similar effect too which is
not due to cross-talk but due to how the counter is able to interpolate
certain frequencies.

> The "large N" plots were measured with the input signal 1.4Hz (0.3ppm)
> higher then 1/2 subharmonic  of the OCXO frequency, with such frequency
> difference that problem completely disappears. I will check for this
> problem again when I will move the HW to the normal PCB.

Yes.

>> If fact, you can do a Omega-style counter you can use for PDEV, you just
>> need to use the right approach to be able to decimate the data. Oh,
>> there's a draft paper on that:
>>
>> https://arxiv.org/abs/1604.01004
> 
> Thanks for the document. It needs some time to study and maybe I will
> add the features to the counter to calculate correct PDEV.

It suggest a very practical method for FPGA based counters, so that you
can make use of the high rate of samples that you have and reduce it in
HW before handing of to SW. As you want to decimate data, you do not
want to lose the Least Square property, and this is a practical method
of achieving it.

>>> If ADEV is needed, the averaging
>>> interval can be reduced and several measurements (more then eight) can
>>> be combined into one point (creating the new weighting function which
>>> resembles the usual Pi one, as shown in the [1] p.54), it should be
>>> possible to calculate usual ADEV using such data. As far as I
>>> understand, the filter which is formed by the resulting weighting
>>> function will have wider bandwidth, so the impact on ADEV will be
>>> smaller and it can be computed correctly. Am I missing something?
>>
>> Well, you can reduce averaging interval to 1 and then you compute the
>> ADEV, but it does not behave as the MDEV any longer.
> 
> With no averaging it will be a simple reciprocal counter with time
> resolution of only 2.5ns. The idea was to use trapezoidal weighting, so
> the counter will become somewhere "between" Pi and Delta counters. When
> the upper base of the weighting function trapezium is 0 length
> (triangular weighting) it is usual Delta counter, if it is infinitely
> long the result should converge to usual Pi counter. Prof. Rubiola
> claims if the ratio of upper to lower base is more than 8/9 the ADEV
> plots made from such data should be sufficiently close to usual ADEV. Of
> cause the gain from the averaging will be at least 3 times less than
> from the usual Delta averaging.

You do not want to mix pre-filtering and ADEV that way. We can do things
better.

> Maybe I need to find or make "not so good" signal source and measure its
> ADEV using above method and compare with the traditional. It should be
> interesting experiment.

It is always good to experiment and learn from both not so stable stuff,
stuff with significant drift and very stable stuff.

>> What you can do is that you can calculate MDEV or PDEV, and then apply
>> the suitable bias function to convert the level 

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

[Bob kb8tq]

Hi

As mentioned a number of times, quadrafilar antennas were only popular for a 
very short
while back in the 1980’s. Once people started using GPS for “stuff” they 
rapidly lost out in
the antenna race. They were made popular by an early NIST paper. Later on NIST 
effectively 
said “oops !!” in reference to that paper. 

So yes, any modern GPS antenna is likely to be a patch antenna. Trimble and 
Novatel both 
have “exotic” antennas, but they still are fundamentally a patch. 

Why all of this? Multi-path.  You want to *reject* signals close to the horizon 
since they are
the ones most likely to be distorted by reflections.  Indeed choke rings and 
the various other
exotic approaches are all aimed at multiparty rejection by reducing gain at (or 
below) the horizon. 

