In a closer-to-safety example, I've seen mobile radio affect screening devices
at a courthouse doorway
(I was parking for jury duty). Key down; lights up. Key up, works normally (40
meter band, about 10
meters away).
I've seen a poorly wired burglar alarm go off 30 meters from my car when I
A worst case -- real world -- is probably just behind a radio equipped car,
mounting a capacitively top-loaded
antenna at its rear edge, and about 600 watts of RF.
With rather less power, 100 watts, I've occasionally seen adjacent cars'
engines stop when I transmit. It would be
interesting to
Remember the "Miss Piggy" driver? He wore a rubber mask so he could challenge
photo-radar citations. When I was there he had not lost a case, because
the photograph could not identify the driver, and there was at the time
no law requiring a driver to refrain from wearing a mask. I do believe
We need to separate specific regulation from general. The FCC does not care if
a radio front end is wide open, though
it now requires scanning receivers to have 38 dB image rejection. This does
not mean they have narrow front ends,
however. A SW receiver with a 75 MHz If may well have
There is a difference between extending a warranty and being liable for
failure. If your seat belts fail some time
after the warranty is up, the manufacturer won't pay for fixing them on your
car. But the manufacturer may well be
held liable for the failure.
Cortland
Andrews, Kurt wrote:
AIrbag testing? Well, since it costs about $US 1500 to replace them (here), I
suppose there WOULD be a price hike!
One of the tests run on a modern, computerized auto when the ignition is
turned on is for airbag activation
circuitry.
Cortland
James, Chris wrote:
I don't
Some cars do this? Nonsense! As you of course know.
1. It may be that your windshield antenna will not work with the particular
model radio you got, which would only mean drilling a small hole and
installing a whip. You should be able to find this out by calling the
manufacturer and asking.
I have it from a message on the r...@contesting.com list that Phillips bulbs
produce less RF noise than others.
I can't vouch for that, however.
Cortland
(What I write here is mine alone.
My employer does not
Concur, agree or else endorse
These words, their tone, or thought.)
Rich Nute wrote:
to build or no one will be
able to sell them at a profit. They can't be
unreliable in the field or people won't buy them at
all. And they can't cause too many problems, or the
company will be sued. One factor weighs against
another.
We are at the balance point.
Regards,
Cortland Richmond
(What I write
I'm old enough, Ken, to remember ADF approaches! But
laptop switchers often operate inband to frequencies
used by aviation non-directional beacons. This makes
them more of a threat than the harmonics from
lower-frequency ones. It is also, of course,
possible for the laptop's other emissions to
If they meant "radio compass," that is a different can of monkeys.
The radio compass was traditionally the indicator for the ADF set , pointing
to the ground station, and was usually mounted so as to revolve in front
of a scale which rotated with the aircraft's' magnetic heading. A noisy
It appears that a lot depends on what we mean by the
word safety. If this means the elimination of
as-yet-unknown risks, why, nothing can be shown to
be safe. If we mean the prevention of hazards that
are reasonably predictable, we do that already. Or
should! The existence of standards which
to interference with aircraft navigational or
communications systems. In one case, a specific frequency was reported.
Yet when the computer was checked, I could find no trace of an emission
anywhere near the frequency supposedly affected.
Cheers,
Cortland Richmond
(my opinion's, not my employers
Doesn't sound like you're missing anything. We are just talking about
different things. Common disease, here! Certainly, for the same directive
gain, the aperture of an antenna is smaller at higher frequencies. However,
I'm not holding gain constant, but size.
If the two antennas are the same
An antenna of some physical size will indeed have gain increasing with
frequency. There is some justification, a 1 GHz antenna being reasonably
small, for assuming that antennas will have similar sizes -- and increasing
gain -- above 960 MHz. However, I suspect that the original limit was
simply
The navigation systems which are protected by regulation were developments
of the 1940's, and -- except for interference! -- work pretty well. They
are analog technology, using phase and amplitudes of audio frequency tones
to determine position and/or deviation from course.
