Re: [time-nuts] Anybody have suggestions for time related science fair projects?
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?).
--
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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Re: [time-nuts] Weird Stuff WareHouse shutting down
> Thanks
> It has to have been Apex that I visited. The back areas were a mix of open
> sky and sort of sheds.
> The air was typically pretty dry so the stuff held up well.
I did see some populated circuit boards absolutely caked with dirt (was
probably dust at first). Maybe not just outside, either.
> There were
> things I would have liked to have grabbed.
> Could easily see a day digging around.
> Inside its stacked to the 20 ft ceilings and they have ladders like
> you see
> in home depot to get to the top.
I didn't see any ladders, but I didn't look everywhere (too dangerous)
and I wasn't dressed for it. I told the guy I wasn't tall enough to
shop there (could not read model numbers of test equipment 15 feet up).
I inquired about a Tek 465B ($50) and Tek 1910 ($100). Those weren't
irresistible bargains, and I'm already trying to fix a similar scope.
Everything is as-is where-is. Didn't ask about a Tek T932, either.
It reminded me a bit of AxMan Surplus in Minneapolis (where I didn't buy
a 465M for $75, either).
>
> I did not go to C&H as I simply ran out of time. Pretty good?
I'd say it's an appetizer for the Silicon Valley stores. (APEX is in a
league of its own.) I picked up a Fluke 1900A multi-counter for $20
because of the engraved tag on it "GIFT FROM / JOHN FLUKE / MARCH 1986".
There's one left. Alas, they're only 6 digits, but have very sharp LEDs
for kHz, MHz, and Overflow. A SHARP EL-5120 with LCD faults overpriced
at $5. And an ailing GC-1000H clock. Other stuff I took pictures of
include a Fluke 1953A, an HP 8006B? Pulse Generator, an EDC Programmable
DC Voltage Standard, and an external dbx dBm meter. There's also a
Tek 7704A with 7A26, 7A15A, 7D11, 7D12/M2 sitting on a 203 scopemobile
(and an empty one with just plugins (5B31, 7B80, 7A12, 7A19)) outside
the front door (much like Halted/HSC did at their previous location) for
$50 (just the 7704A). I didn't have room in the car for it.
C&H days/hours are limited; I lucked out.
> Regards
> Paul
> WB8TSL
--
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] Weird Stuff WareHouse shutting down
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&H 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] IEEE 1588 PTP devices
I ran across some Agilent LXI 1588 Demomstration [sic] Kits for far, far
less (beer money) than what
https://www.ebay.com/itm/Agilent-IEEE-1588-Demonstration-Kit-New-in-box/161954792190
wants. There are 4 BNCs on the back, labelled 1PPS, TT, TS, and TEST.
With that, and Ethernet and serial and USB on the back, they looked
intersting enough to take one home and play with. That's all I knew
about them. I thought I might be able to inject PTP time with 1PPS from
my GPSDO into my NTP network.
I found that it had a webserver for configuring from a browser, and
that's the only way I've found (so far) to set the time. So it's an
island of precision unto itself and any brethren it finds. I tried to
get linuxptp to talk to it, but it could only listen (I guess the LXI
box thinks that itself is the best master clock). I wondered how well
it would sync to another PTP box. So I went and picked up another one.
It seems they sync to each other pretty well. I was hoping that the
1PPS BNC was an input. Alas, it's an output. (The GUI also told me
that the TEST input is an external 100MHz clock.) I put each one's PPS
on a scope and measure the difference as about -11ns to +40ns
(jittering). Tried the same thing on a 53131A (also Agilent). It was so
noisy I couldn't trust/believe what it reported, though a single 22.8ns
did come up. I couldn't do that on the 5316A, since its resolution is
100ns, so I had it report GPSDO 1PPS vs LXI GPS.
LinuxPTP can at least tell me the difference between NTP (host) time and
PTP time (but not when it is a master), and it takes a couple days to
roll over one second. I'd been arguing with these things a while trying
to get it to timestamp an external event. Only one seems to be able to
do that so far. So I gave it the GPSDO 1PPS to TimeStamp, and data
started accumulating. From the TS log, I can see that its clock is a
bit less than 3ppm slow (slower if it gets colder in the lab, er,
garage). It reports everything to nanosecond precision.
typical timestamp: 1519980450.210347925 linuxptp reports difference
between PTP and host in nanoseconds, typical value 786979741 . That
sums close to the next second. The difference is positive and rising now.
==
Does anyone out there have any info on these things? I did look through
time-nuts archives around 2012.
--
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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Re: [time-nuts] Leap Second result on PST Model 1020
That's only about the third unit I've ever even heard of. They seem to be rarer than hen's teeth these days. All the more reason to kick myself for giving back the one I borrowed around Hallowe'en 1990 or so to compare it with my GC-1000 and watch Daylight Saving Time end for the year. It did so right at 2AM when it was supposed to. I was always impressed that that clock does as much as it can with what it's got so far (i.e. units of seconds start counting after the 2nd good 10-second marker, and so on.) I still want one. There have to be more than three out there. -- Jeff Woolsey j...@jlw.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