Bob

> On May 12, 2018, at 4:07 PM, Larry McDavid  wrote:
> 
> I recently had an unexpected failure of a white-conical-dome HP/Symmetricom 
> 58532A GPS antenna that had been in-place about 5 feet above the roof of my 
> two-story home in Southern California for about ten years. I have two similar 
> GPS antennas located about ten feet apart on this roof, one fed with about 50 
> feet of Andrews Heliax and the other with LMR400; the other antenna continued 
> to work ok. The antennas feed 4x and 8x amplified GPS Source (brand name) 
> antenna splitters. I noticed the failure when several GPSDO units and a GPS 
> Clock failed to sync with the GNSS. I confirmed the failure was not the 
> antenna splitter and I replaced the failed GPS antenna one of the same type, 
> after which all returned to normal.
> 
> I removed the conical radome from the failed antenna and was surprised to 
> find the antenna element was actually a patch, not the quadrafilar I expected 
> under that conical dome. Subsequently I opened the radomes of three other 
> similar GPS timing antennas made by various manufacturers and found that all 
> use patch antennas. I had believed these timing antennas used a quadrafilar 
> design to benefit from higher low-angle gain.
> 
> So, it appears the conical radome shape is really only to prevent snow 
> accumulation. Well... from my experience here on the flatlands of Anaheim 
> near Disneyland, that seems to be completely effective as I've surely had no 
> snow buildup! :) But, I had surely expected the conical radome covered a 
> quadrafilar antenna. Am I alone in expecting a quadrafilar antenna?
> 
> Further troubleshooting of this failed antenna revealed many discrete 
> components on the underside of the round board holding the patch antenna. The 
> circuit uses a three-stage gain amplifier with three Toko bandpass filters, 
> numerous bypass capacitors and stripline inductors. Probing the circuit with 
> a sig gen and spectrum analyzer showed that all three gain stages were 
> working about as expected. Of course, even with 26-30 dB gain in the antenna, 
> the SA did not have enough gain nor low enough noise floor to see any GPS 
> signal from the antenna. But, each gain stage seemed to be working ok. So, 
> what was the failure?
> 
> Upon removing the radome, one unexpected thing was seen. The construction 
> uses a short coax cable up from the N connector, through a hole in the 
> circuit board, where it is bent over and finally soldered to circuit board 
> pads for the shield and center conductor. There was a great deal of very dark 
> flux residue around this coax solder connection. The appearance was so bad it 
> even looked like a cracked solder joint, though that proved not to be the 
> case when the flux residue was thoroughly removed. It did not occur to me to 
> functionally test the antenna at this point. Later, it was necessary to 
> unsolder this coax so the board could be removed to access the components on 
> the underside for detailed testing. But, stage-by-stage RF gain testing did 
> not reveal any problems, so the antenna was reassembled for actual field 
> testing.
> 
> The result? The antenna now works ok; locking sync to the GPS GNSS. I gotta 
> conclude the flux residue was attenuating the signal out of the antenna. 
> Careful inspection of that coax solder joint absolutely did not show any 
> problem after the flux was removed so I believe continuity was ok.
> 
> I next removed the radome from one of my (new) Symmetricom antennas to 
> inspect its coax solder joint and discovered this (perhaps newer) version has 
> a metal shield-can soldered over the coax solder pads; I am loathe to remove 
> that shield just to inspect the solder joint flux. However, there is no flux 
> evident on the solder tabs where the metal shield-can is soldered to the 
> circuit board so the whole thing must have been defluxed after soldering. 
> That would be a better process anyway.
> 
> To make this very long story into a short one, I learned that the 
> HP/Symmetricom 58532A GPS Reference (timing) antennas use a simple patch 
> antenna instead of a quadrafilar antenna and that old solder flux residue 

[time-nuts] GPS Timing Antenna Failure - Long

[Larry McDavid]

I recently had an unexpected failure of a white-conical-dome 
HP/Symmetricom 58532A GPS antenna that had been in-place about 5 feet 
above the roof of my two-story home in Southern California for about ten 
years. I have two similar GPS antennas located about ten feet apart on 
this roof, one fed with about 50 feet of Andrews Heliax and the other 
with LMR400; the other antenna continued to work ok. The antennas feed 
4x and 8x amplified GPS Source (brand name) antenna splitters. I noticed 
the failure when several GPSDO units and a GPS Clock failed to sync with 
the GNSS. I confirmed the failure was not the antenna splitter and I 
replaced the failed GPS antenna one of the same type, after which all 
returned to normal.


I removed the conical radome from the failed antenna and was surprised 
to find the antenna element was actually a patch, not the quadrafilar I 
expected under that conical dome. Subsequently I opened the radomes of 
three other similar GPS timing antennas made by various manufacturers 
and found that all use patch antennas. I had believed these timing 
antennas used a quadrafilar design to benefit from higher low-angle gain.


So, it appears the conical radome shape is really only to prevent snow 
accumulation. Well... from my experience here on the flatlands of 
Anaheim near Disneyland, that seems to be completely effective as I've 
surely had no snow buildup! :) But, I had surely expected the conical 
radome covered a quadrafilar antenna. Am I alone in expecting a 
quadrafilar antenna?


Further troubleshooting of this failed antenna revealed many discrete 
components on the underside of the round board holding the patch 
antenna. The circuit uses a three-stage gain amplifier with three Toko 
bandpass filters, numerous bypass capacitors and stripline inductors. 
Probing the circuit with a sig gen and spectrum analyzer showed that all 
three gain stages were working about as expected. Of course, even with 
26-30 dB gain in the antenna, the SA did not have enough gain nor low 
enough noise floor to see any GPS signal from the antenna. But, each 
gain stage seemed to be working ok. So, what was the failure?


