What can cause standing waves on a transmission cable?

Standing waves on a transmission cable occur when there is a mismatch between the impedance of the cable and the connected load or source. When impedance values are not properly matched, some of the signal reflects back towards the source instead of being fully transmitted. This reflection creates points of constructive and destructive interference along the cable, resulting in standing waves.

Poor termination at either end of the transmission line can lead to this impedance mismatch, thus directly causing standing waves. Proper termination is crucial, as it ensures that the signal is absorbed rather than reflected. An improperly terminated cable results in energy being reflected back towards the source, which can create the conditions for standing waves to form.

While excessive cable length, high ambient temperatures, and improper impedance matching can have various effects on transmission performance, it is mainly the inadequate termination that leads directly to standing wave generation. In many cases, corrective measures such as using terminators or ensuring that the load impedance matches the characteristic impedance of the cable can alleviate the standing wave issue.