Electronic – frequency at which jumpers start to become a problem

impedancejumper

Pin header jumpers (like these) can be used to make optional connections between parts.

I would expect at certain frequencies that the these kind of parts become primarily reactive (the imaginary part of the impedance becomes greater than the real part). At what frequencies does this typically happen?

Best Answer

From a microwave engineers point of view, things really start to become a problem when the physical dimensions of the component are comparable to the wavelength of the signal you are considering.

The length of the pins onto which this jumper mounts are 0.230" (5.84mm) and the separation is 0.100" (2.54mm) so the signal path length is approximately 0.560" (14.22mm)

This dimension represents 1/10 of a wavelength at about 2.5GHz. To reasonably represent a square wave, I would include upto the fifth harmonic - so I would place an upper limit of 500MHz on this part. This is a heavily simplified first off starting point based on rough dimensions and rules of thumb and obviously you should verify the performance by either a full 3D EM simulation if you have the facility, or by direct measurement of a test piece using a network analyser.