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
