If you’ve read the last few blogs, you’ll know we’ve been discussing balanced lines, differential signals, and common-mode noise rejection. But one of the key factors we really haven’t discussed is the cable itself.
In the last blog, we talked about how electromagnetic noise signals, called common mode noise, hits both wires in our twisted pair and cancels out. But, to be truthful, the noise is cancelled out only if the two signals are identical. The closer to identical they are, the greater the rejection or common mode rejection ratio, CMRR will be.
We have a saying in cable manufacturing: physicals equal electricals. What this means is that the two wires need to be physically identical if we want the noise signals to also be identical, and the noise rejection to be 100%.
Well, aren’t the two wires in a twisted pair ‘automatically’ identical? After all, we twist those wires together. Isn’t that enough? Sure, twisting helps a lot, but it doesn’t make the two wires identical. Those two wires should also be the same AWG (gauge) size. Read more