ONE WEIRD TRICK! – For Probing High Frequency Signals

As you may or may not not know, when you are probing high frequency signals with an oscilloscope it is critical to keep the ground lead as short as possible.  In the extreme, special probe sockets must be designed into the PCB. A more practical solution is the grounding “spring” contacts that are available for many oscilloscope probes.  The problem with these springs is that they tend to slip off the contact point and can short out the device under test.  One solution is to include grounded plated-through-holes strategically scattered around the PCB.  These holes can be used to contain the contact end of the spring.  But what if you did not include these holes or did not put them in the right place?

The answer I came up with – solder a tiny metal tube to any convenient pad, such as a decoupling capacitor.  There is always a decoupling cap nearby.  These tiny tubes are both cheap and readily available – they are “crimp beads” or “crimp tubes” used for making jewelry and can be purchased at any craft store.  Crimp beads come in various sizes; the ones that I use, and seemingly the most common type, are described as 2 mm.  Since the tubes are both 2 mm long and 2 mm in diameter, I don’t know to which dimension this description refers.

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