Yes, I am aware of that. Bayonet and threaded connectors can be mated, or
partially mated as I said. This applies to BNC, C, N, HN, TNC, SMA, APC-7,
and MS at least, but not to LEMO and some families of military and
commercial multipin connectors.

Improper mating can easily be seen on a VNA, and can sometimes destroy a
TWTA if it is not protected with an internal isolator.

Normally FO connectors have their faces lapped very flat and exactly
normal to the fiber axis. If they are not lapped properly or mated
properly, the insertion loss increases dramatically.

It was happenstance that the OPERA connector was mated enough to work, but
not enough to work properly.

-John

============

when

in optical power induced by the loose connection resulted in big changes
in delay through the mechanism of charging and discharging the
capacitance associated with the photodiode. At least that is my crude
understanding of the matter,

was trying to go a bit more concrete and suggest that redundant

errors which may have gone undetected using other means, like

space electronics I think I don't have to convince you of the benefits
of redundancy, as well as of the fact that the probability of making
mistakes is never 0. If you think about it, this whole issue was solved
thanks to redundancy: there was another experiment in the same lab which
detected cosmic muons, and it was through the

slip between time bases was discovered. I think redundancy is a good
complement, not necessarily a substitute, to other quality

Sorry. "click" is a bad choice of words. It's more a feel as you mate them
than an audible click.

-John

=============

Hi Achim:

SMA RF connectors have a very limited life (number of matings) until they are worn out.  That probably doesn't apply to
SMA threaded fiber optic connectors.
Where can I get short fiber optic cables that mate with the Ocean Optics HR2000 Optical Spectrum Analyzer?
http://www.prc68.com/I/ML-OSA.shtml#HR2000

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/Brooke4Congress.html

Achim Vollhardt wrote:

Brooke,

Try eBay. I got mine ther (maybe from a guy in Utah). He was also sel;ling
similar spectrometers, but for a lot more money than Roland.

BTW, There are more Ocean Optics spectrometers available. If interested,
drop me a note off-list.

-John

==================

On 3/31/12 12:24 PM, Achim Vollhardt wrote:

On bad connectors.. "K" connectors are horrible.. they can intermate
with SMA, but they don't tolerate the range of SMA mechanical variation,
so it's possible to damage a K jack by mating an SMA plug with it. Not
all SMA plugs, but some percentage of them.  And it's not obvious that
the jack has been damaged unless you measure it.  You can mate a K or
SMA (properly) with it, it will work, mostly, but now, there's a tiny
gap in the center conductor, sometimes, depending on the connector flex,
etc.

We have a dreadful connector at JPL which is a mini twinax (used for
balanced pairs, like MIL-STD-1553).  The key is a stamped metal bump so
small that it's easy to mismate in the 180 degree reversed position.
There's a much better version which is hermaphroditic (each side has one
male and one female pin) and it can only mate one way.  But that other
connector hangs on, and on, because you get the "device A uses connector
type X", so you build test equipment with mating Connector Type X, then
the next device B has that connector, so we can re-use the test
harnesses.  The next batch of test equipment is made to be compatible
with device B, and so it goes.  The last people I know (not at JPL) who
bought those connectors called up the mfr and was quoted a spectacularly
long lead time (6 months or a year), so they asked who else had bought
them, maybe they could buy the half dozen they needed.  Naturally, JPL
had bought the last batch, something like 15 or 20 years ago, and of
course, we had dozens of them sitting in bonded stores.

I was at an IEEE conference a few years ago on high speed interconnects
(10 Gbps is slow for those guys), and a bunch of the folks were talking
about how too much time is being spent on trying to get impedance
controlled connectors, instead of reliable connectors.  Their point was
that in any real high speed (which would, for time nuts be "high timing
precision") system, you already have multiple transitions: die to IC
package pin to PWB trace to connector pin to connector, before you worry
about the connector's potential mismatch.  These other ones are even
harder to control the impedance on, and trying to do so makes the boards
hard to route, etc, so why not bite the bullet and just implement a good
adaptive equalizer in your high speed interface.  Then you can use a
mechanically robust connector that has a positive mating, can't be
mismated or partially mated, and in fact, the equalizer can tell you if
the cabling is screwed up.

From a cost standpoint, it might actually be cheaper.  Implementing the
equalizers in a standard high speed SERDES doesn't cost much more in
silicon (yes, the IP development costs money, so the selling price is
higher), and you save a lot in the rest of the system.

On 3/31/12 1:15 PM, Brooke Clarke wrote:

I don't think so.  Yes, they're only rated for 500 cycles, but there's a
paper by a guy at Maury Microwave that I ran across when trying to get
statistics on the reflection coefficient variation, and he set up a
automated rig to mate/demate SMAs something like 10,000 times.

I suspect that there is a WIDE variation among mfrs in terms of life
performance and manufacturing precision.

the 3.5mm connector (sort of a precision, super SMA), is rated for 3000
cycles.

Remember, there are two varieties of SMA: Those with a gold plated center
pin soldered onto the center conductor and those with a sharpened center
conductor of 0.141 hard line.

The latter are near junk, IMO.

-John

==============

On 3/31/12 1:46 PM, J. Forster wrote:

Only if you're planning on multiple mates/demates.  The crimp on 0.141
style works fine for the first couple mates.  Good inspection and
gaging is needed to make sure you don't get little shreds of copper from
when you sharpen the point, and that your tooling got the length of the
"pin" correct.