Upon removing the radome, one unexpected thing was seen. The 
construction uses a short coax cable up from the N connector, through a 
hole in the circuit board, where it is bent over and finally soldered to 
circuit board pads for the shield and center conductor. There was a 
great deal of very dark flux residue around this coax solder connection. 
The appearance was so bad it even looked like a cracked solder joint, 
though that proved not to be the case when the flux residue was 
thoroughly removed. It did not occur to me to functionally test the 
antenna at this point. Later, it was necessary to unsolder this coax so 
the board could be removed to access the components on the underside for 
detailed testing. But, stage-by-stage RF gain testing did not reveal any 
problems, so the antenna was reassembled for actual field testing.


The result? The antenna now works ok; locking sync to the GPS GNSS. I 
gotta conclude the flux residue was attenuating the signal out of the 
antenna. Careful inspection of that coax solder joint absolutely did not 
show any problem after the flux was removed so I believe continuity was ok.


I next removed the radome from one of my (new) Symmetricom antennas to 
inspect its coax solder joint and discovered this (perhaps newer) 
version has a metal shield-can soldered over the coax solder pads; I am 
loathe to remove that shield just to inspect the solder joint flux. 
However, there is no flux evident on the solder tabs where the metal 
shield-can is soldered to the circuit board so the whole thing must have 
been defluxed after soldering. That would be a better process anyway.


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


I welcome your constructive comments.

--
Best wishes,

Larry McDavid W6FUB
Anaheim, California  (SE of Los Angeles, near Disneyland)
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Re: [time-nuts] Question about frequency counter testing

[Bob kb8tq]

Hi


> On May 12, 2018, at 1:20 PM, Oleg Skydan  wrote:
> 
> Hi!
> 
> From: "Bob kb8tq" 
>> There is still the problem that the first post on the graph is different 
>> depending
>> on the technique.
> 
> The leftmost tau values are skipped and they "stay" inside the counter. If I 
> setup counter to generate lets say 1s stamps (ADEV starts at 1s) it will 
> generate internally 1/8sec averaged measurements, but export combined data 
> for 1s stamps. The result will be strictly speaking different, but the 
> difference should be insignificant.

Except here are a *lot* of papers where they demonstrate that the difference 
may be *very* significant. I would
suggest that the “is significant’ group is actually larger than the “is not” 
group. 


> 
>> The other side of all this is that ADEV is really not a very good way to 
>> test a counter.
> 
> Counter testing was not a main reason to dig into statistics details last 
> days. Initially I used ADEV when tried to test the idea of making the counter 
> with very simple HW and good resolution (BTW, it appeared later it was not 
> ADEV in reality :). Then I saw it worked, so I decided to make a "normal" 
> useful counter (I liked the HW/SW concept). The HW has enough power to 
> compute various statistics onboard in real time, and while it is not 
> requisite feature of the project now, I think it will be good if the counter 
> will be able to do it (or at least if it will export data suitable to do it 
> in post process). The rest of the story you know :)

Again, ADEV is tricky and sensitive to various odd things. This whole debate 
about it being sensitive goes 
back to the original papers in the late 1960’s and 1970’s. At every paper I 
attended the issue of averaging
and bandwidth came up in the questions after the paper. The conversation has 
been going on for a *long*
time. 

> 
>> If you are trying specifically just to measure ADEV, then there are a lot of 
>> ways to do that by it’s self.
> 
> Yes, but if it can be done with only some additional code - why not to have 
> such ability? Even if it has some known limitations it is still a useful 
> addition. Of cause it should be done as good as it can be with the HW 
> limitations. Also it was/is a good educational moment.

It’s only useful if it is accurate. Since you can “do code” that gives you 
results that are better than reality,
simply coming up with a number is not the full answer. To be useful as ADEV, it 
needs to be correct. 

> 
> Now it is period of tests/experiments to see the used technology 
> features/limitations(of cause if those experiments can be done with the 
> current "ugly style HW"). I have already got a lot of useful information, it 
> should help me in the following HW/FW development. The next steps are analog 
> front end and GPS frequency correction (I should get the GPS module next 
> week). I have already tested the 6GHz prescaler and now wait for some parts 
> to finish it. Hope this project will have the "happy end" :).

