I wasn't able to see the formatted original message, but by looking over
shoulders in others' replies I could read it. Another advantage of Classic
Compuserve; I can only get ASCII text. Of course this eliminates most
viruses. (grin)
The Telcordia document called Network Equipment Building Standa
body rather than sending it as an attachment.
Thanks,
Cortland Richmond
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>> Can you share with us what experiences you have had with doors of your
steel
clad chambers? If you could share such things as chamber vendor, hinge
adjustments, door maintenance recommended and performed, warranty claims
and
length of time without problems, that would help us understand the 1 y
Tony,
When I was in the computer business, we looked for clean _peripherals_. But
merely having one that has few emissions of its own is not enough. You also
need to get one that neither sends any down its peripheral connections, nor
passes those peripherals contribute to be radiated. This turns
I have an issue of the Antenna Society publication which lists a patent
granted in 1997 to two engineers from Murata, for the pi-network.
Cortland
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V
Art,
What a nice thing to do! I am just getting ready to pick up my stuff from
the office, and then ... Why wait for the outplacement firm? Forward
momentum!
Cortland
(I cannot speak for Alcatel
They cannot speak for me;
OF all that we might choose to say,
The other now is free!)
Boardstation software.
For more information, please contact me at one of the e-mail addresses
below.
Cortland Richmond
72146@compuserve.com
k...@earthlink.net
cortlandk...@netscape.net
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Fortunate? Good fortune, or bad? Heh!
Cortland
(I didn't write a thing that speaks
For my employer at all;
If anything I say is wrong,
I'm the one to take the fall!)
"Pettit, Ghery" wrote:
> David,
>
> Ideally an OATS should have no ambient signals within 6 dB of the lowest
> limit that you i
For an interesting report of EMC troubles besetting
police departments using 800 Mhz in the US, see
http://www.apco911.org/afc/project_39/interim_report.pdf
Cortland
(I'm on my own time now and so
What I've said's just my own, you know.
Don't blame my employer for this,
Just me. It's fine to
Close down? That's alarming. And probably not what needs to happen.
Power Line communication is controversial at the moment, especially with trials
underway in the Netherlands and some
deployments in Germany which generated high levels of RFI. (And appear to have
been exceedingly vulnerable to
Those of us who use weak-signal receiving equipment know there's an EMI
problem generally. But most of the consumer public does not see EMI as a
problem. This may change as 2.4 GHz cordless telephones disrupt more
wireless services, or perhaps as PLC systems affect more European SW
listeners. So
Don, and the group,
This is not so complex. As you surmise, parts of the house wiring are
being switched in and out by devices on it, and the broadcast RF present on
the wiring is being modulated by that switching.
While probing around the house with an untuned RF detector, I've found
power and
Doug,
If I understand your description properly, the AC power cords run from the
power supplies and thence out of the box. This would negate shielding the
box (whose construction, as you describe it, is not encouraging, either)
might offer. It looks to me that as there would be a difference in
I believe you would not be far off to take the IEC waveform as the worst
case.
The amount of charge is pretty well approximated by the IEC ESD simulator.
The discharge waveform shape depends on the impedance of the source - the
person holding it, and the ESD trace on the circuit pack (and its
p
>> Her Majesty Queen Elizabeth Second of The United Kingdom of Great
Britain and Northern Ireland (G*d help us); Defender Of The Faith <<
Funny you should mention that; it relates to certain matters under
discussion here.
Did you know that the first British monarch to bear the title "Defender Of
Some years ago I managed to quiet a similar problem by routing the IDE
cables flat against and along the chassis, and holding it/them tight with
plastic clips; that gave "free" bypass capacitance for the common-mode
currents. I DID have to specify exactly how the cables were to be folded
and tape
Hypothetical:
>>Should a receiver mounted on an antenna be "lit up"
>>during an emissions test? The receiver down-converts
>>the received signal??
