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
[email protected] 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…………