Application Note: Measuring Video Feedthrough in Pulsed Signals

Video feedthrough is a very misunderstood term, which is used in the specification of pulse performance for microwave synthesizers. There are several ways of specifying it. Depending on the application, one way may provide more information than another. This note is an attempt to explain what video feedthrough is, how it can be measured, and what effect it can have on devices being tested.

As far as electronics is concerned, the term video was originally used to describe the "picture" signal, which modulated a RF carrier for television in the 1920's. When this signal was detected and applied to a scanning CRT, a picture was produced. During World War II, video was the term applied to the detected RF pulse received by the radar, as the pulse could be seen on the radar CRT. At that time, oscillographs (oscilloscopes) could not display RF signals. A crystal detector was used to rectify the RF and produce an envelope of the RF signal, which could be displayed by the oscillograph. So, video is also the term applied to the detected RF from a crystal detector. The term video is also used to describe the signal, which modulates a RF carrier.