Tuesday, March 3, 2015

Feedback on the Central Texas EMC Chapter Event and the Upcoming Santa Clara Show

The Central Texas Presentation

The potential audience stayed away in droves with the result that the number attending the presentation was disappointing. This seems strange when you consider the Central Texas Chapter capture area has two major EMC chamber manufacturers, and that previous presentations I have given attracted a big audience. A lot of pizza was taken home – but thanks all the same to Nexio EMC Software for sponsoring this. The chapters are given a pittance to cover expenses such as providing hospitality at presentations.

Still, it is an ill wind that blows no good, and the small audience allowed deep discussions during the presentation as opposed to the normally practical requirement of holding all questions to the end.

And those few that did attend were rewarded by witnessing never before seen animations of a wave striking an angled hot-wall.

Some of what the absentees missed

After I reminded the audience about the various optical phenomena to watch out for, and gave my view on why absorber is shaped the way it is (maximizes the number of pyramids you can cut from a block of absorber material), I introduced my alternative ‘non-polarized’ layered-cone absorber design.

Foam based layered tapered loss approach

Layered approach a candidate for absorber cone design

Non-polarized layered-loss cone design

An astute observer spotted the flaw in the design before I got there, and for now it looks like the non-polarized idea won’t fly.

Any blog readers out there spot the flaw?

I have decided to create an ‘Inner Circle’ as regards early access to simulation results. The circle needs to contain a mix of ‘the right stuff’, from hands-on EMC engineers to engineers from outside the industry. The astute observer mentioned above won his spurs in the discussions and is now a member of the Circle.

The Inner Circle will plow it’s own furrow, and so has no use or time for ‘experts’ that know test standards chapter and verse, and blindly defend existing test set-ups. These guys are as much use to the Inner Circle as a chocolate coffee pot.

The expectation is that members will develop from passive observers to live participants in designing experiments that isolate various phenomena.

As I said, it is an ill wind that blows no good, and Ross Carlton of NI may be interested in my offer of on-site test-staff education on the physics behind EMC chamber tests.

If anyone is as keen as I am on using powerful 3D EM software to examine new ways to solve old issues, maybe we can meet up briefly at the Santa Clara show and I can run through the important slides in the presentation over coffee? Or if you wish to be considered for the Inner-Circle think tank, again, maybe we can meet up at the show? ‘Experts’ need not apply.


Talking of Santa Clara, the show is almost upon us.

The Upcoming EMCSI Show in Santa Clara

I have an admission to make - I was under the impression that the Santa Clara show was created purely as a compensatory gesture to those who cannot make the annual August EMC event taking place in Germany this year. I have touched on the Dresden show in previous posts and, in my usual self-righteous manner, concluded that on occasion, it was good to push the international nature of the IEEE. But it still seems a little like two allied political parties ‘splitting the vote’ to neither party’s benefit.

However, now that I am checking the Santa Clara EMSCI website in preparation for attending, my eyes are opening to the fact that this is likely to be an event on par with Dresden. One key indicator is a booth space count of the two exhibition halls. A quick look shows around 196 booth spaces at Santa Clara (plus 16 table top spaces), against the currently planned space for 140 booths at Dresden (plus 50 table tops). In both totals, I took into account the number of booth spaces taken up by the ‘islands’ the bigger companies utilize.

So to all you Cinderellas out there unable to attend Dresden – “you shall go to the ball”, and on the face of it, it is likely every bit as good as the overseas event. Time alone will tell.

So, what should I go see at the show?

The keynote presentation is a must. Made all the more topical with the North Korean threats to South Korea, I have followed the HEMP topic with interest and would be interested to know how the HEMP filters placed at vital establishments guarantee to ‘catch’ the pulse coming in from the grid. Given the short rise-time of the HEMP induced wave, and given the finite time-constant that dictates the performance of all MOV based circuits, the race between the fast-rising pulse and the trigger time of the MOV is likely a race too close to call. Could be the MOV triggers 10 times faster than the time it takes the pulse to rise to a damage level. Somehow I doubt this. Or maybe giant ferrites slow the leading edge of the pulse giving the MOV time to trigger. The great thing about a show is that there is always someone there that knows.

So that is 8:30 – 10:00AM on Tuesday gone, and given my interest in absorber technology as regards chamber performance, I will definitely shoot at attending two papers on the use of absorbers at 11:00 and at 11:30AM. I already marked them in red on the program.