It's sort of a "works once" scheme (like those head bolts or piston rod
bolts that you can only torque once.  Once stretched, they can't be used
again.)

They're pretty handy when building prototypes.  You get your big length
of 141 and your little bending tool, the die set and crimper from Kings,
and you can cable up stuff (once) pretty quickly and neatly.
If you take a cable off, you just throw it away (or cut the connectors
off and use the remaining cable for something new)

But if you're going to take it apart and reassemble it.. yep.. you want
the real captured gold plated machined center pin.  I use a lot of the
semi-flexible or "formable" stuff from Tensolite and RF-Coax these days.

You can save some bucks by buying a "Little IMP" tubing bender that takes
1/8" OD tubing for about $10 at Home Depot.

1/8" = 0.125" which is very close to 0.141". Two minutes with a rattail
file and Voila.

-John

============

On 03/31/2012 10:29 PM, Jim Lux wrote:

We have equalizers as well as pre/post emphesis to shape the eye of the
signal. It's really required. We adjust the sampling point on our bits.
That's standard business today.

Cheers,
Magnus

On 03/31/12 09:38 PM, Jim Lux wrote:

I suspect that the jig he built does a better job of aligning them than what
humans do. We put them on not quite square, move them around until the thread
mates etc. I wonder if his jig tried to replicate a human or not?

Yes, I've worked in places where they use the cheapest they can get, and others
where the more expensive, but much better quality Huber and Shuner connectors
are used. I would expect the more expensive ones, which are machined more
accurately, would last for more

There is also a relationship between the torque you tighten them and their life.

I happen to work somewhere where I can't get my boss to buy a torque wrench for
them, despite we use a lot of SMA connectors. I don't know how common that
practice is. Everywhere else I have worked does use a torque wrench.

I one tried a quick experiment tightening them up by hand as tight as possible,
then seeing how many extra turns it required to torque them to whatever the
torque wrench was set to (not all SMA torque wrenches are set to the same
figure). As far as I can tell, there is no way of even roughly estimating how
tight they should be by saying "hand tight + x turns".

Dave

On 4/1/12 3:01 AM, Dr. David Kirkby wrote:

Nope.. back and forth in a straight line.  He was measuring repeatability.

Yes.. if you're talking about finger tight, there's a lot of
variability.  With an inexpensive open end wrench, though you can get
pretty consistent.. perhaps it's the "Calibrated thumb" on the little
wrench?

Not anywhere as good as the "click" on the real torque wrench.

If you think about it, tightening torque only relates very roughly to
axial mating pressure.

Torque is essentially the force requires to push an object up an inclined
plane.

That is the sum of two components, the normal component of the mating
force plus the in plane component of (mating force)*(coefficient of
friction).

The latter is a guesstimate at best.

-John

===============

On 04/ 1/12 03:33 PM, Jim Lux wrote:

So it tells us nothing very much about the life of them in normal use, with a
human mating and demating them.  - or even the repeatability of the reflection
coefficient with a human in the equation.

dave

On 4/1/12 2:25 PM, Dr. David Kirkby wrote:

Not a whole lot, but the whole paper goes into the various factors
involved.  Ultimately, it winds up that the mismatch from SMAs is
a) a whole lot less than the usual "worst case" spec of 1.05:1 or 1.03:1
(which is basically a measurement limit)
and
b) doesn't change much with many mate/demate cycles

He did look at things like coupling nut friction and what not.

On 2 April 2012 00:54, Jim Lux jimlux@earthlink.net wrote:

Without seeing the paper, it's difficult to comment much more. Clearly
if he had shown the performance to be worst than the spec, then I
think he would have a useful result, as he would have put a limit on
what was achieveable even with perfect use. But I think the human
element is quite critical with SMA connectors - or pretty much any
connector for that matter.

Anyway, SMAs are pretty good connectors overall for most RF things.
It's a long time since I have used any LEMO connectors - the subject
of orginal discussion.

I've not been following the orignal thread in detail, or looked at the
relevant papers, but I do feel it odd and unjust that someone should
resign over what was a genuine mistake. We all make them from time to
time, and sometimes the consequencies are quite serious - like someone
dies.

dave

If the FTL neutrino "discovery" had been kept quiet until fully vetted, he
probably would not have had to resign.

Compare with the discovery of "Cold Fusion". The desire for PR got ahead
of the science.

In my view, somebody who is in responsible charge of any project that size
morally ought to be held accountable as "The buck stops here".

Frankly, I'm entirely fed up with those in charge of projects who walk
away scott free after a giant disaster.

Those in responsible charge should be held liable, both professionally and
personally, IMO.

YMMV,

-John

========================

[snip]

El 02/04/2012 16:14, J. Forster escribió:

I suppose so... Also, things would have been completely different if the
60ns error would be of the opposite sign, that would lead to the
believing that neutrinos are a bit slower than light and not a bit
faster. This of course would also have been of big impact in the physics
community, but not so big :) and also would not have take even a single
line in the newspapers and other media, except on the specialized ones.
Anyway, I think that it was keep quiet during some time and only made
public when though that it was fully vetted... but as we have seen a
couple of details were overlooked.

In the positive side, as Javier Serrano said, it has been the first time
that neutrino speed has been measured with this precision.

Regards,

Javier

Moin,

On Sun, 01 Apr 2012 16:54:09 -0700
Jim Lux jimlux@earthlink.net wrote:

Do you have the name of the paper? It might be interesting to read.

		Attila Kinali

--
Why does it take years to find the answers to
the questions one should have asked long ago?