Interview with Henry W. Ott

Featured Engineer

Henry W. Ott

Henry W. Ott - Independent EMC Consultant

How did you get into electronics/ engineering and when did you start?

As a kid I was always building things and taking things apart, so I knew that I wanted to be an engineer. The only question was mechanical or electrical. I was leaning towards mechanical, when my mother convinced me that the future would be electronic – and she was right. I got my BSEE from New Jersey Institute of Technology in 1957 and then went into the Air Force for three years. I was in the Air Research and Development Command stationed at Eglin AFB in Florida.

When I came out of the Air Force in 1960 I took a job with Bell Labs, in New Jersey, and received my MSEE from New York University in 1963. While at Bell Labs I published the book “Noise Reduction Techniques in Electronic Systems” in 1976 with a second edition in 1988. The book has been translated into six different languages. In 1988 I left Bell Labs to start my own EMC consulting business, doing EMC consulting and training.

During the 1980’s (while still at Bell Labs as well as after I left Bell Labs) I did EMC consulting for many of the start-up personal computer companies in Silicon Valley. In 2009 I published my most recent book “Electromagnetic Compatibility Engineering.” The book won the Association of American Publishers “PROSE Award” for 2009 in the category of Technology and Engineering. The PROSE award is considered by many to be the equivalent of the “Academy Award” for books.

What are your favorite hardware tools that you use?

Being an EMC Engineer, my list is probably completely different than most other electrical engineers. First and foremost is a common-mode current probe such as a Fischer Custom Communications F-33-1. When connected to a typical spectrum analyzer this probe can measure cable currents as small as 1µA over a frequency range of 2 to 250 MHz with a flat frequency response.

Second, would be a shielded magnetic field loop-probe such as a Fischer Custom Communications F-301 or a Beehive Electronics 100A. This is very useful for probing PCBs for noise sources, and for measuring leakage at the seams of a metallic enclosure.

Last but not least, is a spectrum analyzer. Up until just recently, even a small, portable spectrum analyzer was expensive, heavy, and difficult to move around. I now, however, use a small handheld very portable (it fits in my briefcase with plenty of room left over) spectrum analyzer Model PSA2701T made by a British company Thurlby Thandar Instruments, and sold in the U.S.A. by Newark Electronics and Saelig Company in Pittsford, NY. It has a 3.7” color display and a frequency range of 1 MHz to 2.7 GHz. A companion Model PSA1301T has a frequency range of 0.1 MHz to 1.7 GHz

What are your favorite software tools that you use?

MathCad for general mathematical analysis and EZNEC for antenna modeling.

What is on your bookshelf?

Lot’s of books.

The one’s that I refer to the most are my new book Electromagnetic Compatibility Engineering (Wiley, 2009), High-Speed Digital Design, A Handbook of Black Magic by Johnson and Graham (Prentice Hall, 1993), and High-Speed Digital System Design by Hall, Hall and McCall (Wiley, 2000). Together these three books cover the subject of EMC and Signal Integrity (SI) over the frequency range of DC to light. As a matter of fact, the first sentence of the Hall, Hall, and McCall book is: “The speed of light is just too slow.” All three books are well written, very readable, with very little overlap in material. In addition to design information, all three books also contain useful EMC/SI measurement techniques.

Electromagnetic Compatibility Engineering is a basic EMC book covering a multitude of EMC subjects. High-Speed Digital Design is a crossover book emphasizing the EMC aspects of high-speed digital design and SI. High-Speed Digital System Design is a signal integrity book.

For a more extensive list and mini-reviews of EMC/SI books look here: http://www.hottconsultants.com/book.html

Do you have any tricks up your sleeve?

Most people design a product, check it out functionally, and then send it to a test lab for EMC compliance testing, hoping that it will pass–85% of the time it doesn’t. This is an insane way to manage the EMC design of the product. Would you design and build a product, never test it functionally, and send it to your customer to evaluate its functionality? Of course you would not, then why do the equivalent with respect to EMC.

What you should do is use the probes discussed above under favorite hardware tools and do some precompliance EMC measurements in the comfort of your own lab . Although not as accurate as legitimate EMC tests performed at a qualified test lab, they can give you a good indication of the EMC performance of the product. I like to call these preliminary tests “workbench EMC measurements,” and they can increase the probability of passing the initial EMC Compliance Test from 15% to 85%. For more information see Chapter 18, “Precompliance EMC Measurements” in Electromagnetic Compatibility Engineering.

Do you have any note-worthy engineering experiences?

While working for Bell Labs (by the way, where have all the great research labs gone?) as a young engineer in the 1960’s I was assigned a project to design instrumentation for an underground nuclear blast in Nevada. The signal I was to measure was a transient and I would only have one chance to capture it. The signal would be displayed on an oscilloscope and recorded by a 35 mm camera attached to the scope (remember this was the 1960’s). The scope was set for a single 100 µs sweep, and was buried in the Nevada desert a month before the detonation.

The challenge was to trigger the scope so that it would sweep the correct 100 µs out of the next 30 days, with no second chances to do it over. I designed a circuit that would detect a gamma ray precursor pulse from the detonation, delay the proper amount of time and then trigger the scope and camera to record the data. The cabling, shielding, and balancing design of the instrumentation and trigger cables was of primary concern, since the nuclear detonation would produce a large electromagnetic pulse which would induce a significant amount of noise current into the cables at the time of the measurement. I also decided to instrument the peak noise current on the cable, and discovered that it was over 500 A at the time I was measuring a 10 mV signal.

One remaining concern was the possibility that cosmic radiation would activate the gamma ray detector and trigger the scope during the 30-day period between when it was buried and the actual event. To preclude this I enclosed the exposed gamma ray detector in an enclosure made out of lead bricks (2” x 4” x 8” bricks) with a small window facing the direction of the intended gamma ray signal. When I went to my boss with a purchase order for two dozen lead bricks he balked at signing it, and asked, “if there wasn’t anything else that I could use other than lead.” I answered, “yes, gold.” Without further comment he picked up his pen and signed the purchase order for the lead bricks.

After the detonation, when the area was determined to be safe to return to we dug up the oscilloscope and camera, processed the film and discovered it all worked, and the data pulse was in the middle of the scope trace. I guess that four-leaf-clover in my wallet really worked. I didn’t know it at the time, but that was the beginning of my EMC career.

What are you currently working on?

I am presently working on coauthoring a new book titled “Antenna Theory Simplified.” If a product, PCB, or cable radiates or is susceptible to electromagnetic energy it is an antenna. Therefore, an understanding of some basic antenna theory would be very useful to an engineer or technician trying to deal with EMC problems. However, the way antenna theory is taught in most schools, it is too theoretical and abstract to be very helpful in this situation. In this new book, antennas will be analyzed using circuit theory instead of field theory. This approach provides the reader a simple, intuitive understanding of antenna operation. The book is for anyone who would like to understand how antennas work, but does not have the time or desire to study the intimidation mathematics normally associated with antenna theory.

What direction do you see your business heading in the next few years?

EMC regulations are not going to go away, if anything they are becoming more restrictive, and more pervasive in the world. Therefore, the need for EMC engineers will not only continue but will grow. Most engineering schools, however, do not include the subject of EMC in their curriculum. Therefore, in addition to EMC consulting, I also teach EMC training courses, both public and in-plant for individual clients.