Monday, September 8, 2014

The Annual IEEE EMC Show in Dresden (continued) Plus Elephant #4 ‘The Zip Code Lottery in Achieving Product Compliance’

Great news, borrowing 3D EM software to diagnose the performance of the automotive radiated emissions test fixture is a go! I have been given a contact at the 3D EM software house and things should pick up quickly after the contact returns from the EMC Europe show in Sweden. I am excited. Meantime ....

The Annual IEEE EMC Show - Why Dresden?

Leaving aside the European location for the time being, why does anyone, whether presenting a paper, attending the technical presentations, or exhibiting, bother to go at all?

Let’s hear it from the exhibit floor first.

The Vendor’s Tale

Motives enticing the vendor to attend are varied and complex. They include but are not limited to:

• It is a place to display application-specific wares to a highly-targeted audience

• It is an economical way of catching up with a lot of key people all in the one place, all at one time, saving the expense of flitting all around the country to meet each in turn.

• It is a low-cost opportunity to provide Rep product training, and a place to meet, interview and recruit reps. This situation is symbiotic as Reps are often touring the hall looking to add lines to their line card too.

• You can arrange to meet local customers either at the show, or visit them just before, or just after the show.

• You get a chance to meet your competitor’s customers. I have seen booth staff look on in abject horror as their best customers wander off in the direction of a competitor’s booth.

• You can check out what is new with the competition – new products, new hires, etc.

• It is a chance to get to know and recruit a competitor’s best staff (recruitment activities such as advertising positions at the booth is banned, but this does not prevent poaching).

• Strangely, it can be seen as dangerous not to exhibit – rumours of solvency issues can spread, prospects may read into it that you are reducing your market presence in this sector, and there is always the concern that a competitor choosing to attend may gain from what turns out to be a ‘good’ show after all.

The main de-motivators to signing up for a trade show include:

• Disappointment with the number and quality of sales leads at last year’s show.
Many vendors go in with unrealistic expectations. In their dreams they would like orders to be placed at the show, or very soon afterwards. More savvy companies know exhibition attendance plants the seeds of future sales by reinforcing market presence.

• It is hard to measure the return on the dollars invested
The problem of how to measure return on dollars spent is not limited to exhibiting. If that full page advertisement in a magazine resulted in a major sale 18 months later – how would you know? If not attending a show or looking small (you decided to reduce the booth size) at a show cost you the opportunity of a major sale, how would you know?

• Other marketing opportunities competing for scarce marketing dollars
With little hard measurement data to compare the return on investment types, adding an exhibition to the marketing mix will always be a dilemma for companies.

• Opportunity costs
These are all the other things the sales and marketing staff twiddling their thumbs at the booth could be devoting their time to (sales presentations, customer visits, etc). The saving grace of emailing from the booth or the hotel room is only ever fire-fighting, or trying to hold things until you get back. It is never as efficient as being at the office.

Before we leave the vendor’s tale, there is a personal reason booth-staff like exhibitions. Depending on the attractiveness of the location, it can mean a cheap vacation of sorts. Your flight and hotel room are already paid for by the company, so you only need to find the airfare for the wife and kids and ‘wham’, you have a vacation. The better shows have tours to amuse family members while you are away working the booth.

Next time we will hear from the attendee principally at the show to learn from the technical presentations. Here is a ‘heads up’. It is in the nature of vendors to complain, and some of the big ones truly believe the show exists because they fund it with their exhibition hall floor-space fees. Nothing could be further from the truth – no technical presentation attendees, no show.

The Linearization of EMC Amplifiers

This topic has not been forgotten, it has just been on hold while Elephant #2 ‘Disharmony in Harmonic Limits’ was explored to the full. The previously proposed minus 13dBc giving 75% field purity may not be good enough. However we haven’t factored in the cable loss (higher for the harmonic), so let’s do a few more calculations.

Meanwhile – as another way of looking at how the linearization is achieved, think of the noise cancelling headsets as used by airplane passengers.

The principle of operation for the headset is to sample the ambient repetitive noise (aircraft engine hum), invert it, and add it to the signal feeding the speakers. The result is cancellation of the hum. The blurb on the box says you can still hear announcements etc, as if this was a designed in feature, but this is a trick. The headsets can only cancel repetitive deterministic noise, they cannot cancel stochastic noise.

For our EMC application things are even simpler. We know the noise frequency in advance and have a PC that has the necessary cancellation signal attributes stored and ready for use.

Elephant in the Test Room #4 - The Zip Code Lottery

Elephant #4, like the other elephants we pretend not to see, is one where many already know about it, but few mention it.

