Monthly Archives: November 2013

Keep Connectors Organized

How many of you store all your connectors and coaxial adapters in one large box? After years of dealing with the jumble of connectors and adapters and the wasted time in pulling out what I needed, I finally decided to make this part of my “spring cleaning.” After rooting around multiple locations for small stashes of these connectors, I cleared off the workbench and sorted them all by size and type. I also decided to collect and sort all the small coaxial connector-related modules, such as combiners, power splitters, amplifiers, etc., as well as other small everyday electronic sub-assemblies I routinely use for experiments.

Once all the various components were sorted out, I paid a visit to our local Walmart and found these five-drawer units (8-1/2″ x 7-1/4″ x 11-1/8″, model 2075) made by Sterilite, which were just the right size to hold the multitude of connectors, adapters, and modules. The drawer modules are stackable, so I can double the storage pretty easily, if required. Because the drawers are clear, I can see at a glance what I need.

For more on this and other storage ideas, click here…

PC Board Resonance

 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.

For my answer, click here…