For landing, the ILS
I've been watching this discussion with interest. It appears you are
agreeing with each other - at some length. (grin) The subject of
interference to airborne navigation and communications receivers seems
never to go away. Since it was the probability of just such interference
which lead the FAA
Chris,
You SURE you want to do this? I believe CO's strictly isolate AC powered
gear. They have this thing about AC hum, you know...
Cortland
---
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Technical Committee emc-pstc discussion list.
a ground isolator. At RF, one MUST return current to
source in a short distance, which a typical CO ground system cannot
satisfy, or see radiated emissions and undesired coupling between units
increase.
Cheers,
Cortland Richmond
---
This message is from the IEEE
One need only have a battery short in a pocket to receive a heated
reminder that batteries are not inherently safe devices. I've a pair of
trousers with a hole melted in them from an accidental short circuit.
Cortland
---
This message is from the IEEE
Why not turn off the lower voltage that RUNS the supply? You can also
ground the test sample when the door is open, using a contact separated
from ground during the test by a wedge able to withstand 10 kV.
Cortland
---
This message is from the IEEE EMC
Brian Kunde wrote:
Sometimes when we have a system tested for CE (emissions and immunity),
one of the other companies pieces of equipment will cause the system to
fail.
Yes, indeed. Luckily, I worked for a computer manufacturer and we could
find other vendors. Still, I have found it
Dave Palmer wrote:
Assuming that what I am actually taking about is dipole gain (I am a bit
of an ignoramus I'm afraid) Can anyone give me a basic approximate formula
for the variation of gain with frequency for frequencies that are up to a
factor of (say) 10 away (above and below) from the
I've used the approach that one doesn't design compliance IN, one designs
non-compliance OUT. People who have the view that EMI reduction is a matter
of filters, shields and spring fingers, find out, if they don't know
already, that this is the expensive way to do things. They become more
When we started seeing 50 volt caps blowing up on a 5 volt output it became
evident that the problem _we_ had, instant mortality (grin), was
over-current, not over-voltage. We didn't actually see a voltage transient
- a 'scope had in fact ruled that out - but someone in management had
apparently
Chris,
The issue isn't voltage rating; low-ESR caps such as these are susceptible
to excessive charging current at turn-on. At a former employer, we saw
REALLY GOOD, expensive caps used on a computer's 5V bus exploding at
turn-on, even ones rated at 50 volts. Replacing them with cheaper
So, what will happen to PLC (PowerLine Communication) in US ? I
know an application called CEBus and they operate in the frequency
band 100kHz-400kHz. Those folks using CEBus will not meet the new
conducted emission requirements.
Maybe, that sort of equipment is not within the scope of FCC
I don't have access to the documentation I did where I used to work (darn
it) but luckily, Jim Quarfoot at TI wrote a great article about ADSL
problems in the 25 July 2002 _Comms Design_. I recommend it.
( http://www.commsdesign.com/main/9812/9812feat1.htm )
Per the article, maximum ADSL
Derek Walton wrote:
I'm testing a product that's switching at 50 kHz, modulated by a 1 kHz
signal.
I'm getting a great deal of noise between 9 kHz to 13 kHz, I think is
related. Specifically, it goes when I stop the modulation... Any ideas on
ways to clean this up. Filtering seems to be
I'd be interested in seeing what you've got. Remember, not only the board
can resonate, but structures on and in it, and at lower frequencies, too.
Don't send the file to my Compuserve address, though; I can only see text
here.
Cortland Richmond
k...@earthlink.net
Some years ago, I had to show a TV-card vendor (their card made a compliant
computer fail Class B) the right way to do this. They were passing normal
video through, and had apparently never TESTED in standby mode to see what
interrupting shields with pigtails would do. I bundled all the video
Joe Martin (marti...@appliedbiosystems.com) asked:
Our company is planning on moving the Chemical Compliance Department from
the Quality Systems Department to the Compliance Engineering Department
(Product Safety/EMC). What do you see the advantages are in this
restructuring?