I’m sure it will come out to be a very cool counter. My *only* concern here is 
creating inaccurate results
by stretching to far with what you are trying to do. Keep it to the stuff that 
is accurate.

Bob


> 
> All the best!
> Oleg 
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Re: [time-nuts] Commercially available empty ovens for oscillator testing?

[Bob kb8tq]

Hi

There are places that sell them. Most are looking for a couple thousand dollars 
for 
one. If that is inside your budget you might get in touch with them. Far 
cheaper to
get an eBay scrap OCXO and use its parts. 

An OCXO depends on the combination of two things to make it stable:

1) The oven holds temperature well

2) The crystal in the oscillator is cut to be *very* flat temperature wise at 
the oven temperature. 

(yes there’s more to it than that, but we’re keeping things simple) 

Both are equally important if you are after the sort of thing you see in a 
normal OCXO. 
A typical oscillator may well have a crystal that is 100 to 1,000 times “less 
flat” than 
what is used in an OCXO. 

Bob

> On May 12, 2018, at 12:55 PM, Julien Goodwin  
> wrote:
> 
> Does anyone know if there's anyone who sells essentially just the oven &
> casing for an OCXO on its own?
> 
> I have a project for which I'm currently using a VCTCXO, but I'm
> wondering if enclosing a plain VCXO, plus the control DAC & voltage
> reference in a single small oven would end up more stable, and possibly
> not even much more expensive.
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Re: [time-nuts] Question about frequency counter testing

[Magnus Danielson]

Hi Oleg,

On 05/12/2018 07:20 PM, Oleg Skydan wrote:
> Hi!
> 
> From: "Bob kb8tq" 
>> There is still the problem that the first post on the graph is
>> different depending
>> on the technique.
> 
> The leftmost tau values are skipped and they "stay" inside the counter.
> If I setup counter to generate lets say 1s stamps (ADEV starts at 1s) it
> will generate internally 1/8sec averaged measurements, but export
> combined data for 1s stamps. The result will be strictly speaking
> different, but the difference should be insignificant.

What is your motivation for doing this?

I'm not saying you are necessarilly incorrect, but it would be
interesting to hear your motivation.

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

[Oleg Skydan]

Hi!

From: "Magnus Danielson" 

ADEV assumes brick-wall filtering up to the Nyquist frequency as result
of the sample-rate. When you filter the data as you do a Linear
Regression / Least Square estimation, the actual bandwidth will be much
less, so the ADEV measures will be biased for lower taus, but for higher
taus less of the kernel of the ADEV will be affected by the filter and
thus the bias will reduce.


Thanks for clarification. Bob already pointed me to problem and after some 
reading *DEV theme seems to be clearer.



Does the ADEV plots I got looks reasonable for the used "mid range"
OCXOs (see the second plot for the long run test)?


You probably want to find the source of the wavy response as the orange
and red trace.


I have already found the problem. It is HW problem related to poor isolation 
between reference OCXO signal and counter input signal clock line (it is 
also possible there are some grounding or power supply decoupling problems - 
the HW is made in "ugly construction" style). When the input clock frequency 
is very close (0.3..0.4Hz difference) to the OCXO subharmonic this problem 
become visible (it is not FW problem discussed before, cause counter 
reference is not a harmonic of the OCXO anymore). It looks like some 
commercial counters suffers from that problem too. After I connected OCXO 
and input feed lines with short pieces of the coax this effect greatly 
decreased, but not disappeared. The "large N" plots were measured with the 
input signal 1.4Hz (0.3ppm) higher then 1/2 subharmonic  of the OCXO 
frequency, with such frequency difference that problem completely 
disappears. I will check for this problem again when I will move the HW to 
the normal PCB.



If fact, you can do a Omega-style counter you can use for PDEV, you just
need to use the right approach to be able to decimate the data. Oh,
there's a draft paper on that:

https://arxiv.org/abs/1604.01004


Thanks for the document. It needs some time to study and maybe I will add 
the features to the counter to calculate correct PDEV.



If ADEV is needed, the averaging
interval can be reduced and several measurements (more then eight) can
be combined into one point (creating the new weighting function which
resembles the usual Pi one, as shown in the [1] p.54), it should be
possible to calculate usual ADEV using such data. As far as I
understand, the filter which is formed by the resulting weighting
function will have wider bandwidth, so the impact on ADEV will be
smaller and it can be computed correctly. Am I missing something?