Sure. It has oscillators whose emissions might cause interference. Even if
not required by law (Part 15 and receiver above 960 MHz not a radar
detecto
Ken,
You may have a problem using brass. It will have rather higher resistive
loss than copper shielding. Small diameter copper tubing, such as is used
to connect (say) a sink's drinking-water dispenser, is probably a better
choice. In fact, even copper tape should be a good ad-hoc test, and not
Don't forget that nearby conductors will also affect gain (or lack of it)
of an antenna. There are few EUT's built such that their antennas may be
treated as if they existed in isolation.
Cortland
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It looks like you've answered your own earlier question, Ken; yes, you CAN
see a difference between a leaky coax and good coax. I don't know that you
can rely on the usual clamp-on current probe up at 400 MHz, but the
relative difference tells you a good deal. And at 400 Mhz you only need a
few fe
Now that I've re-read the message, I see where you are coming from.
I thought you were looking at common-mode loss of the cable (as a whole,
shield included) *above ground*; you are looking at the center conductor
common mode with respect to the overshield, almost as a coaxial cable
itself. Yes,
Ken, a few thoughts.
Did you account for radiation resistance? You have described not merely a
single-wire transmission line but ALSO, a fairly good antenna.
The impedance is probably higher than you calculate. A coax cable with the
same ratio of shield radius (height above ground) to inner con
My avionics shop in Vietnam in 1970 had a similar problem. A 40 watt bulb
would light up if connected between the AC safety ground and an earth
ground at the building. This turned out to be due to unbalanced loads and a
loose connection about a half mile away.
Cortland
David,
Telecom ("Bellcore") usage is to keep signal, surge and power currents off
chassis and safety grounds. This is understandable. It is due not only to
audio sensitivity, but to the need to protect equipment from substantial
peak (hundred of amps) surges at fairly high (thousands of volts) pe
John Crabb asked
>> Has anyone encountered problems in the use of
"pre-plated" sheet steel in IT equipment metalwork ?
Typically such material is cheaper to use than
having to plate parts after they have been produced,
but there may be issues with sharp edges produced
when the material is punch
We don't disagree that at 30 Mhz, 3 meters is too close for a dipole. It's
too big for the distance, even if we are often compelled to use it that
way.
In this case, however, an AF of 5 dB puts the dipole at about 50 MHz -- 3
meters long. The distance to the source, 3 meters at the dipole's cen
AMund,
That's correct. One adds the antenna factor in dB to measured dBuv to get
the field.
Ken Javor points out that you do need to worry about being in the
plane-wave, far-field. 5 dB dipole AF is typical of around 50 MHz, where a
three meter distance is enough to be in the far field - for a
Alex,
Are you speaking of radiation directly from a SMPS on a table? If this is
the case, why, yes, you may, ASK for margin, but you may find few vendors
willing to bid to that requirement. Few ITE makers would warrant their own
boards to meet FCC limits outside a cabinet! But a SMPS should neve
>>Now I just need to get the Z meter.<<
For one, you might try an MFJ 259B. Covers 1.6-170 Mhz with some degree of
accuracy -- though certainly NOT lab quality! -- and can be had for as low
as $220 or so, new, if you can bargain with the seller. I've found mine
useful even where I DO have access
dance of a one-eighth
wave stub is equal to its characteristic impedance. Adjust spacing for
desired impedance.
Cortland Richmond
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In a former job, I prevailed on them to follow (mostly) a rule of 100 mils
clearance between any inner OR outer layer conductor, and conducting
objects directly exposed to ESD. This, after a helpful layout designer
decided to improve things by adding internal ESD traces interlaced with
power and g
Ed Price wrote:
>> BTW, audio provides a dramatic lab effect and should always be used
during executive
tours of your lab. <<
Back in '91 or so, at a large electronics retailer's R&D operation, I was
doing a prescan of an EUT with a CD-player/CD-ROM drive in it. Testing
with a bunch of corpora
Just a note about telling clocks apart... unless they're phase locked
(sometimes even then) a receiver with a BFO can let you distinguish from
among clocks only 100's of Hz apart. Sometimes it can let you tell which
of several clocks is slower to lock as well, as you can hear the varying
tone tha
Joe Martin wrote:
>> Credence Technologies manufactures a probe with a built in low noise
amplifier<<
Ohmygosh, yes. How could I have forgotten THEM! An untuned probe, with
output to a scope or analyzer, too. Neat tool.
