Using current probes to estimate E-fields – Current probes are one of my most-used EMI troubleshooting tools. Frequently, a product’s I/O or power cables are often an appreciable fraction of a wavelength, so are a source of radiated emissions. This occurs if common-mode currents are allowed to travel along the cable or cable shield. Current probes may be used to measure these small (frequently in the uA) currents. Reducing such noise currents on those lines can often reduce the radiated emissions from the equipment under test.
Gaps in return planes – yes or no? – As a participant during the panel discussion on EMC versus SI at the recent DesignCon 2014, I sensed (along with some in the audience) that there was disagreement as to whether it was OK to cross a gap in the return plane with a high speed, fast-edged, signal. Unfortunately, there was too little time in which to come to an agreement or to illustrate the conditions in which it was OK, or not OK. This article explains why this is NOT a good idea.
Troubleshooting EMI on your bench top – If your product is failing radiated emissions at the test lab, it’s often more cost-effective to perform any detailed troubleshooting at your own facility where you can take time to methodically isolate the source and try out several potential fixes. Unfortunately, many companies don’t have the equipment or training to make these simple measurements. This article describes a easy method for measuring radiated emissions and providing a rough estimate of pass/fail.
Review: Signal Hound BB60C real time 6 GHz spectrum analyzer (Part 1) – The Signal Hound series of spectrum analyzers are about as small as three large-size Hershey chocolate bars stacked on top of each other. The unit offered for review is the recently released model BB60C real time analyzer, which can tune from 9 kHz to 6 GHz with a dynamic range of +10 to approximately -158 dBm (DANL, which is dependent on resolution BW). It can easily fit within a standard briefcase with room left over for a medium sized laptop.
Review: Signal Hound BB60C real time 6 GHz spectrum analyzer (Part 2) – In Part 1 of this review, we discussed the basic architecture, specifications and controls of the Signal Hound BB60C real-time spectrum analyzer. In Part 2, we’ll show you some actual measurements and several screen captures.
Sorry about getting a little behind in postings. Here are some of the highlights of postings on the EDN.com site:
Review: inexpensive RF generator – During one of my presentations on low-cost EMC troubleshooting tools at the IEEE EMC Symposium last August, one of the attendees, Doug Miller, mentioned a small PC-controllable RF generator for just $190. Of course, I had to buy one and try it out!
Review: Windfreak Technologies SynthNV RF generator – Every once in a while, I discover a product that is so incredible I wonder why it hasn’t been publicized more widely. This is the case with Windfreak Technologies $599 miniature RF generator, the model “SynthNV” (Figure 1). In case you’re wondering, their company is named after the owner’s sailboat!
Detecting ESD Events – In my experience, electrostatic discharge (ESD) issues have now become the second-most prevalent issue other than radiated emissions. If you find your product has exhibits random upsets, such as loss of data or unusual circuit resets, it could very well be caused by ESD. This article describes several methods to detect these events.
Harmonic Analyzer Tool – Because of their typically fast edge rates, crystal oscillators can generate a large number of high-order harmonics. This harmonic analyzer was created by my coauthor, Patrick André, with additional formatting tweaks by myself. I find this really handy to calculate harmonics from clock oscillators.
Review: TTi PSA2702T handheld spectrum analyzer – One thing that I find handy is a small hand held spectrum analyzer for use in troubleshooting EMI issues. As I travel a lot in my job, I like to take the minimum amount of test equipment possible. Unfortunately, most good quality analyzers are large, heavy and expensive. About ten years ago, I ran into the Thurlby Thandar Instruments (TTi) PSA2701T and have used it extensively since then. During that time, I reviewed it several times. In May 2013, TTi completely redesigned and repackaged this analyzer and released it as the PSA2702T. This is a review of the new PSA2702T, which I have used for several months now.