Well, you can reduce averaging interval to 1 and then you compute the
ADEV, but it does not behave as the MDEV any longer.


With no averaging it will be a simple reciprocal counter with time 
resolution of only 2.5ns. The idea was to use trapezoidal weighting, so the 
counter will become somewhere "between" Pi and Delta counters. When the 
upper base of the weighting function trapezium is 0 length (triangular 
weighting) it is usual Delta counter, if it is infinitely long the result 
should converge to usual Pi counter. Prof. Rubiola claims if the ratio of 
upper to lower base is more than 8/9 the ADEV plots made from such data 
should be sufficiently close to usual ADEV. Of cause the gain from the 
averaging will be at least 3 times less than from the usual Delta averaging.


Maybe I need to find or make "not so good" signal source and measure its 
ADEV using above method and compare with the traditional. It should be 
interesting experiment.



What you can do is that you can calculate MDEV or PDEV, and then apply
the suitable bias function to convert the level to that of ADEV.


That can be done if the statistics is calculated inside the counter, but it 
will not make the exported data suitable for post processing with the 
TimeLab or other software that is not aware of what is going on inside the 
counter.



Yes, they give relatively close values of deviation, where PDEV goes
somewhat lower, indicating that there is a slight advantage of the LR/LS
frequency estimation measure over that of the Delta counter, as given by
it's MDEV.


Here is another question - how to correctly calculate averaging length in 
Delta counter? I have 5e6 timestamps in one second, so Pi and Omega counters 
process 5e6 samples totally and one measurement have also 5e6 samples, but 
the Delta one processes 10e6 totally with each of the averaged measurement 
having 5e6 samples. Delta counter actually used two times more data. What 
should be equal when comparing different counter types - the number of 
samples in one measurement (gating time) or the total number of samples 
processed?


Thanks!
Oleg 


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Re: [time-nuts] Commercially available empty ovens for oscillator testing?

[paul swed]

Julien
Yes you could stabilize the temperature at some level.
But your really adding complexity that will tend to interact.
You have the natural TCXO behavior and then the oven behavior. Hard to say
how it all will behave.

But I suspect your suggesting warming the TCXO to something in its best
stability range. (Center)
Not the typical oven range. It would indeed help. But then even putting the
TCXO in a insulated box would also.
Depends on what you are trying to get to.

I use a GPSDO with a TCXO from Jackson lab and simply insulated it.
It was appropriate for instant on testing and radio references without
wasting power all day long.
If I am more serious I flip to an external GPDO through the same
distribution system after its warmed up.
Typically a TBolt or Z380.

Hope that helps.
Regards
Paul
WB8TSL




On Sat, May 12, 2018 at 12:55 PM, Julien Goodwin  wrote:

> Does anyone know if there's anyone who sells essentially just the oven &
> casing for an OCXO on its own?
>
> I have a project for which I'm currently using a VCTCXO, but I'm
> wondering if enclosing a plain VCXO, plus the control DAC & voltage
> reference in a single small oven would end up more stable, and possibly
> not even much more expensive.
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Re: [time-nuts] Question about frequency counter testing

[Oleg Skydan]

Hi!

From: "Bob kb8tq" 
There is still the problem that the first post on the graph is different 
depending

on the technique.


The leftmost tau values are skipped and they "stay" inside the counter. If I 
setup counter to generate lets say 1s stamps (ADEV starts at 1s) it will 
generate internally 1/8sec averaged measurements, but export combined data 
for 1s stamps. The result will be strictly speaking different, but the 
difference should be insignificant.


The other side of all this is that ADEV is really not a very good way to 
test a counter.


Counter testing was not a main reason to dig into statistics details last 
days. Initially I used ADEV when tried to test the idea of making the 
counter with very simple HW and good resolution (BTW, it appeared later it 
was not ADEV in reality :). Then I saw it worked, so I decided to make a 
"normal" useful counter (I liked the HW/SW concept). The HW has enough power 
to compute various statistics onboard in real time, and while it is not 
requisite feature of the project now, I think it will be good if the counter 
will be able to do it (or at least if it will export data suitable to do it 
in post process). The rest of the story you know :)


If you are trying specifically just to measure ADEV, then there are a lot 
of ways to do that by it’s self.


Yes, but if it can be done with only some additional code - why not to have 
such ability? Even if it has some known limitations it is still a useful 
addition. Of cause it should be done as good as it can be with the HW 
limitations. Also it was/is a good educational moment.