I spent a fun half hour or so talking to their very bright son last year
a
Lisa,
On the expensive end, Noise-Ken has been at Symposia (which I can't afford
this year) with a sniffer. It apparently uses four or five broadly tuned
peak detectors and gives a bar-graph display for each band as its sensor is
brought near the EUT. But, like others, I've found that a spectrum
But do note that the Part 15 revision of July 2002 does add radar detectors
as an exception to the 960 MHz limit.
Cortland
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Well, maybe.
I think you mean the word spelled "fey."
Also from the Encarta World English Dictionary:
fey 1.
(omitted)
2. SUPERNATURAL - relating to or typical of magic or the supernatural
3. CLAIRVOYANT - supposedly able to see into the future
4. SCOTLAND - DOOMED TO DIE [Old English faege,
The Encarta World English Dictionary says:
Fay to join pieces of wood together tightly, or fit tightly inside
another piece of wood.
Do note this is a hard-cover dictionary, NOT an online one. I have not
(yet) looked online.
Cortland
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This messag
So, what about an isolation transformer?
Cortland
>>Sam Wismer wrote
however that would seem to go against the intent of the test so I
decided to consult the mfg of the AC source to see what it would take to
modify the unit to true single phase Euro power. The expensive option
is to retro-fit
When using a stub, its reflected signal combines with the incident signal
at the junction. If this reflected signal were equal in amplitude to the
incident signal, it would offer (theoretically) infinite rejection. Because
a stub has a non-zero loss, there is never complete cancellation. If the
We agree. The "gray area" arises from the fact that
"residential" is not strictly defined. When the
distinction was first made in subpart B, it hinged on
whether equipment was sold for use in the home, not
whether it was installed close to a home or farther
away.
I take the position that the nee
Amund Westin write:
>>If this is correct, why can't we just put the surge pulse onto the
shielded
loop and assume that the whole loop was tested at once?
<<
I've not done this test. But thinking about it, failure at anything in the
loop can prevent the surge from stressing the rest of the EUT's.
Probably, you won't get much choice. I've often found older, slower,
quieter logic impractical or even uneconomical to use. It may be made only
by one (thus off limits single-source) manufacturer, or it may be built
using older, more expensive technologies and cost an arm and a leg. And it
may h
of it to Class B, rather than
install Class B retrofit kits on a case-by-case basis. This is a decision I
believe has to be made when the product is proposed.
Regards,
Cortland Richmond
(unemployed, and looking)
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There's another problem with batteries. What do the local authorities
require?
Some years ago, the firm for which I worked made a residential burglar
alarm circuit with back-up battery power. However, we could not include the
batteries in California, because they were too small to meet that stat
Gary,
WHY have the floating system? In order to reduce corrosion in the Outside
Plant wiring, telephone lines are held negative with respect to Earth. This
imposes a need to hold circuitry directly connected to them negative as
well. Specifically, both the tip and ring conductors are maintaine
regretting that they have done so. If you
are beaten and robbed for a display of wealth, it is no use protesting that
the money was counterfeit.
Cortland Richmond
(I speak for myself alone and not for my employer)
== Original Message Follows
>&
or build your loops?
Doug
Cortland Richmond wrote:
>
> I have been using plane shielded loops for over 15 years. Small magnetic
> loops allow localizing defects to small areas and use of small samples. I
> don't claim objective figures, but by comparing the material unde
I have been using plane shielded loops for over 15 years. Small magnetic
loops allow localizing defects to small areas and use of small samples. I
don't claim objective figures, but by comparing the material under test to
a known good shield (i.e.: galvanized iron sheet) and to air, one gets a
goo
creased up to the point where
the profile of emissions, as well as the amplitude, stops changing markedly
from one increment to the next.
Once we have dealt with number, size and shape, we can test with some
confidence that things won't get worse.