With this particular elephant, whether a company’s product passes RF emission tests can depend on which test house it is taken to. Most companies prefer to use a local test house for ease of transport of the product, and for the ease of having one of their engineers at the site to try and fix problems as they arise.

Some years ago, a round robin study showed that for the self-same test-piece sent out to several test houses, the measured emissions levels varied by many dBs. The word around the water cooler was it was up to 10dB difference between the labs.

So if a company is unfortunate enough to be in the ‘capture’ area of a test house that measured high emission levels from the round robin test-piece, then their new product may fail the test. Conversely, and somewhat ironically, a second company’s product, with worse emissions than the first one’s, could pass at a test house that measured lower emissions during the round robin exercise.

You may argue that there could be myriad reasons as to why this situation exists, including operator error, the stacking of uncertainties in one direction, etc. But to my mind it is because we are using an unevenly damped reverberation chamber to try to contain and control the fields within the overall test space.

To put this in context, we will start next time by looking at the layout and equipment arrangement of open area test sites.

To be continued

-Tom Mullineaux

Thursday, August 28, 2014


At long last, Department of Defense Instruction 3222.01, the DoD Electromagnetic Environmental Effects Program, has been signed and released. For those of you following along, its been a long road! See the post from Dec 2013.

So, we have a new DoD E3 Instruction…what does that mean? First of all, as the title indicates, it's an Instruction, not a Directive – the difference is that directives tend to be very broad brush with a lot of “thou shalt” but not a lot of “how shalt I?” That is, the Directive has no procedures in it, while the Instruction does. While the new Instruction isn’t chock full of new procedures, it does strengthen the requirements to consider E3 in military procurements and to assign various responsibilities to DoD organizations at every level.

So, what’s new and exciting in DoD Instruction 3222.01?

  1. The policy section is a lot more specific in the new document. There is reference to operations without degradation due to EMI, the operational EME and Joint Service control through DoD –wide techniques and procedures. Definitely trying to get the Services to play as a team, E3-wise.
  2.  It formalizes the DoD E3 Integrated Product Team, which holds monthly meeting to discuss E3-related topics and issues relevant to all military services.
  3. It provides a more formal and expanded description of the DoE E3 Program details of which are managed by the Defense Spectrum Office under DISA. It details many of the requirements for E3 control through the life cycle of a military system.
  4. It incorporates the criteria for the installation and operation of systems and equipment in the vicinity of designated DoD sites, which was previously the topic of a separate Directive.
  5. It provides greater references and procedures for controlling electromagnetic hazards.
  6. And finally, it greatly emphasizes the need for E3 related awareness and training. This includes several references in the Responsibilities section requiring DoD organizations to develop and provide such training to both operational personnel as well as the acquisition corps.

OK, maybe its not as exciting as running a full threat lightning test on an aircraft you’re sure is going to fail, but it's great news for those us of in the E3 business. The Instruction strengthens the requirements to implement E3 control and to make sure that everyone involved in military systems acquisition is aware of the importance of E3 control. And at the end of the day, it's to make sure that our soldiers, sailors, marines and airmen have equipment and systems they can count on in today’s operational electromagnetic environment.

Download the Instruction from….go to Policy and Instructions!

-Brian Farmer

Tuesday, August 26, 2014

The Annual IEEE EMC Show – Why Dresden? Plus Proof of the Arbitrary Selection of Automotive Amplifier Harmonic Limits

Read other posts in the "Elephant in the Test Room" series here.

It is looking good for using 3D software to diagnose the performance of the radiated emissions test fixture. Should get the go ahead any day now. Meantime, let’s explore this year’s hot topic.

The Annual IEEE EMC Show - Why Dresden?

It is no surprise that some USA residents in the EMC industry are wondering why the 2015 symposium is being held in Germany. Here is my take.

I learned long ago in history class that the first duty of the State (Monarch, Oligarchy, elected Government, Dictator) is to protect the State’s borders. Other duties may be of the utmost importance, but are always secondary to this first duty.

Likewise, when it comes to the board presiding over an engineering society symposium, the board’s first duty is to ensure the survival of the symposium.

With this in mind, let’s examine the decision to hold the 2015 symposium in Dresden.

History on a Postage Stamp

The symposium really took off with the explosive growth in interest caused by European legislation stating that Electrical/Electronic goods must be stamped with the CE mark.

Before being stamped with the CE mark the goods had to comply with regulations on electromagnetic compatibility. No CE mark, no sales into the European Common Market.

This got the attention of US companies intent on selling into Europe, many of whom were completely ignorant of European EMC regulations. Employer backed symposium attendees hungry for knowledge went through the roof. Subsequently, so did the number of fee paying vendors buying booth space. A happy time in the history of the symposium, and a time of plenty for the vendors.