Depends if the
Phooey! How DARE you bring my musings down to the prosaic probabilities of
promiscuous spell checking?
Cortland
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Visit our web site at:
I swear this is true. From job requirements for a job, on monster.com:
·Ability to research and interrupt Bellcore, ANSI, IEEE, NEMA, and JIC
standards as applies to telecommunication and electrical equipment
required.
Cortland Richmond
Rick Busche wrote:
Speaking of surge and EFT I have been looking into
the real life performance of equipment installed
in the field. My equipment is three phase ITE and
is typically in operation in a Heavy Industrial
environment previously defined in EN 50082-2. In
particular this equipment
As a victim of the older plug, I welcome such protection. At age 8, having
been told that I could be hurt by sticking my finger in the receptacle, I
of course had to try it, and am lucky to be alive.
Cortland
---
This message is from the IEEE EMC Society
(the unplugging process may need to be repeated a few times until the
capacitor is disconnected when the mains is high at the time of
disconnection and so gets a decent charge!)
At a former employer, we monitored the wave form with a 'scope, and
repeatedly opened and closed the connection to
Chris,
I had a thought, reading your message, that even a plain metal sheet, if it
is close to a half wavelength across, has an RF hot spot in the middle. In
that case, you must keep one side of the sheet (plane) cold, while the
other is not. This means good grounds (UHF RF returns) at the
List-Post: emc-pstc@listserv.ieee.org
Date: 20-Feb-02 13:38:27 MsgID: OUTBOX
MgTo: Gabi Hoffknecht INTERNET:gab...@simex.ca
Subj: Re: Using PCB traces as transient voltage suppressor
Hi, Gabi,
I have a bad feeling about spark gaps on a board. There may be conductive
material left on the
When do you need a fuse? Level II is the only time you are allowed to lose
functionality, and the requirement for THAT is, it can't catch fire or
explode. I've seen trace fuses tried. The problem comes after the trace
blows. You are at the mercy of your board shop, and if you use a number of
Except... I (and other classic Compuserve users) won't see these messages
at all, unless and until they appear in someone else's REPLY in a form
Compuserve can send. It LOOKS great - but please don't send HTML to the
list.
Cortland
---
This message is
Your state that NEBS requires UL1950 safety testing. This may be true
for CPE but not equipment sitting at the CO. Please correct if I am
mistaken.
There's been a long wrangle but, yes, NEBS does now follow 60950. Some
accommodations appear to have been necessary, as it's evident that
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
body rather than sending it as an attachment.
Thanks,
Cortland Richmond
---
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To cancel
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
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
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
---
This message is from the IEEE EMC Society Product Safety
Technical
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 intend
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
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
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
The
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
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
detector) it's
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
---
This message is from the IEEE EMC Society Product
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
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.
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
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)
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 punched
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
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
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 to
of a one-eighth
wave stub is equal to its characteristic impedance. Adjust spacing for
desired impedance.
Cortland Richmond
---
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Technical Committee emc-pstc discussion list.
Visit our web site
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
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 RD operation, I was
doing a prescan of an EUT with a CD-player/CD-ROM drive in it. Testing
with a bunch of corporate
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
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
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
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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Visit our web site at:
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
---
This
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 need
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.
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)
---
This message is from the IEEE EMC Society Product Safety
Technical
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
Another interesting susceptibility issue is usually not addressed. Snow. I
have seen (in Germany) a radar stoplight camera flashing over and over
again as it tried to capture on film snowflakes rash enough to pass while
the light was red.
