WTF are Ground Loops?

These magical creatures crop up out of nowhere and fry your electronics or annoy your ear holes. Understanding them will doubtless save you money and hassle. The ground loop in a nutshell is what happens when two separate devices (A and B) are connected to ground separately, and then also connected to each other through some kind of communication cable with a ground, creating a loop. This provides two separate paths to ground (B can go through its own connection to ground or it can go through the ground of the cable to A and then to A’s ground), and means that current may start flowing in unanticipated ways. This is particularly noticeable in analog AV setups, where the result is audio hum or visible bars in a picture, but is also sometimes the cause of unexplained equipment failures. Continue reading “WTF are Ground Loops?”

An excellent introduction to transmission lines

[Bertho] sent in a great tutorial on terminating transmission lines. If you’ve ever tried to send a high frequency signal a long way down a wire, you know the problems that can crop up due to electronic strangeness. Luckily [Bertho]’s tutorial explains just about everything, from where and when to terminate a cable and why signals get screwed up in long wires.

[Bertho] begins his lesson by taking two oscilloscopes and 20 m of CAT5 cable with the twisted pairs wired in series to make an 80 meter long transmission line. A ~100kHz square wave was sent down the cable after being displayed on the first oscilloscope, and picked up on the other end by the second oscilloscope. It’s a great way to show the changes in a signal over a long cable run, and how small changes in the circuit (just adding a simple resistor) can affect the signal coming out of a cable.

It’s a great post that demystifies the strange electrical gremlins that pop up when you’re running a length of wire. Great job, [Bertho].