Then between 1:30 and 3:00PM there are panel discussions where the second panellist, and I quote, ‘.... will present aspects of absorber material and their principles of operation including various test methodologies for quantifying absorber effectiveness.’ Right up my street - yes please.

Naturally I shall be meeting with Dr Andreas Barchanski of CST at booth #412 to discuss the work on diagnosing the underperformance of 3m chambers. Add to this a bunch of scheduled meetings, and add a hunt on the exhibit floor for the newest and greatest new products out there, and I doubt there will be much time for lazing around.

To be continued .......

Tom Mullineaux
Lionheart Southwest

Friday, February 27, 2015

SSRA Components

As we noted, the purpose of the spectrum supportability risk assessment is to identify and assess regulatory, technical, and operational spectrum issues with the potential to affect the required operational performance of the candidate system. For example, in addition to determining that a system’s bandwidth requirement complies with an individual nation’s frequency allocation scheme, a new or modified system must also be evaluated with respect to:

• The system’s potential to cause interference to or suffer from other military and civilian RF systems currently in use or planned for operational environments.
• The effect of the system’s proposed spectrum use on the ability of the force structure to access the RF spectrum without interference.
• How the system’s spectrum use conforms to the tables of frequency allocation of intended host nations, ensuring regulatory protection from other national co-band spectrum users.
• If individual host-nation frequency allocations include enough bandwidth to fully support the system’s operational mission, for example, required data rate.

An SSRA should include the following components:
Regulatory component: Addressing the compliance of the RF system with US national and international tables of frequency allocation as well as with regulatory agreements reached at the International Telecommunication Union.
Technical component: Quantifying the mutual interactions between a candidate system and other co-band, adjacent band, and harmonically related RF systems, including the identification of suggested methods to mitigate the effects of possible mutual interference.
Operational component: Identifying and quantifying the mutual interactions among the candidate system and other US military RF systems in the operational environment and identifying suggested methods to mitigate for possible instances of interference.
E3 Assessment: At a minimum, EMC and EMI are to be addressed to determine the potential for interactions between the proposed system and its anticipated operational EME.

When conducting an SSRA, operational restrictions, availability of frequencies, host nation approval (HNA), and known incidents of electromagnetic interference (EMI) must be considered. S-D systems and equipment cannot be operated legally until they have been granted equipment spectrum certification (ESC) by National and DoD authorities; in addition, a frequency assignment must be obtained from the appropriate area frequency manager. For systems that will operate outside the United States & Possessions, an HNA also is requested prior to operation in each foreign country designated for use.

Additionally, the program must be monitored to determine the EMC and EMI impact of any changes to such operational RF parameters such as tuning range, emission characteristics, antenna gain and height, bandwidth, or output power, etc. Changes to these parameters may require additional E3 analyses or tests. The E3 Assessment should:

• Identify and resolve co-site EMI issues during system acceptance testing.
• Demonstrate repeatable EMC utilizing appropriate development models.
• Maintain system E3 design integrity during operations.
• Implement procedures for EMI problem reporting.

Producing an SSRA isn’t a trivial exercise! Next time we’ll take a look at some of the challenges in putting an acceptable product together.

-Brian Farmer

Friday, February 20, 2015

The Diagnosis of Under-Performing Semi-Anechoic Chamber Designs #2, and a Report on the Joint Dallas EMC Chapter/Northwest EMC Event

I apologize for the prolonged absence, my career has taken a new path and the preparation for this took up all my spare time. Things are freeing up once more, so I am glad to say I can now return slowly to blog writing.

I actually made the time recently to attend a technical presentation on obtaining wireless device approvals, jointly hosted by the Dallas IEEE EMC Chapter and Northwest EMC. The event took place on Wednesday 18 February at Northwest EMC’s new test facility in Plano Texas. I found the presentations full of useful information and the hospitality was simply great. If there is one of these free technical events locally, you are crazy not to go. And talking of events, I shall be making a presentation myself at the Central Texas IEEE EMC Chapter on Wednesday 25 February (see below). If you are local – you are crazy not to go.

Getting back to the Dallas event, the theme was on how to obtain wireless device approvals at home and abroad. After watching the presentations, if I was forced to summarize the current wireless device approval situation in a single clause, I would say ‘A fluid maze with many pitfalls in foreign approval processes’.

Harry Ward (of Regulatory Consultancy Approvals) kicked things off with an overview of what an approval is and the route to getting one. This was followed by Greg Kiemel (Director of Engineering at Northwest EMC) who filled in the drivers behind the explosion in the number of wireless devices and the current role of TCBs (TCB = Telecommunications Certification Body)

According to the presentations, service providers are spending billions at spectrum auctions because kids want video streaming, which translates to ever faster data rates. Apparently faster data rates became a reality when MIMO married OFDM, and the technology grew exponentially with spatial multiplexing in conjunction with OFDM achieving rates of 20Mbps.

