A vertical interval test signal inserter, or VITS inserter inserts test patterns into the vertical interval of a television signal. Unlike test signal generators; a VITS inserter is used to insert the test signal into live programming, so that inline measurements of a transmission chain can be made while the chain is operational. (As the vertical interval is typically not visible on end-user televisions, this can be done without producing any artifacts noticeable to viewers). Since VITS signals can often be transmitted, it is also possible for a television station to receive its own on-air feed, and use the VITS to detect and troubleshoot problems in on-air transmission.