Cables or other metal (antenna-like) structures often couple to sources of common-mode currents and end up radiating, causing product failures during compliance testing. During the troubleshooting process, it would be helpful to determine the resonance of these cables or structures to confirm they are the source of certain harmonic signals.
We could certainly measure the length of the cables or metal structures, but often, they are connected to other conductive assemblies, such as circuit boards or brackets. Because of these system inter-relationships, it’s not always easy to predict the resonances within a system, and so there’s always a little uncertainty as to where to start the troubleshooting process. These simple techniques may help quickly identify potential resonances within your system or product.
How many of you have beat down a harmonic at one end of the spectrum, only to have an otherwise low harmonic rise up above the limit at the higher end of the spectrum? This is often termed the “ballon effect”, where squeezing one end of a balloon makes it expand at the other end. This is usually due to board resonances within the PC board itself.
I recently received an interesting observation from fellow EMC consultant, Mike Farnet
, following an experiment he performed on reducing the emissions from a client’s embedded ARM processor board with Ethernet. There were strong 25 MHz harmonics from the PHY circuit, as is usual for these low-cost boards. The original harmonic was peaking strongly at 150 MHz. Here is his discussion:I use a 5407 EMCO GTEM and a Rigol DSA-815 TG+EMC spectrum analyzer. I use LabView to collect the data from my spectrum analyzer.
I am working on a 25 MHz issue on an embedded ARM board with Ethernet. The strongest offending harmonic is at 150 MHz. See Figure 1.
Figure 1 – The harmonic profile before the capacitors were changed.
I was growing tired of waiting to collect 16000 data points for the 3 positions in the GTEM and was contemplating limiting the scan window to the 150 MHz target for faster debugging when the scan in Figure 2 told me “Bad Idea.”
Figure 2 – The harmonic profile after the capacitors were changed.
I recently upgraded my old Radio Shack AM radio, which I used for ESD detection, for the Grundig (Eton) Mini400 AM/FM/SW pocket radio. This $30 (street price) pocket-sized radio (4.25 x 2.75 x .5 inch) seems to have plenty of sensitivity to nearby ESD events. By tuning off-station, you can clearly hear the “clicking” from the ESD from several feet away. Using one of these radios is handy for correlating random product glitches with possible ESD events.
I’m also finding it’s quite useful in locating low frequency switch mode power supply (SMPS) EMI. The shortwave bands are especially sensitive to this noise. For example, the CFL and newer LED lamps each have a SMPS built in to their bases. The multitude of these lamps in homes today can create a cacophony of EMI well above the shortwave spectrum. This is a real issue for amateur radio operators and those who enjoy radio astronomy.
The radio has an analog tuner with digital display. It runs on a pair of AAA cells and seems to have plenty of audio. It also comes with a padded case with belt loop. The only caution I might point out is that the power switch is a momentary button, which could get pressed inadvertently if pressed during shipping or if packed tightly in your troubleshooting kit. The radio does have a “Lock” switch on the side that disables the power button, so that ought to alleviate that issue. You just have to remember to unlock the radio prior to use.
AM: 517 to 1782 kHz (1 kHz steps)
SW1: 5.700 to 10.380 (5 kHz steps)
SW2: 11.600 to 18.450 (5 kHz steps)
FM: 85.8 to 108.7 MHz (0.1 MHz steps)
I bought mine from Radio Shack for $40, but you can find one on Amazon.com for $30. Recommended.
Following the recent webinar sponsored by Rohde & Schwarz, I received way too many questions to answer during the live presentation, so I’m following up gradually and posting my answers on The EMC Blog, now hosted by EDN.com.
I just posted my third article:
3. Questions on EMC pre-compliance testing for radiated emissions
I’ll be posting one more on the questions I received on general EMC topics some time in August.
In the meantime, I’ll be attending Doug Smith’s ESD/EMC three-day seminar next week and may write up a description with pictures. The week after that, I’ll be attending the annual International Symposium on EMC right here in Denver. I’ll be posting at least two articles on new products and other activities.