Now it is period of tests/experiments to see the used technology 
features/limitations(of cause if those experiments can be done with the 
current "ugly style HW"). I have already got a lot of useful information, it 
should help me in the following HW/FW development. The next steps are analog 
front end and GPS frequency correction (I should get the GPS module next 
week). I have already tested the 6GHz prescaler and now wait for some parts 
to finish it. Hope this project will have the "happy end" :).


All the best!
Oleg 


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[time-nuts] Commercially available empty ovens for oscillator testing?

[Julien Goodwin]

Does anyone know if there's anyone who sells essentially just the oven &
casing for an OCXO on its own?

I have a project for which I'm currently using a VCTCXO, but I'm
wondering if enclosing a plain VCXO, plus the control DAC & voltage
reference in a single small oven would end up more stable, and possibly
not even much more expensive.
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Re: [time-nuts] Anybody have suggestions for time related science fair projects?

[Dana Whitlow]

It may  be that a nicely-written request to Corning could yield the loan of
a big spool of fiber
for the duration of a science fair project.

Another alternative, perhaps easier to implement, might be an
electrically-driven light modulator
at the detector end.  For the source, an LED or diode laser is easy to
modulate at respectable
rates.  This approach should allow use of such high frequencies that an
open optical path using
mirrors might even suffice.

Or here's an intermediate scheme:
If one were to use two modulated sources (or one with a beamsplitter), with
one path delayed
by the long(ish) fiber and the other by a minimal-length local fiber,
something resembling a streak
camera (implemented with a rotating mirror) might permit use of
substantially higher pulse rates
than with a rotating disk, without incurring the need for anything very
fancy in the way of mechanics.
Only the modulated source should require a reasonably accurate drive
frequency- the "detector"
would be essentially self-calibrating.  A small mirror, say of cm size,
could probably be safely
rotated at Dremel speeds approaching 500 rev/s, and if 1 mrad angular
resolution is attained,
this would yield a resolution of ~160 ns.  So a fiber length of 500 ft
(approx 750 ns one-way delay)
should yield an angular separation of nearly five "dots" between delayed
and undelayed dots.
And if the sources are modulated at a rate such that a few pulse
repetitions are visible in the
field of view, the scheme is self-calibrating as long as the PRF and the
velocity factor in the fiber
are known.  Probably the only precision work would be the optics required
to focus a reasonable
amount of light from the source(s) onto the two fibers., and I believe this
requirement could be
adequately met with microscope objectives borrowed from one's school's
biology lab.

A fly in the ointment is that if ordinary (read, inexpensive) IR fiber is
used at convenient visible
wavelengths, propagation will occur in more than one spatial mode, with
different modes propagating
at different speeds.   I don't know how much of a problem this would
raise.  But it may be that if
tweaking of the transmitting end illumination is done, both in angle and
transverse position, most
of the propagating light could be confined to a single mode.  I speak of
visible wavelengths simply
because using these avoids the cost of electronic detectors, oscilloscopes,
etc, potentially saving
a lot on the cost of the experiment as well as making for a more satisfying
presentation.

Dana


On Sat, May 12, 2018 at 9:45 AM, Bob kb8tq  wrote:

> Hi
>
>
>
> > On May 12, 2018, at 7:01 AM, jimlux  wrote:
> >
> > 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.
>
> I think the term “long fiber” in this case should really be “very very
> long”.  Exactly how the typical student
> funds the acquisition of something in the “many miles” range, I have no
> idea.
>
> You could use an optical grating of some sort as your “spinning disk”. The
> end of the fiber is going to be
> mighty small. The spacing on the grating could be quite tight. Where you
> get a circular part like that ….
> again no idea.
>
> Bob
>
>
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Re: [time-nuts] Anybody have suggestions for time related science fair projects?

[Mike Feher]

How about a Stroboscope? - 

 

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

848-245-9115

 

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

[Bob kb8tq]

Hi



> On May 12, 2018, at 7:01 AM, jimlux  wrote:
> 
> 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.

I think the term “long fiber” in this case should really be “very very long”.  
Exactly how the typical student
funds the acquisition of something in the “many miles” range, I have no idea. 

You could use an optical grating of some sort as your “spinning disk”. The end 
of the fiber is going to be 
mighty small. The spacing on the grating could be quite tight. Where you get a 
circular part like that ….
again no idea. 