As an indicator, it seems there is an average of 13 new tablet approval applications every month. With this number of approval applications it was a wise move by the FCC to pass the approvals process to TCBs. Without the introduction of the TCB program the FCC would have been swamped.

The Wisdom of the FCC Policy on Using TCBs
Readers should not run away with the idea that being a TCB is a license to print money. TCBs like Northwest EMC have invested a small fortune on wireless telecom instruments, many $70k to $100k each, and this despite business being very slow in the early days of the FCC program. The plot shows the hand over and pick up of applications over the years.

Getting back to market drivers, it seems it is not all about kids playing games on line. Bluetooth technology is now being used to provide better patient care by relaying monitored vital signs to care providers via MedRadio.

One pitfall that came out of the presentations was the hard to believe situation where companies actually design and build a wireless device without fully researching the approval hurdles set by each country in the World. They then find to their horror that they are not able to achieve the necessary approval for sales into that region.

Another pitfall involved not fully characterizing the emissions pattern of a device. Peaks and nulls can move around with small changes in device azimuth and measurement antenna height. The Northwest EMC solution is to gather emissions data over all permutations of the two. The first picture shows how the emissions pattern changes with antenna height (the red trace is the antenna at 1m high, the blue is at 1.5m high). The second picture shows how the device emissions are fully characterized.

Snaoshot #1 of Emissions from PDF of Presentation

Snapshot #2 of Data Providing a True Picture of EUT Emissions
Without this, there is the very real risk a competitor may inform the governing body that a device is not compliant (market surveillance is the main method of policing devices on the market).

If you want more / better pictures, I suggest you contact Alee Langford
alangford@nwemc.com to see if she will email you the PDFs of the presentations. We lucky attendees received them on a free memory stick.

The event was followed by a tour of the new Plano test facility, where I noticed that the layout was identical to the one I have seen at their California facility. That is different rooms hold different test set ups, and a EUT is simply wheeled from one room to the other. This avoids the need to tear down and re-assemble test set ups time and time again. Of course this makes for excellent measurement consistency and reduced wear and tear on equipment / connections.

Enough about the Dallas Chapter presentation, time to talk about my upcoming Austin presentation.

The full announcement with location, times, etc. can be found at

My Upcoming Presentation on Under-Performing Chamber Designs

I will be explaining my approach on solving why today’s 3m chambers struggle to create a compliant test field over 1-6GHz. To conduct practical experiments would be costly and time consuming. But this is not the case with 3D EM simulation. With software modelling, you can change parameters at a stroke and observe the corresponding change in performance (thanks are due to CST for the loan of their CST Studio Suite® Software).

For those able to attend, it will pay to catch up on the background to these experiments by reading the article in the current issue of Interference Technology’s European Guide

As explained in the article, the first target is the ‘hot wall’ behind the calibration plane, and hence the wall directly illuminated by the antenna.

There is an ever-present potential problem that constructive and destructive interference may occur at the calibration plane when the forward wave and any reflected wave combine. This is a non-issue when the absorber clad wall is doing its job and the reflected wave is small in magnitude. The contention is that the reflected magnitude is far from negligible, and when the electrical length of the return path is just right, worst-case constructive interference, or worst-case destructive interference occurs right at the calibration plane.

With the help of the software we should find be able to find out where and why. But in the olden days of software there was a saying, ‘Garbage In, Garbage Out’. This still applies today, and level heads must prevail in designing and conducting the experiments. That is, we must be able to isolate the contributions of the major phenomena causing the wave to revisit the calibration plane.

The phenomena will likely include partial reflection / scattering from the faces of the pyramid (the pyramidal shape is intended to present a mechanical impedance-taper to match the incident wave to the absorber material), refraction changing the wave direction away from the ideal on entry into the absorber, and reflection from the ferrite tiles behind the absorber. The pyramidal matrix may also look like a diffraction grating to the incident wave, causing further unintended wave redirection.

And let’s not forget that as regards a reflected wave bouncing off the ferrite tile, the mechanically matched absorber arrangement is a two way street providing as good a path back to the calibration plane as it presented to the incident wave.

Hope to see all you Austin locals at the Central Texas Chapter event.

To be continued............

Tom Mullineaux
Lionheart Southwest