The powerhouse behind the regulation was Germany, so to me it is quite fitting that if the event is to be held outside the USA, then it should be in Germany. I have been to the annual EMV show many times in Munich and in Dresden (the cities take turns). Good shows when I used to go, but at the time not as ‘grand’ as the US show. To me, and I dare say many others, the IEEE EMC symposium was and always will be ‘the greatest show on earth’.

At the time (1980s) I saw the European regulation as protectionist, and simply a market barrier erected against low-price / low-quality products flooding in from third world countries. However, since then, EMC has become a world-wide concern in its own right, whether covertly protectionist or not.

All good things come to an end and like most industries, the EMC industry matured and saturated. The hunger for knowledge long since satisfied, symposium attendance has declined with a corresponding shrinkage in the number of vendors. Year on year the show seems to get smaller. This is the current situation faced by the IEEE EMC board.

[Somewhat off topic here, but it is widely acknowledged that the car industry is a key bellwether of looming economic recessions. The first thing people do as times harden is put off buying that new car. Well, guess what? There is another. Sales in the entire EMC industry fell by 75% overnight during the lead up to the last recession (the near financial meltdown, auto-manufacturer bankruptcies, etc). I suppose companies can put off buying that new piece of test equipment just as we can put off buying that new car.]

I heard long ago that the types of attendees at the show were basically made up of one third, one third, one third. That is, one third was made up of vendor booth-staff, one third came from the surrounding area, and one third came from ‘out of state’.

In my view, this will translate across the Atlantic Ocean, with any shortfalls due to the European location made up by local vendors and attendees.

Next time we will look at current incentives / disincentives to attend the show, and why attendees bother to attend at all. Meantime, a heads up on where this is leading - the Dresden decision was a hard-nosed business-style decision, completely in line with the first duty of the board.

Proof of the Arbitrary Nature in the Selection of Automotive Harmonic Limits

When we first questioned the automotive edict stating power amplifiers used in RF immunity testing must have -20dBc harmonics or better, we wanted to know ‘just how sensitive is the test field integrity to amplifier harmonic performance?’ Is it a lot or a little? Is -20dBc a great deal better than -19dBc?

On the way to the answer, we derived the simple equation that determines the integrity of the test field itself,

E2dBc = P2dBc + G2dBc

Where E2dBc is the harmonic field level compared to the fundamental field level in the test field itself (in dBs), P2dBc is the harmonic power level compared to the fundamental from the amplifier (in dBs), and G2dBc is the gain the antenna presents to the harmonic compared to the gain it presents to the fundamental (in dBs).

For our purposes, our 1-18 GHz horn antenna has a fixed worst-case G2dBc of 4dB (fundamental gain to harmonic gain ratio).

Calculating the Percentage of the Intended Field

E2dBc doesn’t give much of a feel for how pure a test field is, other than we know the bigger the magnitude of the number, the better the field (-11dBc is better than -10dBc). Fine, but how much better? To get a true feel for test field integrity, it is best expressed as the percentage of the total test field created by the intended test frequency.

The following example shows how the percentage is calculated: -

For no particular reason we choose E2dBc = -10

E2dBc = 20 log10 [E2/E1]
where E2/E1 is the ratio of the harmonic field to the fundamental field.

20 log10 [E2/E1] = -10
E2/E1 = antilog10 -10/20
E2/E1 = antilog10 -0.5 = 0.316
E2 = 0.316E1

Substituting this into Total field E = E1 + E2

Total Test Field E = E1 + 0.316E1

E = E1 (1 + 0.316)

E = 1.316E1

E1 = E/1.316

E1 = 0.76*E

That is E1 is 76% of the total field

As a demonstration of the diminished return from improving the harmonic performance of the power amplifier by 1dB, look at the table showing the percentage of the intended test field making up the total test field.

As can be seen, an amplifier with worst-case harmonics of -19dBc will result in 85% test field integrity, whereas one with -20dBc results in 86%. One percentage point difference seems tiny, is barely measurable due to uncertainties, and seems unreasonable. Maybe the automotive technical committee that deemed this arbitrary number lacked the engineering grounding that would have allowed them to see just how ridiculous the edict is.

It is down to you as a blog audience to draw your own conclusions, but let me state mine - the responsible automotive technical committee was duped. Look, there is a lot to be said for having industry representatives on committees, they are a ‘calming’ influence on what can, and what cannot be done in terms of the feasibility/affordability of a proposed solution. But how do you stop those supplier influencers from skewing decisions that give the supplier company paying their salary a market advantage?

-Tom Mullineaux