Whether we DO so, I don't want to argue!
certification will have to be agreed upon, or forgo the befits of a "Smart"
firearm.
Cortland Richmond
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Bill Fleury
-Original Message-
From: Cortland Richmond [mailto:72146@compuserve.com]
Sent: Tuesday, September 19, 2000 9:30 AM
To: Fleury, Bill
Subject: Re: compactPCI bus
Some time ago, at a previous employer, we had to modify riser cards with PC
ith provision for an external one) and work the same
way I described for our EMC measuring setup.
Regards,
Cortland Richmond
== Original Message Follows
Rene Charton wrote:
From: r...@twn.tuv.com
List-Post: emc-pstc@listserv.ieee.org
Date: Sun, 26 Mar 20
More on BASIC English, etc:
_The Oxford Companion to the English Language_ (ISBN 0-19-214123-X) has
entries about BASIC English, Airspeak (ICAO English), Seaspeak and
restricted vocabulary English. Things in modern usage we old f*rts might
object to are hardly addressed by these abbreviated Engli
Lou,
What you propose for our professions has long since been adopted for
others. For example, the English of maritime shipping, called "Seaspeak,"
was created in 1982-1983, including not only restricted vocabularies, but
also structured ways of speaking appropriate to maritime affairs.
Internati
Basically, one combines the ambient, a signal whose amplitude is not
dependent on distance from an EUT, in the correct phase and amplitude, with
the signals received by an antenna on the OATS. There are at least three
ways (counting CASSPER) this can be done, ranging from the technically
sophistic
I'd be inclined to look at the design. Bandaids have a way of multiplying
until your product looks like a mummy.
If it's a low-level power problem, make sure the EUT's regulator can
respond to induced ripple. This may be as simple as exchanging a cheap
electrolytic cap for one with better ESR, or
>> telephone products destroyed by all sorts of bazaar events <<
Where IS that bazaar? (grin)
Cortland
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The important thing is, first average the quantities, then convert to dB.
Ever seen folks doing video averaging on a log-scaled analyzer display?
Sure you have. And it's wrong. How wrong?
Take two samples, 100 dBq and 25 dBq. Sum their amplitudes in dB (100dBq +
25dBq= 125dbq) and divide by two,
Sounds to me that while the POWER SUPPLY keeps working, it does not
sufficiently attenuate EFT presented to it that your product keeps working.
It is POSSIBLE you might find a power supply that does, but unless you can
control whose PS customers use, it may be smarter in the long run to fix
the E
If a test is performed on a slowly cycling state machine, then increasing
the rate of discharge may not help. Knowing how many discharges it takes to
stop something is often as helpful as knowing how much energy it takes, and
if we apply fifty where one would have done, we have gained little by th
Yes, it can get complicated. However, we don't HAVE to get involved with
the complications. (We can if we want to.)
What I described is a coupled resonant notch filter, familiar to anyone who
has had to reduce spot frequency interference. It would be easier to build
such a notch circuit into the
I think we may be assuming this overload is caused by the EUT. But this is
just as likely to be caused by something else. Medium Wave and Long Wave
broadcasting produces powerful fields at some distance from an antenna.
This has a fix.
If you place a narrowly resonant loop antenna, with feed poin
Also see Telcordia GR-1089.
Cortland
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At a former employer, we finally ended up putting resistive load banks in
computer chassis' (as shielding) for testing power supplies. But we found
that power supplies can fail at full load from their own emissions, and
later, installed in working equipment at lower loads, due to passing
through b
On 6-Aug-01 John Woodgate j...@jmwa.demon.co.uk wrote
>> In Europe, the limits are specified in dB(uV/m), but no-one has been
daft enough to propose limits like 53.9790009... dB(uV/m). <<
Folks HAVE been "daft" enough; 3 volts per meter is 129.542425 dBuV/m,
right? Result of specifying in two sy
On 14-Aug-01 Dan Pierce dpie...@openglobe.net wrote:
>> I have found that if I bypass the earth ground plug I can measure a 80
VAC potential from my chassis to earth ground. I found this out in the lab
when someone touched the chassis and a grounded bench and got zapped. Is
there guidelines
You need to keep fields below the NEBS immunity limits, which are pretty
low, IMHO. However, a 300 mW cellphone is not the same danger as a 5 watt
high-band HT.