Cortland
---
Almost 20 years ago, my then employer bought a Keytek ESD gun that would go
up to 25kV. We quickly noticed that one could play a bit of a practical
joke with it. With the gun on a tripod, locked on at 25 kV, and using a
contact (pointed) tip, it generated a copious supply of ions, which easily
During my final active duty tour, with the US Army in Germany, we deployed
Korean-War-vintage, manual telephone switchboards for less critical
telephone circuits. That was OK as long as we kept them on US bases and
connected them only to US lines, but as soon as we connected them to
Bundespost
this particular sample has been thoroughly abused in environmental
testing (including several unintentional unfortunate CONDENSING temp
humidity runs - ever look into a chamber and see what looks like your
product sitting in a cloud? Not fun). Months and tests later, the dirt or
grime is
David Heald wrote:
I'm preparing for an emissions test and I had started cleaning some of
my chassis mating surfaces with a pen/pencil eraser then alcohol to
ensure the surface to surface contact was good.
David,
This is an ever present help in time of trouble. Don't do it. (grin)
Cleaning
Russell (r@totalise.co.uk) wrote:
I'm looking at an ambient scan starting at 32dBuV/m @ 30MHz, dropping to
18dBuV/m @ 70MHz then gradually (with small peaks and troughs) rising to
41dBuV/m @ 1GHz.
Russell,
Are you sure these are room ambients? They might be the analyzer noise
floor.
One indicator is actually present BEFORE applying this test; the extension
of the subject's middle finger in the tester's direction!
Cortland
---
This message is from the IEEE EMC Society Product Safety
Technical Committee emc-pstc discussion list.
Visit
identifying
a specific card's contribution from among a whole shelf of similar ones.
Oh yes. When you pull a whole lab out of your jacket pockets, eyebrows may
go up. When you find and fix the problem, jaws will drop. Guaranteed!
Cheers,
Cortland Richmond
DISCLAIMER: I have no financial or other
Another interesting thing -- not the same as this -- is what happens to
the upper-case Omega some documents use instead of spelling out ohms;
some software turns it into W. I could have SWORN I'd see a 1000 W
resistor on a modem card!
Cortland
---
This
worked for firms who could
afford to buy copies of their own. But imagine one day finding that one
has been convicted in absentia of speeding through a town without speed
limit signs, limits available only by subscription.
Cortland Richmond
On 10/7/2013 1135, Peter Tarver wrote
.
Cortland Richmond
-Original Message-
From: Ed Price edpr...@cox.net
Sent: Jun 17, 2014 9:14 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] MIL-STD-461G testing survey question
Ken:
I seem to have misplaced my lab sometime in the past two years, but I
switched to field probes long
Around1991 I was able to demonstrate that a computer that must be shipped with a really well shielded printer cable must also be shipped with really well shielded PRINTER. Luckily, I caught it before we sent it out for an FCC ID, and minor rework made the the poorly placed bypass capacitors
Well, not if we read Part 15::§15.5 General conditions of operation.(b) Operation of an intentional, unintentional, or incidental radiator is subject to the conditions that no harmful interference is caused and that interference must be accepted that may be caused by the operation of an authorized
I forwarded Dr Feynman's appendix to the Rogers Commission report to someone involved in processes that would, if followed, rein in this kind of thing. I am not an optimist.Cortland Richmond-Original Message-
From: msherma...@comcast.net
Sent: Mar 6, 2015 12:16 PM
To: k...@earthlink.net
It's possible the noise quite soon after the door is opened is still below the
limit for unintentional or incidental emitters. That's enough to interfere with
radiotelescopes.
Cortland Richmond
-Original Message-
From: Wiseman, Joshua E BIS joshua.e.wise...@carrier.utc.com
Sent: May 15
Imagine how he'd react to learning there are wet transformers in
deserts. Call it a waste of water?
Cortland, KA5S
Not wet behind the years
On 6/8/2016 1:04 PM, Brian O'Connell wrote:
A customer pointed me to the below link as an authoritative source. Told the
sales manager that the
within an
integrated circuit.
Hmm. An on-board WiFi device "uses" (non-clock) GHz range frequencies
-- internally.
Running for cover ...
Cortland Richmond
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