Bob


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Re: [time-nuts] Help Identifying this surplus Timing Module

[Bob kb8tq]

Hi

Ok, the gizmo on the front it an Altera CPLD. Not a lot of gates, so not a lot 
going 
on there. Whatever the real functions are, they are in the chip with no 
labeling. 

Even with the full information (let’s say): 

Takes in a 16 stream OC-blah blah and provides the following alarms on the 
status
channel. Hookup up the data stream and backup to pins X and Y. Status alarms 
also come
out on A, B, and C. Power is 12 V +/- 10% on pin M. Enable and control are on 
pins
E,F,G. 

Unless you happen to be building an OC-3 system in the basement and have all
the optical fiber stuff to do it …. not a lot of use. It is very similar to a 
lot of product
I designed over the years. It likely does a great job in it’s intended OEM 
application.
It’s pretty much useless for anything more general purpose as it is right now.

Without a schematic, the source code for the DSP and CPLD  and the proper tool 
sets, not much you can modify it to do. Even with all that stuff, probably the 
best you 
could do is a fairly basic 1 pps in. to  38.88 MHz) / M  out PLL. 

Indeed this *is* where timing has gone over the last few decades. TimeNuts 
normally may 
not look at telecom timing as an exciting thing. There is a vast amount of gear 
that 
has been built to distribute signals inside these networks. As far as Crazy Bob 
at
home is concerned, it’s all out of reach. It also is all designed for 
maintenance of 
data sync rather than time of day. It’s still very much time, just a different 
way of
looking at it. 

Bob

> On May 11, 2018, at 11:45 PM, CubeCentral  wrote:
> 
> Thank you bob and Gary for your investigations!  I appreciate it!  Here are a 
> couple more views:
> 
> https://imgur.com/a/auWdXvq
> 
> "This is the picture with sticker removed.   The large IC at the back has its 
> label scratched off.  ... that was intentional, but he has a note saying it 
> is a member of Motorola DSP56300 family. It was likely purchased in 2010 
> based on an eBay invoice which has no date on it, but the scanned date was 
> Feb 2011."
> 
> If anyone else has any more ideas, I would gladly hear them!  Thanks again!
> 
>   -Randal   (at CubeCentral)
> 
> 
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Gary Chatters
> Sent: Friday, May 11, 2018 19:07
> To: time-nuts@febo.com
> Subject: Re: [time-nuts] Help Identifying this surplus Timing Module
> 
> A little Googling found a two page datasheet.  It doesn't tell you much more 
> than what you already found out, but does have specifications.
> 
> I can't figure out the correct link to include here, but a Google search with 
> the string "ATiMe-s 38.88" (don't include the quotes) should bring up the 
> link in the first couple of hits.  It is a PDF at the www.sbtron.co.kr 
> website.
> 
> gc
> 
> On 05/11/2018 07:16 PM, CubeCentral wrote:
>> Hello All!
>> 
>> 
>> 
>> I would like to enlist your help in identifying this "surplus Timing
>> Module":  https://imgur.com/a/Psw8gP7
>> 
>> 
>> 
>> All the hints I've been given are:
>> 
>> - Purchased about a decade ago
>> 
>> - Might use a Motorola DSP as the processor
>> 
>> 
>> 
>> A quick google search lead me to a possible description:
>> 
>> "High speed, hitless, ultra low jitter timing module for OC-N line
>> interfaces:  The TF Systems / ATiMe-LC is a timing reference source for OC-N
>> and STM-N interfaces. It complements TeraSync's central timing modules to
>> provide a complete and redundant timing solution at the system level."
>> 
>> 
>> 
>> ...but I'm unsure if that is 100% the same module.  If you would like to get
>> some different photos, please let me know and I will see what I can do.  Any
>> thoughts or ideas would be greatly appreciated!  Thanks!
>> 
>> 
>> 
>> -Randal   (at CubeCentral)
>> 
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[time-nuts] TruePosition GPSDO Holdover Issues

[gandalfg8--- via time-nuts]

Today using Lady Heather I have observed the TruePostion GPSDO dropping into 
holdover as the number of tracked sats dropped from four to three.
There does seem to be some hysteresis in the system though, the number of 
tracked sats eventually dropped to two and then the unit came out of holdover 
as the number increased from two to three.

I can't say that this explains all the holdover events I've seen but it does 
seem to explain at least some of them.

Nigel, GM8PZR
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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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