Cortland
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ake longer than one second
to show up. You want to do the test in such a way that the tester can note
and adjust to this; I once tested something that had a 30 second delay
before a failure showed up. This can't be helped, and, in this particular
case, one second is far too often
If you want to have your grant of authorization -- or your marking --
challenged by a competitor or discovered noncompliant by the FCC, all you
need to do is play games with the rules. Conservative observance of
reasonable interpretations of the Rules seems prudent to me.
Cortland
If I use a 6 MHz crystal as reference in my 1296 MHz generator chain I
cannot reasonably say that my test must stop at the tenth harmonic of 6
Mhz. I must test to the tenth harmonic of 1296 MHz, and in excess of 10
GHz.
Cortland
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FCC Part 15 goes far beyond digital devices; carrier
current systems, radio and TV receivers, unlicensed
low-power transmitters, and much, much more.
It gives special treatment to digital devices because
they have proven to need special attention. The exemptions
Part 15 contains exist because the
Carmen,
FCC requirements don't directly concern 60950.
They are additional to it. Part 68 is now
handled differently than in the past; check
out the FCC Web page. And you should be aware
that meeting FCC Class A emission limits is
not enough. If sold to the public, your product
must meet the st
Some monitors from the 1990's WILL meet class B with small H's. I know;
I've done it! At a former job (gad, we use that a lot!) we were able to
get monitors scrolling H's in high resolution to pass Class B. Sometimes it
took modifications, which the manufacturer would copy, but it could be
done.
=There really ARE Class B computers, but you
have to work to make them, and you have to look
to FIND them. I've worked on some of them.
Between CRT's and LCD's, the generators are
different, but the levels are not necessarily
lower for an LCD.
A CRT has a fairly powerful, high frequency
amplif
For telecom equipment, one also must bear in mind the required transient
and power-cross stresses. I am just now researching how these differ
between the USA and Europe but one example may suffice: Level 1 common mode
transients of of 1000 volts at 1.2/80 usec are applied to the input under
EN 300
Lower voltages, because of less corona, tend to have more energy, sooner,
relative to the total. You might pass a 15 kV air discharge test -- but
fail, lower.
We ALWAYS want margin, and others ALWAYS want none. My experience in a
previous area of the industry is, this lasts until a rash of field
Since the contact method requires penetrating thin, cosmetic coatings, it
is a bad idea on membrane keypads; bore that sharp point into the contacts
and it's ruined even before you hit the electronics. Not that they'd fare
all that well with direct discharge! In any case, there is often some more
A lump of coal will heat up in a microwave oven. No water needed. It is the
bulk resistivity of an object which allows circulating currents to generate
heat, and while water can help (when we wet something, its chemical bonds
are a source of electrons) it is not the only thing that is heated in a
An STA is basically a permit for operation not normally allowed a license
holder. However, RF immunity testing covers so many frequencies, at such
power, that unless the nearest town is over the horizon, and you have
jungle canopy overhead to absorb RF and keep from jamming satellites, I
think it
systems. A customer might well in
that event call you to task, claiming you
knew, or should have known, that this would
happen when you made a device recognizably
fake. Another reason to add the mark!
Cortland Richmond
== Original Message Follows
(hea
This could get interesting. Does the balun I wound to measure cross talk
require a DoC? I'd have to test it for user safety to be sure, no? Safety
and caution warnings, perhaps? DO NOT CONNECT TO HIGH VOLTAGE.
Seems like a lot of time and money to spend on one toroid through which I
just threaded
HP used to have some information on each probe type's actual impedance in
the instructions packaged with them; it was educational, to say the least.
A 10 meg probe turned into a rather greater load at 200 MHz. Then, too, the
'scope's -3 dB point was much modified by the probe one hung on it.
You
Ed, and list members,
I have for some time been using a digital camera to include data in reports
and e-mail form. It turns out to be as convenient, sometimes more, as
dumping data directly from a digitizing instrument into a computer. I can
use any kind of display -- analog or digital readout, e
Larry,
I had no idea there even WAS such a standard.
Interesting, the things it's possible to learn
here; an assemblage of experts, indeed!
Thanks!
Cortland
== Original Message Follows
>> Date: 24-Jan-01 15:19:07 MsgID: 1078-329 ToID: 72146,373
Fro
Debbie,
Doug Powell explained it as "venting," where slots or holes are added to a
plane in order to let vapor out. However, it is my belief that this is also
done to keep copper balanced during the etching process. I may well be
mistaken, but the EMI and signal integrity concerns we have with th
Where does the term "thieving" come from?
Not having a board-fab background, I guess at it. But it was explained to
me that thieving uses etchant that otherwise would work elsewhere on a
board. One could say thieving steals etchant from other places. I am fully
prepared to be shown wrong, probabl
When fabricating a printed wiring board, if the amount of copper per unit
area differs from one side to anther, undesirable things can happen. One
is, the action of etchant in one area will be less than in another,as
etchant is used up fastest there, than in areas with less copper. This
causes pad
Logically, if it can make emissions worse, it can make them better, too.
Suppose your original board exhibited some resonance, and thieving changed
it. That would certainly lower emissions due to a resonant board. Anything
that resonates will radiate, and this can even be a whole board in its
slot
No, Perry, I have not had problems, even with ungrounded thieving, as long
as the copper islands were very small compared to a wavelength at the
frequency of concern. Under that condition, no significant current flows in
them and they do not contribute to further radiated emissions.
What frequenc
Yes indeed. My preference is for thieving to be done with "dots" or
"islands" small with respect to the shortest wavelength of concern. This is
because thieving can be constructed so as to resonate and aggravate an EMI
problem.
Some years ago, at an employer far away (grin), we had obtained compl
Ken,
When you ask how members "feel," you open a Pandora's box!
We must still meet some kind of installed bottom line; our equipment must
not generate fields above some limit. (We can argue what that should be
some other time.)
However, when _designing_ an EMC solution, we can estimate field st
I'd say either a comb generator, or a sweep generator but use them to
excite a test object of the same general size as the equipment you wish to
test. The smaller your chamber, the more it will be affected by the size of
an EUT sitting in it. If you can be pretty sure what you will test, add its
c
Years ago, I carried some equipment to Marble Falls, Texas, to test at
Professional Testing, Inc's OATS there. I remember one of the sites having
a taut cloth weather shield stretched over a number of bent PVC formers. I
don't know how long those PVC ribs lasted in the Texas sun, but I DO
remembe
Yes, it's important to recognize the limitations of a test method before
relying on it. In this case, the A-B method was used at power frequency and
below, to observe discharge time for UL testing. The MAIN advantage was not
balance so much as that the chassis was isolated from the potential being
>> Can you please explain why? The receiving antenna just responds to the
field strength at its position; it doesn't 'know' anything about the
source - it cold be an EUT at 10 m or a distant TV transmitter or even a
cosmic source. <<
This isn't the issue. The receiving antenna, as you say, can't
Sam,
I think you did it right with one AF and one gain. There's a problem with
that method. You need more information needed to make the _results_
right.
Given a certain power at the antenna terminal, and a known gain and
efficiency, you can calculate the free-space field strength at some
dist
One can also use a pair of probes known to be well balanced and take the
difference between the A and B channels, or
use a differential input accessory or plugin. There is then no possibility of
high-voltage on the instrument chassis.
Cortland
(my own thoughts, and nor those of my employer)
Ri
John Shinn wrote:
> If we refer back to the series, and refer to the n-th term, we
> would all be on the same page (and harmonic).
And in harmony!
Cortland
(disclaimer: my views, not Alcatel's!)
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I can see that this subject hasn't fazed ANYONE.
Cortland
(speaking, as usual, for myself - and not my
employer)
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